2019 Vol. 37, No. 5
Display Method:
2019, 37(5): 1-2.
Abstract:
深水重力流沉积领域是当前全球油气勘探与研究的热点，陆相盆地深水重力流沉积研究在我国已有50年历程，老一辈沉积学家围绕湖相重力流理论及油气勘探实践方面开展了一系列创新性工作，相继建立了断陷型、坳陷型及前陆型湖盆浊流沉积模式，从而使陆相湖盆充填模式与沉积特征研究走在了世界前列。近10年来，随着国际深水沉积理论的发展与我国油气勘探技术的进步，我国湖盆深水沉积研究工作再次呈现出勃勃生机，在湖盆深水搬运—沉积过程、沉积作用、沉积模式、地震响应及技术方法等方面涌现出大量令世人注目的成果，标志着我国陆相湖盆重力流研究进入了一个新的创新发展阶段。
“陆相盆地深水沉积体系研究”专栏针对性地组织了一批相关文章，旨在对这些成果进行总结，进一步完善陆相盆地深水沉积理论认识，推动我国湖盆深水沉积油气勘探事业。专栏共收集论文5篇，主要内容如下：
国际著名地质学家Henry W.Posamentier教授等人撰写的《深水浊流沉积综述》（An Overview of Deep-water Turbidite Deposition）一文，系统总结了层序地层格架下的海平面变化对深水浊流沉积体系的控制作用，对陆相盆地深水沉积体系研究具有重要启示作用。作者认为，浊流沉积体系一般可划分为三个区域：区域1位于上游近物源一端，包括陆棚边缘及支流供给峡谷，在这个区域沉积物重力流完全受峡谷壁的限制。区域2的显著特点是发育单一的供给水道复合体，其中的重力流不完全受水道壁的限制，常常形成与水道相伴生的天然堤沉积。当供给水道过渡为前缘分散体系或末端扇时就让位于区域3。区域3末端扇发育沟道化流体，但天然堤非常有限，因而经常发生决口，形成富砂的溢岸沉积。
李相博等在对我国陆相盆地重力流沉积50年研究历程回顾的基础上，对近10年来湖盆深水沉积研究中涌现出的新成果、新认识进行了总结归纳，主要包括4个方面：1）湖盆中央深水区至少存在浊流、异重流、砂质碎屑流及底流4种类型的重力流与牵引流沉积；2）湖盆中不同类型的流体在搬运与沉积过程中存在互相转化，形成混合事件层（Hybrid eventbed）；3）建立了湖相砂质碎屑流搬运—沉积过程的鉴别标志——“泥包砾”结构（Mud-coated intraclasts）；4）地震沉积学理论与技术方法在湖相重力流内部沉积单元解剖、湖盆深水沉积模式建立等方面取得巨大成功。论文最后对湖盆深水沉积研究未来发展趋势进行了分析。
以往关于砂级、泥级陆源碎屑与碳酸盐组分的混合沉积研究相对较多，而针对扇三角洲内砾级陆源碎屑与碳酸盐组分的混合沉积特征及模式研究较少，缺少典型实例。王越等以露头实测资料为基础，通过对新疆塔尔朗沟剖面中二叠统大河沿组、塔尔朗组扇三角洲的混合沉积特征的分析，结合前人在古气候方面的认识，建立了扇三角洲混合沉积模式。张国栋等对鄂尔多斯盆地南部旬邑地区上三叠统延长组露头剖面的解剖，通过岩石薄片观察和激光粒度分析，研究了块状砂岩的粒度组成、粒度参数及其垂向变化，认为属于洪水成因的异重流沉积。
操应长等通过对准噶尔盆地玛湖凹陷夏子街地区百口泉组砂砾岩储层的研究，认为主要为重力流与牵引流共同控制的扇三角洲体系，并定量划分了扇三角洲体系的岩相—成岩相类型，分析了砂砾岩储层物性的控制因素。
2019, 37(5): 879-903.
doi: 10.14027/j.issn.1000-0550.2019.049
Abstract:
Deep-water turbidites commonly are deposited in water depths below storm wave base. These depths range from a few tens of meters to thousands of meters. Turbidite systems tend to be most active when depocenters lie at or near shelf margins,and this proximity of depocenters to shelf margins tends to be associated most commonly with times of relative sea level lowstand. Deep water depositional episodes can be divided into early and late lowstand time. Deposition during early lowstand is characterized by progressively larger and more frequent flow events,whereas deposition during late lowstand is characterized by progressively smaller and less frequent flow events. Consequently,during early lowstand time,erosion of channels tends to dominate such that channels tend to become progressively deeper with minimal preservation of deposits within feeder channels;successive flows are overfit. Subsequently during late lowstand progressively smaller flows tend to be underfit resulting in preservation of channel fill deposits. Turbidite systems tend to be characterized by three discrete regions:Region 1 corresponds to the most proximal reaches of turbidite systems dominated by canyons that commonly are tributive. Region 2 corresponds to that part of the turbidite system characterized by a single feeder channel complex that was characterized by flows with heights greater than confining walls,hence associated with levees. Region 3 corresponds to that part of the system distally, that is characterized by frequent avulsions and sand-prone overbank as well as channel-fill deposits,which can be described geomorphologically as a terminal fan. From a process perspective,Region 3 can be described as a frontal splay. From a sequence stratigraphic perspective,lowstand deposits commonly are bracketed by mud prone distal highstand and transgressive systems tract deposits. The succession of early to late lowstand deposition commonly is characterized by sand-rich Region 3 fan deposits overlain by leveed channel deposits of region 2.
Deep-water turbidites commonly are deposited in water depths below storm wave base. These depths range from a few tens of meters to thousands of meters. Turbidite systems tend to be most active when depocenters lie at or near shelf margins,and this proximity of depocenters to shelf margins tends to be associated most commonly with times of relative sea level lowstand. Deep water depositional episodes can be divided into early and late lowstand time. Deposition during early lowstand is characterized by progressively larger and more frequent flow events,whereas deposition during late lowstand is characterized by progressively smaller and less frequent flow events. Consequently,during early lowstand time,erosion of channels tends to dominate such that channels tend to become progressively deeper with minimal preservation of deposits within feeder channels;successive flows are overfit. Subsequently during late lowstand progressively smaller flows tend to be underfit resulting in preservation of channel fill deposits. Turbidite systems tend to be characterized by three discrete regions:Region 1 corresponds to the most proximal reaches of turbidite systems dominated by canyons that commonly are tributive. Region 2 corresponds to that part of the turbidite system characterized by a single feeder channel complex that was characterized by flows with heights greater than confining walls,hence associated with levees. Region 3 corresponds to that part of the system distally, that is characterized by frequent avulsions and sand-prone overbank as well as channel-fill deposits,which can be described geomorphologically as a terminal fan. From a process perspective,Region 3 can be described as a frontal splay. From a sequence stratigraphic perspective,lowstand deposits commonly are bracketed by mud prone distal highstand and transgressive systems tract deposits. The succession of early to late lowstand deposition commonly is characterized by sand-rich Region 3 fan deposits overlain by leveed channel deposits of region 2.
2019, 37(5): 904-921.
doi: 10.14027/j.issn.1000-0550.2018.193
Abstract:
Deep-water gravity flow deposition is the hotspot of current global oil and gas exploration and research. The study of deep-water gravity flow sedimentation in continental basins in China has been conducted over the past 50 years. It has occurred in three stages:exploration and development of turbidity flow theory (1970-1980s);the industrial application of turbidity flow theory (1990-2000);and sandy debris flow (since 2010). In the past decade,with the development of international deep-water deposition theory and the progress of oil and gas exploration technology in China,research on deep-water sedimentation in lacustrine basins has progressed rapidly and a great deal of new achievements and new understandings have emerged. There are mainly four aspects: (1)There are at least four kinds of gravity flow and traction flow deposition in the deep waters of the center of a lacustrine basin:turbidity flow,hyperpycnal flow,sandy debris flow and bottom flow. (2)Transformations of different types of fluids in the lacustrine occur during the processes of transportation and deposition,forming a hybrid event bed. (3)It has been established that the presence of mud-coated intraclasts indicates sediment transport in lacustrine sandy debris flows. (4)The theories and techniques of seismic sedimentology have been widely used in the analysis of internal sedimentary units of lacustrine gravity flow and to establish sedimentary models in deep-water lacustrine basins,and have achieved great success. Looking to the future,in order to meet the exploration and development needs of the oil and gas industry,the research and development trends of deep-water sediments in lacustrine basins are mainly as follows: (a)the genetic type division of deepwater sandbody,the transportation-deposition process,and the establishment and improvement of it sedimentary model; (b)the genetic mechanism,type division and its significance to oil and gas in deep-water shale (fine sediments); (c)studies of "source-sink" systems and seismic response and evaluation and prediction; (d)experimental simulation of the process of transportation-sedimentation of deep-water sediments;and (e)the establishment of new theories about systems of deep-water deposition and their application in oil and gas exploration and development.
Deep-water gravity flow deposition is the hotspot of current global oil and gas exploration and research. The study of deep-water gravity flow sedimentation in continental basins in China has been conducted over the past 50 years. It has occurred in three stages:exploration and development of turbidity flow theory (1970-1980s);the industrial application of turbidity flow theory (1990-2000);and sandy debris flow (since 2010). In the past decade,with the development of international deep-water deposition theory and the progress of oil and gas exploration technology in China,research on deep-water sedimentation in lacustrine basins has progressed rapidly and a great deal of new achievements and new understandings have emerged. There are mainly four aspects: (1)There are at least four kinds of gravity flow and traction flow deposition in the deep waters of the center of a lacustrine basin:turbidity flow,hyperpycnal flow,sandy debris flow and bottom flow. (2)Transformations of different types of fluids in the lacustrine occur during the processes of transportation and deposition,forming a hybrid event bed. (3)It has been established that the presence of mud-coated intraclasts indicates sediment transport in lacustrine sandy debris flows. (4)The theories and techniques of seismic sedimentology have been widely used in the analysis of internal sedimentary units of lacustrine gravity flow and to establish sedimentary models in deep-water lacustrine basins,and have achieved great success. Looking to the future,in order to meet the exploration and development needs of the oil and gas industry,the research and development trends of deep-water sediments in lacustrine basins are mainly as follows: (a)the genetic type division of deepwater sandbody,the transportation-deposition process,and the establishment and improvement of it sedimentary model; (b)the genetic mechanism,type division and its significance to oil and gas in deep-water shale (fine sediments); (c)studies of "source-sink" systems and seismic response and evaluation and prediction; (d)experimental simulation of the process of transportation-sedimentation of deep-water sediments;and (e)the establishment of new theories about systems of deep-water deposition and their application in oil and gas exploration and development.
2019, 37(5): 922-933.
doi: 10.14027/j.issn.1000-0550.2018.190
Abstract:
Based on careful measurement and detailed observation of the Permian outcrop of the Taerlanggou profile in Xinjiang province,the mixed sedimentary characteristics of the land debris and carbonate components in the delta facies of Permian Daheyan Formation and Taerlang Formation were systematically studied. Daheyan Formation consists mainly of fan delta plain distributary channel sediments. At its base it is mainly brownish-red medium conglomerate with coarse gravel,and carbonate components are rarely found. At the top it is mainly brownish-red fine conglomerate and medium gravel,mixed with many gravelly micrite bands. The Taerlang Formation was a fan delta front underwater distributary channel and underwater bay between the channels from the base bottom upwards. The underwater distributary channel,a glutenite convex at the bottom and flat-topped,developed a grayish-green fine conglomerate with medium gravel and gravelly micrite in discontinuous bands of short extent at the bottom,but extending a long distance horizontally at the top. The underwater bay between the distributary channels mainly developed a grayishgreen mudstone and layered sandy micrite distributed evenly in all horizontal directions. In combination with previous studies of the Middle Permian paleoclimate,sedimentary environment and other aspects of the study area,the mixed sedimentary model of the fan delta was established.
Based on careful measurement and detailed observation of the Permian outcrop of the Taerlanggou profile in Xinjiang province,the mixed sedimentary characteristics of the land debris and carbonate components in the delta facies of Permian Daheyan Formation and Taerlang Formation were systematically studied. Daheyan Formation consists mainly of fan delta plain distributary channel sediments. At its base it is mainly brownish-red medium conglomerate with coarse gravel,and carbonate components are rarely found. At the top it is mainly brownish-red fine conglomerate and medium gravel,mixed with many gravelly micrite bands. The Taerlang Formation was a fan delta front underwater distributary channel and underwater bay between the channels from the base bottom upwards. The underwater distributary channel,a glutenite convex at the bottom and flat-topped,developed a grayish-green fine conglomerate with medium gravel and gravelly micrite in discontinuous bands of short extent at the bottom,but extending a long distance horizontally at the top. The underwater bay between the distributary channels mainly developed a grayishgreen mudstone and layered sandy micrite distributed evenly in all horizontal directions. In combination with previous studies of the Middle Permian paleoclimate,sedimentary environment and other aspects of the study area,the mixed sedimentary model of the fan delta was established.
2019, 37(5): 934-944.
doi: 10.14027/j.issn.1000-0550.2018.186
Abstract:
Deep-water massive sandstones are a significant target for hydrocarbon exploration because of their good reservoir quality,weak heterogeneity and well accumulation conditions. Sedimentary process identification for massive sandstones is more difficult than for cross bedded sandstones. Therefore,the study of the genesis of massive sandstones directly affects the understanding of their sedimentary process,and restricts reconstruction both of their sedimentary model and of their reservoir predictive geological model. In this study,the grain composition,grain size parameters and their vertical changes in massive sandstone were examined using thin sections and laser particle size analysis of high-density rock samples of Late Triassic medium-bed and very-thick-bed sandstones in the Sanshuihe outcrop in Xunyi county,southern Ordos Basin. The study showed the following. (1)The massive sandstones are fine to very fine feldspathic sandstones containing floating gray-black and red-brown muddy clasts,with ball-and-pillow structures and groove casts. (2)The massive sandstone and the overlying and underlying massive sandstones and cross-bedded sandstone layers contain thin to very thin layers of gray-black mudstones and oil shale,commonly with abrupt contacts between the massive sandstone and mudstone/oil shale. (3)Thin section analyses indicated that the massive sandstones are poorly sorted,angular to sub-angular,and of lower-to-medium maturity in composition and structure. (4)In terms of particle size composition,the jump component and suspended component each account for about 50%,indicating that the bed load and the suspended load are both present and contribute equally. (5)The skewness of each component is similar to that of turbidites,but their sorting is slightly worse,and is far worse than in delta deposits. (6)In the vertical direction,there are multi-period decimeter-level compound rhythms in the massive sandstone,with thicknesses ranging from 10 to 30 cm. The geological background,sedimentary and microscopic structures,grain size composition,handling process and sedimentary differentiation throughout the study area all suggest that the massive sandstones are deposits from flood-induced hyperpycnal flows. This study adds to the understanding of the genesis of deep-water massive sandstones and the structure of hyperpycnally formed massive sandstones, and provides a guide for the identification of hyperpycnal flow deposits.
Deep-water massive sandstones are a significant target for hydrocarbon exploration because of their good reservoir quality,weak heterogeneity and well accumulation conditions. Sedimentary process identification for massive sandstones is more difficult than for cross bedded sandstones. Therefore,the study of the genesis of massive sandstones directly affects the understanding of their sedimentary process,and restricts reconstruction both of their sedimentary model and of their reservoir predictive geological model. In this study,the grain composition,grain size parameters and their vertical changes in massive sandstone were examined using thin sections and laser particle size analysis of high-density rock samples of Late Triassic medium-bed and very-thick-bed sandstones in the Sanshuihe outcrop in Xunyi county,southern Ordos Basin. The study showed the following. (1)The massive sandstones are fine to very fine feldspathic sandstones containing floating gray-black and red-brown muddy clasts,with ball-and-pillow structures and groove casts. (2)The massive sandstone and the overlying and underlying massive sandstones and cross-bedded sandstone layers contain thin to very thin layers of gray-black mudstones and oil shale,commonly with abrupt contacts between the massive sandstone and mudstone/oil shale. (3)Thin section analyses indicated that the massive sandstones are poorly sorted,angular to sub-angular,and of lower-to-medium maturity in composition and structure. (4)In terms of particle size composition,the jump component and suspended component each account for about 50%,indicating that the bed load and the suspended load are both present and contribute equally. (5)The skewness of each component is similar to that of turbidites,but their sorting is slightly worse,and is far worse than in delta deposits. (6)In the vertical direction,there are multi-period decimeter-level compound rhythms in the massive sandstone,with thicknesses ranging from 10 to 30 cm. The geological background,sedimentary and microscopic structures,grain size composition,handling process and sedimentary differentiation throughout the study area all suggest that the massive sandstones are deposits from flood-induced hyperpycnal flows. This study adds to the understanding of the genesis of deep-water massive sandstones and the structure of hyperpycnally formed massive sandstones, and provides a guide for the identification of hyperpycnal flow deposits.
2019, 37(5): 945-956.
doi: 10.14027/j.issn.1000-0550.2019.002
Abstract:
A detailed study of the sandy conglomerate reservoir in the Xiazijie, Baikouquan Formation, Mahu Depression,Junggar Basin,included the observation of cores,thin sections,X-ray tomography (XRT),cathodoluminescence (CL)analysis and quantitative statistical analysis,to assess the reservoir petrology,properties,diagenesis and control factors. The main lithology in the study area is glutenite,with fan delta plain and fan delta front subfacies. These were classified into eleven lithofacies types:matrix-supporting medium and fine conglomerate; particle-supporting medium and fine conglomerate;calcareous sandstone;gravel-bearing sandstone;coarse,medium and fine sandstone;siltstone;and mudstone,along with six combined facies types vertically. The main storage space is secondary porosity, consisting of dissolution pores in feldspars, debris and matrix. The reservoir in the study area has low porosity (2.5% 21.2%,average 7.94%)and low permeability (0.01×10-3 982×10-3 μm2,average 5.6×10-3 μm2). It was found that compaction, cementation and dissolution have led to eight types of diagenetic facies which, when combined with the lithofacies, controlled reservoir development. The debris flow reservoir of the fan delta plain mainly developed matrix-supporting medium-to-fine conglomerate facies and medium-to-fine sandstone facies. The high matrix content and strong compaction, together with weak cementation and dissolution in the reservoir, indicate poor storage capability. The underwater channel reservoir of the fan delta front mainly developed matrix-supporting medium-to-fine conglomerate facies,gravel-bearing sandstone facies and fine sandstones facies. The diagenesis in this reservoir is complex. The bottom of the phase sequence is generally strongly compacted;the central zones are cemented with zeolite and carbonates,in which a small number of primary intergranular pores have been retained. Unstabilized rock fragments and dissolved zeolite cements form secondary pore space and improve the physical properties of the reservoir.
A detailed study of the sandy conglomerate reservoir in the Xiazijie, Baikouquan Formation, Mahu Depression,Junggar Basin,included the observation of cores,thin sections,X-ray tomography (XRT),cathodoluminescence (CL)analysis and quantitative statistical analysis,to assess the reservoir petrology,properties,diagenesis and control factors. The main lithology in the study area is glutenite,with fan delta plain and fan delta front subfacies. These were classified into eleven lithofacies types:matrix-supporting medium and fine conglomerate; particle-supporting medium and fine conglomerate;calcareous sandstone;gravel-bearing sandstone;coarse,medium and fine sandstone;siltstone;and mudstone,along with six combined facies types vertically. The main storage space is secondary porosity, consisting of dissolution pores in feldspars, debris and matrix. The reservoir in the study area has low porosity (2.5% 21.2%,average 7.94%)and low permeability (0.01×10-3 982×10-3 μm2,average 5.6×10-3 μm2). It was found that compaction, cementation and dissolution have led to eight types of diagenetic facies which, when combined with the lithofacies, controlled reservoir development. The debris flow reservoir of the fan delta plain mainly developed matrix-supporting medium-to-fine conglomerate facies and medium-to-fine sandstone facies. The high matrix content and strong compaction, together with weak cementation and dissolution in the reservoir, indicate poor storage capability. The underwater channel reservoir of the fan delta front mainly developed matrix-supporting medium-to-fine conglomerate facies,gravel-bearing sandstone facies and fine sandstones facies. The diagenesis in this reservoir is complex. The bottom of the phase sequence is generally strongly compacted;the central zones are cemented with zeolite and carbonates,in which a small number of primary intergranular pores have been retained. Unstabilized rock fragments and dissolved zeolite cements form secondary pore space and improve the physical properties of the reservoir.
2019, 37(5): 957-967.
doi: 10.14027/j.issn.1000-0550.2018.184
Abstract:
The burial paleoenvironment of Nothosaurs during the Anisian Stage of the Poduan Formation,Guojiawan area,southwest of Guizhou province,is chacterized in detail. Analysis of carbon and oxygen isotopes in the lithofacies showed that the Poduan Formation consisted of an open platform and a platform-edge reef. The reef edge slope subfacies comprises five sedimentary microfacies types. Whole rock isotope analysis revealed a δ18O(PDB) value of -6.28‰ to -2.11‰,averaging 4.36‰;the δ13C(PDB) was +0.50‰ to +2.86‰,at an average of 1.58‰. Both values are consistent with the carbon and oxygen isotopic composition in southwestern Guizhou province and adjacent region during the Anisian Stage. The study showed that the ancient seawater temperature was 16℃ to 20℃,and the salinity was between 125.77 and 131.62,indicating a normal warm marine environment. The slight negative deviation of the δ13C(PDB) and δ18O(PDB) was caused by the mingling of fresh water with the seawater. Based on a comprehensive analysis,the following burial process of the Nothosaur is proposed. Earthquakes led to local instability of the carbonate platform,causing a debris flow. This is evident from the large number of Nothosaur bones deposited on the reef edge slope,ultimately forming the present-day fossil bed. This study provides more information for the analysis of Triassic biota in southwestern Guizhou province and adjacent areas.
The burial paleoenvironment of Nothosaurs during the Anisian Stage of the Poduan Formation,Guojiawan area,southwest of Guizhou province,is chacterized in detail. Analysis of carbon and oxygen isotopes in the lithofacies showed that the Poduan Formation consisted of an open platform and a platform-edge reef. The reef edge slope subfacies comprises five sedimentary microfacies types. Whole rock isotope analysis revealed a δ18O(PDB) value of -6.28‰ to -2.11‰,averaging 4.36‰;the δ13C(PDB) was +0.50‰ to +2.86‰,at an average of 1.58‰. Both values are consistent with the carbon and oxygen isotopic composition in southwestern Guizhou province and adjacent region during the Anisian Stage. The study showed that the ancient seawater temperature was 16℃ to 20℃,and the salinity was between 125.77 and 131.62,indicating a normal warm marine environment. The slight negative deviation of the δ13C(PDB) and δ18O(PDB) was caused by the mingling of fresh water with the seawater. Based on a comprehensive analysis,the following burial process of the Nothosaur is proposed. Earthquakes led to local instability of the carbonate platform,causing a debris flow. This is evident from the large number of Nothosaur bones deposited on the reef edge slope,ultimately forming the present-day fossil bed. This study provides more information for the analysis of Triassic biota in southwestern Guizhou province and adjacent areas.
2019, 37(5): 968-980.
doi: 10.14027/j.issn.1000-0550.2018.189
Abstract:
The Benxi Formation,Taiyuan Formation and Shanxi Formation in the Zibo Boshan area of the Bohai Bay Basin were analyzed to reveal the formation sequence of coal-bearing strata and coal accumulation within the stratigraphic sequence framework,against the background of epicontinental sea in the Late Paleozoic. A series of sequence boundaries following tectonic movement of the basin basement were identified:a regional unconformity surface formed as a result of paleotectonic movement;a scouring surface of incised valleys following normal regression;a transition surface in the transgressive direction;the first flooding surface;the maximum flooding surface;and the lowest regression surface. The coal-bearing strata in the study area occur in seven third-order sequences. A comparative study indicated that the peat flat of the tidal flat,the lagoon and the peat swamp of the delta plain were the most favorable facies belts for the development of coal seams. Recoverable coal seams were developed in sequences SQ2, SQ3, SQ4, SQ5 and SQ6.
The Benxi Formation,Taiyuan Formation and Shanxi Formation in the Zibo Boshan area of the Bohai Bay Basin were analyzed to reveal the formation sequence of coal-bearing strata and coal accumulation within the stratigraphic sequence framework,against the background of epicontinental sea in the Late Paleozoic. A series of sequence boundaries following tectonic movement of the basin basement were identified:a regional unconformity surface formed as a result of paleotectonic movement;a scouring surface of incised valleys following normal regression;a transition surface in the transgressive direction;the first flooding surface;the maximum flooding surface;and the lowest regression surface. The coal-bearing strata in the study area occur in seven third-order sequences. A comparative study indicated that the peat flat of the tidal flat,the lagoon and the peat swamp of the delta plain were the most favorable facies belts for the development of coal seams. Recoverable coal seams were developed in sequences SQ2, SQ3, SQ4, SQ5 and SQ6.
2019, 37(5): 981-991.
doi: 10.14027/j.issn.1000-0550.2018.180
Abstract:
Ordovician karst reservoirs in the Jizhong Depression are well developed,but the development of vugs, caverns and channels varies greatly in each stratum and in each area,indicating different main karst controlling factors. At least three phases of fracture occurrence and cutting relationship were identified by microscopy analysis and at the outcrop. The study suggests that the phases correspond to the rock rupture events of the Indosinian,Yanshan and Himalayan movements. The outcrop and microscopy study of the shape of the pores,and the cathodoluminescence of the cement,indicated that the Jizhong Depression developed syngenetic karsts,burial karsts and epigenetic karsts during the Ordovician. The present karst reservoirs in the Ordovician were formed by multi-phase karstification. The tectonic activities of different periods resulted in different forms of karstification in the Jizhong Depression:the strongest near-surface tectonic activity resulted in the most rapid development of dissolution pores. A comparison of karst paleogeomorphology data and drilling breaks and mud losses in the Jizhong Depression shows that karst depressions are a favorable paleogeomorphological type. It is considered that such karst depressions were non-water storage structures. The karst highlands,slopes and depressions have horizontal karst zones of different vertical depth,which correspond to the vadose and phreatic zones that existed in different paleogeomorphologies. Large numbers of drilling breaks and mud losses occur near deep fault zones,and the homogenization temperature of fluid inclusions indicates the existence of a hydrothermal fluid. Thin interbedded sections of dolomite and limestone are favorable karst-development sites in areas with weak karstification and a low development rate of dissolution pores.
Ordovician karst reservoirs in the Jizhong Depression are well developed,but the development of vugs, caverns and channels varies greatly in each stratum and in each area,indicating different main karst controlling factors. At least three phases of fracture occurrence and cutting relationship were identified by microscopy analysis and at the outcrop. The study suggests that the phases correspond to the rock rupture events of the Indosinian,Yanshan and Himalayan movements. The outcrop and microscopy study of the shape of the pores,and the cathodoluminescence of the cement,indicated that the Jizhong Depression developed syngenetic karsts,burial karsts and epigenetic karsts during the Ordovician. The present karst reservoirs in the Ordovician were formed by multi-phase karstification. The tectonic activities of different periods resulted in different forms of karstification in the Jizhong Depression:the strongest near-surface tectonic activity resulted in the most rapid development of dissolution pores. A comparison of karst paleogeomorphology data and drilling breaks and mud losses in the Jizhong Depression shows that karst depressions are a favorable paleogeomorphological type. It is considered that such karst depressions were non-water storage structures. The karst highlands,slopes and depressions have horizontal karst zones of different vertical depth,which correspond to the vadose and phreatic zones that existed in different paleogeomorphologies. Large numbers of drilling breaks and mud losses occur near deep fault zones,and the homogenization temperature of fluid inclusions indicates the existence of a hydrothermal fluid. Thin interbedded sections of dolomite and limestone are favorable karst-development sites in areas with weak karstification and a low development rate of dissolution pores.
2019, 37(5): 992-1005.
doi: 10.14027/j.issn.1000-0550.2018.192
Abstract:
Trace elements in ostracod shells in sedimentary deposits have important significance for studies of the paleoclimate and paleoenvironment. Variation in trace element content in ostracod shells combined with the characteristics of the ecological environment of ostracod fossil assemblages yielded more details about the paleoenvironmental and paleoclimatic evolution during the middle-upper section of Upper Ganchaigou Formation in the western Qaidam Basin. The trace element ratios Sr/Ca,Ba/Ca and U/Ca,and the trace amounts of Sr,Ba and U in the ostracod shells were low in phase A (28.35-22.33 Ma);their values were high in phase B (26.42-23.08 Ma),declining at the end of this phase. In phase C (23.08 22.33 Ma)they increased significantly,although the Mn/Ca ratio and Mn content showed approximately the opposite change. The average values of Sr/Ca and Sr (respectively 0.002 278 and 37.76×10-9)were low in phase A and higher in phase B (respectively 0.003 347 and 41.46×10-9),and their average values were also higher in phase C (respectively 0.003 346 and 56.06×10-9). The average values of Ba/Ca,U/Ca,Ba and U changed similarly,whereas the average values for Mn/Ca and Mn showed opposite changes. The ostracod shell assemblages also differed in the corresponding phases. Combining these trace element variations in the ostracod shell fossils and their assemblages with synchronous deep-sea oxygen isotopes,and noting previous research results,the evolution of the paleoenvironment and paleoclimate in the middle-upper section of Upper Ganchaigou Formation was determined to be the following. In phase A,the ancient lake of the western Qaidam Basin was a deep,low-salinity,strongly reducing lake environment with high water level;the climate was relatively warm and moist. In phase B,the lake was shallow,with high salinity,strongly oxidizing and low water level,and the overall climate was hot and arid. At the end of phase B,the salinity and oxidizing properties of the lake water decreased as the water level rose,and the climate became less arid. In phase C,the salinity and oxidation of the lake water increased as the water level fell, and the climate became cold and arid,similar to the inland aridity of northwestern China in the early Miocene. The paleoclimate during this geological period was mainly influenced by global climate evolution and uplift of the Tibetan Plateau, and also the retreat of the Paratethys Sea to the west.
Trace elements in ostracod shells in sedimentary deposits have important significance for studies of the paleoclimate and paleoenvironment. Variation in trace element content in ostracod shells combined with the characteristics of the ecological environment of ostracod fossil assemblages yielded more details about the paleoenvironmental and paleoclimatic evolution during the middle-upper section of Upper Ganchaigou Formation in the western Qaidam Basin. The trace element ratios Sr/Ca,Ba/Ca and U/Ca,and the trace amounts of Sr,Ba and U in the ostracod shells were low in phase A (28.35-22.33 Ma);their values were high in phase B (26.42-23.08 Ma),declining at the end of this phase. In phase C (23.08 22.33 Ma)they increased significantly,although the Mn/Ca ratio and Mn content showed approximately the opposite change. The average values of Sr/Ca and Sr (respectively 0.002 278 and 37.76×10-9)were low in phase A and higher in phase B (respectively 0.003 347 and 41.46×10-9),and their average values were also higher in phase C (respectively 0.003 346 and 56.06×10-9). The average values of Ba/Ca,U/Ca,Ba and U changed similarly,whereas the average values for Mn/Ca and Mn showed opposite changes. The ostracod shell assemblages also differed in the corresponding phases. Combining these trace element variations in the ostracod shell fossils and their assemblages with synchronous deep-sea oxygen isotopes,and noting previous research results,the evolution of the paleoenvironment and paleoclimate in the middle-upper section of Upper Ganchaigou Formation was determined to be the following. In phase A,the ancient lake of the western Qaidam Basin was a deep,low-salinity,strongly reducing lake environment with high water level;the climate was relatively warm and moist. In phase B,the lake was shallow,with high salinity,strongly oxidizing and low water level,and the overall climate was hot and arid. At the end of phase B,the salinity and oxidizing properties of the lake water decreased as the water level rose,and the climate became less arid. In phase C,the salinity and oxidation of the lake water increased as the water level fell, and the climate became cold and arid,similar to the inland aridity of northwestern China in the early Miocene. The paleoclimate during this geological period was mainly influenced by global climate evolution and uplift of the Tibetan Plateau, and also the retreat of the Paratethys Sea to the west.
2019, 37(5): 1006-1015.
doi: 10.14027/j.issn.1000-0550.2019.048
Abstract:
Jiayuguan, located in the northern Qilian Mountains, is a new steel industry and tourism city in NW China at the transportation junction of the ancient Silk Road. To measure the concentration of heavy metals in the surface soil of Jiayuguan city and evaluate their concentration and determine the sources of heavy metal pollution, the amounts of six heavy metal elements (Cr, Cd, Cu, Pb, Ni, Zn)in 134 surface soil samples were determined by inductively coupled plasma mass spectrometer (ICP-MS). The average concentrations were:Cr 281.6 mg/kg; Cd 0.35 mg/kg; Cu 60.68 mg/kg; Pb 51.39 mg/kg; Zn 108.65 mg/kg; and Ni 161.0 mg/kg. Their concentration in the soil was evaluated by the Nemero comprehensive index (PN)and the geoaccumulation index (Igeo). The pollution levels of the geoaccumulation index were in the order of Cr > Cd > Pb > Cu > Zn > Ni. The overall heavy metal pollution levels in each functional area was industrial area > gobi area > living area > agricultural area. The concentration of heavy metal elements (except Ni)in the gobi area were higher than those in agricultural areas. In addition to industrial factors, the absence of surface vegetation aggravated the enrichment of heavy metal elements. The possible sources of pollution of each element were analyzed by principal component analysis, combined with the spatial distribution of concentration, Nemero index and the geoaccumulation index. Cr and Zn are mainly industrial products of steel production and processing. Traffic is the source of Cd, Cu and Pb. The sources of Ni are possibly related to the steel industry of background value.
Jiayuguan, located in the northern Qilian Mountains, is a new steel industry and tourism city in NW China at the transportation junction of the ancient Silk Road. To measure the concentration of heavy metals in the surface soil of Jiayuguan city and evaluate their concentration and determine the sources of heavy metal pollution, the amounts of six heavy metal elements (Cr, Cd, Cu, Pb, Ni, Zn)in 134 surface soil samples were determined by inductively coupled plasma mass spectrometer (ICP-MS). The average concentrations were:Cr 281.6 mg/kg; Cd 0.35 mg/kg; Cu 60.68 mg/kg; Pb 51.39 mg/kg; Zn 108.65 mg/kg; and Ni 161.0 mg/kg. Their concentration in the soil was evaluated by the Nemero comprehensive index (PN)and the geoaccumulation index (Igeo). The pollution levels of the geoaccumulation index were in the order of Cr > Cd > Pb > Cu > Zn > Ni. The overall heavy metal pollution levels in each functional area was industrial area > gobi area > living area > agricultural area. The concentration of heavy metal elements (except Ni)in the gobi area were higher than those in agricultural areas. In addition to industrial factors, the absence of surface vegetation aggravated the enrichment of heavy metal elements. The possible sources of pollution of each element were analyzed by principal component analysis, combined with the spatial distribution of concentration, Nemero index and the geoaccumulation index. Cr and Zn are mainly industrial products of steel production and processing. Traffic is the source of Cd, Cu and Pb. The sources of Ni are possibly related to the steel industry of background value.
2019, 37(5): 1016-1030.
doi: 10.14027/j.issn.1000-0550.2019.038
Abstract:
Beach and bar sandbodies are an important research area in the petroleum exploration industry,since they are the result of repeated elutriation by wave action and are therefore favorable to the development of hydrocarbon reservoirs. A field investigation of modern sediments at Qinghai Lake (the largest inland lake in China)has established detailed identifying markers for beach and bar sandbodies from many aspects,such as sedimentary environment,hydrodynamics and sedimentation characteristics. Low-angle forewash cross-bedding,inversely graded (beach sand), normally graded (bar sand)and the absence of mud are typical for identifying signs. Further analysis showed that the material source and provenance,hydrodynamic forces,bottom morphology of the lake basin,lake shoreline and lake base level cycles are the main controlling factors marking the development,both formation and preservation,of beach and bar sandbodies. The provenance supplies the material base for beach and bar formation,and hydrodynamic forces boost sediment reshaping and beach and bar formation. The bottom morphology and shoreline of a lake basin determines its position in plan,and the extent of beach and bar formation;fluctuations in the lake base level determine the extent to which the beach and bar formations have been preserved. This study also points out that the formation of beach and bar sandbodies in a lacustrine basin occurs relatively easily,but their preservation is problematic. When suitable conditions of provenance,lake basin bottom morphology and hydrodynamics are present,low-stand system tracts,high-stand system tracts and lacustrine transgressive system tracts may form beach and bar sand deposits,but only the sand deposits at the early stage of the second order sequence,or at the lacustrine transgression phase of the third-order sequence,are well-preserved. Since beach and bar sand deposits are universal in continental lacustrine basins,this study has a particular reference significance for oil and gas reservoir lithology for exploration and development in continental basins in China.
Beach and bar sandbodies are an important research area in the petroleum exploration industry,since they are the result of repeated elutriation by wave action and are therefore favorable to the development of hydrocarbon reservoirs. A field investigation of modern sediments at Qinghai Lake (the largest inland lake in China)has established detailed identifying markers for beach and bar sandbodies from many aspects,such as sedimentary environment,hydrodynamics and sedimentation characteristics. Low-angle forewash cross-bedding,inversely graded (beach sand), normally graded (bar sand)and the absence of mud are typical for identifying signs. Further analysis showed that the material source and provenance,hydrodynamic forces,bottom morphology of the lake basin,lake shoreline and lake base level cycles are the main controlling factors marking the development,both formation and preservation,of beach and bar sandbodies. The provenance supplies the material base for beach and bar formation,and hydrodynamic forces boost sediment reshaping and beach and bar formation. The bottom morphology and shoreline of a lake basin determines its position in plan,and the extent of beach and bar formation;fluctuations in the lake base level determine the extent to which the beach and bar formations have been preserved. This study also points out that the formation of beach and bar sandbodies in a lacustrine basin occurs relatively easily,but their preservation is problematic. When suitable conditions of provenance,lake basin bottom morphology and hydrodynamics are present,low-stand system tracts,high-stand system tracts and lacustrine transgressive system tracts may form beach and bar sand deposits,but only the sand deposits at the early stage of the second order sequence,or at the lacustrine transgression phase of the third-order sequence,are well-preserved. Since beach and bar sand deposits are universal in continental lacustrine basins,this study has a particular reference significance for oil and gas reservoir lithology for exploration and development in continental basins in China.
2019, 37(5): 1031-1043.
doi: 10.14027/j.issn.1000-0550.2018.182
Abstract:
Diagenesis directly affects the pore evolution of reservoirs and controls the physical properties and oil content of reservoirs. It is of great significance to clarify the differential diagenesis of reservoirs and the sequence of hydrocarbon charging. Several techniques were used to study the sandstone reservoir rocks of the delta plain subfacies in the Yan' an Fm (J1y) in the Yinjiacheng-Hedao area:observation of cores and thin-section optical microscopy, XRD, fluorescence, physical properties, mercury injection, and other testing methods. The study has shown that the differences in the original sedimentary features and diagenetic fluids are the main reasons for the differences in reservoir diagenesis. There is good correspondence between diagenetic facies, reservoir types and oil production.Medium-tocoarse-grained sandstones in distributary channel sedimentary microfacies have large initial porosity, strong acid dissolution, well-developed grain mold pores and throats, and good pore-throat connectivity. The porosity range is 11%18% and the permeability range is (20-1 000)×10-3 μm2. Displacement pressure fluctuates between 0.02 MPa and 0.1 MPa, and the median pressure ranges from 0.04 MPa to 1.3 MPa. The median radius range is 16-27.1 μm. This develops large pores and throats and results in medium-porosity and medium-to-high permeability reservoirs. This type of reservoir rock has undergone phases 1, 2 and 3 hydrocarbon charging, which produces industrial-grade oil flow and is classified as a Type I reservoir.The diagenetic evolution of medium-to-fine sandstone in distributary channel sedimentary microfacies is relatively slow and homogeneous. Acid dissolution produces a large number of dispersed dissolution pores but the connectivity is poor and therefore its permeability is low. This is its main difference from a Type I reservoir with similar porosity. The porosity range is 11%-17% and the permeability range is (3-60)×10-3 μm2. The displacement pressure fluctuates between 0.03 MPa and 0.41 MPa, and the median pressure ranges from 0.1 MPa to 2.0 MPa. The median radius is 0.8-7.2 μm. Small-to-mesopores and throats are developed, forming medium-porosity and medium to low permeability reservoirs. This type of reservoir rock has undergone phases 1, 2 and 3 hydrocarbon charging, and has low oil flow. It is classified as a Type Ⅱ reservoir.Pelitic fine siltstone in natural levee sedimentary microfacies is strongly compacted, which is the main cause of the small pore size. It is characterized by the bending deformation of mica. This type of reservoir has a porosity from 5% to 13% and a permeability from (0.05-3)×10-3 μm2. The displacement pressure fluctuates between 0.4 MPa and 0.9 MPa; median pressure ranges from 2 MPa to 5 MPa. The median radius ranges from 0.4 μm to 1.3 μm. Such reservoirs are low-porosity and extra-low-permeability reservoirs, or ‘tight’ reservoirs. Depending to the calcite content, this kind of reservoir may be further divided into two types. One kind has no obvious calcite cementation, and because it develops extra-small pore throats, it is regarded as a low-porosity and extra-low-permeability reservoir. This kind of reservoir has undergone stages 1 and 2 hydrocarbon charging, which has high water production. The other kind has developed both strong compaction and a large amount of calcite cementation. This kind has no hydrocarbon display, and is regarded as a ‘dense’ or ‘invalid’ reservoir. This kind of reservoir is a ‘dry layer’. Both of these are classified as Type Ⅲ reservoirs.Strong relationships were found between the spatial distribution of the different reservoir rock types and the oil yields of individual wells, so it is suggested that this study provides theoretical support for the prediction of further productive reservoirs.
Diagenesis directly affects the pore evolution of reservoirs and controls the physical properties and oil content of reservoirs. It is of great significance to clarify the differential diagenesis of reservoirs and the sequence of hydrocarbon charging. Several techniques were used to study the sandstone reservoir rocks of the delta plain subfacies in the Yan' an Fm (J1y) in the Yinjiacheng-Hedao area:observation of cores and thin-section optical microscopy, XRD, fluorescence, physical properties, mercury injection, and other testing methods. The study has shown that the differences in the original sedimentary features and diagenetic fluids are the main reasons for the differences in reservoir diagenesis. There is good correspondence between diagenetic facies, reservoir types and oil production.Medium-tocoarse-grained sandstones in distributary channel sedimentary microfacies have large initial porosity, strong acid dissolution, well-developed grain mold pores and throats, and good pore-throat connectivity. The porosity range is 11%18% and the permeability range is (20-1 000)×10-3 μm2. Displacement pressure fluctuates between 0.02 MPa and 0.1 MPa, and the median pressure ranges from 0.04 MPa to 1.3 MPa. The median radius range is 16-27.1 μm. This develops large pores and throats and results in medium-porosity and medium-to-high permeability reservoirs. This type of reservoir rock has undergone phases 1, 2 and 3 hydrocarbon charging, which produces industrial-grade oil flow and is classified as a Type I reservoir.The diagenetic evolution of medium-to-fine sandstone in distributary channel sedimentary microfacies is relatively slow and homogeneous. Acid dissolution produces a large number of dispersed dissolution pores but the connectivity is poor and therefore its permeability is low. This is its main difference from a Type I reservoir with similar porosity. The porosity range is 11%-17% and the permeability range is (3-60)×10-3 μm2. The displacement pressure fluctuates between 0.03 MPa and 0.41 MPa, and the median pressure ranges from 0.1 MPa to 2.0 MPa. The median radius is 0.8-7.2 μm. Small-to-mesopores and throats are developed, forming medium-porosity and medium to low permeability reservoirs. This type of reservoir rock has undergone phases 1, 2 and 3 hydrocarbon charging, and has low oil flow. It is classified as a Type Ⅱ reservoir.Pelitic fine siltstone in natural levee sedimentary microfacies is strongly compacted, which is the main cause of the small pore size. It is characterized by the bending deformation of mica. This type of reservoir has a porosity from 5% to 13% and a permeability from (0.05-3)×10-3 μm2. The displacement pressure fluctuates between 0.4 MPa and 0.9 MPa; median pressure ranges from 2 MPa to 5 MPa. The median radius ranges from 0.4 μm to 1.3 μm. Such reservoirs are low-porosity and extra-low-permeability reservoirs, or ‘tight’ reservoirs. Depending to the calcite content, this kind of reservoir may be further divided into two types. One kind has no obvious calcite cementation, and because it develops extra-small pore throats, it is regarded as a low-porosity and extra-low-permeability reservoir. This kind of reservoir has undergone stages 1 and 2 hydrocarbon charging, which has high water production. The other kind has developed both strong compaction and a large amount of calcite cementation. This kind has no hydrocarbon display, and is regarded as a ‘dense’ or ‘invalid’ reservoir. This kind of reservoir is a ‘dry layer’. Both of these are classified as Type Ⅲ reservoirs.Strong relationships were found between the spatial distribution of the different reservoir rock types and the oil yields of individual wells, so it is suggested that this study provides theoretical support for the prediction of further productive reservoirs.
2019, 37(5): 1044-1057.
doi: 10.14027/j.issn.1000-0550.2019.006
Abstract:
Carbonate ramps in the post-rift filling stage have gradually become recognized as areas having the greatest potential for deep hydrocarbon exploration. In the Lower Cambrian Xiaoerbulake Formation in the Tarim Basin, for example,the pre-depositional paleotectonic framework and the lithofacies response to the paleogeography,as well as the regional distribution of reservoirs and the differences in their internal architecture were systematically analyzed from 42 of the most recently processed 2D seismic lines,nine outcrops in the Keping area and data from 12 wells, etc. The results show that (1)the paleotectonic pattern of three uplifts and two sags occurred during the early Cambrian,and exerted obvious control of the sedimentary differentiation in the Xiaoerbulake carbonate ramp system. Highenergy grain shoals and mound-shoal complexes developed around the paleo-highs. Paleocurrents complicated the sediment composition. Three sub-types of ramp are recognized in the Xiaoerbulake Formation:a slope-plateau ramp dominated by grain shoals at the northern margin of the paleo-high of the SW Tarim Basin;a homoclinal ramp dominated by a mound-shoal complex on Keping-Wsu lower high,and an isolated ‘island’ sub-type in the Lunnan-Yaha lower high. (2)A peripheral high-energy facies belt of the paleo-uplift constitutes an important carrier for the Xiaoerbulake Formation reservoir. Early dolomitization has effectively preserved the original pores throughout the subsequent burial period. The reservoirs are mainly located in the peripheral high-energy facies belts of the three paleo-highs,covering an area of about 9×104 km2. The reservoirs in the different ramp systems have obvious differences. The grain-shoal dominated type ramp in the SW Tarim uplift shows the greatest potential for future exploration for extra-large-scale Type Ⅱ reservoirs. From the example anatomy,it is believed that the paleotectonic pattern was the primary control of carbonate ramp formation during the post-rift filling stage,and needs further work to fully understand its influence on the distribution of reservoir facies and internal architecture.
Carbonate ramps in the post-rift filling stage have gradually become recognized as areas having the greatest potential for deep hydrocarbon exploration. In the Lower Cambrian Xiaoerbulake Formation in the Tarim Basin, for example,the pre-depositional paleotectonic framework and the lithofacies response to the paleogeography,as well as the regional distribution of reservoirs and the differences in their internal architecture were systematically analyzed from 42 of the most recently processed 2D seismic lines,nine outcrops in the Keping area and data from 12 wells, etc. The results show that (1)the paleotectonic pattern of three uplifts and two sags occurred during the early Cambrian,and exerted obvious control of the sedimentary differentiation in the Xiaoerbulake carbonate ramp system. Highenergy grain shoals and mound-shoal complexes developed around the paleo-highs. Paleocurrents complicated the sediment composition. Three sub-types of ramp are recognized in the Xiaoerbulake Formation:a slope-plateau ramp dominated by grain shoals at the northern margin of the paleo-high of the SW Tarim Basin;a homoclinal ramp dominated by a mound-shoal complex on Keping-Wsu lower high,and an isolated ‘island’ sub-type in the Lunnan-Yaha lower high. (2)A peripheral high-energy facies belt of the paleo-uplift constitutes an important carrier for the Xiaoerbulake Formation reservoir. Early dolomitization has effectively preserved the original pores throughout the subsequent burial period. The reservoirs are mainly located in the peripheral high-energy facies belts of the three paleo-highs,covering an area of about 9×104 km2. The reservoirs in the different ramp systems have obvious differences. The grain-shoal dominated type ramp in the SW Tarim uplift shows the greatest potential for future exploration for extra-large-scale Type Ⅱ reservoirs. From the example anatomy,it is believed that the paleotectonic pattern was the primary control of carbonate ramp formation during the post-rift filling stage,and needs further work to fully understand its influence on the distribution of reservoir facies and internal architecture.
2019, 37(5): 1058-1068.
doi: 10.14027/j.issn.1000-0550.2019.029
Abstract:
Because of the relatively low resolution of seismic data in the study area,continuous sand beds in interbedded sand-shale reservoirs cannot be distinguished by this method alone. By combining seismic,drilling and logging data in the study area,paleogeomorphological and sedimentary paleo-environment analysis revealed by drilling was carried out on the basis of precise time depth calibration. The distribution range of interbedded sand-shale reservoirs was obtained by combining this data with seismic minimum amplitude properties. The formation process of individual sand bodies in the complex interbedded sand-shale reservoir eventually led to locating a continuous monolayer sand body. Using an acoustic and apparent-thickness correction method of reconstruction established an isochronous stratigraphic framework of interbedded sand-shale reservoirs;the minimum amplitudes of the seismic data and the distribution characteristics of the interbedded sand-shale reservoir were obtained. Restricting the boundary of an individual sand body by using a sedimentary combination model and geological knowledge base enabled us to reconstruct the location of the single sand body. Finally,the reasoning behind this method of single sand body distribution was verified by dynamic data,including pressure measurement while drilling together with production and suction profile testing. The actual production data of P19 oilfield in Bohai Bay confirmed the reliability of the research results,guided well location deployment and optimization in a comprehensive adjustment project,and improved the accuracy of predicting the location of single sand bodies and the corresponding injection production rate.
Because of the relatively low resolution of seismic data in the study area,continuous sand beds in interbedded sand-shale reservoirs cannot be distinguished by this method alone. By combining seismic,drilling and logging data in the study area,paleogeomorphological and sedimentary paleo-environment analysis revealed by drilling was carried out on the basis of precise time depth calibration. The distribution range of interbedded sand-shale reservoirs was obtained by combining this data with seismic minimum amplitude properties. The formation process of individual sand bodies in the complex interbedded sand-shale reservoir eventually led to locating a continuous monolayer sand body. Using an acoustic and apparent-thickness correction method of reconstruction established an isochronous stratigraphic framework of interbedded sand-shale reservoirs;the minimum amplitudes of the seismic data and the distribution characteristics of the interbedded sand-shale reservoir were obtained. Restricting the boundary of an individual sand body by using a sedimentary combination model and geological knowledge base enabled us to reconstruct the location of the single sand body. Finally,the reasoning behind this method of single sand body distribution was verified by dynamic data,including pressure measurement while drilling together with production and suction profile testing. The actual production data of P19 oilfield in Bohai Bay confirmed the reliability of the research results,guided well location deployment and optimization in a comprehensive adjustment project,and improved the accuracy of predicting the location of single sand bodies and the corresponding injection production rate.
2019, 37(5): 1069-1078.
doi: 10.14027/j.issn.1000-0550.2019.047
Abstract:
Uncertainty as to the controlling factors and classification methods for the medium-to-deep glutenite reservoirs in the lower member of Shahejie Formation in the Yong1 block,Dongying Sag,has been a bottleneck for oil and petroleum exploration efforts. To determine the characteristics,controlling factors and methods of classifying and evaluating glutenite reservoirs,the reservoirs were examined by a variety of techniques,including 3D seismic interpretation,core and thin section observation,reservoir property analysis and oil testing. A combination of lithofacies, diagenetic facies and fractures controlled the reservoir formation. Of these,lithofacies is the primary factor. The most favorable are sandstone and pebbly sandstone. Conglomerate and gravelly sandstone are less favorable,and the least useful are siltstone,muddy sandstone and calcareous sandstone. Diagenetic facies enhance the heterogeneity of reservoirs. The most favorable of these is mainly controlled by moderate to strong dissolution;those that are mainly controlled by compaction are moderately favorable;and the least favorable diagenetic facies are mainly controlled by cementation and high matrix content. In the highest structural part of the structure,fractures improve reservoir properties,tending to have better properties closer to the structural line. Based on reservoir characteristics and combinations of all the controlling factors,glutenite reservoirs are divided into four types and six subtypes. Type Ⅰ (combination of favorable lithofacies,diagenesis and tectonic location)reservoirs possess the best properties and have the highest oil output;these are classified as high-quality reservoirs. Type Ⅱ1 (combination of favorable lithofacies,diagenesis and adverse tectonic location) or Ⅱ3 (combination of favorable diagenesis,tectonic location and adverse lithofacies)reservoirs have medium properties and medium oil output,which of moderate quality. Type Ⅲ2 (combination of adverse diagenesis,lithofacies and favorable tectonic location)or Ⅲ3 (combination of adverse diagenesis,tectonic location and favorable lithofacies)reservoirs have quite poor properties and low output of low-quality oil. Finally, Type Ⅳ (combination of adverse lithofacies,diagenesis and tectonic location)reservoirs have the poorest properties and lowest output, and are classified as ineffective reservoirs.
Uncertainty as to the controlling factors and classification methods for the medium-to-deep glutenite reservoirs in the lower member of Shahejie Formation in the Yong1 block,Dongying Sag,has been a bottleneck for oil and petroleum exploration efforts. To determine the characteristics,controlling factors and methods of classifying and evaluating glutenite reservoirs,the reservoirs were examined by a variety of techniques,including 3D seismic interpretation,core and thin section observation,reservoir property analysis and oil testing. A combination of lithofacies, diagenetic facies and fractures controlled the reservoir formation. Of these,lithofacies is the primary factor. The most favorable are sandstone and pebbly sandstone. Conglomerate and gravelly sandstone are less favorable,and the least useful are siltstone,muddy sandstone and calcareous sandstone. Diagenetic facies enhance the heterogeneity of reservoirs. The most favorable of these is mainly controlled by moderate to strong dissolution;those that are mainly controlled by compaction are moderately favorable;and the least favorable diagenetic facies are mainly controlled by cementation and high matrix content. In the highest structural part of the structure,fractures improve reservoir properties,tending to have better properties closer to the structural line. Based on reservoir characteristics and combinations of all the controlling factors,glutenite reservoirs are divided into four types and six subtypes. Type Ⅰ (combination of favorable lithofacies,diagenesis and tectonic location)reservoirs possess the best properties and have the highest oil output;these are classified as high-quality reservoirs. Type Ⅱ1 (combination of favorable lithofacies,diagenesis and adverse tectonic location) or Ⅱ3 (combination of favorable diagenesis,tectonic location and adverse lithofacies)reservoirs have medium properties and medium oil output,which of moderate quality. Type Ⅲ2 (combination of adverse diagenesis,lithofacies and favorable tectonic location)or Ⅲ3 (combination of adverse diagenesis,tectonic location and favorable lithofacies)reservoirs have quite poor properties and low output of low-quality oil. Finally, Type Ⅳ (combination of adverse lithofacies,diagenesis and tectonic location)reservoirs have the poorest properties and lowest output, and are classified as ineffective reservoirs.
2019, 37(5): 1079-1086.
doi: 10.14027/j.issn.1000-0550.2019.017
Abstract:
In previous studies,the development scheme of the Ed2 of 4-3 zone of Nanpu oil field was based on the traditional sedimentary fan delta model,which established the relationships by noting similarities between injection-production and a layered model; however, the results do not perfectly reflect actual development. This is particularly represented by non-uniform oil-water contact and inaccurate and poor efficiency of water-driven oil. Guided by modern sedimentological methods combined with a comprehensive analysis of core data from a large number of wells and geophysical data,the D2 of the 4-3 zone was determined as a typical shallow-water delta. The study area was a delta front deposit,and the sedimentary tectonic background was a small lake in a step-fault zone. Compared to shallow-water deltas on gentle slopes in large lake basins,it is obvious that the sedimentary characteristics in this case were controlled by accommodation space. This is mainly evident from the channel sand dominated by middle-fine sandstone of sub-maturity and poor sorting,and the short transportation distance of the sediments. The sedimentary structure was mainly massive bedding,parallel bedding and cross-bedding,The sedimentation rhythm is interactive-positive. Guided by seismic sedimentology and seismic facies characteristics,it was seen that complex delta lobes resulted from frequent shifting of the distributary channels,so the flow line is indistinct and imprecise. It was difficult to determine the deposit microfacies. Single lobes were deposited when the channel changed course. This is the primary element of a delta whose internal features are layer-isochronous. Many lobes overlapped in 3D space with a very complex interrelationship,and were not layer-isochronous. The contact between lobes and the properties of the surface between them determined their connectivity,which significantly influenced fluid flow in the reservoir. The different seismic resolution ratios distinguished between the bigger lobe deposits and allowed their scale and form to be deconstructed,revealing the history of the lower levels of the lobe deposits. Ultimately,three high-level lobes and 28 low-level lobes were picked out in this way. Guided by this new knowledge,we established an exploitation strategy that included reorganizing the well network pattern. Oil recovery efficiency has significantly improved as a result.
In previous studies,the development scheme of the Ed2 of 4-3 zone of Nanpu oil field was based on the traditional sedimentary fan delta model,which established the relationships by noting similarities between injection-production and a layered model; however, the results do not perfectly reflect actual development. This is particularly represented by non-uniform oil-water contact and inaccurate and poor efficiency of water-driven oil. Guided by modern sedimentological methods combined with a comprehensive analysis of core data from a large number of wells and geophysical data,the D2 of the 4-3 zone was determined as a typical shallow-water delta. The study area was a delta front deposit,and the sedimentary tectonic background was a small lake in a step-fault zone. Compared to shallow-water deltas on gentle slopes in large lake basins,it is obvious that the sedimentary characteristics in this case were controlled by accommodation space. This is mainly evident from the channel sand dominated by middle-fine sandstone of sub-maturity and poor sorting,and the short transportation distance of the sediments. The sedimentary structure was mainly massive bedding,parallel bedding and cross-bedding,The sedimentation rhythm is interactive-positive. Guided by seismic sedimentology and seismic facies characteristics,it was seen that complex delta lobes resulted from frequent shifting of the distributary channels,so the flow line is indistinct and imprecise. It was difficult to determine the deposit microfacies. Single lobes were deposited when the channel changed course. This is the primary element of a delta whose internal features are layer-isochronous. Many lobes overlapped in 3D space with a very complex interrelationship,and were not layer-isochronous. The contact between lobes and the properties of the surface between them determined their connectivity,which significantly influenced fluid flow in the reservoir. The different seismic resolution ratios distinguished between the bigger lobe deposits and allowed their scale and form to be deconstructed,revealing the history of the lower levels of the lobe deposits. Ultimately,three high-level lobes and 28 low-level lobes were picked out in this way. Guided by this new knowledge,we established an exploitation strategy that included reorganizing the well network pattern. Oil recovery efficiency has significantly improved as a result.
2019, 37(5): 1087-1103.
doi: 10.14027/j.issn.1000-0550.2019.014
Abstract:
The Ordos Basin experienced uplift and bending in the Paleozoic,then started to subside and deposit the sea-land transition phase clastics of the Benxi Formation. Data from outcrops,cores and various analytical testing tools were used to clarify the provenance of the Benxi Formation,including conglomerate distribution,light mineral debris component,quartz cathodoluminescence,heavy mineral suites,stability coefficient and zircon ages. Different provenance systems were recognized from consistent source-rock types from different sources,as well as the tectonic evolutionary history of the southern part of the basin. The study revealed two main provenance systems,which were further subdivided into four systems,two in the northern basin and two in the south. The northern provenance supply ability was found to be greater than in the south. The source rocks of the NW provenance were metamorphics,together with a small amount of volcanic rocks. The NE source rocks were acidic intrusives. The SW source rocks were highgrade metamorphics,with some magmatic rocks and a small proportion of sedimentary rocks. The SE source rocks were high-grade metamorphics. During deposition of the Benxi formation,the southern provenance extended as far as the center of the basin. A main component of the southern provenance system at that time was the collision of the North Qinling terrace and the North China Block.
The Ordos Basin experienced uplift and bending in the Paleozoic,then started to subside and deposit the sea-land transition phase clastics of the Benxi Formation. Data from outcrops,cores and various analytical testing tools were used to clarify the provenance of the Benxi Formation,including conglomerate distribution,light mineral debris component,quartz cathodoluminescence,heavy mineral suites,stability coefficient and zircon ages. Different provenance systems were recognized from consistent source-rock types from different sources,as well as the tectonic evolutionary history of the southern part of the basin. The study revealed two main provenance systems,which were further subdivided into four systems,two in the northern basin and two in the south. The northern provenance supply ability was found to be greater than in the south. The source rocks of the NW provenance were metamorphics,together with a small amount of volcanic rocks. The NE source rocks were acidic intrusives. The SW source rocks were highgrade metamorphics,with some magmatic rocks and a small proportion of sedimentary rocks. The SE source rocks were high-grade metamorphics. During deposition of the Benxi formation,the southern provenance extended as far as the center of the basin. A main component of the southern provenance system at that time was the collision of the North Qinling terrace and the North China Block.
