2011 Vol. 29, No. 1
Display Method:
Deposition and Reservoir Characteristics of Terminal Fan in Kongdian Formation of Huimin Depression
2011, 29(1): 1-13.
Abstract:
Sedimentary facies of Kongdian sandstones is terminal fan. Middle zone is the main part of the tripartite terminal fan which can be divided into distributary channel, overbank and mudflat according to observation and description of cores combined with the numerous data of seismic. The sandstones type of Kongdian Formation are of finemedium grained arkose and lithic arkose. Terminal fan sandstone has undergone many types of diagenesis. Authigenic minerals in Kongdian reservoir include clay minerals, carbonate, quartz, feldspar and so on. Based on the study of burial history, the diagenetic stage of Kongdian Formation is in A period of mesodiagenesis. Reservoir quality of terminal fan in Kongdian Formation is mainly controlled by sandbody microfacies and diagenesis. Sedimentary microfacies resolves reservoir's original physical property, while diagenesis dominates final status of sandstone reservoir. There exists five diagenetic lithofacies in Kongdian sandstone, for example plastic composition dissolution lithofacies, chlorite gasket lithofacies, carbonate cementation lithofacies, compaction and filling lithofacies, quartz overgrowth lithofacies and so on. Diagenetic lithofacies is comprehensive reflection of diagenetic change and reservoir evolution of different microfacies sand. Distributary channel sandstone in connection with plastic composition dissolution or chlorite coating lithofacies is usually nice hydrocarbon pay bed, whereas overbank sandstone related with carbonate cementation or compaction and filling lithofacies is often low permeability layer. Terminal fan reservoir shows facies controlled feature.
Sedimentary facies of Kongdian sandstones is terminal fan. Middle zone is the main part of the tripartite terminal fan which can be divided into distributary channel, overbank and mudflat according to observation and description of cores combined with the numerous data of seismic. The sandstones type of Kongdian Formation are of finemedium grained arkose and lithic arkose. Terminal fan sandstone has undergone many types of diagenesis. Authigenic minerals in Kongdian reservoir include clay minerals, carbonate, quartz, feldspar and so on. Based on the study of burial history, the diagenetic stage of Kongdian Formation is in A period of mesodiagenesis. Reservoir quality of terminal fan in Kongdian Formation is mainly controlled by sandbody microfacies and diagenesis. Sedimentary microfacies resolves reservoir's original physical property, while diagenesis dominates final status of sandstone reservoir. There exists five diagenetic lithofacies in Kongdian sandstone, for example plastic composition dissolution lithofacies, chlorite gasket lithofacies, carbonate cementation lithofacies, compaction and filling lithofacies, quartz overgrowth lithofacies and so on. Diagenetic lithofacies is comprehensive reflection of diagenetic change and reservoir evolution of different microfacies sand. Distributary channel sandstone in connection with plastic composition dissolution or chlorite coating lithofacies is usually nice hydrocarbon pay bed, whereas overbank sandstone related with carbonate cementation or compaction and filling lithofacies is often low permeability layer. Terminal fan reservoir shows facies controlled feature.
2011, 29(1): 23-30.
Abstract:
Lower submember of the 8th of middle Permain Shihezi Formation is quartz sandstone and lithic quartzsandstone with higher compositional and textural maturity and light greywhite color, and is one of the main reservoirs in the basin with the thickness generally 15~40 m, tempesitites frequently occur in some well cores. According to thickness of single tempesitite bed, grain size, fragment contents of external land carbonaceous mudstone and coal, profile feature, especially the scale of hummocky crossbedding and pot cast, and more or less of the stacked tempesitites and so on, three ended type tempesitites could be divided approximately by varying degrees of energy stone wave current in cores. (1) The tempesitite generated by higher energy storm wave current appeared large scale pot cast cute into the top of underlying quartz sandstone or lithic quartzsandstone, the super stratum tempesitite consists of flaky conglomerate of carbonous and light yellow grey mudstones, mixed with some quartz and coal clastics, thickness of single bed the same as 20~50 cm, some are too thick, graded bedding, and frequently show the stacked secession. (2)The tempesitites generated by the middle energy storm wave current show the integrated or nonintegrated tempesitite sequence, with developed hummocky cross bedding, and contain more or less some carbonous mudstone and coal clastics, the thickness of single bed is always 10~40 cm, and stacked sequence often occurred. (3) The tempesitite generated by lower energy storm wave current appeared the thickness about 5~10 cm, only develops the hummocky and swaley cross stratification, not only is single bed, but also stacked by several beds. Tempesitites frequently occur in quartzitic sandstones of Lower submember of the 8th is questioned to viewpoint of fluvial facies.
Lower submember of the 8th of middle Permain Shihezi Formation is quartz sandstone and lithic quartzsandstone with higher compositional and textural maturity and light greywhite color, and is one of the main reservoirs in the basin with the thickness generally 15~40 m, tempesitites frequently occur in some well cores. According to thickness of single tempesitite bed, grain size, fragment contents of external land carbonaceous mudstone and coal, profile feature, especially the scale of hummocky crossbedding and pot cast, and more or less of the stacked tempesitites and so on, three ended type tempesitites could be divided approximately by varying degrees of energy stone wave current in cores. (1) The tempesitite generated by higher energy storm wave current appeared large scale pot cast cute into the top of underlying quartz sandstone or lithic quartzsandstone, the super stratum tempesitite consists of flaky conglomerate of carbonous and light yellow grey mudstones, mixed with some quartz and coal clastics, thickness of single bed the same as 20~50 cm, some are too thick, graded bedding, and frequently show the stacked secession. (2)The tempesitites generated by the middle energy storm wave current show the integrated or nonintegrated tempesitite sequence, with developed hummocky cross bedding, and contain more or less some carbonous mudstone and coal clastics, the thickness of single bed is always 10~40 cm, and stacked sequence often occurred. (3) The tempesitite generated by lower energy storm wave current appeared the thickness about 5~10 cm, only develops the hummocky and swaley cross stratification, not only is single bed, but also stacked by several beds. Tempesitites frequently occur in quartzitic sandstones of Lower submember of the 8th is questioned to viewpoint of fluvial facies.
2011, 29(1): 41-54.
Abstract:
Sedimentary geochemistry of detrital rocks from the upper Devonian Shaliushui Formation in Jingyuan, Gansu suggest that sandstone contain higher SiO2 and plagioclase content than mudstone; Mudstone, however, occupy higher femic mineral and mineral Kbearing than sandstone. All samples are depleted in Nb, Ta and Sr elements. Some of sandstones are enriched with Zr and Hf elements, with strong negative Eu anomalies, and others are depleted in Zr and Hf without negative Eu anomalies. All mudstones display enrichment of Ni and Cr elements, with strong negative Eu anomalies. Characteristics of samples from the Shaliushui Formation show that rocks in the source consist of the basic and acidic rocks with ancient sediments recycled from passive continental margin. And source underwent middle intense chemical weathering (CIA: 74~81). Tectonic setting discriminations suggest that rocks in the source were mainly formed in the continental arc and active continental margin, with minor the oceanic arc and passive continental margin. Evidences combining tectonic discriminations and comparisons with potential provenances revealed that sediments in the Shaliushui Formation were derived mainly from the North Qilian Continental arc and the Central Qilian Block, with minor the North Qilian subducted complex and North China Plate. Integrated in the sedimentary evolution from the upper Ordovician to Lower and Middle Devonian and igneous rocks, the North Qilian Orogenic Belt completed the transfer from compression to extension during the Late Devonian, which indicate that the upper Devonian Shaliushui Formation is the sedimentary record of this process.
Sedimentary geochemistry of detrital rocks from the upper Devonian Shaliushui Formation in Jingyuan, Gansu suggest that sandstone contain higher SiO2 and plagioclase content than mudstone; Mudstone, however, occupy higher femic mineral and mineral Kbearing than sandstone. All samples are depleted in Nb, Ta and Sr elements. Some of sandstones are enriched with Zr and Hf elements, with strong negative Eu anomalies, and others are depleted in Zr and Hf without negative Eu anomalies. All mudstones display enrichment of Ni and Cr elements, with strong negative Eu anomalies. Characteristics of samples from the Shaliushui Formation show that rocks in the source consist of the basic and acidic rocks with ancient sediments recycled from passive continental margin. And source underwent middle intense chemical weathering (CIA: 74~81). Tectonic setting discriminations suggest that rocks in the source were mainly formed in the continental arc and active continental margin, with minor the oceanic arc and passive continental margin. Evidences combining tectonic discriminations and comparisons with potential provenances revealed that sediments in the Shaliushui Formation were derived mainly from the North Qilian Continental arc and the Central Qilian Block, with minor the North Qilian subducted complex and North China Plate. Integrated in the sedimentary evolution from the upper Ordovician to Lower and Middle Devonian and igneous rocks, the North Qilian Orogenic Belt completed the transfer from compression to extension during the Late Devonian, which indicate that the upper Devonian Shaliushui Formation is the sedimentary record of this process.
2011, 29(1): 64-71.
Abstract:
Lower Ordovician Majiagou Formation is composed of six members in which Ma1,Ma3 and Ma5 are evaporate including dolomite, anhydrite and salt and Ma2, Ma4, Ma6 are limestone with dolomite in Ordos Basin. Majiagou Formation is formed by cyclic sedimentation by intermeshed evaporite and carbonate. Upwarps around the basin and a downwarp in the centre of the basin constitute the EarlyOrdovician Palaeogeomorphologic pattern. Upwarps as underwater barriers led to exchange limitation between lagoon and exterior sea and weakness of lagoon hydrodynamic force during high sea level stage. During low sea level stage, upwarps resulted in the entire isolation between lagoon and exterior sea. Owing to the strong evaporation, lagoon level was greatly lower than exterior sea level .So lagoon margin flat was partly exposed to atmosphere and the deep sag in the centre of the basin was covered by concentrated bittern.
〓〓Analysis of single well and well tie sedimentary facies demonstrates the depositional setting from Ma1 and Ma2 member is composed of two integrating cycles from transgression to regression due to sea water invasion from the east and southeast of the basin. Ma3 member is mainly composed of regressive deposition owing to the rapid extensive transgression in the early Ma3 stage. North China sea, Qilian oceanic trough and Qinling oceanic trough formed a united basin and the centre uplift zone was developed to a platform margin , the west of the centre uplift zone was developed to a basin and a slope and the east of the centre uplift zone was developed to a broad lagoon during the biggest sea water invasion in Ma4 stage. Ordos Basin was isolated from exterior sea and the salty lagoon was changed to a salt lake gradually during Ma5 stage owing to sea level descend and barrier of the centre uplift zone. In Ma6 stage the Basin was changed to a broad lagoon.
〓〓Based on the pioneer research of paleostructure, paleogeography, paleohydrodynamic as well as paleoclimate, a new model barrierlagoon sedimentary model of Majiagou Formation is developed. The model includes three phases during transgression to high sea level (phaseⅠ), carbonate deposits in broad barrierlagoon, and mixed carbonate /evaporate succession in concentrated lagoon during regression (phaseⅡ), and anhydrite and salt in saline during low sea level( phaseⅢ).
〓〓And two main types of carbonate reservoir including the dolomite reservoir in relation to karstification and the crystallization dolomite reservoir in connection with dolomitization are discovered in this paper. The authors further analyze the carbonate reservoir distribution law within the mentioned model, conclude that beachflat of platform edge of the model(phase Ⅰ)and lagoon margin flat of phaseⅡ are favorable for reservoir growth and point out that the reservoir of Majiagou Formation is karst type and is mainly distributed on the top of Ma5,Ma3 and Ma1 Formation. Anhydrite and salt of phase Ⅲ are important seal rock.
Lower Ordovician Majiagou Formation is composed of six members in which Ma1,Ma3 and Ma5 are evaporate including dolomite, anhydrite and salt and Ma2, Ma4, Ma6 are limestone with dolomite in Ordos Basin. Majiagou Formation is formed by cyclic sedimentation by intermeshed evaporite and carbonate. Upwarps around the basin and a downwarp in the centre of the basin constitute the EarlyOrdovician Palaeogeomorphologic pattern. Upwarps as underwater barriers led to exchange limitation between lagoon and exterior sea and weakness of lagoon hydrodynamic force during high sea level stage. During low sea level stage, upwarps resulted in the entire isolation between lagoon and exterior sea. Owing to the strong evaporation, lagoon level was greatly lower than exterior sea level .So lagoon margin flat was partly exposed to atmosphere and the deep sag in the centre of the basin was covered by concentrated bittern.
〓〓Analysis of single well and well tie sedimentary facies demonstrates the depositional setting from Ma1 and Ma2 member is composed of two integrating cycles from transgression to regression due to sea water invasion from the east and southeast of the basin. Ma3 member is mainly composed of regressive deposition owing to the rapid extensive transgression in the early Ma3 stage. North China sea, Qilian oceanic trough and Qinling oceanic trough formed a united basin and the centre uplift zone was developed to a platform margin , the west of the centre uplift zone was developed to a basin and a slope and the east of the centre uplift zone was developed to a broad lagoon during the biggest sea water invasion in Ma4 stage. Ordos Basin was isolated from exterior sea and the salty lagoon was changed to a salt lake gradually during Ma5 stage owing to sea level descend and barrier of the centre uplift zone. In Ma6 stage the Basin was changed to a broad lagoon.
〓〓Based on the pioneer research of paleostructure, paleogeography, paleohydrodynamic as well as paleoclimate, a new model barrierlagoon sedimentary model of Majiagou Formation is developed. The model includes three phases during transgression to high sea level (phaseⅠ), carbonate deposits in broad barrierlagoon, and mixed carbonate /evaporate succession in concentrated lagoon during regression (phaseⅡ), and anhydrite and salt in saline during low sea level( phaseⅢ).
〓〓And two main types of carbonate reservoir including the dolomite reservoir in relation to karstification and the crystallization dolomite reservoir in connection with dolomitization are discovered in this paper. The authors further analyze the carbonate reservoir distribution law within the mentioned model, conclude that beachflat of platform edge of the model(phase Ⅰ)and lagoon margin flat of phaseⅡ are favorable for reservoir growth and point out that the reservoir of Majiagou Formation is karst type and is mainly distributed on the top of Ma5,Ma3 and Ma1 Formation. Anhydrite and salt of phase Ⅲ are important seal rock.
2011, 29(1): 80-87.
Abstract:
Chang6 reservoir is the leading pay formation of the Yanchang Formation in the center of Ordos basin, but reservoir quality of genetic sandbodies shows a big difference in horizontal. By studying the light and heavy mineral combination characteristics of chang6 reservoir sandstone and typical outcrops, it is believed that there exist five main source directions of the west, northeast, northwest, north and southeast in the depositional period of chang6 oilbed of Yangchang Formation in the center of Ordos basin. The characteristics of the light and heavy mineral combination, interstitial matrix and diagenetic mineral of chang6 reservoir sandstone controlled by different source directions were different. In addition, there exist some mixed sources areas which were converged by the west, northeast, northwest, north and southeast sources. The characteristics of light and heavy mineral combination, interstitial matrix, diagenetic mineral and porosity of its reservoir were affected by the main source. The controlling factors of the sandstone reservoir porosity development of Chang 6 include the sandstone maturity, grain size, detritus composition, interstitial matrix and diagenesis. The reservoir porosity is closely related to the various provenances. As a result, porosity distribution is predictable.
Chang6 reservoir is the leading pay formation of the Yanchang Formation in the center of Ordos basin, but reservoir quality of genetic sandbodies shows a big difference in horizontal. By studying the light and heavy mineral combination characteristics of chang6 reservoir sandstone and typical outcrops, it is believed that there exist five main source directions of the west, northeast, northwest, north and southeast in the depositional period of chang6 oilbed of Yangchang Formation in the center of Ordos basin. The characteristics of the light and heavy mineral combination, interstitial matrix and diagenetic mineral of chang6 reservoir sandstone controlled by different source directions were different. In addition, there exist some mixed sources areas which were converged by the west, northeast, northwest, north and southeast sources. The characteristics of light and heavy mineral combination, interstitial matrix, diagenetic mineral and porosity of its reservoir were affected by the main source. The controlling factors of the sandstone reservoir porosity development of Chang 6 include the sandstone maturity, grain size, detritus composition, interstitial matrix and diagenesis. The reservoir porosity is closely related to the various provenances. As a result, porosity distribution is predictable.
2011, 29(1): 97-104.
Abstract:
Yanchang Formation sited in the southerneastern Ordos Basin has been proven a prolific reservoir unit for hydrocarbon resources. Featured by relatively low porosity and effective permeability, the quality of the reservoir has a significant impact on the migration and accumulation of oil and gas. By analyzing the petrophysic data from thinsection samples, BSE, Energy Spectrum Analysis and core plugs, we reached the following conclusions: 1. The rimming of chlorite has an important control on the reservoir quality such diagenetic process is characterized as a product of delta front depositional environment where is mineralogically rich in black mica and feldspar. 2. It effectively reduced the compaction effect from the overburden through burial history, therefore contributed to the preservation of primary porosity, simultaneously, ceased the diagenetic overgrowth of quartz grains. 3. The associate presence of calcite reorientated the grains into porphyroblastic structure, but arbitrarily distributed due to the small quantity.4.Authquartz has a prominent vertical change, which is often observed as small crystal forming with chlorite rimming in a close space. However, in semiclosed spaces, quartz is prone to migrate upwards, stop and develop as overgrowth where the intergranular space is not fully taken by chlorite. Through the study, we sorted out the controls and developing mechanisms of qualified reservoirs in Yanchang Formation, and therefore guide the future exploration.
Yanchang Formation sited in the southerneastern Ordos Basin has been proven a prolific reservoir unit for hydrocarbon resources. Featured by relatively low porosity and effective permeability, the quality of the reservoir has a significant impact on the migration and accumulation of oil and gas. By analyzing the petrophysic data from thinsection samples, BSE, Energy Spectrum Analysis and core plugs, we reached the following conclusions: 1. The rimming of chlorite has an important control on the reservoir quality such diagenetic process is characterized as a product of delta front depositional environment where is mineralogically rich in black mica and feldspar. 2. It effectively reduced the compaction effect from the overburden through burial history, therefore contributed to the preservation of primary porosity, simultaneously, ceased the diagenetic overgrowth of quartz grains. 3. The associate presence of calcite reorientated the grains into porphyroblastic structure, but arbitrarily distributed due to the small quantity.4.Authquartz has a prominent vertical change, which is often observed as small crystal forming with chlorite rimming in a close space. However, in semiclosed spaces, quartz is prone to migrate upwards, stop and develop as overgrowth where the intergranular space is not fully taken by chlorite. Through the study, we sorted out the controls and developing mechanisms of qualified reservoirs in Yanchang Formation, and therefore guide the future exploration.
2011, 29(1): 118-124.
Abstract:
This paper studied highresolution sedimentary pollen sequence (1.5 yr/e) of Wanghu Lake, in the middle reach of Yangtze River, and analyzed the relationships of changes in pollen types and contents, sediment granularity, and climatehydrology features during the past hundred years when the lake turned from an open water system into closed basin. Correlation analysis for time series of pollen, granularity, catchment precipitation and river discharge, showed that significant linear relationships with 95% confidence level. Major pollen types showed a 27%40% synchronous changes with time series of granularity and precipitation during the past 130 years, and a 47%57% synchronous changes with time series of granularity and river discharge before the mid1960's when the lake naturally connected with Yangtze River, suggesting pollen deposition controlled by sediments and catchment precipitation. The author found synchronous changes among sedimentary granularity and pollen with precipitation and river discharge which all experienced 34 years and 911 years cycles in the time series, suggesting sedimentation responding to climate changes. This study may provide scientific basis to reconstruct past environmental changes using sediment and pollen records, and to understand biosedimentology dynamics in the lake sediments.
This paper studied highresolution sedimentary pollen sequence (1.5 yr/e) of Wanghu Lake, in the middle reach of Yangtze River, and analyzed the relationships of changes in pollen types and contents, sediment granularity, and climatehydrology features during the past hundred years when the lake turned from an open water system into closed basin. Correlation analysis for time series of pollen, granularity, catchment precipitation and river discharge, showed that significant linear relationships with 95% confidence level. Major pollen types showed a 27%40% synchronous changes with time series of granularity and precipitation during the past 130 years, and a 47%57% synchronous changes with time series of granularity and river discharge before the mid1960's when the lake naturally connected with Yangtze River, suggesting pollen deposition controlled by sediments and catchment precipitation. The author found synchronous changes among sedimentary granularity and pollen with precipitation and river discharge which all experienced 34 years and 911 years cycles in the time series, suggesting sedimentation responding to climate changes. This study may provide scientific basis to reconstruct past environmental changes using sediment and pollen records, and to understand biosedimentology dynamics in the lake sediments.
2011, 29(1): 134-142.
Abstract:
A 426 cm core from Lake Barkol, eastern Tian Shan, provides the evidence of Holocene climate in Westerly dominated Asia. Here, we present a grainsize component series decomposed by empirical orthogonal function and the chronology is based on radio carbon dating. The results show that the EOF1 component has a high correlation coefficient (0.64) with the volume percentage of the component less than 2 μm, furthermore it is similar to the evolution pattern of oxygen isotope from carbonate which is a proxy indicating the regional effective moisture, so the EOF1 component is an indicator of the effective moisture in the region. Modern dust grainsize analysis from Barkol shows a peak percentage around 61.2 μm. Coincidently, the EOF2 component has a high positive correlation coefficient with the grainsize ranging from 45 to 138 μm, which suggests that the EOF2 indicates the regional dust activity. EOF results suggested that the effective moisture was low and the dust activity was strong in midHolocene, which was consistent with the midHolocene arid interval occurred in the northern Mongolia Plateau. The enhanced Siberia high intensified the Westerly circulation and winter monsoon, and which could be the main reason for the arid and dusty midHolocene climate in the research region.
A 426 cm core from Lake Barkol, eastern Tian Shan, provides the evidence of Holocene climate in Westerly dominated Asia. Here, we present a grainsize component series decomposed by empirical orthogonal function and the chronology is based on radio carbon dating. The results show that the EOF1 component has a high correlation coefficient (0.64) with the volume percentage of the component less than 2 μm, furthermore it is similar to the evolution pattern of oxygen isotope from carbonate which is a proxy indicating the regional effective moisture, so the EOF1 component is an indicator of the effective moisture in the region. Modern dust grainsize analysis from Barkol shows a peak percentage around 61.2 μm. Coincidently, the EOF2 component has a high positive correlation coefficient with the grainsize ranging from 45 to 138 μm, which suggests that the EOF2 indicates the regional dust activity. EOF results suggested that the effective moisture was low and the dust activity was strong in midHolocene, which was consistent with the midHolocene arid interval occurred in the northern Mongolia Plateau. The enhanced Siberia high intensified the Westerly circulation and winter monsoon, and which could be the main reason for the arid and dusty midHolocene climate in the research region.
2011, 29(1): 151-157.
Abstract:
Based on the fundamental data of core, log and well logging，we studied the sedimentary microfacies types and evolutionary feature of Chang 6 in Hujianshan area and analyzed the distribution regular pattern of the oil and water and geologic condition which controlled the distribution of oil and water layers. The result showed there were four sandmicrofacies in Hujianshan area，including the subaqueous distributary channel, channelmouth bar, distal bar and interdistributary. The schedule of exploration indicates that oil reservoir can be found in different sedimentary microfacies and water layer almost seize thicklystratified sand. Oilbearing capability of different parts of sedarenite deposited at the same time is not exactly the same. The complex character about distribution regularity of oil and water shows that sedimentary facies are not the unique factor which controls the complicate distribution of oil and water. Internal reservoir structure ,calcarinate degree，the capability of oil lateral migration and the connectivity of sedarenite in different periods all had an effect on distribution regularity of oil and water, but the important reasons were the sand distribution feature，the capability of oil lateral migration and internal reservoir structure.
Based on the fundamental data of core, log and well logging，we studied the sedimentary microfacies types and evolutionary feature of Chang 6 in Hujianshan area and analyzed the distribution regular pattern of the oil and water and geologic condition which controlled the distribution of oil and water layers. The result showed there were four sandmicrofacies in Hujianshan area，including the subaqueous distributary channel, channelmouth bar, distal bar and interdistributary. The schedule of exploration indicates that oil reservoir can be found in different sedimentary microfacies and water layer almost seize thicklystratified sand. Oilbearing capability of different parts of sedarenite deposited at the same time is not exactly the same. The complex character about distribution regularity of oil and water shows that sedimentary facies are not the unique factor which controls the complicate distribution of oil and water. Internal reservoir structure ,calcarinate degree，the capability of oil lateral migration and the connectivity of sedarenite in different periods all had an effect on distribution regularity of oil and water, but the important reasons were the sand distribution feature，the capability of oil lateral migration and internal reservoir structure.
2011, 29(1): 164-172.
Abstract:
Mohe basin is a fault basin infilled with Lower Cretaceous volcanic rock and with growth of dual structure consisting of volcanic rock and sedimentary rock. The Yiliekede group source rock in Mohe basin belongs to limnetic facies and is developed in basaltic series. The source rocks including oil shale, shale and coal. The source rocks were deposited in the same time with the basalts, and the igneous rock were formed for the volcanic lava or pyroclastic into lake water directly. Based on the analytic technique of GC and GCMS, the depositional environment, biogenetic derivation and maturity of the source rocks were discussed. The results show that the abundance of the organic material of source rock is rather high, the kerogen of the oil shale is mainly of type Ⅱ, the coal and the shale is mainly of type Ⅲ; The source rocks were not heated by the basalt magma (Ro=0.56%~0.59%), and the thermal evolution of the samples have reached low maturation stage, and just entered the oil generation threshold. Thus the source rock is a set of excellent source rock measures with much better hydrocarbon generation potential. The source rocks are deposited in an water body of strong weakly reduction. The salt of the water bowere changed between salt and freshwatertiny salt quickly. The hydrocarbon came from the mixedsource of organics from the input of aquatic organisms and terrigenous plant, and the terrigenous plant is more enough in coals.
Mohe basin is a fault basin infilled with Lower Cretaceous volcanic rock and with growth of dual structure consisting of volcanic rock and sedimentary rock. The Yiliekede group source rock in Mohe basin belongs to limnetic facies and is developed in basaltic series. The source rocks including oil shale, shale and coal. The source rocks were deposited in the same time with the basalts, and the igneous rock were formed for the volcanic lava or pyroclastic into lake water directly. Based on the analytic technique of GC and GCMS, the depositional environment, biogenetic derivation and maturity of the source rocks were discussed. The results show that the abundance of the organic material of source rock is rather high, the kerogen of the oil shale is mainly of type Ⅱ, the coal and the shale is mainly of type Ⅲ; The source rocks were not heated by the basalt magma (Ro=0.56%~0.59%), and the thermal evolution of the samples have reached low maturation stage, and just entered the oil generation threshold. Thus the source rock is a set of excellent source rock measures with much better hydrocarbon generation potential. The source rocks are deposited in an water body of strong weakly reduction. The salt of the water bowere changed between salt and freshwatertiny salt quickly. The hydrocarbon came from the mixedsource of organics from the input of aquatic organisms and terrigenous plant, and the terrigenous plant is more enough in coals.
2011, 29(1): 184-191.
Abstract:
Based on the research of saturated hydrocarbon biomarkers of crude oils in Eastern Xinjiang area (including the TurpanHami Basin and Santanghu Basin), a comprehensive analysis and geochemistry study were carried out on aromatic fractions of crude oils. Through analysis of the composition of aromatic hydrocarbon, types of crude oils were divided. The distribution of compounds (alkyl naphthalene, F,OF and SF' , cadalene and retene )shows sedimentary environment of Carboniferous organic matter crude oils in Santanghu Basin were low water salinity, weak reduction, the oilrich parent materials from terrestrial input, and sedimentary facies transition phase for the land and sea. Optimization of dimethyl phenanthrene, the top three phenanthrene indexes and thermal evolution of the two sterane isomerization indexs have good correlation and consistency, and can effectively indicate the high evolution stage. In addition, application of the two indicators to determine Santanghu Carboniferous Basin Karaoke Gang Unit, department of crude oil is the high maturity crude oil, and Haerjiawu group is overmature crude oil.
Based on the research of saturated hydrocarbon biomarkers of crude oils in Eastern Xinjiang area (including the TurpanHami Basin and Santanghu Basin), a comprehensive analysis and geochemistry study were carried out on aromatic fractions of crude oils. Through analysis of the composition of aromatic hydrocarbon, types of crude oils were divided. The distribution of compounds (alkyl naphthalene, F,OF and SF' , cadalene and retene )shows sedimentary environment of Carboniferous organic matter crude oils in Santanghu Basin were low water salinity, weak reduction, the oilrich parent materials from terrestrial input, and sedimentary facies transition phase for the land and sea. Optimization of dimethyl phenanthrene, the top three phenanthrene indexes and thermal evolution of the two sterane isomerization indexs have good correlation and consistency, and can effectively indicate the high evolution stage. In addition, application of the two indicators to determine Santanghu Carboniferous Basin Karaoke Gang Unit, department of crude oil is the high maturity crude oil, and Haerjiawu group is overmature crude oil.
2011, 29(1): 199-206.
Abstract:
Advance on sedimentology and sequence stratigraphy were summed up in view of point from oil and gas exploration in petroliferous basins. It included as follows: the third order sequence and types of systems tract and its significance of petroleum geology; sequence stratigraphic application in unconventional oil and gas exploration; palaeosoil and trace fossils and its significance in sequence identification; basin types and depositional systems including basin fills such as tectonic, climate and deposits, foreland basin deposits, faulted basin deposits, stripslide basin deposits etc., as well as depositional sequence of clastic system such as lacustrine, glacial and eolian system； deep water sedimentology； basin analysis and resource sedimentology including coal, oil and gas, placer mine, source rocks and reservoirs etc. ; volcanic rocks reservoirs including volcanic deposits, volcanic eruption, volcanic diffusion and facies model； element geochemistry including clastic geochemistry such as diagenetic petrology, clastic petrology and geochemistry, provenance and weathering, and clay mineral geochemistry；and advance on carbonate rocks sedimentology including microbial carbonate sedimentology, mixed carbonate and clastic rocks, cold water carbonate rocks, and diagenetic changes and geochemistry of carbonate rocks. It also finally points out that future emphasis in oil and gas exploration focus on outcrops and modern deposits research, laboratory technique and sedimentary geochemistry, laboratory model and numerical simulation, and sequence stratigraphy and foreland basin analysis.
Advance on sedimentology and sequence stratigraphy were summed up in view of point from oil and gas exploration in petroliferous basins. It included as follows: the third order sequence and types of systems tract and its significance of petroleum geology; sequence stratigraphic application in unconventional oil and gas exploration; palaeosoil and trace fossils and its significance in sequence identification; basin types and depositional systems including basin fills such as tectonic, climate and deposits, foreland basin deposits, faulted basin deposits, stripslide basin deposits etc., as well as depositional sequence of clastic system such as lacustrine, glacial and eolian system； deep water sedimentology； basin analysis and resource sedimentology including coal, oil and gas, placer mine, source rocks and reservoirs etc. ; volcanic rocks reservoirs including volcanic deposits, volcanic eruption, volcanic diffusion and facies model； element geochemistry including clastic geochemistry such as diagenetic petrology, clastic petrology and geochemistry, provenance and weathering, and clay mineral geochemistry；and advance on carbonate rocks sedimentology including microbial carbonate sedimentology, mixed carbonate and clastic rocks, cold water carbonate rocks, and diagenetic changes and geochemistry of carbonate rocks. It also finally points out that future emphasis in oil and gas exploration focus on outcrops and modern deposits research, laboratory technique and sedimentary geochemistry, laboratory model and numerical simulation, and sequence stratigraphy and foreland basin analysis.
2011, 29(1): 14-22.
Abstract:
In western Liaoning province, the Yixian Basin is thought as the subdepression of Cretaceous FuxinYixian Basin, the intrabasin Yixian Formation section is cropped out in MashenmiaoDaobadiSanbailongJingangshan, strikingly from east to west. As the middle part of Yixian Formation, Zhuanchengzi layer consists of lacustrine sediments in Yingwoshan area. These sedimentary piles are divided into three subdivisions. The lower part comprises coarser turbidites(T, Ta1, Ta2)and finer turbidites(Tb1, Tb2), the former is made up of bentonitic gritstone, mottle gompholite, grayishgreen tuffaceous conglomerate, earthy granular conglomerate, the latter is grayishgreen bentonitic siltsone, containing carbonized debris, sedimentary tuffite and mudstone. Influenced by turbidity and regional tectonic processes, the water column becomes shallower, the coarser and finer turbidites divisions (Ta3Ta6, Tb3Tb6)were formed around lake margin and thinbedded silicified dolomite deposits on the finer turbidite divisions. The middle part of Zhuangchengzi layer consists of silicified dolomite, containing chert nodules, dolomitic limestone, laminae dolomite and slumping dolomitic limestone. The upper part of Zhuangchengzi layer is characterized by hemi to deep and hemi to shallow lacustrine facies, the rock assemblage is of tuffaceous calcarenite, bentonitic marl, dolomite, bentonite and greyblack shale. The sedimentary rock association indicates that there were marginal turbidity processes, lacustrineplat environment, dolomitic limestone formed around lacustrine ramp, laminae dolomiteshale formed in deep lacustine facies, and a lot of volcanic and terrestrial clastic debris filled the basin.
In western Liaoning province, the Yixian Basin is thought as the subdepression of Cretaceous FuxinYixian Basin, the intrabasin Yixian Formation section is cropped out in MashenmiaoDaobadiSanbailongJingangshan, strikingly from east to west. As the middle part of Yixian Formation, Zhuanchengzi layer consists of lacustrine sediments in Yingwoshan area. These sedimentary piles are divided into three subdivisions. The lower part comprises coarser turbidites(T, Ta1, Ta2)and finer turbidites(Tb1, Tb2), the former is made up of bentonitic gritstone, mottle gompholite, grayishgreen tuffaceous conglomerate, earthy granular conglomerate, the latter is grayishgreen bentonitic siltsone, containing carbonized debris, sedimentary tuffite and mudstone. Influenced by turbidity and regional tectonic processes, the water column becomes shallower, the coarser and finer turbidites divisions (Ta3Ta6, Tb3Tb6)were formed around lake margin and thinbedded silicified dolomite deposits on the finer turbidite divisions. The middle part of Zhuangchengzi layer consists of silicified dolomite, containing chert nodules, dolomitic limestone, laminae dolomite and slumping dolomitic limestone. The upper part of Zhuangchengzi layer is characterized by hemi to deep and hemi to shallow lacustrine facies, the rock assemblage is of tuffaceous calcarenite, bentonitic marl, dolomite, bentonite and greyblack shale. The sedimentary rock association indicates that there were marginal turbidity processes, lacustrineplat environment, dolomitic limestone formed around lacustrine ramp, laminae dolomiteshale formed in deep lacustine facies, and a lot of volcanic and terrestrial clastic debris filled the basin.
2011, 29(1): 31-40.
Abstract:
Bioclastic and biohermal limestones, which are widely exposed in the orogenic belt, should be formed in different tectonic environments. Identifying their composition and fossil occurrence state is of fundamental importance for palaeogeographical reconstructions and orogenic evolution. Carbonate rocks, which are closely related to alkaline basalts with high TiO2 abundance, have been regarded as platform deposits of passive margin in the North Daba Mountains. They are composed of biohermal limestone, bioclastic limestone, calcarenite, and marlstone with abundant bioclastic and volcanic fragments. Thinner pyroclastic interlayers generally occur in the calcarenite and bioclastic limestone assemblages. Graded, parallel, wavy beddings and slump structure are very common in the outcrops. Bioclastic limestone, tuffaceous sandstone and mudstone generally show rhythmic features. Volcanic fragments within the bioclastic limestone are mainly composed of 0.5 to 3 mm angularsubangular basalt and tuff, indicating proximal sedimentary deposits. Volcanic fragments of the biohermal limestone are dominated by 1~2.5 cm angularsubangular basalts and 0.51 mm subrounded basalt fragments are also abundant in the sandstone beds which are interbeded within the biochermal limestone beds. Two types of volcanic fragments occur in the calcarenite: basalt and pyroxene. They are angular and subangular, and pyroxene fragments range from 1 to 2 mm in size. Abundant pyrite grains in the calcarenite show normal graded structures because of their size variation. Breccia limestone is composed of calcarenite, biohermal and bioclastic limestones, and basalt fragments only exist in the breccia biohermal limestone. Fossil clasts/fragments in the calcarenite and bioclastic limestone are mainly subrounded, suggesting that these fossil fragments had ever been transported for a long distance. Additionally, the growth orientation and distribution of fossils in the biochermal limestone are generally parallel to the sandstone interbeds, and slump structures are very common in this lithology. These characters coevally suggest that these carbonate assemblages are sincerely associated with the underlying basalts with alkaline geochemical affinity spatially; they have the similar framework and constitute characters of modern oceanic island/sea mountain. The carbonate generally developed around the underlying basalts and deposited in the deepwater and slope environments. Moreover, fossils within these carbonates should be derived from other place and were modified during transport, indicating the ages of these fossils should be earlier to the age of carbonate rocks.
Bioclastic and biohermal limestones, which are widely exposed in the orogenic belt, should be formed in different tectonic environments. Identifying their composition and fossil occurrence state is of fundamental importance for palaeogeographical reconstructions and orogenic evolution. Carbonate rocks, which are closely related to alkaline basalts with high TiO2 abundance, have been regarded as platform deposits of passive margin in the North Daba Mountains. They are composed of biohermal limestone, bioclastic limestone, calcarenite, and marlstone with abundant bioclastic and volcanic fragments. Thinner pyroclastic interlayers generally occur in the calcarenite and bioclastic limestone assemblages. Graded, parallel, wavy beddings and slump structure are very common in the outcrops. Bioclastic limestone, tuffaceous sandstone and mudstone generally show rhythmic features. Volcanic fragments within the bioclastic limestone are mainly composed of 0.5 to 3 mm angularsubangular basalt and tuff, indicating proximal sedimentary deposits. Volcanic fragments of the biohermal limestone are dominated by 1~2.5 cm angularsubangular basalts and 0.51 mm subrounded basalt fragments are also abundant in the sandstone beds which are interbeded within the biochermal limestone beds. Two types of volcanic fragments occur in the calcarenite: basalt and pyroxene. They are angular and subangular, and pyroxene fragments range from 1 to 2 mm in size. Abundant pyrite grains in the calcarenite show normal graded structures because of their size variation. Breccia limestone is composed of calcarenite, biohermal and bioclastic limestones, and basalt fragments only exist in the breccia biohermal limestone. Fossil clasts/fragments in the calcarenite and bioclastic limestone are mainly subrounded, suggesting that these fossil fragments had ever been transported for a long distance. Additionally, the growth orientation and distribution of fossils in the biochermal limestone are generally parallel to the sandstone interbeds, and slump structures are very common in this lithology. These characters coevally suggest that these carbonate assemblages are sincerely associated with the underlying basalts with alkaline geochemical affinity spatially; they have the similar framework and constitute characters of modern oceanic island/sea mountain. The carbonate generally developed around the underlying basalts and deposited in the deepwater and slope environments. Moreover, fossils within these carbonates should be derived from other place and were modified during transport, indicating the ages of these fossils should be earlier to the age of carbonate rocks.
2011, 29(1): 55-63.
Abstract:
Depositional characteristics and environment of the Lower Cambrian Suzhong Formation in Aershan area of Inner Mongolia are analyzed through integrating areal stratum, lithology, section characteristics, and distribution of the grain size. Grain size of the sandstone in the Suzhong Formation presents the following characters: with double or multimodal anisomerous peaks in grain size distribution frequency curves; mainly in positive skewed distribution; numerous but low peak values; poor sorting and most of the grain consists of those of coarse materials. Based on the size parameters, we located in the Sahu diagram and calculated with discriminate function, it is ascertained that the sandstone in the Lower Cambrian Suzhong Formation which lies in Aershan area of Inner Mongolia are deposited in marine delta environment. Nevertheless, most clastic deposits of the Suzhong Formation is macrograin materials with their grain size distribution similar to wave sand of neritic, and with larger suspension population as well; the mixing deposited sandstone and limestone appears lenticular bedding and rhythmic bedding; so we conclude that the sandstone of this area is deposited in the mixed flat of tide dominate delta. The limestone in the area studied mainly are Greyish white sandy limestone, dolomitic limestone, being recrystallized, with honeycombed surface and horizontal bedding, through these, we draw the following conclusion that limestone of the Lower Cambrian Suzhong Formation in Aershan area of Inner Mongolia are deposited in limemud flat.
Depositional characteristics and environment of the Lower Cambrian Suzhong Formation in Aershan area of Inner Mongolia are analyzed through integrating areal stratum, lithology, section characteristics, and distribution of the grain size. Grain size of the sandstone in the Suzhong Formation presents the following characters: with double or multimodal anisomerous peaks in grain size distribution frequency curves; mainly in positive skewed distribution; numerous but low peak values; poor sorting and most of the grain consists of those of coarse materials. Based on the size parameters, we located in the Sahu diagram and calculated with discriminate function, it is ascertained that the sandstone in the Lower Cambrian Suzhong Formation which lies in Aershan area of Inner Mongolia are deposited in marine delta environment. Nevertheless, most clastic deposits of the Suzhong Formation is macrograin materials with their grain size distribution similar to wave sand of neritic, and with larger suspension population as well; the mixing deposited sandstone and limestone appears lenticular bedding and rhythmic bedding; so we conclude that the sandstone of this area is deposited in the mixed flat of tide dominate delta. The limestone in the area studied mainly are Greyish white sandy limestone, dolomitic limestone, being recrystallized, with honeycombed surface and horizontal bedding, through these, we draw the following conclusion that limestone of the Lower Cambrian Suzhong Formation in Aershan area of Inner Mongolia are deposited in limemud flat.
2011, 29(1): 72-79.
Abstract:
〓With thin section analysis and scanning electron microscopic analysis, the diagenetic phenomenon of Yanchan Formation sandstone in the Ordos basin were systematically studied, and it shows that chlorite film was the important diagenetic phenomenon in this area. Depending on the studies relevant to the features including occurrence, structural characteristics, relations between other diagenetic minerals of sandstones in this area, the formation mechanism was discussed in detail. Chlorite rim had some relevance with the original porosity of reservoirs, its formation had more closely relationship with hydrodynamic conditions during the contemporaneous deposition. They belonged to a mark of water power conditions for they occur mainly in the subaqueous distributary channel and mouth bar in the deltaic front, and had strong environmental specificity; chlorite rim had double layer structure in which isopachous rim cement of internal layer was relative dense, and formed during the early diagenetic stage. Outerlayer authigenic chlorite grown on the rim surface vertically with better crystal form was formed during the late diagenetic stage; chlorite film was of a limited ability to protect the sandstone porosity. The reason for this is that the porosity of sandstones with chlorite clay rim was better mainly depended on the petrological characteristics of sedimentary sandstones under strong hydrodynamic condition. It had little relation with the chlorite clay rim. So the formation model of chlorite clay rim was put forward. It was considered that the formation of the chlorite film experienced five steps: sedimentary stage of original particles, stage of clay adsorption and film formation on the surface of original particles, early compaction stage of particles, stage of rim chloritization, authigenic chlorite forming stage; In view of this, the sedimentary sandstone reservoirs that had chlorite clay rims under strong hydrodynamic conditions should be the target in the process of oil exploration.
〓With thin section analysis and scanning electron microscopic analysis, the diagenetic phenomenon of Yanchan Formation sandstone in the Ordos basin were systematically studied, and it shows that chlorite film was the important diagenetic phenomenon in this area. Depending on the studies relevant to the features including occurrence, structural characteristics, relations between other diagenetic minerals of sandstones in this area, the formation mechanism was discussed in detail. Chlorite rim had some relevance with the original porosity of reservoirs, its formation had more closely relationship with hydrodynamic conditions during the contemporaneous deposition. They belonged to a mark of water power conditions for they occur mainly in the subaqueous distributary channel and mouth bar in the deltaic front, and had strong environmental specificity; chlorite rim had double layer structure in which isopachous rim cement of internal layer was relative dense, and formed during the early diagenetic stage. Outerlayer authigenic chlorite grown on the rim surface vertically with better crystal form was formed during the late diagenetic stage; chlorite film was of a limited ability to protect the sandstone porosity. The reason for this is that the porosity of sandstones with chlorite clay rim was better mainly depended on the petrological characteristics of sedimentary sandstones under strong hydrodynamic condition. It had little relation with the chlorite clay rim. So the formation model of chlorite clay rim was put forward. It was considered that the formation of the chlorite film experienced five steps: sedimentary stage of original particles, stage of clay adsorption and film formation on the surface of original particles, early compaction stage of particles, stage of rim chloritization, authigenic chlorite forming stage; In view of this, the sedimentary sandstone reservoirs that had chlorite clay rims under strong hydrodynamic conditions should be the target in the process of oil exploration.
2011, 29(1): 88-96.
Abstract:
The reservoir in Shannbei structural slope is affected by the depositional environment, diagenesis and structural factor, so the compaction and cementation effects are intense in Shanbei slope center. In this paper relative high quality reservoirs of hyposmosis reservoir were filtered, in which diagenetic reservior facies mode of quantitative classification of Chang 61 reservoir in AS oilfield of extralow permeability was used. With the work of sandstone diagenesis and porosity evolution analysis of Chang 61, different types of diagenetic reservoir facies model of quantitative classification and comprehensive evaluation index system of diagenesis reservoir facies was established. The evolution parameter of diagenesis in different diagenetic reservior facies and the characteristic of reservoir & flow are obviously not the same. The compaction porosity loss rate of I, II diagenetic reservior facies is 5.1%~6.6%; cement prosity loss rate is 30.1%~36.0%; dissolution of secondary porosity increased up to 9.7% with an average of increasing porosity of 5.1%~6.5%. It can be the standard of diagenetic reservior facies "dessert" because of less loss of pore compaction cementation and great increase of dissolution porosity. And these can be used to quantitatively evaluate reservior.
〓〓Diagenetic stage of pore evolution parameter of different wells in Chang 61 could get by the results' deduction of pore evolution analysis along diagenetic process, and the results come from the material analysis and the identification of pore space of different samples in Chang 61. Though the integration of gray theory of the following parameters, compaction loss porosity, cementation loss porosity, dissolution increased porosity, porosity, permeability and thin section porosity, the matrix analysis of evaluation parameters and evaluation indicator can be normalized, the absolute difference extreme of standard indicators could be weighted combination & amplification and integrated analysis and processing. With the integration of multiple information in diagenesis, theⅠ,Ⅱtype diagenesis reservoir facies “dessert” was filtered. They mainly distributed in the vicinity of generating rock of the centre of acidic lake basin, and were located in favorable reservoir sand in overlying location of the underwater distributary channel of delta front subfacies, more primary porosity was remained in the formation of organic acids water period in diagenetic process, diffluent clastic particles and cementing material were dissolved by acidic water, secondary laumontite and feldspar pore was generated. Thus, relative highquality reservoirs which controlled and blocked out favorable oilbearing areas in extralow permeability Chang 61 reservoir were formed.
〓〓The scale and scope of favorable oil field with the direction from the center to the southwest in the lake area could be identified by the above mentioned highquality reservoir. Using sedimentation, diagenesis, posttectonic and the role of fluid transformation draw the scope of favorable diagenetic reservoir unit, the geological features of highquality reservoir could be reflect, and with a further characterization of the distribution pattern, extend the direction and characteristics of nonhomogeneous in this low permeability oil field. Thus, the awareness of reservoir sedimentation, diagenesis features and the distribution of favorable oil area was raised, which is benefit to extralow permeability oil field to reach a high output.
The reservoir in Shannbei structural slope is affected by the depositional environment, diagenesis and structural factor, so the compaction and cementation effects are intense in Shanbei slope center. In this paper relative high quality reservoirs of hyposmosis reservoir were filtered, in which diagenetic reservior facies mode of quantitative classification of Chang 61 reservoir in AS oilfield of extralow permeability was used. With the work of sandstone diagenesis and porosity evolution analysis of Chang 61, different types of diagenetic reservoir facies model of quantitative classification and comprehensive evaluation index system of diagenesis reservoir facies was established. The evolution parameter of diagenesis in different diagenetic reservior facies and the characteristic of reservoir & flow are obviously not the same. The compaction porosity loss rate of I, II diagenetic reservior facies is 5.1%~6.6%; cement prosity loss rate is 30.1%~36.0%; dissolution of secondary porosity increased up to 9.7% with an average of increasing porosity of 5.1%~6.5%. It can be the standard of diagenetic reservior facies "dessert" because of less loss of pore compaction cementation and great increase of dissolution porosity. And these can be used to quantitatively evaluate reservior.
〓〓Diagenetic stage of pore evolution parameter of different wells in Chang 61 could get by the results' deduction of pore evolution analysis along diagenetic process, and the results come from the material analysis and the identification of pore space of different samples in Chang 61. Though the integration of gray theory of the following parameters, compaction loss porosity, cementation loss porosity, dissolution increased porosity, porosity, permeability and thin section porosity, the matrix analysis of evaluation parameters and evaluation indicator can be normalized, the absolute difference extreme of standard indicators could be weighted combination & amplification and integrated analysis and processing. With the integration of multiple information in diagenesis, theⅠ,Ⅱtype diagenesis reservoir facies “dessert” was filtered. They mainly distributed in the vicinity of generating rock of the centre of acidic lake basin, and were located in favorable reservoir sand in overlying location of the underwater distributary channel of delta front subfacies, more primary porosity was remained in the formation of organic acids water period in diagenetic process, diffluent clastic particles and cementing material were dissolved by acidic water, secondary laumontite and feldspar pore was generated. Thus, relative highquality reservoirs which controlled and blocked out favorable oilbearing areas in extralow permeability Chang 61 reservoir were formed.
〓〓The scale and scope of favorable oil field with the direction from the center to the southwest in the lake area could be identified by the above mentioned highquality reservoir. Using sedimentation, diagenesis, posttectonic and the role of fluid transformation draw the scope of favorable diagenetic reservoir unit, the geological features of highquality reservoir could be reflect, and with a further characterization of the distribution pattern, extend the direction and characteristics of nonhomogeneous in this low permeability oil field. Thus, the awareness of reservoir sedimentation, diagenesis features and the distribution of favorable oil area was raised, which is benefit to extralow permeability oil field to reach a high output.
2011, 29(1): 105-117.
Abstract:
Based on illustrating chronosequence framework, this article has proved the existence of nonperiodicity of shoreline trajectory within fourdivided model in current sequence stratigraphy, presenting one vertical periodicity corresponding to one and onesixth of lateral periodicities due to the unreasonably assigned highstand normal regression. Authors of this article suggest that the terms of highstand normal regression (HNR) and previous highstand systems tract HST formed during HNR should be abolished or reinterpreted. Depositional sequence has been adjusted as bounded by remnant maximum flooding surfaces (RMFS) and their correlative subaerial unconformities (CSU), and is composed of falling stage, lowstand, transgressive systems tracts upwards, i.e., FSSTLSTTST superposition. At the same time, this paper has united the boundaries between depositional sequence, genetic sequence and RT sequence on the basis of abolishing highstand normal regression and previously assigned highstand systems tract to avoid that genetic sequence and TR sequence span two depositional sequences.
Based on illustrating chronosequence framework, this article has proved the existence of nonperiodicity of shoreline trajectory within fourdivided model in current sequence stratigraphy, presenting one vertical periodicity corresponding to one and onesixth of lateral periodicities due to the unreasonably assigned highstand normal regression. Authors of this article suggest that the terms of highstand normal regression (HNR) and previous highstand systems tract HST formed during HNR should be abolished or reinterpreted. Depositional sequence has been adjusted as bounded by remnant maximum flooding surfaces (RMFS) and their correlative subaerial unconformities (CSU), and is composed of falling stage, lowstand, transgressive systems tracts upwards, i.e., FSSTLSTTST superposition. At the same time, this paper has united the boundaries between depositional sequence, genetic sequence and RT sequence on the basis of abolishing highstand normal regression and previously assigned highstand systems tract to avoid that genetic sequence and TR sequence span two depositional sequences.
2011, 29(1): 125-133.
Abstract:
The majority of presentday evaporite deposition occurs in arid closed continental basins in which the playa lake is most common. The distribution of evaporite minerals and sedimentary features of salt crust are usually zonal in a playa lake. The integrated zonal configuration is preserved well in the Lop Nor playa, which is represented by a series of concentric rings that closely resemble a great human ear in satellite images. This type of natural phenomenon is very rarely seen in a playa lake. The Lop Nor basin consists of a broad, flat salt plain, and salt crusts covering approximately 5,500 km2 with the lowest parts at 780 m above sea level. After investigating the fracture texture of salt crust, sedimentary structures, evaporite mineral composition, and the condition of groundwater brine discharge in the multicyclic "Great Ear" rings, we can discuss the origin of different salt crust types, the connection between adjacent concentric zones, and the evolutionary process of the concentric configuration of the "Great Ear" salt pans. This research also gives a general overview of the sedimentary features in different cycles of saltpan evaporite, as well as the relationship between the development of polygonal fissure structures of salt crust and the groundwater brine table. The types of saltcrust structure include polygon crack, welldeveloped honeycombshaped halite crusts, moundshaped pattern and plateshaped halite crusts. However, the sediment beneath the surface is typically saturated with concentrated brines and displacive evaporites. There is visual evidence of discharging groundwater in the numerous moist salt pans covering most of the salt plain, suggesting that the capillary fringe of the groundwater table is close to the surface of the salt pans.The development of salt crust structures were generally controlled by the groundwater table with a depth of < 2m in the Lop Nor playa. But it is also affected by many factors such as sediment permeability, brine density, evaporites, cracks and atmospheric conditions.
The majority of presentday evaporite deposition occurs in arid closed continental basins in which the playa lake is most common. The distribution of evaporite minerals and sedimentary features of salt crust are usually zonal in a playa lake. The integrated zonal configuration is preserved well in the Lop Nor playa, which is represented by a series of concentric rings that closely resemble a great human ear in satellite images. This type of natural phenomenon is very rarely seen in a playa lake. The Lop Nor basin consists of a broad, flat salt plain, and salt crusts covering approximately 5,500 km2 with the lowest parts at 780 m above sea level. After investigating the fracture texture of salt crust, sedimentary structures, evaporite mineral composition, and the condition of groundwater brine discharge in the multicyclic "Great Ear" rings, we can discuss the origin of different salt crust types, the connection between adjacent concentric zones, and the evolutionary process of the concentric configuration of the "Great Ear" salt pans. This research also gives a general overview of the sedimentary features in different cycles of saltpan evaporite, as well as the relationship between the development of polygonal fissure structures of salt crust and the groundwater brine table. The types of saltcrust structure include polygon crack, welldeveloped honeycombshaped halite crusts, moundshaped pattern and plateshaped halite crusts. However, the sediment beneath the surface is typically saturated with concentrated brines and displacive evaporites. There is visual evidence of discharging groundwater in the numerous moist salt pans covering most of the salt plain, suggesting that the capillary fringe of the groundwater table is close to the surface of the salt pans.The development of salt crust structures were generally controlled by the groundwater table with a depth of < 2m in the Lop Nor playa. But it is also affected by many factors such as sediment permeability, brine density, evaporites, cracks and atmospheric conditions.
2011, 29(1): 143-150.
Abstract:
A 106 m long sediment core named BDQ0608 was drilled from the Hohxil area in hinterland of the Tibet Plateau, and the lithology is mostly reseda lake sediments with part of a thin oxide color layer. The thermal demagnetization indicates that magnetic mineral in BDQ0608 core mainly includes magnetite, maghemite, goethite, melnikovite, and trace hematite. Magnetic susceptibility was directly related to the composition of magnetic mineral. Magnetite, which abounds in sandy and argillaceous samples, was considered to derive from the detrital minerals in the basin and be a major contributor to magnetic susceptibility of the whole core. The hematite and goethite generated under postoxidation and oxidationreduction conditions are both lowmagnetic minerals, so they have relatively little contributions to the magnetic susceptibility. Furthermore, it should be specially pointed out that ferromagnetic iron sulfide which dominates magnetism of sediments in the argillaceous sediments would induce much higher magnetic susceptibility than the others. In addition, magnetic susceptibility, grain size, TOC and color reflectance were analyzed at 10 cm intervals. The positive correlation between magnetic susceptibility and clay content is attributed to the destruction of the mucus pyrite formed late and magnetic minerals from sand sediments. Meanwhile, comparing magnetic susceptibility with TOC and color reflectance a* separately, the results indicated that there are both positive correlation between them, which may be mainly affected by temperature and humidity. On the one hand, high TOC content implied that the climate during this period was warm and humid corresponding to high lake water level, which could avoid destroying magnetic minerals in the sediments. On the other hand, it was beneficial to the generation of ferromagnetic sulfide in the lakes with high TOC content. The amount of hematite could have a certain contribution to the change of magnetic susceptibility, but it mainly dominated red degrees value(color reflectance a* values) of sediments. So, low color reflectance values of the sediments show less hematite content, but it may also be the reason for the poor performance of the thermal demagnetization process of hematite. The good positive correlation between color reflectance a* values and the changes in magnetic susceptibility curve showed that the varieties of them were subjected to the same environmental factors. Nevertheless, the fluctuation of magnetic susceptibility is not in line with other proxies, and influenced by ambient environment condition during the period of sediment formation. Although as an environmental proxy magnetic susceptibility can reflect environmental changes well, we must combine with other high accurate environmental proxies to improve the accuracy of paleoenvironmental reconstruction.
A 106 m long sediment core named BDQ0608 was drilled from the Hohxil area in hinterland of the Tibet Plateau, and the lithology is mostly reseda lake sediments with part of a thin oxide color layer. The thermal demagnetization indicates that magnetic mineral in BDQ0608 core mainly includes magnetite, maghemite, goethite, melnikovite, and trace hematite. Magnetic susceptibility was directly related to the composition of magnetic mineral. Magnetite, which abounds in sandy and argillaceous samples, was considered to derive from the detrital minerals in the basin and be a major contributor to magnetic susceptibility of the whole core. The hematite and goethite generated under postoxidation and oxidationreduction conditions are both lowmagnetic minerals, so they have relatively little contributions to the magnetic susceptibility. Furthermore, it should be specially pointed out that ferromagnetic iron sulfide which dominates magnetism of sediments in the argillaceous sediments would induce much higher magnetic susceptibility than the others. In addition, magnetic susceptibility, grain size, TOC and color reflectance were analyzed at 10 cm intervals. The positive correlation between magnetic susceptibility and clay content is attributed to the destruction of the mucus pyrite formed late and magnetic minerals from sand sediments. Meanwhile, comparing magnetic susceptibility with TOC and color reflectance a* separately, the results indicated that there are both positive correlation between them, which may be mainly affected by temperature and humidity. On the one hand, high TOC content implied that the climate during this period was warm and humid corresponding to high lake water level, which could avoid destroying magnetic minerals in the sediments. On the other hand, it was beneficial to the generation of ferromagnetic sulfide in the lakes with high TOC content. The amount of hematite could have a certain contribution to the change of magnetic susceptibility, but it mainly dominated red degrees value(color reflectance a* values) of sediments. So, low color reflectance values of the sediments show less hematite content, but it may also be the reason for the poor performance of the thermal demagnetization process of hematite. The good positive correlation between color reflectance a* values and the changes in magnetic susceptibility curve showed that the varieties of them were subjected to the same environmental factors. Nevertheless, the fluctuation of magnetic susceptibility is not in line with other proxies, and influenced by ambient environment condition during the period of sediment formation. Although as an environmental proxy magnetic susceptibility can reflect environmental changes well, we must combine with other high accurate environmental proxies to improve the accuracy of paleoenvironmental reconstruction.
2011, 29(1): 158-163.
Abstract:
Through drilling and seismic data, development and distribution of caprock of Xushen gas field was studied. It was considered that caprock of Xushen gas field is mainly mudstone caprock of K1d2 and volcanic caprock on top of K1yc1, and the former which distributes in the whole of depression is caprock of gas reserved in K1yc4 volcanic breccia in the south of depression and caprock of gas reserved in K1yc3 volcanic in the north of depression, the later which distributes in the south of depression is caprock of gas reserved in volcanic. Through test and logging data, displacement pressure of caprock and reservoir and excessive pressure of gas reservoirs were studied. It was considered that displacement pressure of caprock in 12 gas reservoirs is larger than the sum of displacement pressure of gas reservoirs. Their seal gas ability effectiveness is good, and it is favorable for gas to accumulate and preserve. Through the study of evolution of seal gas ability of caprock and relation between formation period of seal gas ability and massive expulsion gas period of seal source rock, it was considered that formation period of seal gas of K1d2 caprock and K1yc1caprock are sedimentary period of K1q1,2 and K1d4 and they are earlier than massive expulsion gas period of gas source rock(Sedimentary period of K1 sh). Their seal gas time effectiveness is good. It is favorable for largescaled gas accumulation.
Through drilling and seismic data, development and distribution of caprock of Xushen gas field was studied. It was considered that caprock of Xushen gas field is mainly mudstone caprock of K1d2 and volcanic caprock on top of K1yc1, and the former which distributes in the whole of depression is caprock of gas reserved in K1yc4 volcanic breccia in the south of depression and caprock of gas reserved in K1yc3 volcanic in the north of depression, the later which distributes in the south of depression is caprock of gas reserved in volcanic. Through test and logging data, displacement pressure of caprock and reservoir and excessive pressure of gas reservoirs were studied. It was considered that displacement pressure of caprock in 12 gas reservoirs is larger than the sum of displacement pressure of gas reservoirs. Their seal gas ability effectiveness is good, and it is favorable for gas to accumulate and preserve. Through the study of evolution of seal gas ability of caprock and relation between formation period of seal gas ability and massive expulsion gas period of seal source rock, it was considered that formation period of seal gas of K1d2 caprock and K1yc1caprock are sedimentary period of K1q1,2 and K1d4 and they are earlier than massive expulsion gas period of gas source rock(Sedimentary period of K1 sh). Their seal gas time effectiveness is good. It is favorable for largescaled gas accumulation.
2011, 29(1): 173-183.
Abstract:
The Paleogene system in the Dongying sag is a representative lacustrine basin in the eastern China. To investigate the distribution and characteristics of the homohopane maturation parameters, the main source rocks from Member 3 (deposited in fresh and brackish water) and Member 4 (deposited in salty water) in Shahejie Formation (burial depth from 1 300 m to 4 000 m) were investigated. The range 2 800~4 200 m coincides with the "oil window" from the early of oil generation to the late of oil generation, which can well represent the evolution of homohopane maturation parameters during the process of oil generation.
〓〓The results demonstrate that the main controlling factors for the distribution of C31, C32, C33, C34, C35 (17α) homohopane parameters are the isomerization and different decomposition rates as well as generation rates between different isomers. Depositional environment (such as highsalt environment) also impacts their distribution to some extent. For immature and lowmature samples, the related parameters 22S/(22S+22R) increase with burial depth from a disperse state to a equilibrium state, while for the matured samples the parameters increase slowly and then transit to a continuous thermal equilibrium state. In highsalt environment most homohopanes show reversal in different degree except C33 homohopane which remains unchanged in an equilibrium state, indicating that high content of saline minerals also has inhibited or retarded the homohopane maturity parameters. The thermal equilibrium of the parameters coincides with the threshold of oil generation and can be seen as a good indicator for oil generation. The distribution patterns of C31, C32, C33, C34, C35(17α) 22S/(22S+22R) are complex and diversified. For the matured source rock samples, the C35 homohopane 22S/ (22S+22 R) shows a strong change and is characterized by obvious "rise and" "fall". While for the immature samples, C3222S/(22S+22R) displays some remarkable high value, and most immature samples demonstrate characteristics of C31C33 C35 and exhibits an advantage of evennumber carbon. The study shows that the thermal equilibrium values for C31, C32, C33 isomerization parameters are 0.6 consistently , while the equilibrium values for C34 and C35 homohopanes are comparatively high (the equilibrium of C3422S/(22S+22R) for Member 3 and Member 4 are 0.63, 0.62 respectively, and the equilibrium of C3522S/(22S+22R) for Member 4 reaches 0.65). The homohopane index C35/Σ(C31C35) is also impacted by thermal evolution. In the oil window the index firstly decreases as the burial depth increases, and in the 3.6km highsalt environment, the index shows opposite trend and relatively high values. The study indicates that its change is dominated by 22R isomers. The parameters C31/Σ(C31C35), C32/Σ(C31C35), C33/Σ(C31C35), C34/Σ(C31C35), C35/Σ(C31C35) show different characteristics in their distribution and evolution in the profile.
The Paleogene system in the Dongying sag is a representative lacustrine basin in the eastern China. To investigate the distribution and characteristics of the homohopane maturation parameters, the main source rocks from Member 3 (deposited in fresh and brackish water) and Member 4 (deposited in salty water) in Shahejie Formation (burial depth from 1 300 m to 4 000 m) were investigated. The range 2 800~4 200 m coincides with the "oil window" from the early of oil generation to the late of oil generation, which can well represent the evolution of homohopane maturation parameters during the process of oil generation.
〓〓The results demonstrate that the main controlling factors for the distribution of C31, C32, C33, C34, C35 (17α) homohopane parameters are the isomerization and different decomposition rates as well as generation rates between different isomers. Depositional environment (such as highsalt environment) also impacts their distribution to some extent. For immature and lowmature samples, the related parameters 22S/(22S+22R) increase with burial depth from a disperse state to a equilibrium state, while for the matured samples the parameters increase slowly and then transit to a continuous thermal equilibrium state. In highsalt environment most homohopanes show reversal in different degree except C33 homohopane which remains unchanged in an equilibrium state, indicating that high content of saline minerals also has inhibited or retarded the homohopane maturity parameters. The thermal equilibrium of the parameters coincides with the threshold of oil generation and can be seen as a good indicator for oil generation. The distribution patterns of C31, C32, C33, C34, C35(17α) 22S/(22S+22R) are complex and diversified. For the matured source rock samples, the C35 homohopane 22S/ (22S+22 R) shows a strong change and is characterized by obvious "rise and" "fall". While for the immature samples, C3222S/(22S+22R) displays some remarkable high value, and most immature samples demonstrate characteristics of C31
2011, 29(1): 192-198.
Abstract:
16 mudstone samples from wells of F8, Fs1 and Fs2 in Minfeng area of Dongying depression were selected for understanding the origin and the preservation of the organic matter and their significances. By the application of organic analysis including: total organic carbon content, extraction of soluble organic matter, group composition of soluble organic matter and GCMS of saturated hydrocarbon, the abundance, type and the maturity of the organic matter were studied.
〓〓The formation with the depth from 3 000 m to 5 000 m was divided into three units considering the existence of the gypsumsalt rock: the upper layer of the gypsumsalt rock, the gypsum layer and the lower layer of the gypsumsalt rock. There are great variations of the abundance of organic matter between each unit. The upper layer is much higher than others, so as to the content of chloroform bitumen "A". Both the TOC and the chloroform bitumen "A" of the gypsum layer are lower than the upper layer. The lower layer of the gypsumsalt rock is the lowest in chloroform bitumen "A", although one sample from F8 well has the TOC as high as 2.29%.
The group composition of the soluble organic matter shows that: in three members of source rocks, the type of organic matter of gypsum layer is the best, and the upper layer of the gypsumsalt rock followed, at last is the lower layer of the gypsumsalt rock. Analysis of the gammacerane index and the ratio of Pr/Ph indicate that the upper layer of the gypsumsalt rock and the gypsum layer have similar sedimentary environment which is reducing deep lacustrine deposional environment under semihumid climate conditions, and the salinity of the lake is normal in Dongying depression with fresh to brackish water. However, the depositional environment of gypsum layer is quite different for that is strong reducing saline lacustrine facies under semiarid climate conditions with high salinity. The climate condition of the upper layer of the gypsumsalt rock is relatively more humid and huge amounts of terrestrial organic matter come into the lacustrine basin with surface runoff. As a result, the source of the sedimentary organic matter is lower hydrobiont, lacustrine algae and terrestrial organic matter transported by the river. As the climate conditions get more aridity, the input of terrestrial organic matter decease due to the river discharge reduced. Meanwhile, the salinity of the lake get stronger because of the degree of drought is pricked up gradually, but many species of halophilic bacteria and variety kinds of algae adapted to the hypersaline environment growth rapidly. Therefore, the organic matter of the gypsum layer is mainly originated from lower hydrobiont and algae, which is supported mainly from the dominance of the isoprenoid to the normal alkanes. Because of the existence of the gypsumsalt rock, the difference of maturity of organic matter is significant from routine variation, which performance as the maturity of the gypsum layer is lower than both the upper and the lower layers.
〓〓The biomarker parameters of the crude oil from northern Dongying depression were collected to make sure the source of the oil had been exploited. According to the data, the crude oil can be separated into two species, one with high Pr/Ph ratio and low Pr/nC17 and Ph/nC18 ratios, the other with low Pr/Ph ratio while high Pr/nC17 and Ph/nC18 ratios, and the latter is distributed broadly in this area. The comparison of the biomarker parameters between the source rocks and the crud oil indicated that the former kind of crude oil probably derived from the upper layer of the gypsumsalt rock, and the latter kind of crude oil might be derived from the gypsum layer.
Furthermore, the existence of the thick gypsumsalt rock explained the extensive distribution of the latter type.
In conclusion, the gypsumsalt rock from Dongying depression has great hydrocarbon generation potential. The crude oil exploited in this area may be mainly generated from the upper layer of the gypsumsalt rock and the gypsum layer, and the latter is dominated.
16 mudstone samples from wells of F8, Fs1 and Fs2 in Minfeng area of Dongying depression were selected for understanding the origin and the preservation of the organic matter and their significances. By the application of organic analysis including: total organic carbon content, extraction of soluble organic matter, group composition of soluble organic matter and GCMS of saturated hydrocarbon, the abundance, type and the maturity of the organic matter were studied.
〓〓The formation with the depth from 3 000 m to 5 000 m was divided into three units considering the existence of the gypsumsalt rock: the upper layer of the gypsumsalt rock, the gypsum layer and the lower layer of the gypsumsalt rock. There are great variations of the abundance of organic matter between each unit. The upper layer is much higher than others, so as to the content of chloroform bitumen "A". Both the TOC and the chloroform bitumen "A" of the gypsum layer are lower than the upper layer. The lower layer of the gypsumsalt rock is the lowest in chloroform bitumen "A", although one sample from F8 well has the TOC as high as 2.29%.
The group composition of the soluble organic matter shows that: in three members of source rocks, the type of organic matter of gypsum layer is the best, and the upper layer of the gypsumsalt rock followed, at last is the lower layer of the gypsumsalt rock. Analysis of the gammacerane index and the ratio of Pr/Ph indicate that the upper layer of the gypsumsalt rock and the gypsum layer have similar sedimentary environment which is reducing deep lacustrine deposional environment under semihumid climate conditions, and the salinity of the lake is normal in Dongying depression with fresh to brackish water. However, the depositional environment of gypsum layer is quite different for that is strong reducing saline lacustrine facies under semiarid climate conditions with high salinity. The climate condition of the upper layer of the gypsumsalt rock is relatively more humid and huge amounts of terrestrial organic matter come into the lacustrine basin with surface runoff. As a result, the source of the sedimentary organic matter is lower hydrobiont, lacustrine algae and terrestrial organic matter transported by the river. As the climate conditions get more aridity, the input of terrestrial organic matter decease due to the river discharge reduced. Meanwhile, the salinity of the lake get stronger because of the degree of drought is pricked up gradually, but many species of halophilic bacteria and variety kinds of algae adapted to the hypersaline environment growth rapidly. Therefore, the organic matter of the gypsum layer is mainly originated from lower hydrobiont and algae, which is supported mainly from the dominance of the isoprenoid to the normal alkanes. Because of the existence of the gypsumsalt rock, the difference of maturity of organic matter is significant from routine variation, which performance as the maturity of the gypsum layer is lower than both the upper and the lower layers.
〓〓The biomarker parameters of the crude oil from northern Dongying depression were collected to make sure the source of the oil had been exploited. According to the data, the crude oil can be separated into two species, one with high Pr/Ph ratio and low Pr/nC17 and Ph/nC18 ratios, the other with low Pr/Ph ratio while high Pr/nC17 and Ph/nC18 ratios, and the latter is distributed broadly in this area. The comparison of the biomarker parameters between the source rocks and the crud oil indicated that the former kind of crude oil probably derived from the upper layer of the gypsumsalt rock, and the latter kind of crude oil might be derived from the gypsum layer.
Furthermore, the existence of the thick gypsumsalt rock explained the extensive distribution of the latter type.
In conclusion, the gypsumsalt rock from Dongying depression has great hydrocarbon generation potential. The crude oil exploited in this area may be mainly generated from the upper layer of the gypsumsalt rock and the gypsum layer, and the latter is dominated.
