2018 Vol. 36, No. 5
Display Method:
2018, 36(5): 853-863.
doi: 10.14027/j.issn.1000-0550.2018.062
Abstract:
The characteristics of Lower Ordovician stromatolites in the Songzi area of Hubei province were studied systematically for the first time, and the stromatolites were distributed in the Lower Ordovician Nanjinguan, Fenxiang and Honghuayuan formations in the study area. They were characterized by decrease of scales, thickness and quantity gradually on the vertical profiles. The stromatolite types were changed laterally from the horizontal bedded, wavy-shaped and gradually into columnar type. According to the geometric classification scheme, the stromatolites in the study area could be divided into the following types, namely, lamellar-shaped, wavy-shaped, columnar-shaped, mound-shaped and clotted-shaped stromatolite, respectively. Among them, the clotted-shaped stromatolite and double cone-shaped stromatolite were discovered for the first time and newly named by the authors. Based on detailed analysis for the sedimentary characteristics of each type of stromatolite, combined with lithology, microphase and microscopic characteristics, the depositional environments were studied for different types of stromatolite, and their sedimentary models were also summarized. According to the corresponding relationship between the increase of metazoon in the early stage of Middle Ordovician period and the rapid reduction of the stromatolites, combined with the phenomenon of a lot of drilling and predatory gastropods Ecculiomphalus fossils inside the stromatolites, the authors believed that the reduction and decline of stromatolites could be related to the increase in abundance of metazoan. Drilling predators not only grazed bacteria algae microorganisms forming stromatolites and resulted in a decrease of stromatolites, but also destroyed the growth of stromatolites, and lead to the formation of clotted-shaped stromatolite. In addition, the author argues that the rapid rise of the sea level could be also one of the reasons for the reduction and disappearance of stromatolites from the beginning of the Middle Ordovician period in the study area.
The characteristics of Lower Ordovician stromatolites in the Songzi area of Hubei province were studied systematically for the first time, and the stromatolites were distributed in the Lower Ordovician Nanjinguan, Fenxiang and Honghuayuan formations in the study area. They were characterized by decrease of scales, thickness and quantity gradually on the vertical profiles. The stromatolite types were changed laterally from the horizontal bedded, wavy-shaped and gradually into columnar type. According to the geometric classification scheme, the stromatolites in the study area could be divided into the following types, namely, lamellar-shaped, wavy-shaped, columnar-shaped, mound-shaped and clotted-shaped stromatolite, respectively. Among them, the clotted-shaped stromatolite and double cone-shaped stromatolite were discovered for the first time and newly named by the authors. Based on detailed analysis for the sedimentary characteristics of each type of stromatolite, combined with lithology, microphase and microscopic characteristics, the depositional environments were studied for different types of stromatolite, and their sedimentary models were also summarized. According to the corresponding relationship between the increase of metazoon in the early stage of Middle Ordovician period and the rapid reduction of the stromatolites, combined with the phenomenon of a lot of drilling and predatory gastropods Ecculiomphalus fossils inside the stromatolites, the authors believed that the reduction and decline of stromatolites could be related to the increase in abundance of metazoan. Drilling predators not only grazed bacteria algae microorganisms forming stromatolites and resulted in a decrease of stromatolites, but also destroyed the growth of stromatolites, and lead to the formation of clotted-shaped stromatolite. In addition, the author argues that the rapid rise of the sea level could be also one of the reasons for the reduction and disappearance of stromatolites from the beginning of the Middle Ordovician period in the study area.
Micropore Characteristics and Geological Significance of Pyrite in Shale Rocks of Longmaxi Formation
2018, 36(5): 864-876.
doi: 10.14027/j.issn.1000-0550.2018.077
Abstract:
The study on shale gas reservoirs has become much more meticulously and quantitatively along with the rapid improvement of shale gas geological theories. As a common material composition of shale gas reservoirs, the mineralogical and pore development characteristics as well as geological significance of pyrite has drawn a lot of attention, especially the nanoscale pores in framboidal pyrite. By using Argon Ion Polishing-Field Emission Scanning Electron Microscopy (FE-SEM), Energy Dispersive Spectroscopy (EDS), and X-ray Diffraction (XRD) combined with Image Processing technology to study on the mineralogical characteristics of different types of pyrite in reservoir rocks and to make quantitative characterization and evaluation of nanoscale pore characteristics as well as the reservoir significance of pyrite in high quality shale reservoir rocks of middle-lower Longmaxi Formation in Southeast Chongqing area, the results showed that the framboidal pyrite was the most developed type of pyrite in the shale matrix of Longmaxi Formation with aggregate diameter ranging between 3-10 μm. The pores in the framboidal pyrite aggregate were mainly nanoscale pores developed in organic matter filling among the crystallites with diameters mainly concentrated below 100 nm. The pores in framboidal pyrite provided the reservoir with 0.7%-7% proportion of pore network in shale matrix and should be classified into Organic-Matter pores. Characterization and evaluation of classified pores based on Image Processing might provide a new approach to study on reservoir pores, being a feasible method to quantitatively study on different types of pores in different compositions. In addition to the reservoir space contributed by framboidal pyrite to the reservoir, the favorable conditions of organic matter preservation under reducing environments provided a basis for the study of high-quality reservoir formation mechanism and the prediction of high-quality reservoirs. Thus, pyrite, especially framboidal pyrite developed in shale matrix, has important geological significance for shale gas in both reservoir study and the exploration of high-quality reservoirs.
The study on shale gas reservoirs has become much more meticulously and quantitatively along with the rapid improvement of shale gas geological theories. As a common material composition of shale gas reservoirs, the mineralogical and pore development characteristics as well as geological significance of pyrite has drawn a lot of attention, especially the nanoscale pores in framboidal pyrite. By using Argon Ion Polishing-Field Emission Scanning Electron Microscopy (FE-SEM), Energy Dispersive Spectroscopy (EDS), and X-ray Diffraction (XRD) combined with Image Processing technology to study on the mineralogical characteristics of different types of pyrite in reservoir rocks and to make quantitative characterization and evaluation of nanoscale pore characteristics as well as the reservoir significance of pyrite in high quality shale reservoir rocks of middle-lower Longmaxi Formation in Southeast Chongqing area, the results showed that the framboidal pyrite was the most developed type of pyrite in the shale matrix of Longmaxi Formation with aggregate diameter ranging between 3-10 μm. The pores in the framboidal pyrite aggregate were mainly nanoscale pores developed in organic matter filling among the crystallites with diameters mainly concentrated below 100 nm. The pores in framboidal pyrite provided the reservoir with 0.7%-7% proportion of pore network in shale matrix and should be classified into Organic-Matter pores. Characterization and evaluation of classified pores based on Image Processing might provide a new approach to study on reservoir pores, being a feasible method to quantitatively study on different types of pores in different compositions. In addition to the reservoir space contributed by framboidal pyrite to the reservoir, the favorable conditions of organic matter preservation under reducing environments provided a basis for the study of high-quality reservoir formation mechanism and the prediction of high-quality reservoirs. Thus, pyrite, especially framboidal pyrite developed in shale matrix, has important geological significance for shale gas in both reservoir study and the exploration of high-quality reservoirs.
2018, 36(5): 877-889.
doi: 10.14027/j.issn.1000-0550.2018.067
Abstract:
The lacustrine near-shore sand bank is one type of good reservoirs, being the key target for oil and gas exploration and development recently. However, lacking clearly understanding of the inner architecture in this type of reservoir significantly restricts the further reservoir development. In southeastern Xiashan Lake, located in the center of Shandong Province, there are a series of modern sand banks observed parallelly to the lake shoreline. By using shallow wells, pits and other methods, a comprehensive research has been conducted to analyze the inner architecture of sand banks. The result shows that a sand bank has a general coarsening upward structure and is made up of one or more accretions. Between two accretions a thin layer of mud deposition can be found. There are two kinds of accretion stack patterns in a single sand bank which are one overlay pattern and one top-set pattern. The former pattern can usually be well persevered and presents a gradually expanding accretion from bottom to top due to strong aggradation. The latter pattern is easily destructed by flush erosion of wave actions and presents a gradually reducing accretion from bottom to top due to weak aggradation. The distribution of mud layer between two accretions is also determined by accretion stack patterns. The mud layer within an overlay pattern displays a continuous draping shape inclining to the lake center, while the mud layers, within a top-set pattern are isolated and discrete which are parallel to the interface of two accretions. A clear understanding of inner architecture in modern sand banks not only provides a real prototype model for better understanding in accretion stack patterns and spatial distribution of sand bodies in sand banks, but also offers quantitative constraints for 3D sand bank geological modeling.
The lacustrine near-shore sand bank is one type of good reservoirs, being the key target for oil and gas exploration and development recently. However, lacking clearly understanding of the inner architecture in this type of reservoir significantly restricts the further reservoir development. In southeastern Xiashan Lake, located in the center of Shandong Province, there are a series of modern sand banks observed parallelly to the lake shoreline. By using shallow wells, pits and other methods, a comprehensive research has been conducted to analyze the inner architecture of sand banks. The result shows that a sand bank has a general coarsening upward structure and is made up of one or more accretions. Between two accretions a thin layer of mud deposition can be found. There are two kinds of accretion stack patterns in a single sand bank which are one overlay pattern and one top-set pattern. The former pattern can usually be well persevered and presents a gradually expanding accretion from bottom to top due to strong aggradation. The latter pattern is easily destructed by flush erosion of wave actions and presents a gradually reducing accretion from bottom to top due to weak aggradation. The distribution of mud layer between two accretions is also determined by accretion stack patterns. The mud layer within an overlay pattern displays a continuous draping shape inclining to the lake center, while the mud layers, within a top-set pattern are isolated and discrete which are parallel to the interface of two accretions. A clear understanding of inner architecture in modern sand banks not only provides a real prototype model for better understanding in accretion stack patterns and spatial distribution of sand bodies in sand banks, but also offers quantitative constraints for 3D sand bank geological modeling.
2018, 36(5): 890-902.
doi: 10.14027/j.issn.1000-0550.2018.069
Abstract:
Since the Oligocene, thousands of meters of marine strata have been deposited in the deep water area of the Qiongdongnan Basin in the northern South China Sea, in which micro-fossils are enriched. Twenty-one planktonic foraminiferal fossil zones (N22 zone-P19 zone) and twelve calcareous nannofossil zones (NN19 zone-NP24 zone) were recognized by fossil identification of the cored samples from drilling LS33a in deep water area. Combined with previous results of the ODP184 Leg implemented in the South China Sea and the Geologic Time Scale 2012, the geological ages of the fossil events were discussed, and the chronostratigraphic framework based on micro-paleontological data from drilling LS33a was constructed. On this basis, this paper discusses the position of the stratigraphic boundary between the Pleistocene and the Pliocene, the Upper Pliocene and the Lower Pliocene, the Pliocene and the Miocene, the Upper Miocene and the Middle Miocene, the Middle Miocene and the Lower Miocene, the Miocene and the Oligocene, the Upper Oligocene and the Lower Oligocene, defines the age assignment of Yacheng Formation, Lingshui Formation, Sanya Formation, Meishan Formation, Huangliu Formation, Yinggehai Formation and Ledong Formation, and finally establishes a high-resolution comprehensive chronostratigraphic framework suitable for the deep water area of the northern South China Sea.
Since the Oligocene, thousands of meters of marine strata have been deposited in the deep water area of the Qiongdongnan Basin in the northern South China Sea, in which micro-fossils are enriched. Twenty-one planktonic foraminiferal fossil zones (N22 zone-P19 zone) and twelve calcareous nannofossil zones (NN19 zone-NP24 zone) were recognized by fossil identification of the cored samples from drilling LS33a in deep water area. Combined with previous results of the ODP184 Leg implemented in the South China Sea and the Geologic Time Scale 2012, the geological ages of the fossil events were discussed, and the chronostratigraphic framework based on micro-paleontological data from drilling LS33a was constructed. On this basis, this paper discusses the position of the stratigraphic boundary between the Pleistocene and the Pliocene, the Upper Pliocene and the Lower Pliocene, the Pliocene and the Miocene, the Upper Miocene and the Middle Miocene, the Middle Miocene and the Lower Miocene, the Miocene and the Oligocene, the Upper Oligocene and the Lower Oligocene, defines the age assignment of Yacheng Formation, Lingshui Formation, Sanya Formation, Meishan Formation, Huangliu Formation, Yinggehai Formation and Ledong Formation, and finally establishes a high-resolution comprehensive chronostratigraphic framework suitable for the deep water area of the northern South China Sea.
2018, 36(5): 903-913.
doi: 10.14027/j.issn.1000-0550.2018.064
Abstract:
According to the stratigraphic lithologic data and thermal physical parameters, we use 50 sets of vitrinite reflectance data, 46 sets of mudstone sonic slowness data and geothermal data of 3 boreholes to reconstruct the burial history, thermal evolution history and hydrocarbon generation history of the Shengli coalfield since Late Cretaceous period. The result shows: 1) The burial characteristics of "the subsidence of the study area was accompanied by uplifting in the early stage and stopped in the late stage" are expressed in the Shengli coalfield. From Aershan period to early Duhongmu period, the study area entered the accelerated rapid subsidence progress, and the first stage of uplifting and erosion occurred at the end of this sedimentary period. The amount of denudation was about 410 m. From late Duhongmu period to Saihantala period, the study area once again entered the rapid subsidence progress, and then it was in the second stage of uplifting, and the denudation amount was about 580 m. Since late deposition of the Saihantala period, the study area was in a slow-ending subsidence period; 2) From Aershan period to early Duhongmu period, the geotemperature of the study area gradually increased. At the end of early Duhongmu period, the geotemperature reached a peak value of about 90 ℃, and then entered the first stage of uplifting, the temperature decreased rapidly. In the Saihantala period, the geotemperature increased rapidly and reached the peak of 120 ℃ at the end of the deposition, in abnormally high temperature state, and then entered the second stage of uplifting, the geotemperature decreased. After that it was in the stable stage in study area; 3)The maturity of source rocks was controlled by paleo geotemperature. The hydrocarbons source rocks of the Aershan Formation and the Tenggeer Formation were in a low to medium maturity stage and had a certain potential for hydrocarbons generation. The Duhongmu Formation and Saihantala Formation should be in immature stage and had almost no hydrocarbon generating potential.
According to the stratigraphic lithologic data and thermal physical parameters, we use 50 sets of vitrinite reflectance data, 46 sets of mudstone sonic slowness data and geothermal data of 3 boreholes to reconstruct the burial history, thermal evolution history and hydrocarbon generation history of the Shengli coalfield since Late Cretaceous period. The result shows: 1) The burial characteristics of "the subsidence of the study area was accompanied by uplifting in the early stage and stopped in the late stage" are expressed in the Shengli coalfield. From Aershan period to early Duhongmu period, the study area entered the accelerated rapid subsidence progress, and the first stage of uplifting and erosion occurred at the end of this sedimentary period. The amount of denudation was about 410 m. From late Duhongmu period to Saihantala period, the study area once again entered the rapid subsidence progress, and then it was in the second stage of uplifting, and the denudation amount was about 580 m. Since late deposition of the Saihantala period, the study area was in a slow-ending subsidence period; 2) From Aershan period to early Duhongmu period, the geotemperature of the study area gradually increased. At the end of early Duhongmu period, the geotemperature reached a peak value of about 90 ℃, and then entered the first stage of uplifting, the temperature decreased rapidly. In the Saihantala period, the geotemperature increased rapidly and reached the peak of 120 ℃ at the end of the deposition, in abnormally high temperature state, and then entered the second stage of uplifting, the geotemperature decreased. After that it was in the stable stage in study area; 3)The maturity of source rocks was controlled by paleo geotemperature. The hydrocarbons source rocks of the Aershan Formation and the Tenggeer Formation were in a low to medium maturity stage and had a certain potential for hydrocarbons generation. The Duhongmu Formation and Saihantala Formation should be in immature stage and had almost no hydrocarbon generating potential.
2018, 36(5): 914-926.
doi: 10.14027/j.issn.1000-0550.2018.081
Abstract:
The Wuchuan-Zheng'an-Daozhen Bauxite metallogenic belt, located in the contiguous area of north Guizhou and south Chongqing, is an important bauxite resource area in Guizhou with more than 10 large deposits and 800 million tons reserves discovered. The bauxite occurred in the lower Silurian Hanjiadian formation of clastic rocks or the lower Permian Dazhuyuan Formation above the ancient erosion surface of Carboniferous Huanglong formation of carbonate. The deposits belongs to ancient weathering sedimentary type. Based on previous researchs of ore-forming sources, ore-forming environments, mineralization and ore deposit genesis types, the relationship between regional tectonic evolution and bauxite formation was studied in this paper, to disclosure the geology-geochemistry evolution process of bauxite mineralization combined with special geological features. According to extraction of 1:100 000-1:10 000 remote sensing image features, the series of ore-bearing rocks and adjacent layers, main structure identification, relationship among iron, mud anomaly and the space distribution of the rock series were summarized to establish a remote sensing 3D image model in large scale. Through the application and comparative study of multiple bauxite mining areas by geophysical methods, such as Shallow seismic reflection wave method, high density resistivity method, frequency domain tripole sounding method, audio earth electromagnetic sounding method, high power excitation sounding method, the geophysical prospecting marks of “high, sunken, concave, thick” and typical mine 3D geological and geophysical prospecting prediction model of the bauxite deposit was established. On the study above, the technical method system of bauxite exploration and furtheron the geological, geophysical, geochemical and remote sensing prospecting models may demonstrate guidance to prospect and acquire remarkable prospecting effect through engineering verification, indicating the proposed mining model is suitable and effective in the exploration of bauxite in the study area.
The Wuchuan-Zheng'an-Daozhen Bauxite metallogenic belt, located in the contiguous area of north Guizhou and south Chongqing, is an important bauxite resource area in Guizhou with more than 10 large deposits and 800 million tons reserves discovered. The bauxite occurred in the lower Silurian Hanjiadian formation of clastic rocks or the lower Permian Dazhuyuan Formation above the ancient erosion surface of Carboniferous Huanglong formation of carbonate. The deposits belongs to ancient weathering sedimentary type. Based on previous researchs of ore-forming sources, ore-forming environments, mineralization and ore deposit genesis types, the relationship between regional tectonic evolution and bauxite formation was studied in this paper, to disclosure the geology-geochemistry evolution process of bauxite mineralization combined with special geological features. According to extraction of 1:100 000-1:10 000 remote sensing image features, the series of ore-bearing rocks and adjacent layers, main structure identification, relationship among iron, mud anomaly and the space distribution of the rock series were summarized to establish a remote sensing 3D image model in large scale. Through the application and comparative study of multiple bauxite mining areas by geophysical methods, such as Shallow seismic reflection wave method, high density resistivity method, frequency domain tripole sounding method, audio earth electromagnetic sounding method, high power excitation sounding method, the geophysical prospecting marks of “high, sunken, concave, thick” and typical mine 3D geological and geophysical prospecting prediction model of the bauxite deposit was established. On the study above, the technical method system of bauxite exploration and furtheron the geological, geophysical, geochemical and remote sensing prospecting models may demonstrate guidance to prospect and acquire remarkable prospecting effect through engineering verification, indicating the proposed mining model is suitable and effective in the exploration of bauxite in the study area.
2018, 36(5): 927-936.
doi: 10.14027/j.issn.1000-0550.2018.065
Abstract:
Typical loess deposits are widely distributed in the eastern Tibetan Plateau(ETP), which are sensitive to environmental change of the Plateau region. The geochemical analyses of the surface soil, loess, paleosol samples in the ETP, show that major elements of the loess are mainly SiO2, Al2O3, Fe2O3 and CaO, and the contents of the SiO2 and CaO in loess vary largely. The contents of the Rb, Sr, Ba, Zr, V account mainly for the trace elemental composition of all samples, which have different characters among the surface soil, loess, paleosol. In comparison of major and trace elements of the loess with the ETP, the Chinese Loess Plateau(CLP) and the Hexi Corridor, the ratios between the major elemental oxides(SiO2/Al2O3, TiO2/Al2O3), the element ratios(Zr/Al, Zr/Ti), and the major elemental ternary(Ca-Mg-K, Ca-Mg-Na) show that the ETP loess are distinctly different from other regions. While ETP loess and top soil, fluvial sand, aeolian sand samples have no obvious difference. These results may indicates that the loess in the ETP has different source region against with the loess in the CLP and the Hexi corridor. We infer that the interior dry land, river drainage basin and active glacials in the Tibetan Plateau may provide the most silt materials for the loess deposit in the ETP.
Typical loess deposits are widely distributed in the eastern Tibetan Plateau(ETP), which are sensitive to environmental change of the Plateau region. The geochemical analyses of the surface soil, loess, paleosol samples in the ETP, show that major elements of the loess are mainly SiO2, Al2O3, Fe2O3 and CaO, and the contents of the SiO2 and CaO in loess vary largely. The contents of the Rb, Sr, Ba, Zr, V account mainly for the trace elemental composition of all samples, which have different characters among the surface soil, loess, paleosol. In comparison of major and trace elements of the loess with the ETP, the Chinese Loess Plateau(CLP) and the Hexi Corridor, the ratios between the major elemental oxides(SiO2/Al2O3, TiO2/Al2O3), the element ratios(Zr/Al, Zr/Ti), and the major elemental ternary(Ca-Mg-K, Ca-Mg-Na) show that the ETP loess are distinctly different from other regions. While ETP loess and top soil, fluvial sand, aeolian sand samples have no obvious difference. These results may indicates that the loess in the ETP has different source region against with the loess in the CLP and the Hexi corridor. We infer that the interior dry land, river drainage basin and active glacials in the Tibetan Plateau may provide the most silt materials for the loess deposit in the ETP.
2018, 36(5): 937-945.
doi: 10.14027/j.issn.1000-0550.2018.138
Abstract:
The analysis of major elements in samples from the Shijiaya(SJY)profile in Tianshui of Gansu Province, China showed the similar curves trend of SiO2, Fe2O3, K2O, and Al2O3, with relatively high concentration all in the paleosol layer while lower in the loess. However, the variation tendency of CaO and Na2O were different from that of SiO2, Fe2O3, K2O and Al2O3. Some typically chemical parameters in the SJY Profile such as K/Na radio, Ca/Mg radio, residual coefficient, leaching coefficient, the chemical index of alteration(CIA) indicated that chemical weathering was strong during the paleosol deposition and weak during the loess loading. Chemical activity of various elements on the section showed obvious variability. Compared to the stable element Ti, other major elements such as Ca and Na were migrated and leached, while the elements Si、Fe、K and Al were enriched, probably indicating some incipient stage of chemical weathering. The chemical weathering process of the Shijiaya profile could be divided into three stages, the stage of regional chemical weathering was relatively weaker, then it was unstedaily stronger and finally became weaker and weaker. The climate was cool in early Holocene (11 500-8 500 a B.P.), generally warm and humid during mid Holocene(8 500-3 100 a B.P.), and then became no stable with climatic fluctuation at 7 000-6 000 a B.P.. In the late Holocene (3 100 a B.P.-today), the climate entered a period of relatively cool with less rain.
The analysis of major elements in samples from the Shijiaya(SJY)profile in Tianshui of Gansu Province, China showed the similar curves trend of SiO2, Fe2O3, K2O, and Al2O3, with relatively high concentration all in the paleosol layer while lower in the loess. However, the variation tendency of CaO and Na2O were different from that of SiO2, Fe2O3, K2O and Al2O3. Some typically chemical parameters in the SJY Profile such as K/Na radio, Ca/Mg radio, residual coefficient, leaching coefficient, the chemical index of alteration(CIA) indicated that chemical weathering was strong during the paleosol deposition and weak during the loess loading. Chemical activity of various elements on the section showed obvious variability. Compared to the stable element Ti, other major elements such as Ca and Na were migrated and leached, while the elements Si、Fe、K and Al were enriched, probably indicating some incipient stage of chemical weathering. The chemical weathering process of the Shijiaya profile could be divided into three stages, the stage of regional chemical weathering was relatively weaker, then it was unstedaily stronger and finally became weaker and weaker. The climate was cool in early Holocene (11 500-8 500 a B.P.), generally warm and humid during mid Holocene(8 500-3 100 a B.P.), and then became no stable with climatic fluctuation at 7 000-6 000 a B.P.. In the late Holocene (3 100 a B.P.-today), the climate entered a period of relatively cool with less rain.
2018, 36(5): 946-956.
doi: 10.14027/j.issn.1000-0550.2018.079
Abstract:
The sandstone reservoirs in the Kuqa foreland area of Tarim Basin have the characteristics of very low physical properties, strong heterogeneity and high-stable production, in which the dissolution of reservoir rocks is significant, but their formation mechanism is not very clear by far. A series of thermal simulation experiments under high temperature and high pressure were performed to restitute the dissolution effects of target layers in addition of one epidiagenetic fluid and two kinds of burial fluids for a better understanding of the diagenetic process, and then to realize the diagenetic evolution of minerals and spatial changes of reservoir structures. In the epidiagenetic stage, there was weak acidic fluid environments leached by atmospheric fresh water and replaced with saturated CO2 solution (pCO2=1 MPa) in the experiment. The results showed that the dissolution was very significant and feldspar minerals emerged significant dissolution, while the quartz and clay minerals were relatively insoluble. Na+, Ca2+ and K+ were separated out more obviously with Si4+ and Al3+ less. Many suspected polygonal quartz and aluminosilicate minerals have precipitated on the sample surface. The dissolution was secondary in the acidic environment (instead by acetic acid solution, 2 mL/L) formed by hydrocarbons filling in the later diagenetic stage and dolomite, gypsum and feldspar minerals were easily to be dissolved. Ca2+, Mg2+, Na+ and Si4+ were separated out apparently without precipitation. The dissolution is relatively weak in NaHCO3 solution (pH=7.46, HCO3-=0.6 mol/L) which is instead of the alkaline environment of early-middle diagenetic stage and the dissolution of quartz, feldspar and clay minerals appeared in different degrees which increase with the increase of temperatures and pressures. Comprehensive analysis showed that superficial fluid was the key factor for dissolved pore development of sandstone reservoirs in the study area, followed by organic acid and alkaline buried fluid. This understanding not only enriches the theory of porosity and genesis evolution of tight sandstone reservoirs, but also provides theoretical support for the next prospecting of scale reserves and effective development of gas fields.
The sandstone reservoirs in the Kuqa foreland area of Tarim Basin have the characteristics of very low physical properties, strong heterogeneity and high-stable production, in which the dissolution of reservoir rocks is significant, but their formation mechanism is not very clear by far. A series of thermal simulation experiments under high temperature and high pressure were performed to restitute the dissolution effects of target layers in addition of one epidiagenetic fluid and two kinds of burial fluids for a better understanding of the diagenetic process, and then to realize the diagenetic evolution of minerals and spatial changes of reservoir structures. In the epidiagenetic stage, there was weak acidic fluid environments leached by atmospheric fresh water and replaced with saturated CO2 solution (pCO2=1 MPa) in the experiment. The results showed that the dissolution was very significant and feldspar minerals emerged significant dissolution, while the quartz and clay minerals were relatively insoluble. Na+, Ca2+ and K+ were separated out more obviously with Si4+ and Al3+ less. Many suspected polygonal quartz and aluminosilicate minerals have precipitated on the sample surface. The dissolution was secondary in the acidic environment (instead by acetic acid solution, 2 mL/L) formed by hydrocarbons filling in the later diagenetic stage and dolomite, gypsum and feldspar minerals were easily to be dissolved. Ca2+, Mg2+, Na+ and Si4+ were separated out apparently without precipitation. The dissolution is relatively weak in NaHCO3 solution (pH=7.46, HCO3-=0.6 mol/L) which is instead of the alkaline environment of early-middle diagenetic stage and the dissolution of quartz, feldspar and clay minerals appeared in different degrees which increase with the increase of temperatures and pressures. Comprehensive analysis showed that superficial fluid was the key factor for dissolved pore development of sandstone reservoirs in the study area, followed by organic acid and alkaline buried fluid. This understanding not only enriches the theory of porosity and genesis evolution of tight sandstone reservoirs, but also provides theoretical support for the next prospecting of scale reserves and effective development of gas fields.
2018, 36(5): 957-968.
doi: 10.14027/j.issn.1000-0550.2018.072
Abstract:
Pinghu Formation of the Xihu sag developed sea-land transition sedimentary systems with the characteristic of thin interbedding among sand, clay and coal layers. The accumulation conditions of narrow thin sand body are superior, which gradually become the hotspot of rolling exploration and development. To determine the genetic type of narrow thin sand body, plane size, evolution rules and main control factors, the indication function of stable coal seam to high frequency sequence formation was fully used to set up their constructions based on the analysis of core, logging and seismic data, and the sedimentary characteristics were studied intensively by using seismic sedimentology strata slice technology. Firstly, a high frequency sequence framework of coal-bearing strata was established, and the one and second segment of Pinghu formation was divided into two third-order sequences and seven fourth-order sequences. Secondly, three kinds of narrow thin sandstone geneses were identified as distributary channel, flood fan and tidal channel. The width of distributary channel was from 500 m to 1 000 m, the plane size of flood fan was from 1 km2 to 10 km2, both of which were developed in regressive sequence, however, the tidal channel width was only from 80 m to 360 m, and developed much more in transgressive sequence. Finally, the vertical evolution and main controlling factors of narrow thin sand body were discussed and pointed out that the distributary channel and its associated flood fan sand body had good accumulation coupling relationship in the regressive sequence, which should be the main direction of subtle reservoir exploration.
Pinghu Formation of the Xihu sag developed sea-land transition sedimentary systems with the characteristic of thin interbedding among sand, clay and coal layers. The accumulation conditions of narrow thin sand body are superior, which gradually become the hotspot of rolling exploration and development. To determine the genetic type of narrow thin sand body, plane size, evolution rules and main control factors, the indication function of stable coal seam to high frequency sequence formation was fully used to set up their constructions based on the analysis of core, logging and seismic data, and the sedimentary characteristics were studied intensively by using seismic sedimentology strata slice technology. Firstly, a high frequency sequence framework of coal-bearing strata was established, and the one and second segment of Pinghu formation was divided into two third-order sequences and seven fourth-order sequences. Secondly, three kinds of narrow thin sandstone geneses were identified as distributary channel, flood fan and tidal channel. The width of distributary channel was from 500 m to 1 000 m, the plane size of flood fan was from 1 km2 to 10 km2, both of which were developed in regressive sequence, however, the tidal channel width was only from 80 m to 360 m, and developed much more in transgressive sequence. Finally, the vertical evolution and main controlling factors of narrow thin sand body were discussed and pointed out that the distributary channel and its associated flood fan sand body had good accumulation coupling relationship in the regressive sequence, which should be the main direction of subtle reservoir exploration.
2018, 36(5): 969-980.
doi: 10.14027/j.issn.1000-0550.2018.099
Abstract:
The composition, structure and particles arrangement of rocks determine the developmental characteristics of pores. However, there are few researches performed on the influence of detrital particles content and its arrangement patterns on the pore distribution of shale from the structural-genetic perspectives by far. The black shale of the Silurian Longmaxi Formation in northwestern Guizhou Province was taken as an example for the analysis of thin section, XRD and scanning electron microscopy (SEM), and two types of shales were divided as the "particle dispersal" and "lamellar" according to the arrangement patterns of detritus particles. The conceptual models of pore structure of shales were abstracted and the influence of detrital particles content on the pore development was analyzed. For the particle dispersed shale, the main type of pore is micro pores of clay minerals while the content of clastic particles is less than 52.4%, and the porosity decreases with increase of particles content. When the content of clastic particles reaches 52.4%, the porosity becomes the lowest and the interpartical pores are filled with clay. The interpartical pores will increase with the clastic particles content increasing, and the porosity will increase rapidly. For the laminar shale, the increase of grain content leads to the increase of intergranular pores and the increase of porosity in sand strip, and then result in the transformation of shale reservoir to conventional clastic reservoir gradually. These models can be helpful for a deepen understanding of the development mechanism of porosity in shale, tight sandstone and conventional sandstone, and also important implications to predict and evaluate unconventional reservoirs.
The composition, structure and particles arrangement of rocks determine the developmental characteristics of pores. However, there are few researches performed on the influence of detrital particles content and its arrangement patterns on the pore distribution of shale from the structural-genetic perspectives by far. The black shale of the Silurian Longmaxi Formation in northwestern Guizhou Province was taken as an example for the analysis of thin section, XRD and scanning electron microscopy (SEM), and two types of shales were divided as the "particle dispersal" and "lamellar" according to the arrangement patterns of detritus particles. The conceptual models of pore structure of shales were abstracted and the influence of detrital particles content on the pore development was analyzed. For the particle dispersed shale, the main type of pore is micro pores of clay minerals while the content of clastic particles is less than 52.4%, and the porosity decreases with increase of particles content. When the content of clastic particles reaches 52.4%, the porosity becomes the lowest and the interpartical pores are filled with clay. The interpartical pores will increase with the clastic particles content increasing, and the porosity will increase rapidly. For the laminar shale, the increase of grain content leads to the increase of intergranular pores and the increase of porosity in sand strip, and then result in the transformation of shale reservoir to conventional clastic reservoir gradually. These models can be helpful for a deepen understanding of the development mechanism of porosity in shale, tight sandstone and conventional sandstone, and also important implications to predict and evaluate unconventional reservoirs.
2018, 36(5): 981-994.
doi: 10.14027/j.issn.1000-0550.2018.078
Abstract:
The classification of reservoir pore configurations and differential genesis for the Cretaceous Mishrif formation in the Halfaya oilfield, Iraq, restrains as one of the key question for reservoir evaluation. The pores and throats are studied by cores, cast thin sections, scanning electron microscopy, routine physical properties and mercury analysis, to define the types and criteria of pore configuration. The pore configuration are divided into six types: (a) thin throat with low-middle porosity and ultra-low permeability; (b) thin throat with low-middle porosity and low permeability; (C) middle-thin throat with high-middle porosity and low-middle permeability;(d) thin throat with high porosity and low-middle permeability; (e) thin throat with high-middle porosity and low-middle permeability; (f) medium throat with high-middle porosity and low-middle permeability. Five shapes (from I to V) of capillary pressure curves are also divided. The research area is located in an open platform facies with eight types of rocks deposited, including micrite limestone, bioclastic wackestone, bioclastic packstone, intraclast bioclastic packstone, bioclastic grainstone, intraclast bioclastic grainstone, shell floatstone and karstic rock, respectively. Besides, the karstic rock is a special network structure. It is comprehensively suggested that the Mishrif reservoir in Halfaya was mainly affected by eogenetic karstification obviously controlled by facies. So the eogenetic karstification is the key factor controlling the diversity of pore configuration and further improving the reservoir quality greatly.
The classification of reservoir pore configurations and differential genesis for the Cretaceous Mishrif formation in the Halfaya oilfield, Iraq, restrains as one of the key question for reservoir evaluation. The pores and throats are studied by cores, cast thin sections, scanning electron microscopy, routine physical properties and mercury analysis, to define the types and criteria of pore configuration. The pore configuration are divided into six types: (a) thin throat with low-middle porosity and ultra-low permeability; (b) thin throat with low-middle porosity and low permeability; (C) middle-thin throat with high-middle porosity and low-middle permeability;(d) thin throat with high porosity and low-middle permeability; (e) thin throat with high-middle porosity and low-middle permeability; (f) medium throat with high-middle porosity and low-middle permeability. Five shapes (from I to V) of capillary pressure curves are also divided. The research area is located in an open platform facies with eight types of rocks deposited, including micrite limestone, bioclastic wackestone, bioclastic packstone, intraclast bioclastic packstone, bioclastic grainstone, intraclast bioclastic grainstone, shell floatstone and karstic rock, respectively. Besides, the karstic rock is a special network structure. It is comprehensively suggested that the Mishrif reservoir in Halfaya was mainly affected by eogenetic karstification obviously controlled by facies. So the eogenetic karstification is the key factor controlling the diversity of pore configuration and further improving the reservoir quality greatly.
2018, 36(5): 995-1007.
doi: 10.14027/j.issn.1000-0550.2018.070
Abstract:
High production of oils and gases from the biological limestone at the first member bottom of the Shahejie Formation in Changdi area, Zhanhua sag lead to extremely frequent exploration activities in recent years, which used to be weak in petroleum exploration. Due to a relative low exploration in the whole first member of the Shahejie Formation, the development pattern and distribution features of limestone has not been entirely understood yet. Based on cores, well logs and high-resolution 3-D seismic data, many aspects of the biological limestone have been studied systematically in this paper and several results are summarized as the followings: Firstly, with help of seismic and wellbore data, the first member of the Shahejie Formation is considered as one third-level sequence by the previous method of sequences division, the bottom of which could also be divided into three fourth-level sequences depending on high frequency sequence division theory and the biological limestone developed in this part. Secondly, the distribution of organic bank is controlled by paleoclimate, the relative paleo-water depth and paleogeomorphology, the first member of the Shahejie Formation in the study area existed in subtropical brackish lake environment under a humid-arid climate, and the organic bank was mainly developed in the regressive systems tracting high-energy turbulent lake with a stably declining paleo-water depth. The logging data also confirmed the biological limestone are located in the southwest gentle slope and east depression. Thirdly, the development patterns of the organic bank are established and further divided into gentle-slope and depression patterns. The stratigraphic evolution pattern of the biological limestone is determined for three sets of limestone developed and retrograde to the north. Fourthly, by analyzing vertical and horizontal distribution of biological limestone in each fourth-level sequence, the prediction of horizontal distribution of sensitive seismic attributes and paleogeomorphology, the thickness of the biological limestone is small in north but big in south with a strip-like distribution. Finally, this study determines the distribution and development patterns of the limestone in the lower part of the first member of Shahejie Formation, which deepens the theoretical study on the developing pattern of lake-type biological limestone, and guides the development of lithological reservoir and traps optimization of the first member of Shahejie Formation, Jiyang depression.
High production of oils and gases from the biological limestone at the first member bottom of the Shahejie Formation in Changdi area, Zhanhua sag lead to extremely frequent exploration activities in recent years, which used to be weak in petroleum exploration. Due to a relative low exploration in the whole first member of the Shahejie Formation, the development pattern and distribution features of limestone has not been entirely understood yet. Based on cores, well logs and high-resolution 3-D seismic data, many aspects of the biological limestone have been studied systematically in this paper and several results are summarized as the followings: Firstly, with help of seismic and wellbore data, the first member of the Shahejie Formation is considered as one third-level sequence by the previous method of sequences division, the bottom of which could also be divided into three fourth-level sequences depending on high frequency sequence division theory and the biological limestone developed in this part. Secondly, the distribution of organic bank is controlled by paleoclimate, the relative paleo-water depth and paleogeomorphology, the first member of the Shahejie Formation in the study area existed in subtropical brackish lake environment under a humid-arid climate, and the organic bank was mainly developed in the regressive systems tracting high-energy turbulent lake with a stably declining paleo-water depth. The logging data also confirmed the biological limestone are located in the southwest gentle slope and east depression. Thirdly, the development patterns of the organic bank are established and further divided into gentle-slope and depression patterns. The stratigraphic evolution pattern of the biological limestone is determined for three sets of limestone developed and retrograde to the north. Fourthly, by analyzing vertical and horizontal distribution of biological limestone in each fourth-level sequence, the prediction of horizontal distribution of sensitive seismic attributes and paleogeomorphology, the thickness of the biological limestone is small in north but big in south with a strip-like distribution. Finally, this study determines the distribution and development patterns of the limestone in the lower part of the first member of Shahejie Formation, which deepens the theoretical study on the developing pattern of lake-type biological limestone, and guides the development of lithological reservoir and traps optimization of the first member of Shahejie Formation, Jiyang depression.
2018, 36(5): 1008-1022.
doi: 10.14027/j.issn.1000-0550.2018.101
Abstract:
In order to further clarify the role of different geological conditions on hydrocarbons accumulation process, the major controlling factors of Ordovician hydrocarbons accumulation in the Tazhong Uplift, Tarim Basin are studied based on the view points of diverse geological conditions and their relationship in space. The results showed that the vertical hydrocarbons migration distance and accumulation layers were controlled by vertical source-reservoir distribution, faults, and caprocks. Structures played a major role in lateral direction of hydrocarbons migration. The lateral migration pathways were governed by unconformities, transport faults, and porous permeable carrier beds. Apart from the excellent reservoir controls, hydrocarbons enrichment was controlled by tectonic events. Based on the analysis of factors mentioned above and coupled with oil sources conditions and excellent reservoirs, two types of hydrocarbon accumulation models could be retained based on the vertical hydrocarbon migration distance, including a multi-sourced area model and a single-sourced area model. In addition, the accumulation models could be also classified into near source accumulation and far source accumulation based on the lateral hydrocarbons migration distance.
In order to further clarify the role of different geological conditions on hydrocarbons accumulation process, the major controlling factors of Ordovician hydrocarbons accumulation in the Tazhong Uplift, Tarim Basin are studied based on the view points of diverse geological conditions and their relationship in space. The results showed that the vertical hydrocarbons migration distance and accumulation layers were controlled by vertical source-reservoir distribution, faults, and caprocks. Structures played a major role in lateral direction of hydrocarbons migration. The lateral migration pathways were governed by unconformities, transport faults, and porous permeable carrier beds. Apart from the excellent reservoir controls, hydrocarbons enrichment was controlled by tectonic events. Based on the analysis of factors mentioned above and coupled with oil sources conditions and excellent reservoirs, two types of hydrocarbon accumulation models could be retained based on the vertical hydrocarbon migration distance, including a multi-sourced area model and a single-sourced area model. In addition, the accumulation models could be also classified into near source accumulation and far source accumulation based on the lateral hydrocarbons migration distance.
2018, 36(5): 1023-1031.
doi: 10.14027/j.issn.1000-0550.2018.071
Abstract:
The discovery of H2-producing bacteria is a great advance in modern scientific research of microbiology. The hydrogen supersession (the generation and utilization of hydrogen) is the important link for microbially degradation of organic matters and generation of hydrocarbons in geological systems. During the progress of petroleum-formation, hydrogen is a middle product and also a major product. Addition of extra hydrogen is necessary all for the degradation of macromolecular compounds into low molecule ones, the elimination of oxygen-containing groups and also the transformation of alkenes into saturated hydrocarbons. If there are no hydrogen supersession, there would be no abundant petroleum formed. H2-producing bacteria contain hydrogenase with the ability to generate hydrogen. Some kinds of microbes produce H2 in the process of organic matter degradation while others utilize H2 for their living, thus for both the production and utilization of hydrogen can be always kept on a steady dynamic equilibrium. Only when H2-expending microbial existed, those of H2-producing can be grown up. H2-expending function of the bacteria can further improve the continuous reaction of hydrogen production. Those mutualistic symbioses can take place in every stage of petroleum formation. Hydrogen transformation is one of the most important characteristics to distinguish anaerobic decomposition of organic matters from aerobia ones.
The growth and breeding of microbial are influenced under temperature, nutrient and sedimentary environments. Microbial populations are replaced unceasingly from shallow to deep layers, of which the primary population died and disappeared for the change of living conditions and new bacteria might be multiplied in a great quantity. Those died microorganisms can be deposited into sedimentary layers and then transformed into hydrocarbons.
The enzyme is one protein with catalytic activity, from which all life actions of microbes can not be available. One kind of enzyme can only catalyze one certain reaction and/or complicate one kind of reactions, of which there is unique enzyme system at every stage. The enzyme might be also transformed into petroleum component after its special metabolism routing complicated. Such as chlorophyll can be transformed into F430-coenzyme of methanogen,and then converted to porphyrin compounds.
The stratigraphic geothermal can promote the thermosplitting decomposition of organic matters and result in the breaking of C-C bond much more frequently. In addition, the degradation by anaerobic activity might also be able to improve the degradation of organic matters. Both two different pathways are unanimous, each other and cooperative to speed up the splitting decomposition of organic matters. The function of hydrocarbons formation through reform and/or transformation of organic matters by microbes also include the elimination of oxygen containing groups, the production and utilization of hydrogen to generate saturated hydrocarbons etc. and thus their significance could be much more important and comprehensive for discussion on the formation of crude oils and natural gases.
The discovery of H2-producing bacteria is a great advance in modern scientific research of microbiology. The hydrogen supersession (the generation and utilization of hydrogen) is the important link for microbially degradation of organic matters and generation of hydrocarbons in geological systems. During the progress of petroleum-formation, hydrogen is a middle product and also a major product. Addition of extra hydrogen is necessary all for the degradation of macromolecular compounds into low molecule ones, the elimination of oxygen-containing groups and also the transformation of alkenes into saturated hydrocarbons. If there are no hydrogen supersession, there would be no abundant petroleum formed. H2-producing bacteria contain hydrogenase with the ability to generate hydrogen. Some kinds of microbes produce H2 in the process of organic matter degradation while others utilize H2 for their living, thus for both the production and utilization of hydrogen can be always kept on a steady dynamic equilibrium. Only when H2-expending microbial existed, those of H2-producing can be grown up. H2-expending function of the bacteria can further improve the continuous reaction of hydrogen production. Those mutualistic symbioses can take place in every stage of petroleum formation. Hydrogen transformation is one of the most important characteristics to distinguish anaerobic decomposition of organic matters from aerobia ones.
The growth and breeding of microbial are influenced under temperature, nutrient and sedimentary environments. Microbial populations are replaced unceasingly from shallow to deep layers, of which the primary population died and disappeared for the change of living conditions and new bacteria might be multiplied in a great quantity. Those died microorganisms can be deposited into sedimentary layers and then transformed into hydrocarbons.
The enzyme is one protein with catalytic activity, from which all life actions of microbes can not be available. One kind of enzyme can only catalyze one certain reaction and/or complicate one kind of reactions, of which there is unique enzyme system at every stage. The enzyme might be also transformed into petroleum component after its special metabolism routing complicated. Such as chlorophyll can be transformed into F430-coenzyme of methanogen,and then converted to porphyrin compounds.
The stratigraphic geothermal can promote the thermosplitting decomposition of organic matters and result in the breaking of C-C bond much more frequently. In addition, the degradation by anaerobic activity might also be able to improve the degradation of organic matters. Both two different pathways are unanimous, each other and cooperative to speed up the splitting decomposition of organic matters. The function of hydrocarbons formation through reform and/or transformation of organic matters by microbes also include the elimination of oxygen containing groups, the production and utilization of hydrogen to generate saturated hydrocarbons etc. and thus their significance could be much more important and comprehensive for discussion on the formation of crude oils and natural gases.
2018, 36(5): 1033-1039.
doi: 10.14027/j.issn.1000-0550.2018.063
Abstract:
The molecular geochemical characteristics of a total 87 samples of lacustrine and coal measure hydrocarbon source rocks collected from the Songliao Basin and Ordos Basin are systematically analyzed in order to evaluate thermal effect on the distribution characteristics of rearranged hopanes in hydrocarbon source rocks. The results indicate that both lacustrine and coal measure hydrocarbon source rocks contain abundantly four series of rearranged hopanes and their distributions in geological bodies from different depositional environments or parent material sources show similar variation trends. The relatively lower abundant rearranged hopanes are distributed from low mature to high mature stages, whereas the abnormally high or higher abundant rearranged hopanes are mainly presented in mature stage. The linear correlations between the 17α(H)-diahopane series and other three series of rearranged hopanes including 18α(H)-neohopane series, the early-eluting rearranged hopane series and 21-methyl-28-nor-hopane series, are diverse clearly. In addition, the variations of relative abundance of rearranged hopanes from the two sets of samples show similar trend. For example, the relative abundances of 17α(H)-diahopane and 18α(H)-neohopane display an initial increase and a following decrease with increasing maturity and the highest amounts appear to be distributed in the range of maturity 0.8%-0.9% Ro. On the other hand, the absolute concentrations of rearranged hopanes have consistent variation for the hydrocarbon source rocks derived from different sedimentary environments with increasing maturity. Rearranged hopanes are formed at immature to mature stage corresponding to Ro=0.5%-0.7%. With the source rocks into mature stage (Ro=0.7%-0.8%), the absolute concentration decreases remarkably with the decreasing extent more than 90%. The consistency of variation of relative abundance and absolute concentration of rearranged hopanes in different depositional systems indicate that thermal effect has much more important impact on the distribution and composition of rearranged hopanes compared with sedimentary environments and biological sources.
The molecular geochemical characteristics of a total 87 samples of lacustrine and coal measure hydrocarbon source rocks collected from the Songliao Basin and Ordos Basin are systematically analyzed in order to evaluate thermal effect on the distribution characteristics of rearranged hopanes in hydrocarbon source rocks. The results indicate that both lacustrine and coal measure hydrocarbon source rocks contain abundantly four series of rearranged hopanes and their distributions in geological bodies from different depositional environments or parent material sources show similar variation trends. The relatively lower abundant rearranged hopanes are distributed from low mature to high mature stages, whereas the abnormally high or higher abundant rearranged hopanes are mainly presented in mature stage. The linear correlations between the 17α(H)-diahopane series and other three series of rearranged hopanes including 18α(H)-neohopane series, the early-eluting rearranged hopane series and 21-methyl-28-nor-hopane series, are diverse clearly. In addition, the variations of relative abundance of rearranged hopanes from the two sets of samples show similar trend. For example, the relative abundances of 17α(H)-diahopane and 18α(H)-neohopane display an initial increase and a following decrease with increasing maturity and the highest amounts appear to be distributed in the range of maturity 0.8%-0.9% Ro. On the other hand, the absolute concentrations of rearranged hopanes have consistent variation for the hydrocarbon source rocks derived from different sedimentary environments with increasing maturity. Rearranged hopanes are formed at immature to mature stage corresponding to Ro=0.5%-0.7%. With the source rocks into mature stage (Ro=0.7%-0.8%), the absolute concentration decreases remarkably with the decreasing extent more than 90%. The consistency of variation of relative abundance and absolute concentration of rearranged hopanes in different depositional systems indicate that thermal effect has much more important impact on the distribution and composition of rearranged hopanes compared with sedimentary environments and biological sources.
2018, 36(5): 1040-1048.
doi: 10.14027/j.issn.1000-0550.2018.080
Abstract:
Most experiments are using gold bags to investigate the effect of pressure on maturation of organic matters, and no significant differences have been found in the majority of the results. However, the results from high-pressure fixed volume autoclave hydrous experiments usually showed pressure retardation on organic matters maturation. Although fixed volume autoclave hydrous pyrolysis may partly simulate the geological conditions under which hydrocarbons are being generated, the WYMN-3 HTHP instrument developed by Lanzhou Institute of Geology, Chinese Academy of Sciences or formation pore space pyrolysis built in Wuxi Research Institute of Petroleum Geology are better to investigate the organic matter maturation in overpressure basins because they also take into account of the lithostatic pressure. And high water pressure enhances the activation energy via increasing the pV work; it also reduces the entropy(ΔS) to decrease the pre-exponential factor(A). At present, using PreRoTM and T-P-Ro models would be better for overpressure basins, but both only take account of excess fluid pressure, rather than absolute fluid pressure. So a kinetic model incorporated absolute fluid pressure is needed in further studies. Given that it is hard to compare the results obtained from different experimental methods or instruments, it is quite necessary to establish a set of standard experimental rules to fully understand the pressure effect on organic matter maturation. In addition, the exploration and development of shale gas with high maturity levels provide valuable geological data for studying the effect of pressure on hydrocarbon generation at overmature stages, but this requires the accurate determination of thermal maturity levels of marine shales in which the vitrinite macerals are usually absent or rare.
Most experiments are using gold bags to investigate the effect of pressure on maturation of organic matters, and no significant differences have been found in the majority of the results. However, the results from high-pressure fixed volume autoclave hydrous experiments usually showed pressure retardation on organic matters maturation. Although fixed volume autoclave hydrous pyrolysis may partly simulate the geological conditions under which hydrocarbons are being generated, the WYMN-3 HTHP instrument developed by Lanzhou Institute of Geology, Chinese Academy of Sciences or formation pore space pyrolysis built in Wuxi Research Institute of Petroleum Geology are better to investigate the organic matter maturation in overpressure basins because they also take into account of the lithostatic pressure. And high water pressure enhances the activation energy via increasing the pV work; it also reduces the entropy(ΔS) to decrease the pre-exponential factor(A). At present, using PreRoTM and T-P-Ro models would be better for overpressure basins, but both only take account of excess fluid pressure, rather than absolute fluid pressure. So a kinetic model incorporated absolute fluid pressure is needed in further studies. Given that it is hard to compare the results obtained from different experimental methods or instruments, it is quite necessary to establish a set of standard experimental rules to fully understand the pressure effect on organic matter maturation. In addition, the exploration and development of shale gas with high maturity levels provide valuable geological data for studying the effect of pressure on hydrocarbon generation at overmature stages, but this requires the accurate determination of thermal maturity levels of marine shales in which the vitrinite macerals are usually absent or rare.
2018, 36(5): 1049-1058.
doi: 10.14027/j.issn.1000-0550.2018.073
Abstract:
The geochemistry of n-alkane and n-alkan-2-one in the Mildred peat bog of the Athabasca region is systematically analyzed in order to determine the source material of organic matters in peat, and explore the genetic correlation between n-alkane and n-alkan-2-one, which reveals some biological information and vegetation evolution characteristics in the study peat bog. The distributions of n-alkane and n-alkan-2-one are characterized by high molecular weight and post peak pattern, with strong odd over even predominances, which indicates that the peat organic materials are primarily derived from in situ terrigenous higher plants, whereas the contribution from sphagnum and aquatic plants seems to be small. In accordance with principal component analysis (PCA) and n-alkane proxies distributions, the Mildred peat profile is divided into three intervals, the peat-forming plant in the upper interval (living layer to -17 cm) containing mainly Sphagnum fuscum; the middle interval (-17 cm to -41 cm) with woody plants, Ericaceae, piece needles and minor Cyperaceous as the in situ accumulated plants; and the deeper interval (-41 cm to the bottom) containing a number of Cyperaceous plants increased with some woody debris and Ericaceae grow. The similar distribution between n-alkane and n-alkan-2-one suggests microbial oxidation of related n-alkanes as the primary source of n-alkan-2-one in the Mildred peat bog. A direct input from peat-forming plants also contributes to n-alkan-2-one formation, particularly in the top profile. Microbial β-oxidation and decarboxylation of n-fatty acids can be also considered as an alternative origin of n-alkan-2-ones but its contribution is not significant.
The geochemistry of n-alkane and n-alkan-2-one in the Mildred peat bog of the Athabasca region is systematically analyzed in order to determine the source material of organic matters in peat, and explore the genetic correlation between n-alkane and n-alkan-2-one, which reveals some biological information and vegetation evolution characteristics in the study peat bog. The distributions of n-alkane and n-alkan-2-one are characterized by high molecular weight and post peak pattern, with strong odd over even predominances, which indicates that the peat organic materials are primarily derived from in situ terrigenous higher plants, whereas the contribution from sphagnum and aquatic plants seems to be small. In accordance with principal component analysis (PCA) and n-alkane proxies distributions, the Mildred peat profile is divided into three intervals, the peat-forming plant in the upper interval (living layer to -17 cm) containing mainly Sphagnum fuscum; the middle interval (-17 cm to -41 cm) with woody plants, Ericaceae, piece needles and minor Cyperaceous as the in situ accumulated plants; and the deeper interval (-41 cm to the bottom) containing a number of Cyperaceous plants increased with some woody debris and Ericaceae grow. The similar distribution between n-alkane and n-alkan-2-one suggests microbial oxidation of related n-alkanes as the primary source of n-alkan-2-one in the Mildred peat bog. A direct input from peat-forming plants also contributes to n-alkan-2-one formation, particularly in the top profile. Microbial β-oxidation and decarboxylation of n-fatty acids can be also considered as an alternative origin of n-alkan-2-ones but its contribution is not significant.
