Petroleum geochemistry contributes to exploration successes by providing key constraints for geological models and critical input to exploration scenarios. One of the most important tasks in a typical exploration pr...Petroleum geochemistry contributes to exploration successes by providing key constraints for geological models and critical input to exploration scenarios. One of the most important tasks in a typical exploration program is to identify the most effective source intervals or kitchens in a basin, through oil-source correlation. The results of correlation are valid only if the geochemical parameters used address adequately the genetic characteristics of the source rocks as well as the mass transport and mixing processes of hydrocarbon fluids occurring in the carrier beds and reservoirs. This manuscript discusses four of the major contentious petroleum geochemical issues in China’s sedimentary basins. It is suggested that marine incursions played a significant role in the formation of prolific petroleum source rocks in the gigantic, dominantly freshwater, Songliao Basin. Several models are proposed to account for the occurrence of immature oils in the Cathaysian rift system including the Bohai Bay Basin, thus immature source rocks are considered a mere minor contributor to the known economic immature oil resources. Both geological and geochemical evidence are reviewed to refute a dominantly coaly source for the petroleum discovered in the Turpan Basin. Results of case studies are presented to demonstrate the importance of recognizing petroleum fluid mixing to solve the oil-source correlation issues in the structurally complex Tarim Basin. In addressing the fundamental assumptions and potential flaws of the molecular geochemical parameters commonly used for oil-source correlation, the need of a mass fraction approach is proposed to deal with such contentious issues as marine versus lacustrine, coal versus lacustrine, and mature versus immature oils.展开更多
The Gan-Hang Belt in Southeast China is characterized by several igneous and siliciclastic basins associated with crustal extension during Late Mesozoic. The sedimentary evolution of the red basins is still poorly und...The Gan-Hang Belt in Southeast China is characterized by several igneous and siliciclastic basins associated with crustal extension during Late Mesozoic. The sedimentary evolution of the red basins is still poorly understood. In this study, sedimentary fades analysis and pebble counting were performed on outcrop sections of the Late Cretaceous Guifeng Group in the Yongfeng-Chongren Basin in central Jiangxi Province. Thirty-five conglomerate outcrops were chosen to measure pebble lithology, size, roundness, weathering degree and preferred orientation. Results show that gravels are mostly fine to coarse pebbles and comprise dominantly quartzites, metamorphic rocks, granitoids and sandstones. Rose diagrams based on imbricated pebbles indicate variable paleocurrent directions. Combining with typical sedimentary structures and vertical successions, we suggest that the Guifeng Group were deposited in alluvial fan, river and playa lake depositional systems. The proposed depositional model indicates that the Hekou Formation represents the start-up stage of the faulted basin, accompanied by sedimentation in alluvial fan and braided river environments. Then this basin turned into a stable expansion stage during the deposition of the Tangbian Formation. Except for minor coarse sediments at the basin margin, the other area is covered with fine-grained sediments of lake and river environments. The Lianhe Formation, however, is once again featured by conglomerates, suggesting a probable tectonic event. Therefore, the study region possibly suffered two tectonic events represented by the conglomerates of the Hekou and Lianhe formations in the context of the crustal extension in Southeast China.展开更多
The total organic carbon (TOC) content series from the lake sediment of Minqin Basin (100°57′–104°57′E, 37°48′–39°17′N) in northwestern China, which has a 10 000-year-long paleo-climatic prox...The total organic carbon (TOC) content series from the lake sediment of Minqin Basin (100°57′–104°57′E, 37°48′–39°17′N) in northwestern China, which has a 10 000-year-long paleo-climatic proxy record, was used to analyze the Holocene climate changes in the local region. The proxy record was established in the Sanjiaocheng (SJC), Triangle Town in Chinese, Section (103°20′25″E, 39°00′38″N), which is located at the northwestern boundary of the present Asian summer monsoon in China, and is sensitive to global environmental and climate changes. Applying singular spectrum analysis (SSA) to the TOC series, principal climatic oscillations and periodical changes were studied. The results reveal 3 major patterns of climate change regulated by reconstructed components (RCs). The first pattern is natural long-term trend of climatic change in the local area (Minqin Basin), indicating a relatively wetter stage in early Holocene (starting at 9.5 kaBP), and a relatively dryer stage with a strong lake desiccation and a declined vegetation cover in mid-Holocene (during 7–6 kaBP). From 4.0 kaBP to the present, there has been a gradually decreasing trend in the third reconstructed component (RC3) showing that the local climate changed again into a dryer stage. The second pattern shows millennial-centennial scale oscillations containing cycles of 1 600 and 800 years that have been present throughout almost the entire Holocene period of the last 10 000 years. The third pattern is a millennial-centennial scale variation with a relatively smaller amplitude and unclear cycles showing a nonlinear interaction within the earth’s climate systems.展开更多
The Upper Ordovician Lianglitag Formation carbonate rocks are important oil and gas reservoirs in the Tarim Basin, Northwest China, with obviously distinct reservoir properties among different oilfields. As a case are...The Upper Ordovician Lianglitag Formation carbonate rocks are important oil and gas reservoirs in the Tarim Basin, Northwest China, with obviously distinct reservoir properties among different oilfields. As a case area of the above carbonate reser- voirs correlation, Tahe and Tazhong oilfields are chosen for the study through an integrated analysis of biostratigraphic isoch- ronous framework, cores, thin sections, logs, and strontium isotopes. The research shows that the two areas were respectively attributed to different carbonate platforms during the Lianglitag Formation depositional phase. For the Lianglitag Formation, five fourth-order sequences may be divided in Tazhong, whereas only four fourth-order sequences are preserved in Tahe that correspond to the lower ones observed in Tazhong. The Lianglitag Formation carbonate platform in Tahe was characterized by ramp and/or weak rimmed types, with low depositional rates （37 ktm/a）, higher whole-rock clastic contents, and higher 878r/86Sr isotope ratios of carbonate matrix, showing relatively deep-water environment and evident terrigenous input for car- bonate deposition. However, a strongly rimmed carbonate platform was developed in Tazhong, with high depositional rates of 250 p.m/a and less whole-rock clastic contents, indicating a high-energy depositional environment. Because of the sedimentary environment differences mentioned above, less high-energy facies but relatively intense syndepositional （early diagenetic） sea-water cementation of carbonates were developed in Tahe, and ubiquitous high-energy reef and shoal facies, with a frequent exposure to subaerial, and weak syndepositional sea-water cementation of carbonates in Tazhong. Therefore, fewer primary pores occurred in the Lianglitag Formation carbonate rocks of Tahe, whereas more primary pores were preserved in the same lithostratigraphic unit of the Tazhong （No. 1 fault zone）. Available high-energy reef-shoal facies and early diagenesis, with more primary pores preserved, provided a key material basis for the Lianglitag Formation carbonate reservoirs that largely oc- curred in Tazhong.展开更多
文摘Petroleum geochemistry contributes to exploration successes by providing key constraints for geological models and critical input to exploration scenarios. One of the most important tasks in a typical exploration program is to identify the most effective source intervals or kitchens in a basin, through oil-source correlation. The results of correlation are valid only if the geochemical parameters used address adequately the genetic characteristics of the source rocks as well as the mass transport and mixing processes of hydrocarbon fluids occurring in the carrier beds and reservoirs. This manuscript discusses four of the major contentious petroleum geochemical issues in China’s sedimentary basins. It is suggested that marine incursions played a significant role in the formation of prolific petroleum source rocks in the gigantic, dominantly freshwater, Songliao Basin. Several models are proposed to account for the occurrence of immature oils in the Cathaysian rift system including the Bohai Bay Basin, thus immature source rocks are considered a mere minor contributor to the known economic immature oil resources. Both geological and geochemical evidence are reviewed to refute a dominantly coaly source for the petroleum discovered in the Turpan Basin. Results of case studies are presented to demonstrate the importance of recognizing petroleum fluid mixing to solve the oil-source correlation issues in the structurally complex Tarim Basin. In addressing the fundamental assumptions and potential flaws of the molecular geochemical parameters commonly used for oil-source correlation, the need of a mass fraction approach is proposed to deal with such contentious issues as marine versus lacustrine, coal versus lacustrine, and mature versus immature oils.
基金supported by China Geological Survey projects (Grant Nos.1212011120836,1212011220248)China Scholarship Council (Grant No.201308360142)+2 种基金Gan-Po Excellent Talents 555 Project of Jiangxi Province (GCZ 2012-1)Research Foundation of Jiangxi Education Department (Grant No.GJJ13438)the open fund of Fundamental Science on Radioactive Geology and Exploration Technology Laboratory (Grant No.RGET1304)
文摘The Gan-Hang Belt in Southeast China is characterized by several igneous and siliciclastic basins associated with crustal extension during Late Mesozoic. The sedimentary evolution of the red basins is still poorly understood. In this study, sedimentary fades analysis and pebble counting were performed on outcrop sections of the Late Cretaceous Guifeng Group in the Yongfeng-Chongren Basin in central Jiangxi Province. Thirty-five conglomerate outcrops were chosen to measure pebble lithology, size, roundness, weathering degree and preferred orientation. Results show that gravels are mostly fine to coarse pebbles and comprise dominantly quartzites, metamorphic rocks, granitoids and sandstones. Rose diagrams based on imbricated pebbles indicate variable paleocurrent directions. Combining with typical sedimentary structures and vertical successions, we suggest that the Guifeng Group were deposited in alluvial fan, river and playa lake depositional systems. The proposed depositional model indicates that the Hekou Formation represents the start-up stage of the faulted basin, accompanied by sedimentation in alluvial fan and braided river environments. Then this basin turned into a stable expansion stage during the deposition of the Tangbian Formation. Except for minor coarse sediments at the basin margin, the other area is covered with fine-grained sediments of lake and river environments. The Lianhe Formation, however, is once again featured by conglomerates, suggesting a probable tectonic event. Therefore, the study region possibly suffered two tectonic events represented by the conglomerates of the Hekou and Lianhe formations in the context of the crustal extension in Southeast China.
基金the National Natural Science Foundation of China (NSFC) (No. 40571169)the NSFC’s Innovation Team Project (No. 40421101), and the NSFC’s Key Program Project (No. 90502008)
文摘The total organic carbon (TOC) content series from the lake sediment of Minqin Basin (100°57′–104°57′E, 37°48′–39°17′N) in northwestern China, which has a 10 000-year-long paleo-climatic proxy record, was used to analyze the Holocene climate changes in the local region. The proxy record was established in the Sanjiaocheng (SJC), Triangle Town in Chinese, Section (103°20′25″E, 39°00′38″N), which is located at the northwestern boundary of the present Asian summer monsoon in China, and is sensitive to global environmental and climate changes. Applying singular spectrum analysis (SSA) to the TOC series, principal climatic oscillations and periodical changes were studied. The results reveal 3 major patterns of climate change regulated by reconstructed components (RCs). The first pattern is natural long-term trend of climatic change in the local area (Minqin Basin), indicating a relatively wetter stage in early Holocene (starting at 9.5 kaBP), and a relatively dryer stage with a strong lake desiccation and a declined vegetation cover in mid-Holocene (during 7–6 kaBP). From 4.0 kaBP to the present, there has been a gradually decreasing trend in the third reconstructed component (RC3) showing that the local climate changed again into a dryer stage. The second pattern shows millennial-centennial scale oscillations containing cycles of 1 600 and 800 years that have been present throughout almost the entire Holocene period of the last 10 000 years. The third pattern is a millennial-centennial scale variation with a relatively smaller amplitude and unclear cycles showing a nonlinear interaction within the earth’s climate systems.
基金supported by National Major Project of China (Grant No. 2011ZX05008-003)National Natural Science Foundation of China (Grant No. 41172096)
文摘The Upper Ordovician Lianglitag Formation carbonate rocks are important oil and gas reservoirs in the Tarim Basin, Northwest China, with obviously distinct reservoir properties among different oilfields. As a case area of the above carbonate reser- voirs correlation, Tahe and Tazhong oilfields are chosen for the study through an integrated analysis of biostratigraphic isoch- ronous framework, cores, thin sections, logs, and strontium isotopes. The research shows that the two areas were respectively attributed to different carbonate platforms during the Lianglitag Formation depositional phase. For the Lianglitag Formation, five fourth-order sequences may be divided in Tazhong, whereas only four fourth-order sequences are preserved in Tahe that correspond to the lower ones observed in Tazhong. The Lianglitag Formation carbonate platform in Tahe was characterized by ramp and/or weak rimmed types, with low depositional rates （37 ktm/a）, higher whole-rock clastic contents, and higher 878r/86Sr isotope ratios of carbonate matrix, showing relatively deep-water environment and evident terrigenous input for car- bonate deposition. However, a strongly rimmed carbonate platform was developed in Tazhong, with high depositional rates of 250 p.m/a and less whole-rock clastic contents, indicating a high-energy depositional environment. Because of the sedimentary environment differences mentioned above, less high-energy facies but relatively intense syndepositional （early diagenetic） sea-water cementation of carbonates were developed in Tahe, and ubiquitous high-energy reef and shoal facies, with a frequent exposure to subaerial, and weak syndepositional sea-water cementation of carbonates in Tazhong. Therefore, fewer primary pores occurred in the Lianglitag Formation carbonate rocks of Tahe, whereas more primary pores were preserved in the same lithostratigraphic unit of the Tazhong （No. 1 fault zone）. Available high-energy reef-shoal facies and early diagenesis, with more primary pores preserved, provided a key material basis for the Lianglitag Formation carbonate reservoirs that largely oc- curred in Tazhong.
