Tight sandstone reservoirs represent a pivotal unconventional oil and gas production target.The upper section of the deeply buried Huagang Formation in the Xihu Depression is abundant in hydrocarbons and forms a tight...Tight sandstone reservoirs represent a pivotal unconventional oil and gas production target.The upper section of the deeply buried Huagang Formation in the Xihu Depression is abundant in hydrocarbons and forms a tight reservoir.It exhibits substantial diagenetic variability and strong heterogeneity in sand bodies,which is reflected in variations in physical properties and grain size.Through integrated geological analysis,including rock thin sections,scanning electron microscopy,X-ray diffraction,well logging and production test data,we investigated the diagenesis,reservoir formation mechanisms,and controlling factors of high-quality reservoirs within the superposed sandstone bodies exceeding 100 m thick in the deeper Huagang Formation.We also studied the formation characteristics of these ultrathick sandstones,clarifying that diagenesis and post-depositional modification are crucial for developing high-quality reservoirs in this formation.Our findings indicate that the sandstone underwent compaction,cementation(by chlorite,calcite and quartz),dissolution(of K-feldspar and carbonate cement),and authigenic clay mineral cementation(such as illite,chlorite,kaolinite).Multiple dissolution zones are present within the thick sandstone units.The distribution of these dissolution zones is mainly controlled by temperature and sandstone composition.With increasing temperature,acidic fluids derived from coal-bearing strata and early hydrocarbon source rocks promoted feldspar dissolution.The thick sandstone units in different intervals of varying depths are at various diagenetic stages.The petrophysical zoning of the reservoir is collectively controlled by diagenetic facies dominated by sedimentation,compaction,and dissolution processes.These findings provide valuable guidance and reference for oil and gas exploration and development in this area,particularly within the ultra-thick sandstone layers.展开更多
By using thin section identification, cathodoluminescence, major and trace elements and fluid inclusion tests and authigenic illite dating, based on observation of core cracks, combined with the microscopic characteri...By using thin section identification, cathodoluminescence, major and trace elements and fluid inclusion tests and authigenic illite dating, based on observation of core cracks, combined with the microscopic characteristics and imaging logging characteristics of fractures, the stages of the fractures in the Huagang Formation of the central reversal tectonic belt of the Xihu Sag in the East China Sea, and the matching relationship between the fracture development stages and the oil and gas charging stages are clarified. There are diagenetic fractures and tectonic fractures in the reservoirs of the Huagang Formation in the study area. The diagenetic fractures developed during the diagenetic stage of the reservoirs and have less effect on oil and gas migration and transport. The tectonic fractures are divided into three stages based on tectonic movements controlling the fractures and their relationships with hydrocarbon charging: The first stage of fractures was generated in the early stage of the Himalayan Movement–Longjing Movement(12–13 Ma ago), when the tectonic stress caused the sutures and shale strips to twist, deform, and break. Tectonic microfractures generated in this period had short extension, narrow width, and poor effectiveness, and had little effect on oil and gas migration and transport. The second stage of fractures came up during the middle-late period of Himalayan Movement–Longjing Movement(9–12 Ma ago), when tectonic movements caused the development of tectonic fractures in the central reversal tectonic belt, these fractures are of large scale, long extension, and good effectiveness, and matched with the first stage of large scale oil and gas charging(9–12 Ma ago), so they play an important role in oil and gas migration, transportation, and accumulation. The third stage of fractures were created from Himalayan Movement–Okinawa Trough movement to the present day(0–3 Ma ago), the fractures are tectonic ones developing successively;matching with the second stage(0–3 Ma ago) of large-scale oil and gas charging, they created conditions for continuous natural gas migration and transportation. All these prove that the development of reservoir fractures in the Huagang Formation of Xihu Sag can provide seepage space and continuous and effective channels for efficient migration and accumulation of oil and gas.展开更多
Both Pinghu and Huagang formations are important hydrocarbon reservoirs of the Xihu Depression in the East China Sea Shelf Basin.Clarifying the source suppliers and restoring source-to-sink transport routes are of gre...Both Pinghu and Huagang formations are important hydrocarbon reservoirs of the Xihu Depression in the East China Sea Shelf Basin.Clarifying the source suppliers and restoring source-to-sink transport routes are of great significance to the future petroleum and gas undertakings.Previous researchers were largely confined by either limitation of geological records,highly dependence on a singular method or low-precision dating techniques.Our study integrated heavy mineral assemblages,geochemical analyses and detrital zircon U-Pb dating to reconstruct multiple source-to-sink pathways,and to provide a better understanding on the provenance evolution for the upper Pinghu–lower Huagang depositions of the Xihu Depression.At least three major provenances have been confirmed and systematically investigated for their separate compositional features.The Hupijiao Uplift(or even farther northern area)was dominated by a major Paleoproterozoic population peaked at ca.1830 Ma along with minor Mesozoic clusters.The Haijiao Uplift to the west and the Yushan Low Uplift to the southwest,on the other hand,generate opposite U-Pb age spectra with apparently larger peaks of Indosinian and Yanshanian-aged zircons.To be noted,both Indosinian and Paleoproterozoic peaks are almost identical in proportion for the Haijiao Uplift.The overall sedimentary pattern of late Eocene-early Oligocene was featured by both spatial and temporal distinction.The Hupijiao Uplift was likely to cast limited impact during the late Eocene,whereas the broad southern Xihu Depression was transported by a large abundance of materials from the nearby Haijiao and Yushan Low Uplifts.The northern source substantially extended its influence to the farther south during the early Oligocene by delivering plentiful sediments of higher-degree metamorphic parent rocks.Combined with the proximal western and southwestern suppliers,the overall Xihu Depression was under control from both distant and local provenances.展开更多
The Oligocene Huagang Formation is the main sandstone reservoir in the Xihu Sag, situated in the east of the East China Sea Shelf Basin. With an integrated approach of thin-section petrography, ultra-violet fluorescen...The Oligocene Huagang Formation is the main sandstone reservoir in the Xihu Sag, situated in the east of the East China Sea Shelf Basin. With an integrated approach of thin-section petrography, ultra-violet fluorescence microscopy, scanning electron microscopy, and isotope geochemistry, the different diagenetic features were identified, the typical diagenetic parasequences were established, and the diagenetic fluids evolution history were reconstructed for the Oligocene Huagang Formation sandstone reservoir in the south of Xihu Sag. The Huagang Formation sandstone reservoir is now in Period B of the mesodiagenesis, which has undergone significant diagenetic alterations such as mechanical compaction, Pore-lining chlorite cement, feldspar dissolution, quartz cementation and dissolution, and carbonate cementation. Three types of carbonate cements（early siderite,medium ferrocalcite and late ankerite） were identified in the Huagang Formation sandstone reservoir. The carbon and oxygen isotopic compositions of carbonate cements show that the early calcite precipitate from alkaline lacustrine environment whereas the late carbonate cements were closely related to the organic acids. To the Huagang Formation sandstone reservoir, it has experienced two main episodes of dissolution during diagenesis.The early dissolution is that unstable components such as feldspar, lithic fragments, and carbonate cement were dissolved by acidic water. The second dissolution is that quartz and other silicate minerals were dissolved under the alkaline condition. Two main phases of hydrocarbon charging occurred in this study area. The first hydrocarbon emplacement was prior to the medium carbonate cementation but posterior to feldspar dissolution and the onset of quartz cementation at the end of the Miocene. The second hydrocarbon charging occurred in the Quaternary period after the late carbonate precipitation.展开更多
The Xihu Depression is the largest hydrocarbon-bearing depression of the East China Sea Shelf Basin(also referred to as the ECSSB).However,the depositional systems and reservoir distribution of the Oligocene Huagang F...The Xihu Depression is the largest hydrocarbon-bearing depression of the East China Sea Shelf Basin(also referred to as the ECSSB).However,the depositional systems and reservoir distribution of the Oligocene Huagang Formation in the Xihu Depression are still controversial.Under the guidance of sedimentology and stratigraphy,this study documented a marine-terrestrial transitional environment in the restricted bay setting of the Oligocene Huagang Formation through core description,well logging,and seismic data analysis.This study also revealed that the Oligocene Huagang Formation is dominated by tidal delta,estuary,and gravity flow deposits in the central anticline zone of the Xihu Depression.The new understanding of the sedimentary systems and the discovery of the transgressive gap in the eastern Diaoyu Islands uplift explain the origin of fine-grained sediments and the EW-trending sand bodies in the central depression and the sand bodies parallel to shoreline in the west slope belt,which cannot be explained by previous study results,such as southern transgression or fluvial deltas and even lacustrine deposition.Moreover,the tidal channels,tidal sand flats,and gravity flow sand bodies formed by the transgressive tides are high-quality reservoirs.The study will provide a basis for well placement and serve as guidance for the selection of favorable hydrocarbon exploration areas in the Xihu Depression.展开更多
The fluvial-deltaic reservoirs of the Oligocene Huagang Formation in the Xihu sag of the East China Sea shelf basin reflect rapid lateral change in sedimentary facies and poor morphology of conventional slice attribut...The fluvial-deltaic reservoirs of the Oligocene Huagang Formation in the Xihu sag of the East China Sea shelf basin reflect rapid lateral change in sedimentary facies and poor morphology of conventional slice attributes,which bring difficulties to the reservoir prediction for subsequent exploration and development of lithologic reservoirs.The traditional seismic sedimentology technology is optimized by applying the characteristic technologies such as frequency-boosting interpretation,inversion-conventional–90°phase shift joint construction of seismic lithologic bodies,nonlinear slices,paleogeomorphology restoration,and multi-attribute fusion,to obtain typical slice attributes,which are conducive to geological form description and sedimentary interpretation.The Huagang Formation developed three types of sedimentary bodies:braided river,meandering river and shallow water delta,and the vertical sedimentary evolution was controlled by the mid-term base-level cycle and paleogeomorphology.In the early–middle stage of the mid-term base-level ascending cycle,braided channel deposits were dominant,and vertical superimposed sand bodies were developed.In the late stage of the ascending half-cycle and the early stage of the descending half-cycle,meandering river deposits were dominant,and isolated sand bodies were developed.In the middle–late stage of the descending half-cycle,shallow-water delta deposits were dominant,and migratory medium–thick sand bodies were developed.Restricted paleogeomorphology controlled the sand body distribution,while non-restricted paleogeomorphology had little effect on the sand body distribution.Based on reservoir characterization,the fault sealing type and reservoir updip pinch-out type structural lithological traps are proposed as the main directions for future exploration and development in the Xihu sag.展开更多
The Huagang Formation of the central inverted structural tectonic belt structure A in the Xihu Depression has abundant hydrocarbon resources.This is an important area for exploration and development in the East China ...The Huagang Formation of the central inverted structural tectonic belt structure A in the Xihu Depression has abundant hydrocarbon resources.This is an important area for exploration and development in the East China Sea Basin(ECSB).Due to the high drilling costs in offshore basins and limited drilling in Structure A,the mechanism of hydrocarbon accumulation is complex,and the laws and processes of hydrocarbon accumulation in structure A are still unclear.To clarify the hydrocarbon accumulation process in the Huagang Formation of structure A,this study used thin section observation,scanning electron microscopy,natural gas carbon isotopes,fluid inclusions,and micro thermometry.Combined with structural evolution and burial history,the origin and source of natural gas,hydrocarbon accumulation periods,and processes were systematically analyzed.The research shows that the sandstone reservoir in the Huagang Formation has satisfactory reservoir,trapping,and preservation conditions;the primary hydrocarbon accumulation period was the Longjing Movement.Therefore,early natural gas filling existed before the Longjing Movement.Based on the evolutionary and fluid potential characteristics of the top tectonic peak of the Pinghu Formation,the natural gas generated in the early stage of structure A is stored in the paleo-structural high point of the Pinghu Formation(paleo convergence area).In the early stage of the Longjing Movement,natural gas migrated from the paleo convergence area of the Pinghu Formation to the current tectonic high point and accumulated in the trap.Therefore,three different“convergence ahead of accumulation”reservoir formation models were developed.These reservoir formation models are critical for guiding the exploration of a series of large traps,including structure A and its surrounding structures,and they have important reference significance for natural gas exploration in other basins.展开更多
基金funded by the National Science and Technology Major Project(No.2016ZX05027-004)General Department Project of Shanghai Branch of CNOOC(China)Limited(No.KJ2022-JYZJ-SH01)。
文摘Tight sandstone reservoirs represent a pivotal unconventional oil and gas production target.The upper section of the deeply buried Huagang Formation in the Xihu Depression is abundant in hydrocarbons and forms a tight reservoir.It exhibits substantial diagenetic variability and strong heterogeneity in sand bodies,which is reflected in variations in physical properties and grain size.Through integrated geological analysis,including rock thin sections,scanning electron microscopy,X-ray diffraction,well logging and production test data,we investigated the diagenesis,reservoir formation mechanisms,and controlling factors of high-quality reservoirs within the superposed sandstone bodies exceeding 100 m thick in the deeper Huagang Formation.We also studied the formation characteristics of these ultrathick sandstones,clarifying that diagenesis and post-depositional modification are crucial for developing high-quality reservoirs in this formation.Our findings indicate that the sandstone underwent compaction,cementation(by chlorite,calcite and quartz),dissolution(of K-feldspar and carbonate cement),and authigenic clay mineral cementation(such as illite,chlorite,kaolinite).Multiple dissolution zones are present within the thick sandstone units.The distribution of these dissolution zones is mainly controlled by temperature and sandstone composition.With increasing temperature,acidic fluids derived from coal-bearing strata and early hydrocarbon source rocks promoted feldspar dissolution.The thick sandstone units in different intervals of varying depths are at various diagenetic stages.The petrophysical zoning of the reservoir is collectively controlled by diagenetic facies dominated by sedimentation,compaction,and dissolution processes.These findings provide valuable guidance and reference for oil and gas exploration and development in this area,particularly within the ultra-thick sandstone layers.
基金Supported by the China National Science and Technology Major Project(2016ZX05027,2016ZX05027-002-006)
文摘By using thin section identification, cathodoluminescence, major and trace elements and fluid inclusion tests and authigenic illite dating, based on observation of core cracks, combined with the microscopic characteristics and imaging logging characteristics of fractures, the stages of the fractures in the Huagang Formation of the central reversal tectonic belt of the Xihu Sag in the East China Sea, and the matching relationship between the fracture development stages and the oil and gas charging stages are clarified. There are diagenetic fractures and tectonic fractures in the reservoirs of the Huagang Formation in the study area. The diagenetic fractures developed during the diagenetic stage of the reservoirs and have less effect on oil and gas migration and transport. The tectonic fractures are divided into three stages based on tectonic movements controlling the fractures and their relationships with hydrocarbon charging: The first stage of fractures was generated in the early stage of the Himalayan Movement–Longjing Movement(12–13 Ma ago), when the tectonic stress caused the sutures and shale strips to twist, deform, and break. Tectonic microfractures generated in this period had short extension, narrow width, and poor effectiveness, and had little effect on oil and gas migration and transport. The second stage of fractures came up during the middle-late period of Himalayan Movement–Longjing Movement(9–12 Ma ago), when tectonic movements caused the development of tectonic fractures in the central reversal tectonic belt, these fractures are of large scale, long extension, and good effectiveness, and matched with the first stage of large scale oil and gas charging(9–12 Ma ago), so they play an important role in oil and gas migration, transportation, and accumulation. The third stage of fractures were created from Himalayan Movement–Okinawa Trough movement to the present day(0–3 Ma ago), the fractures are tectonic ones developing successively;matching with the second stage(0–3 Ma ago) of large-scale oil and gas charging, they created conditions for continuous natural gas migration and transportation. All these prove that the development of reservoir fractures in the Huagang Formation of Xihu Sag can provide seepage space and continuous and effective channels for efficient migration and accumulation of oil and gas.
基金The National Natural Science Foundation of China under contract Nos 42076066,92055203 and U20A20100。
文摘Both Pinghu and Huagang formations are important hydrocarbon reservoirs of the Xihu Depression in the East China Sea Shelf Basin.Clarifying the source suppliers and restoring source-to-sink transport routes are of great significance to the future petroleum and gas undertakings.Previous researchers were largely confined by either limitation of geological records,highly dependence on a singular method or low-precision dating techniques.Our study integrated heavy mineral assemblages,geochemical analyses and detrital zircon U-Pb dating to reconstruct multiple source-to-sink pathways,and to provide a better understanding on the provenance evolution for the upper Pinghu–lower Huagang depositions of the Xihu Depression.At least three major provenances have been confirmed and systematically investigated for their separate compositional features.The Hupijiao Uplift(or even farther northern area)was dominated by a major Paleoproterozoic population peaked at ca.1830 Ma along with minor Mesozoic clusters.The Haijiao Uplift to the west and the Yushan Low Uplift to the southwest,on the other hand,generate opposite U-Pb age spectra with apparently larger peaks of Indosinian and Yanshanian-aged zircons.To be noted,both Indosinian and Paleoproterozoic peaks are almost identical in proportion for the Haijiao Uplift.The overall sedimentary pattern of late Eocene-early Oligocene was featured by both spatial and temporal distinction.The Hupijiao Uplift was likely to cast limited impact during the late Eocene,whereas the broad southern Xihu Depression was transported by a large abundance of materials from the nearby Haijiao and Yushan Low Uplifts.The northern source substantially extended its influence to the farther south during the early Oligocene by delivering plentiful sediments of higher-degree metamorphic parent rocks.Combined with the proximal western and southwestern suppliers,the overall Xihu Depression was under control from both distant and local provenances.
基金The National Natural Science Foundation under contract Nos 41502142 and 41502110the National Science and Technology Major Project under contract No.2016ZX05026-007-05the Youth Innovation Promotion Association CAS
文摘The Oligocene Huagang Formation is the main sandstone reservoir in the Xihu Sag, situated in the east of the East China Sea Shelf Basin. With an integrated approach of thin-section petrography, ultra-violet fluorescence microscopy, scanning electron microscopy, and isotope geochemistry, the different diagenetic features were identified, the typical diagenetic parasequences were established, and the diagenetic fluids evolution history were reconstructed for the Oligocene Huagang Formation sandstone reservoir in the south of Xihu Sag. The Huagang Formation sandstone reservoir is now in Period B of the mesodiagenesis, which has undergone significant diagenetic alterations such as mechanical compaction, Pore-lining chlorite cement, feldspar dissolution, quartz cementation and dissolution, and carbonate cementation. Three types of carbonate cements（early siderite,medium ferrocalcite and late ankerite） were identified in the Huagang Formation sandstone reservoir. The carbon and oxygen isotopic compositions of carbonate cements show that the early calcite precipitate from alkaline lacustrine environment whereas the late carbonate cements were closely related to the organic acids. To the Huagang Formation sandstone reservoir, it has experienced two main episodes of dissolution during diagenesis.The early dissolution is that unstable components such as feldspar, lithic fragments, and carbonate cement were dissolved by acidic water. The second dissolution is that quartz and other silicate minerals were dissolved under the alkaline condition. Two main phases of hydrocarbon charging occurred in this study area. The first hydrocarbon emplacement was prior to the medium carbonate cementation but posterior to feldspar dissolution and the onset of quartz cementation at the end of the Miocene. The second hydrocarbon charging occurred in the Quaternary period after the late carbonate precipitation.
文摘The Xihu Depression is the largest hydrocarbon-bearing depression of the East China Sea Shelf Basin(also referred to as the ECSSB).However,the depositional systems and reservoir distribution of the Oligocene Huagang Formation in the Xihu Depression are still controversial.Under the guidance of sedimentology and stratigraphy,this study documented a marine-terrestrial transitional environment in the restricted bay setting of the Oligocene Huagang Formation through core description,well logging,and seismic data analysis.This study also revealed that the Oligocene Huagang Formation is dominated by tidal delta,estuary,and gravity flow deposits in the central anticline zone of the Xihu Depression.The new understanding of the sedimentary systems and the discovery of the transgressive gap in the eastern Diaoyu Islands uplift explain the origin of fine-grained sediments and the EW-trending sand bodies in the central depression and the sand bodies parallel to shoreline in the west slope belt,which cannot be explained by previous study results,such as southern transgression or fluvial deltas and even lacustrine deposition.Moreover,the tidal channels,tidal sand flats,and gravity flow sand bodies formed by the transgressive tides are high-quality reservoirs.The study will provide a basis for well placement and serve as guidance for the selection of favorable hydrocarbon exploration areas in the Xihu Depression.
基金Supported by the China National Science and Technology Major Project(2016ZX05027-004)CNOOC(China)Science and Technology Projects(CNOOC-KJ 135,ZDXM 39 SH03).
文摘The fluvial-deltaic reservoirs of the Oligocene Huagang Formation in the Xihu sag of the East China Sea shelf basin reflect rapid lateral change in sedimentary facies and poor morphology of conventional slice attributes,which bring difficulties to the reservoir prediction for subsequent exploration and development of lithologic reservoirs.The traditional seismic sedimentology technology is optimized by applying the characteristic technologies such as frequency-boosting interpretation,inversion-conventional–90°phase shift joint construction of seismic lithologic bodies,nonlinear slices,paleogeomorphology restoration,and multi-attribute fusion,to obtain typical slice attributes,which are conducive to geological form description and sedimentary interpretation.The Huagang Formation developed three types of sedimentary bodies:braided river,meandering river and shallow water delta,and the vertical sedimentary evolution was controlled by the mid-term base-level cycle and paleogeomorphology.In the early–middle stage of the mid-term base-level ascending cycle,braided channel deposits were dominant,and vertical superimposed sand bodies were developed.In the late stage of the ascending half-cycle and the early stage of the descending half-cycle,meandering river deposits were dominant,and isolated sand bodies were developed.In the middle–late stage of the descending half-cycle,shallow-water delta deposits were dominant,and migratory medium–thick sand bodies were developed.Restricted paleogeomorphology controlled the sand body distribution,while non-restricted paleogeomorphology had little effect on the sand body distribution.Based on reservoir characterization,the fault sealing type and reservoir updip pinch-out type structural lithological traps are proposed as the main directions for future exploration and development in the Xihu sag.
文摘The Huagang Formation of the central inverted structural tectonic belt structure A in the Xihu Depression has abundant hydrocarbon resources.This is an important area for exploration and development in the East China Sea Basin(ECSB).Due to the high drilling costs in offshore basins and limited drilling in Structure A,the mechanism of hydrocarbon accumulation is complex,and the laws and processes of hydrocarbon accumulation in structure A are still unclear.To clarify the hydrocarbon accumulation process in the Huagang Formation of structure A,this study used thin section observation,scanning electron microscopy,natural gas carbon isotopes,fluid inclusions,and micro thermometry.Combined with structural evolution and burial history,the origin and source of natural gas,hydrocarbon accumulation periods,and processes were systematically analyzed.The research shows that the sandstone reservoir in the Huagang Formation has satisfactory reservoir,trapping,and preservation conditions;the primary hydrocarbon accumulation period was the Longjing Movement.Therefore,early natural gas filling existed before the Longjing Movement.Based on the evolutionary and fluid potential characteristics of the top tectonic peak of the Pinghu Formation,the natural gas generated in the early stage of structure A is stored in the paleo-structural high point of the Pinghu Formation(paleo convergence area).In the early stage of the Longjing Movement,natural gas migrated from the paleo convergence area of the Pinghu Formation to the current tectonic high point and accumulated in the trap.Therefore,three different“convergence ahead of accumulation”reservoir formation models were developed.These reservoir formation models are critical for guiding the exploration of a series of large traps,including structure A and its surrounding structures,and they have important reference significance for natural gas exploration in other basins.
