The Chezhen depression,located in the south of Bohai Bay Basin,is an oil-producing basin in China. The third and fourth members of the Shahejie Formation(E(s3) and E(s4)) are the main source rock series in the Chezhen...The Chezhen depression,located in the south of Bohai Bay Basin,is an oil-producing basin in China. The third and fourth members of the Shahejie Formation(E(s3) and E(s4)) are the main source rock series in the Chezhen depression. Widespread overpressures occurred in the E(s3) and E(s4) from the depths of approximately 2 000 to 4 600 m,with the maximum pressure coefficient of 1.98 from drillstem tests(DST). Among the sonic,resistivity and density logs,sonic-log is the only reliable pressure indicator and can be used to predict the pore pressure with Eaton's method. All the overpressured mudstones in the source rock series have higher acoustic traveltimes compared with normally pressured mudstones at a given depth. The overpressured mudstones in the E(s3) and E(s4) units are characterized by a normal geothermal gradient,high average density values up to 2.5 g/cm^3,strong present-day hydrocarbon generation capability,abundant mature organic matter and high contents of residual hydrocarbons estimated by the Rock-Eval S1 values and chloroform-soluble bitumen "A" values. All suggest that the dominant mechanism for overpressure in the mudstones of source rock series in the Chezhen depression is hydrocarbon generation. A comparison between the matrix porosity of the normally pressured sandstones and overpressured sandstones,the quantitative evaluation of porosity loss caused by compaction and the conventional thin section inspection demonstrate that the sandstones in the Chezhen depression were normally compacted. The high contents of hydrocarbons in the overpressured reservoirs prove that the overpressure in the sandstones of the source rock series was caused by pressure transmission from the source rocks.展开更多
The deep buried clastic formation of Paleogene is an important hydrocarbon reservoir in the Chezhen depression.There are two types of diagenetic alteration modes in it.The first mode is weak compaction,strong cementat...The deep buried clastic formation of Paleogene is an important hydrocarbon reservoir in the Chezhen depression.There are two types of diagenetic alteration modes in it.The first mode is weak compaction,strong cementation,fracturing and weak dissolution in the sandstone and conglomerate on the steep slope of the depression.The reservoirs are cemented mainly by carbonate minerals strongly.展开更多
The Chezhen Sag,located in the north-western Jiyang Depression,is one of the most important oil-bearing sags in the Bohai Bay Basin.Due to the low degree of exploration in the sag,paleosalinity and sedimentary environ...The Chezhen Sag,located in the north-western Jiyang Depression,is one of the most important oil-bearing sags in the Bohai Bay Basin.Due to the low degree of exploration in the sag,paleosalinity and sedimentary environment of the sag in the 3rd Member of Paleogene Shahejie Formation(Es3)is not clear.Recovering the paleosalinity and lake level fluctuations is helpful for understanding organic matter rich rocks sedimentation.Therefore,a detailed geochemical,mineralogical and paleontological analysis of the Es3 in the Chezhen Sag was conducted.Index like Sr/Ba ratios,B/Ga ratios,equivalent boron content and methods concluding Adams'formula and Couch's method were adopted to reveal the paleo-salinity and lake level variations.The results indicate that the lower submember(Lower Es3)was deposited in a salt water with high salinity,accompanied by dry climate and transgression event.The middle submember(Middle Es3)and upper submember(Upper Es3)record a freshwater to brackish environment.The paleosalinity and paleoclimate changes are consistent with the global sea level variations.The type and content of sporopollen indicate a dry climate in Lower Es3,which further confirms the reliability of the reconstruction results of paleosalinity.Combined with the paleoclimate and previous marine paleontological evidence,we proposed that the high salinity period is associated with a high lake level and a large-scale transgression event in Lower Es3.According to salinities and corresponding Lake depths,we established a sedimentary environment variation model of the Es3 Member in Chezhen Sag.展开更多
This paper uses pollen climate analysis and coexistence analysis to systematically analyze the climatic evolution of the Shahejie Formation in the Chezhen Depression,Bohai Bay Basin,eastern China and discusses the rel...This paper uses pollen climate analysis and coexistence analysis to systematically analyze the climatic evolution of the Shahejie Formation in the Chezhen Depression,Bohai Bay Basin,eastern China and discusses the relationship between palaeoclimatic evolution and lake level rise.The results show that the sedimentary period of the Shahejie Formation in the Chezhen Depression had an overall temperature change trend from hot to cold and simultaneously experienced a dry and wet balance-wet-dry and wet balance-wet transition process.The climatic parameters of the Shahejie Formation in the Chezhen Depression include a mean annual temperature of 8.1℃-15.1℃,a mean coldest monthly temperature of-0.1℃-2℃,a mean warmest monthly temperature of 18.6℃-28℃,a mean annual precipitation of 389-1164 mm,a wettest monthly precipitation amount of 215-262 mm,and a driest monthly precipitation amount of 8-48 mm.Climate change is believed to affect the rise and fall of lake levels to some extent.The quantitative reconstruction of these climatic parameters allows researchers to more intuitively understand the geological background of the Chezhen Depression and guide the exploration and development of oil and gas resources.展开更多
The accurate determination of geological age is a key to understanding the history and process of paleolake evolution and oil and gas exploration in continental lake basin.However,improving the accuracy of geological ...The accurate determination of geological age is a key to understanding the history and process of paleolake evolution and oil and gas exploration in continental lake basin.However,improving the accuracy of geological age has always been a difficult scientific problem.A 609-m-thick,continuous lacustrine mudstone and sandstone succession in Chezhen Sag(eastern China)provides an ideal middle Eocene sedimentary record for establishing a high-resolution stratigraphic chronology framework.Based on spectrum analysis and sliding window spectrum analysis of the natural gamma(GR)logging data of well Che 271(C271)in Chezhen Sag,the periods of 405 kyr and 40.1 kyr were filtered by a Gaussian bandpass filter,and a“floating”astrochronological time scale(ATS)was established.The total number of 405 kyr eccentricity cycles were 13.6 and 40.1 kyr obliquity cycles were 138 which recorded from the upper member 4(Es4U)to the member 3(Es3)of the Eocene Shahejie Formation,and the depositional duration was 5.53 Myr.Correlation Coefficient(COCO)analysis and evolutionary Correlation Coefficient(eCoCo)analysis found that the optimal sedimentary rate of different strata.Sedimentary noise simulation revealed the history of paleolake water changes in the Middle Eocene in the Chezhen Sag,according to which four sequences are divided.The study shows that the lake level change of Chezhen Sag in the middle Eocene shows prominent 1.2 Myr cycles and an antiphase well-coupled relationship with obliquity modulation.Finally,we propose a model to explain the relationship between the orbital cycle and lake level change in the continental lake basin.When the obliquity of the earth increases,the middle and high latitudes of the earth will be closer to the sun,the direct sunlight will be higher,and the meridional sunshine will increase,thus accelerating the evaporation process of lake basin water.When the seasonal changes are obvious(maximum period of 1.2 Myr ultra-long obliquity),this effect is more significant.The relative lake level change based on the restoration of high-precision ATS has significant scientific and economic value for understanding the vertical evolution of continental stratigraphic sequences and the formation and distribution of oil and gas resources.展开更多
基金sponsored by the China National Science and Technology Major Project (No. 2016ZX05006003-001)the Programme of Introducing Talents of Discipline to Universities (No. B14031)+1 种基金the National Natural Science Foundation of China (Nos. 41572114, 41302110)The SINOPEC Shengli Oilfield is thanked for providing background geological data and support
文摘The Chezhen depression,located in the south of Bohai Bay Basin,is an oil-producing basin in China. The third and fourth members of the Shahejie Formation(E(s3) and E(s4)) are the main source rock series in the Chezhen depression. Widespread overpressures occurred in the E(s3) and E(s4) from the depths of approximately 2 000 to 4 600 m,with the maximum pressure coefficient of 1.98 from drillstem tests(DST). Among the sonic,resistivity and density logs,sonic-log is the only reliable pressure indicator and can be used to predict the pore pressure with Eaton's method. All the overpressured mudstones in the source rock series have higher acoustic traveltimes compared with normally pressured mudstones at a given depth. The overpressured mudstones in the E(s3) and E(s4) units are characterized by a normal geothermal gradient,high average density values up to 2.5 g/cm^3,strong present-day hydrocarbon generation capability,abundant mature organic matter and high contents of residual hydrocarbons estimated by the Rock-Eval S1 values and chloroform-soluble bitumen "A" values. All suggest that the dominant mechanism for overpressure in the mudstones of source rock series in the Chezhen depression is hydrocarbon generation. A comparison between the matrix porosity of the normally pressured sandstones and overpressured sandstones,the quantitative evaluation of porosity loss caused by compaction and the conventional thin section inspection demonstrate that the sandstones in the Chezhen depression were normally compacted. The high contents of hydrocarbons in the overpressured reservoirs prove that the overpressure in the sandstones of the source rock series was caused by pressure transmission from the source rocks.
文摘The deep buried clastic formation of Paleogene is an important hydrocarbon reservoir in the Chezhen depression.There are two types of diagenetic alteration modes in it.The first mode is weak compaction,strong cementation,fracturing and weak dissolution in the sandstone and conglomerate on the steep slope of the depression.The reservoirs are cemented mainly by carbonate minerals strongly.
基金supported by the Sinopec Shengli Oilfield Cooperation Project named“Reunderstanding the sedimentary system of the third to the fourth member of the Shahejie Formation in the Chezhen Depression and the distribution of hidden traps”and China Postdoctoral Science Foundation(No.2021M700537).
文摘The Chezhen Sag,located in the north-western Jiyang Depression,is one of the most important oil-bearing sags in the Bohai Bay Basin.Due to the low degree of exploration in the sag,paleosalinity and sedimentary environment of the sag in the 3rd Member of Paleogene Shahejie Formation(Es3)is not clear.Recovering the paleosalinity and lake level fluctuations is helpful for understanding organic matter rich rocks sedimentation.Therefore,a detailed geochemical,mineralogical and paleontological analysis of the Es3 in the Chezhen Sag was conducted.Index like Sr/Ba ratios,B/Ga ratios,equivalent boron content and methods concluding Adams'formula and Couch's method were adopted to reveal the paleo-salinity and lake level variations.The results indicate that the lower submember(Lower Es3)was deposited in a salt water with high salinity,accompanied by dry climate and transgression event.The middle submember(Middle Es3)and upper submember(Upper Es3)record a freshwater to brackish environment.The paleosalinity and paleoclimate changes are consistent with the global sea level variations.The type and content of sporopollen indicate a dry climate in Lower Es3,which further confirms the reliability of the reconstruction results of paleosalinity.Combined with the paleoclimate and previous marine paleontological evidence,we proposed that the high salinity period is associated with a high lake level and a large-scale transgression event in Lower Es3.According to salinities and corresponding Lake depths,we established a sedimentary environment variation model of the Es3 Member in Chezhen Sag.
基金This research was supported by the Shengli Oilfield,Sinopec,and the project name is“Reunderstanding the sedimentary system of the third to the fourth member of the Shahejie Formation in the Chezhen Depression and the distribution of hidden traps”.
文摘This paper uses pollen climate analysis and coexistence analysis to systematically analyze the climatic evolution of the Shahejie Formation in the Chezhen Depression,Bohai Bay Basin,eastern China and discusses the relationship between palaeoclimatic evolution and lake level rise.The results show that the sedimentary period of the Shahejie Formation in the Chezhen Depression had an overall temperature change trend from hot to cold and simultaneously experienced a dry and wet balance-wet-dry and wet balance-wet transition process.The climatic parameters of the Shahejie Formation in the Chezhen Depression include a mean annual temperature of 8.1℃-15.1℃,a mean coldest monthly temperature of-0.1℃-2℃,a mean warmest monthly temperature of 18.6℃-28℃,a mean annual precipitation of 389-1164 mm,a wettest monthly precipitation amount of 215-262 mm,and a driest monthly precipitation amount of 8-48 mm.Climate change is believed to affect the rise and fall of lake levels to some extent.The quantitative reconstruction of these climatic parameters allows researchers to more intuitively understand the geological background of the Chezhen Depression and guide the exploration and development of oil and gas resources.
文摘The accurate determination of geological age is a key to understanding the history and process of paleolake evolution and oil and gas exploration in continental lake basin.However,improving the accuracy of geological age has always been a difficult scientific problem.A 609-m-thick,continuous lacustrine mudstone and sandstone succession in Chezhen Sag(eastern China)provides an ideal middle Eocene sedimentary record for establishing a high-resolution stratigraphic chronology framework.Based on spectrum analysis and sliding window spectrum analysis of the natural gamma(GR)logging data of well Che 271(C271)in Chezhen Sag,the periods of 405 kyr and 40.1 kyr were filtered by a Gaussian bandpass filter,and a“floating”astrochronological time scale(ATS)was established.The total number of 405 kyr eccentricity cycles were 13.6 and 40.1 kyr obliquity cycles were 138 which recorded from the upper member 4(Es4U)to the member 3(Es3)of the Eocene Shahejie Formation,and the depositional duration was 5.53 Myr.Correlation Coefficient(COCO)analysis and evolutionary Correlation Coefficient(eCoCo)analysis found that the optimal sedimentary rate of different strata.Sedimentary noise simulation revealed the history of paleolake water changes in the Middle Eocene in the Chezhen Sag,according to which four sequences are divided.The study shows that the lake level change of Chezhen Sag in the middle Eocene shows prominent 1.2 Myr cycles and an antiphase well-coupled relationship with obliquity modulation.Finally,we propose a model to explain the relationship between the orbital cycle and lake level change in the continental lake basin.When the obliquity of the earth increases,the middle and high latitudes of the earth will be closer to the sun,the direct sunlight will be higher,and the meridional sunshine will increase,thus accelerating the evaporation process of lake basin water.When the seasonal changes are obvious(maximum period of 1.2 Myr ultra-long obliquity),this effect is more significant.The relative lake level change based on the restoration of high-precision ATS has significant scientific and economic value for understanding the vertical evolution of continental stratigraphic sequences and the formation and distribution of oil and gas resources.
