There are three abnormally high porosity zones developed in buried Paleogene nearshore subaqueous fan and sublacustrine fan clastic＇reservoirs at 2,800-3,200 m, 3,250-3,700 m and 3,900- 4,400 m, respectively, within ...There are three abnormally high porosity zones developed in buried Paleogene nearshore subaqueous fan and sublacustrine fan clastic＇reservoirs at 2,800-3,200 m, 3,250-3,700 m and 3,900- 4,400 m, respectively, within the Shengtuo area of the Dongying Sag. Here the porosity of reservoirs buried deeper than 4,000 m can still be greater than 20%. Investigation of these three abnormally high porosity （AHP） zones in the 3rd to 4th member of the Paleogene Shahejie Formation in the Shengtuo area was carried out with utilization of core observation, thin section identification, SEM observation, image analysis, core physical property testing and other technical methods. The results show that, the AHP zones in 2,800-3,200 m and 3,250-3,700 m are visible pores primary AHP zones dominated by significant primary intergranular pores （more than 50% of the total porosity）, while secondary pores and micropores in authigenic clays may develop in some reservoirs. AHP reservoirs in the AHP zone of 3,900-4,400 m are dominated by micropores in matrix, visible pores are mainly grain dissolution pores but with low absolute content （〈 1%）, so this zone belongs to the micropores primary AHP zone. The genesis of the three AHP zones was studied to distinguish between porosity enhancement and porosity preservation. Our research shows that, in deeply buried clastic reservoirs in the Shengtuo area, mineral dissolution occurred in a relatively closed diagenetic system with high temperature and high salinity. Reservoir rocks underwent extensive feldspar dissolution, while detrital carbonate grains and carbonate cements show no evidence of extensive dissolution. Although significant feldspar dissolution pores developed, feldspar dissolution enhanced porosity only a little due to the precipitation of almost isovolumetric dissolution products in the nearby primary intergranular pores in forms of authigenic clays and quartz cements. Net enhanced porosity originating from feldspar dissolution is generally less than 0.25%. Thus, the sub展开更多
Recent exploration results indicate that a significant exploration potential remains in the Dongying Depression of the Bohai Bay Basin and the undiscovered oil and gas are largely reservoired in subtle traps including...Recent exploration results indicate that a significant exploration potential remains in the Dongying Depression of the Bohai Bay Basin and the undiscovered oil and gas are largely reservoired in subtle traps including turbidite litholigcal traps of the Sha-3 Member. In order to effectively guide the exploration program targeting turbidites, this study will focus on the depositional models of the Sha-3 Member turbidites and oil/gas accumulation characteristics in these turbidites. Two corresponding relationships were found. One is that the East African Rift Valley provides a modern analog for the depositional systems in the Dongying Depression. The other is that the depositional models of line-sourced slope aprons, single point-source submarine fan and multiple source ramp turbidite, established for deep-sea turbidites, can be applied to interpret the depositional features of the turbidite fans of three different origins: slope turbidite aprons, lake floor turbidite fans and delta-fed turbidite fans in the Sha-3 Member. Updip sealing integrity is the key factor determining whether oil/gas accumulates or not in the slope aprons and lake floor fans. The factors controlling oil/gas migration and accumulation in the delta-fed turbidite fans are not very clear. Multiple factors rather than a single factor probably played significant roles in these processes.展开更多
Gypsum-salt rocks and coccolith calcareous shale are widely deposited in the lower part of the Paleogene Shahejie Formation in the Dongying Sag, Sbandong Province. The gypsum-salt rock is believed to be formed during ...Gypsum-salt rocks and coccolith calcareous shale are widely deposited in the lower part of the Paleogene Shahejie Formation in the Dongying Sag, Sbandong Province. The gypsum-salt rock is believed to be formed during the earlier deposition in salt lake, while the overlying coccolith shale in saline lake with relatively low salinity. By comparing the lake environment and la- custrine microbial communities between ancient and recent lakes, cyanobacteria are regarded as the main representative of productivity during the formation of gypsum-salt strata series, with the annual productivity of 1500-2000 gC m-2 yr1. Based on the research of ultramicrofossils in the calcareous shale, coccolith is considered as the main contributor to the productivity during the formation of calcareous shale. On the basis of statistic data of sedimentary rates, shale laminations, and coccolith fossils in each lamination, the quantitative value of productivity is calculated, with the annual productivity of 2250 3810 gC m 2 yr-1 （averagely 3120 gC m-2 yr-1）. Statistic data of large amount of pyrite framboids indicate that the lower water col- umn was persistently in sulfidic or anoxic conditions during the deposition of gypsum-salt strata series, but it changed to be dysoxic when the coccolith calcareous shale was deposited. Both of these water conditions are favorable for the preservation of organic matter. It is estimated that the organic carbon burial efficiency of the Lower Paleogene salt lakes and saline lakes of Dongying Depression is about 10%-15%, which is calculated and analyzed using the multi-parameter geobiological model.展开更多
This paper was conducted on the shale reservoir in the Dongying depression in the Shahejie Formation of Paleogene. Based on detailed core description, rock thin sections, argon ion polishing, scanning electron microsc...This paper was conducted on the shale reservoir in the Dongying depression in the Shahejie Formation of Paleogene. Based on detailed core description, rock thin sections, argon ion polishing, scanning electron microscopy（SEM） analysis, CT scanning and carbon-oxygen isotopic test, the formation mechanism of the inter-laminar fractures（or seams） and their development conditions were discussed by comprehensive analysis of the diagenetic evolution features and the reservoir space evolution characteristics. The results show that the laminated composite pattern in Dongying depression was dominated by vertical distribution of laminated calcite and clay minerals. Contrasted to the traditional understanding, development degree of inter-laminar fractures was much lower. Pure fluid between layers cannot exist without framework minerals, and the pre-existing well connected pore or horizontal overpressure micro seam was favorable paths of fluid migration. From the points of inter-laminar fractures origin mechanism and its evolution, the so called seams, were much more complex than traditional understanding that hydrocarbon generation raised the pore pressure and led to the parallel microfractures. But the inter-laminar fractures had little relationship with that whether the lamination was developed or bedding boundary was clear or not. In fact, the shale reservoir inter-laminar fractures were not rigorous fracture. They were controlled by pre-existing inter-granular pore（or seam） or dissolved pore, which distributed along carbonate laminae boundary and were connected by later super pressure, dissolution and the seepage force. And the development conditions were burial depth（bigger than 3 000 m） and the Ro value（〉0.6%）. Discussion on its origin and evolution has important petroleum geological significance on optimizing reservoir segment and favorable target areas selection.展开更多
The relationships between permeability and dynamics in hydrocarbon accumulation determine oil- bearing potential （the potential oil charge） of low perme- ability reservoirs. The evolution of porosity and permeabilit...The relationships between permeability and dynamics in hydrocarbon accumulation determine oil- bearing potential （the potential oil charge） of low perme- ability reservoirs. The evolution of porosity and permeability of low permeability turbidite reservoirs of the middle part of the third member of the Shahejie Formation in the Dongying Sag has been investigated by detailed core descriptions, thin section analyses, fluid inclusion analyses, carbon and oxygen isotope analyses, mercury injection, porosity and permeability testing, and basin modeling. The cutoff values for the permeability of the reservoirs in the accumulation period were calculated after detailing the accumulation dynamics and reservoir pore structures, then the distribution pattern of the oil-bearing potential of reservoirs controlled by the matching relationship between dynamics and permeability during the accumulation period were summarized. On the basis of the observed diagenetic features and with regard to the paragenetic sequences, the reservoirs can be subdivided into four types of diagenetic facies. The reservoirs experienced two periods of hydro- carbon accumulation. In the early accumulation period, the reservoirs except for diagenetic facies A had middle to high permeability ranging from 10 × 10-3 gm2 to 4207 × 10-3 lain2. In the later accumulation period, the reservoirs except for diagenetic facies C had low permeability ranging from 0.015 × 10-3 gm2 to 62× 10-3 -3m2. In the early accumulation period, the fluid pressure increased by the hydrocarbon generation was 1.4-11.3 MPa with an average value of 5.1 MPa, and a surplus pressure of 1.8-12.6 MPa with an average value of 6.3 MPa. In the later accumulation period, the fluid pressure increased by the hydrocarbon generation process was 0.7-12.7 MPa with an average value of 5.36 MPa and a surplus pressure of 1.3-16.2 MPa with an average value of 6.5 MPa. Even though different types of reservoirs exist, all can form hydrocarbon accumulations in the early accumulation per- iod. Such 展开更多
Diagenetic traps in conglomerate in nearshore subaqueous fans in the steep slope zones of rift basins have been important exploration targets for subtle reservoirs in eastern China. However, the mechanism of how those...Diagenetic traps in conglomerate in nearshore subaqueous fans in the steep slope zones of rift basins have been important exploration targets for subtle reservoirs in eastern China. However, the mechanism of how those traps were formed is not clear, which inhibits further exploration for this type of reservoir. In order to solve the problem, we take as an example nearshore subaqueous fans in the upper part of the fourth member of the Shahejie Formation （Es4s） on the north slope of the Minfeng Subsag in the Dongying Sag. Combining different research methods, such as core observation, thin section examination, scanning electron microscope （SEM） observation, fluid-inclusion analysis, carbon and oxygen isotope analysis of carbonate cements, and analysis of core properties, we studied the genetic mechanisms of diagenetic traps on the basis of diagenetic environment evolution and diagenetic evolution sequence in different sub/micro-facies. Conglomerate in Es4s in the north Minfeng Subsag experienced several periods of transition between alkaline and acidic environments as ＂alkaline-acidic-alkaline-acidic-weak alkaline＂. As a result, dissolution and cementation are also very complex, and the sequence is ＂early pyrite cementation / siderite cementation / gypsum cementation / calcite and dolomite cementation- feldspar dissolution / quartz overgrowth quartz dissolution / ferroan calcite cementation / ankerite cementation / lime-mud matrix recrystallization / feldspar overgrowth carbonate dissolution / feldspar dissolution / quartz overgrowth / pyrite cementation＂. The difference in sedimentary characteristics between different sub/micro-facies of nearshore subaqueous fans controls diagenetic characteristics. Inner fan conglomerates mainly experienced compaction and lime-mud matrix recrystallization, with weak dissolution, which led to a reduction in the porosity and permeability crucial to reservoir formation. Lime-mud matrix recrystallization results in a rapid decrease in porosity and permeability in inne展开更多
基金financially supported by the National Natural Science Foundation of China (No. U1262203, No. 41102058)a National Science and Technology Special Grant (No. 2011ZX05006-003)Foundation for the Author of National Excellent Doctoral Dissertation of China
文摘There are three abnormally high porosity zones developed in buried Paleogene nearshore subaqueous fan and sublacustrine fan clastic＇reservoirs at 2,800-3,200 m, 3,250-3,700 m and 3,900- 4,400 m, respectively, within the Shengtuo area of the Dongying Sag. Here the porosity of reservoirs buried deeper than 4,000 m can still be greater than 20%. Investigation of these three abnormally high porosity （AHP） zones in the 3rd to 4th member of the Paleogene Shahejie Formation in the Shengtuo area was carried out with utilization of core observation, thin section identification, SEM observation, image analysis, core physical property testing and other technical methods. The results show that, the AHP zones in 2,800-3,200 m and 3,250-3,700 m are visible pores primary AHP zones dominated by significant primary intergranular pores （more than 50% of the total porosity）, while secondary pores and micropores in authigenic clays may develop in some reservoirs. AHP reservoirs in the AHP zone of 3,900-4,400 m are dominated by micropores in matrix, visible pores are mainly grain dissolution pores but with low absolute content （〈 1%）, so this zone belongs to the micropores primary AHP zone. The genesis of the three AHP zones was studied to distinguish between porosity enhancement and porosity preservation. Our research shows that, in deeply buried clastic reservoirs in the Shengtuo area, mineral dissolution occurred in a relatively closed diagenetic system with high temperature and high salinity. Reservoir rocks underwent extensive feldspar dissolution, while detrital carbonate grains and carbonate cements show no evidence of extensive dissolution. Although significant feldspar dissolution pores developed, feldspar dissolution enhanced porosity only a little due to the precipitation of almost isovolumetric dissolution products in the nearby primary intergranular pores in forms of authigenic clays and quartz cements. Net enhanced porosity originating from feldspar dissolution is generally less than 0.25%. Thus, the sub
文摘Recent exploration results indicate that a significant exploration potential remains in the Dongying Depression of the Bohai Bay Basin and the undiscovered oil and gas are largely reservoired in subtle traps including turbidite litholigcal traps of the Sha-3 Member. In order to effectively guide the exploration program targeting turbidites, this study will focus on the depositional models of the Sha-3 Member turbidites and oil/gas accumulation characteristics in these turbidites. Two corresponding relationships were found. One is that the East African Rift Valley provides a modern analog for the depositional systems in the Dongying Depression. The other is that the depositional models of line-sourced slope aprons, single point-source submarine fan and multiple source ramp turbidite, established for deep-sea turbidites, can be applied to interpret the depositional features of the turbidite fans of three different origins: slope turbidite aprons, lake floor turbidite fans and delta-fed turbidite fans in the Sha-3 Member. Updip sealing integrity is the key factor determining whether oil/gas accumulates or not in the slope aprons and lake floor fans. The factors controlling oil/gas migration and accumulation in the delta-fed turbidite fans are not very clear. Multiple factors rather than a single factor probably played significant roles in these processes.
基金supported by National Science and Technology Major Project (Grant No. 2009ZX05009)National Basic Research Program of China (Grant No. 2011CB808800)+1 种基金National Natural Science Foundation of China (Grant Nos. 41172036, 40730209)the "111" Project (Grant No. B08030)
文摘Gypsum-salt rocks and coccolith calcareous shale are widely deposited in the lower part of the Paleogene Shahejie Formation in the Dongying Sag, Sbandong Province. The gypsum-salt rock is believed to be formed during the earlier deposition in salt lake, while the overlying coccolith shale in saline lake with relatively low salinity. By comparing the lake environment and la- custrine microbial communities between ancient and recent lakes, cyanobacteria are regarded as the main representative of productivity during the formation of gypsum-salt strata series, with the annual productivity of 1500-2000 gC m-2 yr1. Based on the research of ultramicrofossils in the calcareous shale, coccolith is considered as the main contributor to the productivity during the formation of calcareous shale. On the basis of statistic data of sedimentary rates, shale laminations, and coccolith fossils in each lamination, the quantitative value of productivity is calculated, with the annual productivity of 2250 3810 gC m 2 yr-1 （averagely 3120 gC m-2 yr-1）. Statistic data of large amount of pyrite framboids indicate that the lower water col- umn was persistently in sulfidic or anoxic conditions during the deposition of gypsum-salt strata series, but it changed to be dysoxic when the coccolith calcareous shale was deposited. Both of these water conditions are favorable for the preservation of organic matter. It is estimated that the organic carbon burial efficiency of the Lower Paleogene salt lakes and saline lakes of Dongying Depression is about 10%-15%, which is calculated and analyzed using the multi-parameter geobiological model.
基金supported by the National Basic Research Program of China (No. 2014CB239102)the National Science and Technology Major Project (No. 2016ZX05049-4)the National Natural Science Fundation of China (Nos. 41372107, 41572087)
文摘This paper was conducted on the shale reservoir in the Dongying depression in the Shahejie Formation of Paleogene. Based on detailed core description, rock thin sections, argon ion polishing, scanning electron microscopy（SEM） analysis, CT scanning and carbon-oxygen isotopic test, the formation mechanism of the inter-laminar fractures（or seams） and their development conditions were discussed by comprehensive analysis of the diagenetic evolution features and the reservoir space evolution characteristics. The results show that the laminated composite pattern in Dongying depression was dominated by vertical distribution of laminated calcite and clay minerals. Contrasted to the traditional understanding, development degree of inter-laminar fractures was much lower. Pure fluid between layers cannot exist without framework minerals, and the pre-existing well connected pore or horizontal overpressure micro seam was favorable paths of fluid migration. From the points of inter-laminar fractures origin mechanism and its evolution, the so called seams, were much more complex than traditional understanding that hydrocarbon generation raised the pore pressure and led to the parallel microfractures. But the inter-laminar fractures had little relationship with that whether the lamination was developed or bedding boundary was clear or not. In fact, the shale reservoir inter-laminar fractures were not rigorous fracture. They were controlled by pre-existing inter-granular pore（or seam） or dissolved pore, which distributed along carbonate laminae boundary and were connected by later super pressure, dissolution and the seepage force. And the development conditions were burial depth（bigger than 3 000 m） and the Ro value（〉0.6%）. Discussion on its origin and evolution has important petroleum geological significance on optimizing reservoir segment and favorable target areas selection.
基金supported by the National Natural Science Foundation of China(Grant No.U1262203)the National Science and Technology Special Grant(No.2011ZX05006-003)+1 种基金the Fundamental Research Funds for the Central Universities(Grant No.14CX06070A)the Chinese Scholarship Council(No.201506450029)
文摘The relationships between permeability and dynamics in hydrocarbon accumulation determine oil- bearing potential （the potential oil charge） of low perme- ability reservoirs. The evolution of porosity and permeability of low permeability turbidite reservoirs of the middle part of the third member of the Shahejie Formation in the Dongying Sag has been investigated by detailed core descriptions, thin section analyses, fluid inclusion analyses, carbon and oxygen isotope analyses, mercury injection, porosity and permeability testing, and basin modeling. The cutoff values for the permeability of the reservoirs in the accumulation period were calculated after detailing the accumulation dynamics and reservoir pore structures, then the distribution pattern of the oil-bearing potential of reservoirs controlled by the matching relationship between dynamics and permeability during the accumulation period were summarized. On the basis of the observed diagenetic features and with regard to the paragenetic sequences, the reservoirs can be subdivided into four types of diagenetic facies. The reservoirs experienced two periods of hydro- carbon accumulation. In the early accumulation period, the reservoirs except for diagenetic facies A had middle to high permeability ranging from 10 × 10-3 gm2 to 4207 × 10-3 lain2. In the later accumulation period, the reservoirs except for diagenetic facies C had low permeability ranging from 0.015 × 10-3 gm2 to 62× 10-3 -3m2. In the early accumulation period, the fluid pressure increased by the hydrocarbon generation was 1.4-11.3 MPa with an average value of 5.1 MPa, and a surplus pressure of 1.8-12.6 MPa with an average value of 6.3 MPa. In the later accumulation period, the fluid pressure increased by the hydrocarbon generation process was 0.7-12.7 MPa with an average value of 5.36 MPa and a surplus pressure of 1.3-16.2 MPa with an average value of 6.5 MPa. Even though different types of reservoirs exist, all can form hydrocarbon accumulations in the early accumulation per- iod. Such
基金co-funded by the National Natural Science Foundation of China (41102058)the National Science and Technology Special Grant (2011ZX05006-003)the Fundamental Research Funds for the Central Universities (12CX04001A)
文摘Diagenetic traps in conglomerate in nearshore subaqueous fans in the steep slope zones of rift basins have been important exploration targets for subtle reservoirs in eastern China. However, the mechanism of how those traps were formed is not clear, which inhibits further exploration for this type of reservoir. In order to solve the problem, we take as an example nearshore subaqueous fans in the upper part of the fourth member of the Shahejie Formation （Es4s） on the north slope of the Minfeng Subsag in the Dongying Sag. Combining different research methods, such as core observation, thin section examination, scanning electron microscope （SEM） observation, fluid-inclusion analysis, carbon and oxygen isotope analysis of carbonate cements, and analysis of core properties, we studied the genetic mechanisms of diagenetic traps on the basis of diagenetic environment evolution and diagenetic evolution sequence in different sub/micro-facies. Conglomerate in Es4s in the north Minfeng Subsag experienced several periods of transition between alkaline and acidic environments as ＂alkaline-acidic-alkaline-acidic-weak alkaline＂. As a result, dissolution and cementation are also very complex, and the sequence is ＂early pyrite cementation / siderite cementation / gypsum cementation / calcite and dolomite cementation- feldspar dissolution / quartz overgrowth quartz dissolution / ferroan calcite cementation / ankerite cementation / lime-mud matrix recrystallization / feldspar overgrowth carbonate dissolution / feldspar dissolution / quartz overgrowth / pyrite cementation＂. The difference in sedimentary characteristics between different sub/micro-facies of nearshore subaqueous fans controls diagenetic characteristics. Inner fan conglomerates mainly experienced compaction and lime-mud matrix recrystallization, with weak dissolution, which led to a reduction in the porosity and permeability crucial to reservoir formation. Lime-mud matrix recrystallization results in a rapid decrease in porosity and permeability in inne
