Large numbers of gas reservoirs have been discovered in overpressure basins.Fluid charging has a close relationship with paleo-pressure evolution,affecting the migration of gas reservoirs.To study fluid charging and t...Large numbers of gas reservoirs have been discovered in overpressure basins.Fluid charging has a close relationship with paleo-pressure evolution,affecting the migration of gas reservoirs.To study fluid charging and the related pressure system,we analyzed burial histories and fluid inclusion(PVTx)simulations and conducted basin modeling of the Ledong Slope Zone in the Yinggehai Basin as an example.On the basis of fluid-inclusion assemblages(FIAs),homogenization temperature(Th),final melting temperature(Tm,ice)and Raman spectroscopy in fluid inclusions,there are three stages of fluid charging:during the first and second stage,methane-dominated fluid was charged at 2.2–1.7 Ma and 1.7–0.9 Ma,respectively.In the third stage,CO_(2)-rich hydrothermal fluid was charged since 0.9 Ma.It could be concluded from the well-logging data that the disequilibrium compaction in the Yinggehai Fm.,along with the fluid expansion and clay diagenesis in the Huangliu and Meishan formations,resulted in the overpressure in the Ledong slope zone.The evolution of paleo-pressure was affected by the sedimentation rate of the Yinggehai Fm.,as well as the hydrocarbon generation rate.Additionally,the Ledong Slope Zone is less affected by diapir activity than the nearby diapir area.Based on fluid inclusions,paleo-pressure,basin modeling and geological background,the gas migration history of the Ledong Slope Zone can be divided into four stages:in the first stage,excess pressure was formed around 5 Ma;from 2.2 to 1.7 Ma,there was a reduction in the charging of hydrocarbon fluid and steadily increasing excess pressure;during the 1.7–0.9 Ma period a large amount of hydrocarbon was generated,excess pressure increasing significantly and hydraulic fractures forming in mudstones,With gas reservoirs developing in structural highs;since 0.9 Ma,CO_(2)-rich hydrothermal fluid accumulated in reservoirs adjacent to faults and the pressure coefficient remained stable.The research results are helpful in the study of fluid migration and accumulation mechanisms in overpressure basins.展开更多
The Yinggehai Basin is a strongly overpressured Cenozoic basin developed in the northern continental sheff of the South China Sea. The flow of overpressured fluids in this basin has given rise to strong effects on pet...The Yinggehai Basin is a strongly overpressured Cenozoic basin developed in the northern continental sheff of the South China Sea. The flow of overpressured fluids in this basin has given rise to strong effects on petroleum accumulation. (1) The overpressured fluid flow has enhanced the maturation of shallow-buried source rocks, which has caused the source rocks that would have remained immature under the conduction background to be mature for hydrocarbon generation. As a result, the overpressured fluid flow has increased the volume and interval of mature source rocks. (2) The overpressured fluid flow has strong extraction effects on the immature or low-mature source rocks in the shallow parts. This has increased, to some extent, the expulsion efficiency of the source rocks. More importantly, the extraction effects have strongly limited the effectiveness of biomarker parameters from oil and condensate in reflecting the source and maturity of the oil and gas. (3) The flow has caused the sandstones in the shallow parts to get into the late diagenesis stage, and significantly reduced the porosity and penneability of the sandstones. This study confirms that even in sedimentary basins in which no topography-driven groundwater flow systems have ever developed, the cross-formation migration of overpressured fluids and the resultant energy conduction and material exchange can significantly affect the thermal regime, source rock maturation and sandstone diagenesis. As a result, the effects of overpressured fluid flow must be taken into account in analyzing the mechanism of petroleum accumulation.展开更多
A quantitative two-dimensional model of sequence stratigraphy is formulated to simulate the development of sequence architecture in sedimentary basins. The model takes into account sea level change, tectonic subsidenc...A quantitative two-dimensional model of sequence stratigraphy is formulated to simulate the development of sequence architecture in sedimentary basins. The model takes into account sea level change, tectonic subsidence, compaction of sediments, flexural isostatic compensation, erosion and sedimentation. It may be used to test sequence stratigraphic model, to analyze the development of sequence architecture and sequence boundaries, and to predict facies distribution in basins. The computer model, combined with backstripping technique, is cali- brated to model the sedimentary filling of the Early Cretaceous Erlian basin and the Tertiary Yinggehai basin. The study shows that the development of high order sequences in the basins was closely related to the multiple stretching and inversion. The development of the progradational sequence set of the Yinghuang Formation in Yinggehai basin formed in synrift period was mainly controlled by a large amount of sediment input high fluctuation of sea level and gradual subsidence of the basin.展开更多
Overpressure systems are widely developed in the central depression and paleo-uplift in the Yinggehai and Qiongdongnan basins. They can be divided into three types according to the origin of abnormally high formation ...Overpressure systems are widely developed in the central depression and paleo-uplift in the Yinggehai and Qiongdongnan basins. They can be divided into three types according to the origin of abnormally high formation pressure in the reservoirs, i.e. the autochthonous, vertically-transmitted and laterally-transmitted types. The autochthonous overpressure system results from rapid disequilibrium sediment loading and compaction. In the allochthonous overpressure system, the increase of fluid pressure in sandstone originates from the invasion of overpressured fluid flowing vertically or laterally through the conduit units. The autochthonous overpressure system occurs in the deep-lying strata of Neogene age in the central depression of the Yinggehai and Qiongdongnan basins. The vertically transmitted overpressure system is developed in the shallow strata of Late Miocene and Pliocene ages in the diapiric zone of the central Yinggehai basin, and the laterally transmitted overpressure system occurs in the Oligocene strata of paleo-uplifts, such as the structure of Ya-211 in the Qiongdongnan basin. The results indicate that the autochthonous overpressure system is generally a closed one, which is unfavorable for the migration and accumulation of hydrocarbons. In the allochthonous overpressure system, hydrocarbon accumulation depends on the relationship between the formation of overpressure systems and the spatial location and duration of hydrocarbon migration. The interval overlying the overpressure system is usually a favorable hydrocarbon accumulation zone if the duration of fluid expulsion coincides with that of hydrocarbon accumulation.展开更多
To lower the CO 2 risk for hydrocarbon exploration in the west continental shelf of Yinggehai basin, South China Sea, we do attempt not only to know the CO 2 origins, but also to make an understanding of the degassing...To lower the CO 2 risk for hydrocarbon exploration in the west continental shelf of Yinggehai basin, South China Sea, we do attempt not only to know the CO 2 origins, but also to make an understanding of the degassing processes from the mantle and crust. Based on the stable carbon isotope ratios of CO 2 alone, the organic and inorganic CO 2 can be successively distinguished, but the formation conditions and mixing processes for inorganic CO 2 are still not clear. The relationships between lg[R(= 3He/ 4He)/R a(=1.386×10 -6)] and CO 2 content (%), CO 2/ 3He and δ 13C CO 2 have been employed, respectively, to obtain that the CO 2 gases in the reservoirs can be classified into three categories: (1) organic CO 2 with very low contents but contaminated by mantle-derived helium; (2) inorganic CO 2 gases with lower to higher contents being mixtures of crustal CO 2 with mantle-derived CO 2, the mantle- contributed percentage being in the range of 0 %-27 %, and (3) mainly crust-derived inorganic CO 2 gases being characterized by high contents (more than 50 %) and indicating the crustal addition by metamorphism of rich-in carbon rocks in basement. Nevertheless, some CO 2/ 3He ratios of organic CO 2 fall into the range 10 8-10 10, which made us inquire whether the CO 2/ 3He=(1-10)×10 9 can be the unique signature of magmatic CO 2 or not. All the observation of plutonic activities, fluid inclusion measurements in gas reservoirs, pre-stack depth/time seismic sections and the satellite infrared remote photography taken from Yinggehai basin, South China Sea, during Chichi earthquake in Taiwan on September 21, 1999, supports that the degassing processes are in a discontinuous mode, which may be triggered by igneous intrusion or extrusion, or earthquakes. In the central diapir zone of the basin, at least 3 to 4 orders of discharge of across-formational thermal fluid flows through fractures can be determined in different scales. The mantle degassing process may have a strong effect on overpressured system forming and outgassing in crust. However, it is very difficult to estimate the transferring rates for a special fractured zone at a specific time interval.展开更多
Overpressure developed throughout most of the Yinggehai basin. The burial depth to top overpressure varied from about 1 600 m to 4 500 m, with the shallowest top overpressure occurring in the depocenter. The main caus...Overpressure developed throughout most of the Yinggehai basin. The burial depth to top overpressure varied from about 1 600 m to 4 500 m, with the shallowest top overpressure occurring in the depocenter. The main cause of the overpressure was disequilibrium compaction resulting from rapid sedimentation of fine grained sediments. The overpressure was strengthened by the retention of fluids including gases due to lack of faults before diapir development. The diapirism in the Yinggehai basin was a combined result of the strong overpressure and the tensile stress field caused by the right lateral slip of the boundary fault. The diapirism, a product of the movement of overpressured fluids and plastic shales, shaped the vertical conduits from source to traps that would be absent without overpressured fluid release. Natural gas accumulation in traps in the diapir structure zones was also intermittent, which can be inferred from the inter reservoir compositional heterogeneity, transient thermal effect of fluid flow and migration fractionation.展开更多
The characteristics of reservoir heterogeneity of the marine gravity flow tight sandstone from the Miocene Huangliu Formation under abnormally high pressure setting at LD10 area in Yinggehai Basin are studied,and the ...The characteristics of reservoir heterogeneity of the marine gravity flow tight sandstone from the Miocene Huangliu Formation under abnormally high pressure setting at LD10 area in Yinggehai Basin are studied,and the influencing factors on reservoir heterogeneity are discussed,based on modular formation dynamics test,thin sections,XRD analysis of clay minerals,scanning electron microscopy,measurement of pore throat image,porosity and permeability,and high pressure Hg injection,as well as the stimulation of burial thermal history.The aim is to elucidate characteristics of the heterogeneity and the evolution process of heterogeneity of the reservoir,and predict the favorable reservoirs distribution.(1)The heterogeneity of the reservoir is mainly controlled by the cement heterogeneity,pore throat heterogeneity,quality of the reservoir heterogeneity,and the diagenesis under an abnormally high pressure setting.(2)The differences in pore-throat structure caused by diagenetic evolution affected the intergranular material heterogeneity and the pore throat heterogeneity,and finally controlled the heterogeneity of reservoir quality.(3)Compared with the reservoir under normal pressure,abnormally high pressure restrains strength of the compaction and cementation and enhances the dissolution of the reservoir to some extent,and abnormally high pressure thus weakening the heterogeneity of the reservoir to a certain degree.The favorable reservoirs are mainly distributed in the gravity flow sand body under the strong overpressure zone in the middle and lower part of Huangliu Formation.展开更多
The characteristics, origin and injection history of the Dongfang gas field, the largest gas field found in the Yinggehai basin, are studied by integrated geological, geothermal and geochemical data. The gas field sho...The characteristics, origin and injection history of the Dongfang gas field, the largest gas field found in the Yinggehai basin, are studied by integrated geological, geothermal and geochemical data. The gas field shows considerable variation in hydrocarbon gas, nitrogen and carbon dioxide content, aud has been filled by at least four stage fluids. A strong thermal anomaIy caused by hydrothermal fluid flows occurs in the gas field, as evidenced rrom drill-stem test and fluid iuclusion homogenization temperatures, rock-eval tmax,vitrinite reflectance as well as clay-mineral transformation profiles. Such a thermal anomaly suggests focused, rapid flow of deeply-sourced hydrothermal rluids. The inter-reservoir heterogeneities, the strong migotion rractionation related to abrupt changes in pressure and temperature and tbe short-lived, transient nature of the thermal effect of fluid flow are evidences of episodic rluid injections from the overpressured systems into the reservoirs.展开更多
The Dongfang1-1 gas field(DF1-1)in the Yinggehai Basin is currently the largest offshore self-developed gas field in China and is rich in oil and gas resources.The second member of the Pliocene Yinggehai Formation(YGH...The Dongfang1-1 gas field(DF1-1)in the Yinggehai Basin is currently the largest offshore self-developed gas field in China and is rich in oil and gas resources.The second member of the Pliocene Yinggehai Formation(YGHF)is the main gas-producing formation and is composed of various sedimentary types;however,a clear understanding of the sedimentary types and development patterns is lacking.Here,typical lithofacies,logging facies and seismic facies types and characteristics of the YGHF are identified based on high-precision 3D seismic data combined with drilling,logging,analysis and testing data.Based on 3D seismic interpretation and attribute analysis,the origin of high-amplitude reflections is clarified,and the main types and evolution characteristics of sedimentary facies are identified.Taking gas formation upper II(IIU)as an example,the plane distribution of the delta front and bottom current channel is determined;finally,a comprehensive sedimentary model of the YGHF second member is established.This second member is a shallowly buried“bright spot”gas reservoir with weak compaction.The velocity of sandstone is slightly lower than that of mudstone,and the reflection has medium amplitude when there is no gas.The velocity of sandstone decreases considerably after gas accumulation,resulting in an increase in the wave impedance difference and high-amplitude(bright spot)reflection between sandstone and mudstone;the range of high amplitudes is consistent with that of gas-bearing traps.The distribution of gas reservoirs is obviously controlled by dome-shaped diapir structural traps,and diapir faults are channels through which natural gas from underlying Miocene source rocks can enter traps.The study area is a delta front deposit developed on a shallow sea shelf.The lithologies of the reservoir are mainly composed of very fine sand and coarse silt,and a variety of sedimentary structural types reflect a shallow sea delta environment;upward thickening funnel type,strong toothed bell type and toothed funnel type logging facies are developed.In total,4 stages of delta front sand bodies(corresponding to progradational reflection seismic facies)derived from the Red River and Blue River in Vietnam have developed in the second member of the YGHF;these sand bodies are dated to 1.5 Ma and correspond to four gas formations.During sedimentation,many bottom current channels(corresponding to channel fill seismic facies)formed,which interacted with the superposed progradational reflections.When the provenance supply was strong in the northwest,the area was dominated by a large set of delta front deposits.In the period of relative sea level rise,surface bottom currents parallel to the coastline were dominant,and undercutting erosion was obvious,forming multistage superimposed erosion troughs.Three large bottom current channels that developed in the late sedimentary period of gas formation IIU are the most typical.展开更多
Various deep-water deposits developed in the Yinggehai Basin and Qiongdongnan Basin(Ying-Qiong Basin)in the northern South China Sea,making the two basins significantly hydrocarbon-producing areas and ideal for studyi...Various deep-water deposits developed in the Yinggehai Basin and Qiongdongnan Basin(Ying-Qiong Basin)in the northern South China Sea,making the two basins significantly hydrocarbon-producing areas and ideal for studying the genetic mechanism and sedimentary characteristics of deep-water clastic rocks.Using cores,image well logging,heavy mineral assemblages,and seismic data,we thoroughly studied the geometry,tectonic background,driving mechanism and source-to-sink process of deep-water deposits in the study area.The results showed that:(1)there were five genetic mechanisms of deep-water clastic rock,i.e.,slides,slumps,debris flows,turbidity currents,and bottom currents.(2)The sliding deposits were distributed from the delta front to the continental slope toe.The slumping deposits were mainly distributed at the continental slope toe or the basin’s central area,far from the delta front The turbidity deposits were widely developed in the deep-water area,but with huge differences in thickness.The bottom currents mainly reworked previous deposits far from the slope.(3)Slip and extension along the preexisting fault zone were the main structural factors that drive the axial channel formation at the slope foot.(4)The sand-rich gravity sediment flows in the Ying-Qiong basin were primarily caused by the direct supply of terrigenous debris into the marine environment over the slope break.展开更多
The characteristics and distribution of faults in Yinggehai basin discussed in this paper reveal the structural effects of the overpressure fluid expulsion. The rapid subsidence and mud rich intervals of the marine ro...The characteristics and distribution of faults in Yinggehai basin discussed in this paper reveal the structural effects of the overpressure fluid expulsion. The rapid subsidence and mud rich intervals of the marine rocks dominate the formation of the overpressure systems and the enormous volumes of the overpressure fluids in the basin. Triggered by some faults, the overpressure fluids were expulsed rapidly from the overpressure compartments to form a series of diapirs in the basin, resulting in the dense fractures or faults and folds in the limbs of diapirs. These fractures and faults provided the migration pathway for the vertical flow of hydrocarbons, so that the gas fields arising from this process might migrate upwards to the sandstone reservoir. Therefore, the hydrocarbon accumulations are usually located in the upper parts of diapiric structures.展开更多
The accurate prediction of overpressure is one of the key issues that restrict the effective development of oil and gas resources in the Yinggehai Basin. In this paper, the formation mechanism of overpressure in Yingg...The accurate prediction of overpressure is one of the key issues that restrict the effective development of oil and gas resources in the Yinggehai Basin. In this paper, the formation mechanism of overpressure in Yinggehai Basin is studied. Based on this mechanism, the quantitative prediction model and empirical parameters of overpressure are optimized in Yinggehai Basin and applied in engineering. The results show that the formation mechanism of overpressure in the Yinggehai Basin is complicated, and the causes of overpressure in different blocks of basin are different. The eastern block mainly develops loading-type overpressure, while the Ledong block is dominated by unloading high pressure. Different blocks should employ different abnormal high-pressure prediction models. The East block mainly adopts the Eaton method, and the Ledong block mainly utilizes the Bowers method. The empirical parameters of different models can be determined according to the actual drilling conditions. The practical application demonstrates that the abnormal high-pressure prediction error is within 2%, and it is able to satisfy the requirements of on-site engineering.展开更多
The subtle strike-slip tectonic deformation and its relationship to deposition, overpressure and hydrocarbon migration were studied on the basis of systematic sorting of tectonic data.(1) The local T(tension) fracture...The subtle strike-slip tectonic deformation and its relationship to deposition, overpressure and hydrocarbon migration were studied on the basis of systematic sorting of tectonic data.(1) The local T(tension) fractures derived from sinistral strike-slip process were formed before 10.5 Ma, large in number in the nose structure of the eastern slope, and reactivated episodically under the effect of fluid overpressure in the late stage, they served as dominant vertical hydrocarbon migration paths in the slope area of basin.(2) The dextral strike-slip extension was conducive to the increase of depositional rate and formation of regional under-compacted seal, and induced generation of local T fractures which triggered the development of diapirs; in turn, the development of diapirs made T fractures grow in size further.(3) The sinistral strike-slip process weakened after 10.5 Ma, causing tectonic movement characterized by compression in the north and rotational extension in the south, and the uplift and erosion of strata in Hanoi sag and a surge in clastics supply for south Yinggehai sag. Finally, migrating slope channelized submarine fans and superimposed basin floor fans were developed respectively on the asymmetrical east and west slopes of the Yinggehai sag.展开更多
基金supported by the‘Research on Exploration and Development Technology and New Exploration Fields of high Temperature and High-pressure Gas Reservoirs in the West of the South China Sea’,a subject of the key technology projects of the CNOOC‘Key Technologies for Producing 20 million m~3 of Oil in the Western South China Sea Oilfield’(No.CNOOC-KJ 135 ZDXM 38 ZJ 02 ZJ)The financial support from CNOOC(Hainan)。
文摘Large numbers of gas reservoirs have been discovered in overpressure basins.Fluid charging has a close relationship with paleo-pressure evolution,affecting the migration of gas reservoirs.To study fluid charging and the related pressure system,we analyzed burial histories and fluid inclusion(PVTx)simulations and conducted basin modeling of the Ledong Slope Zone in the Yinggehai Basin as an example.On the basis of fluid-inclusion assemblages(FIAs),homogenization temperature(Th),final melting temperature(Tm,ice)and Raman spectroscopy in fluid inclusions,there are three stages of fluid charging:during the first and second stage,methane-dominated fluid was charged at 2.2–1.7 Ma and 1.7–0.9 Ma,respectively.In the third stage,CO_(2)-rich hydrothermal fluid was charged since 0.9 Ma.It could be concluded from the well-logging data that the disequilibrium compaction in the Yinggehai Fm.,along with the fluid expansion and clay diagenesis in the Huangliu and Meishan formations,resulted in the overpressure in the Ledong slope zone.The evolution of paleo-pressure was affected by the sedimentation rate of the Yinggehai Fm.,as well as the hydrocarbon generation rate.Additionally,the Ledong Slope Zone is less affected by diapir activity than the nearby diapir area.Based on fluid inclusions,paleo-pressure,basin modeling and geological background,the gas migration history of the Ledong Slope Zone can be divided into four stages:in the first stage,excess pressure was formed around 5 Ma;from 2.2 to 1.7 Ma,there was a reduction in the charging of hydrocarbon fluid and steadily increasing excess pressure;during the 1.7–0.9 Ma period a large amount of hydrocarbon was generated,excess pressure increasing significantly and hydraulic fractures forming in mudstones,With gas reservoirs developing in structural highs;since 0.9 Ma,CO_(2)-rich hydrothermal fluid accumulated in reservoirs adjacent to faults and the pressure coefficient remained stable.The research results are helpful in the study of fluid migration and accumulation mechanisms in overpressure basins.
基金This research was supported by the National Natural Science Foundation of China(grants 401 25008 and 40238059).
文摘The Yinggehai Basin is a strongly overpressured Cenozoic basin developed in the northern continental sheff of the South China Sea. The flow of overpressured fluids in this basin has given rise to strong effects on petroleum accumulation. (1) The overpressured fluid flow has enhanced the maturation of shallow-buried source rocks, which has caused the source rocks that would have remained immature under the conduction background to be mature for hydrocarbon generation. As a result, the overpressured fluid flow has increased the volume and interval of mature source rocks. (2) The overpressured fluid flow has strong extraction effects on the immature or low-mature source rocks in the shallow parts. This has increased, to some extent, the expulsion efficiency of the source rocks. More importantly, the extraction effects have strongly limited the effectiveness of biomarker parameters from oil and condensate in reflecting the source and maturity of the oil and gas. (3) The flow has caused the sandstones in the shallow parts to get into the late diagenesis stage, and significantly reduced the porosity and penneability of the sandstones. This study confirms that even in sedimentary basins in which no topography-driven groundwater flow systems have ever developed, the cross-formation migration of overpressured fluids and the resultant energy conduction and material exchange can significantly affect the thermal regime, source rock maturation and sandstone diagenesis. As a result, the effects of overpressured fluid flow must be taken into account in analyzing the mechanism of petroleum accumulation.
文摘A quantitative two-dimensional model of sequence stratigraphy is formulated to simulate the development of sequence architecture in sedimentary basins. The model takes into account sea level change, tectonic subsidence, compaction of sediments, flexural isostatic compensation, erosion and sedimentation. It may be used to test sequence stratigraphic model, to analyze the development of sequence architecture and sequence boundaries, and to predict facies distribution in basins. The computer model, combined with backstripping technique, is cali- brated to model the sedimentary filling of the Early Cretaceous Erlian basin and the Tertiary Yinggehai basin. The study shows that the development of high order sequences in the basins was closely related to the multiple stretching and inversion. The development of the progradational sequence set of the Yinghuang Formation in Yinggehai basin formed in synrift period was mainly controlled by a large amount of sediment input high fluctuation of sea level and gradual subsidence of the basin.
基金supported by the Trans-century Training Programme Foundation for the Talents by the State Education Commission(now the Ministry of Education)of Chinathe key project No.01038 of the Ministry of Education of China
文摘Overpressure systems are widely developed in the central depression and paleo-uplift in the Yinggehai and Qiongdongnan basins. They can be divided into three types according to the origin of abnormally high formation pressure in the reservoirs, i.e. the autochthonous, vertically-transmitted and laterally-transmitted types. The autochthonous overpressure system results from rapid disequilibrium sediment loading and compaction. In the allochthonous overpressure system, the increase of fluid pressure in sandstone originates from the invasion of overpressured fluid flowing vertically or laterally through the conduit units. The autochthonous overpressure system occurs in the deep-lying strata of Neogene age in the central depression of the Yinggehai and Qiongdongnan basins. The vertically transmitted overpressure system is developed in the shallow strata of Late Miocene and Pliocene ages in the diapiric zone of the central Yinggehai basin, and the laterally transmitted overpressure system occurs in the Oligocene strata of paleo-uplifts, such as the structure of Ya-211 in the Qiongdongnan basin. The results indicate that the autochthonous overpressure system is generally a closed one, which is unfavorable for the migration and accumulation of hydrocarbons. In the allochthonous overpressure system, hydrocarbon accumulation depends on the relationship between the formation of overpressure systems and the spatial location and duration of hydrocarbon migration. The interval overlying the overpressure system is usually a favorable hydrocarbon accumulation zone if the duration of fluid expulsion coincides with that of hydrocarbon accumulation.
文摘To lower the CO 2 risk for hydrocarbon exploration in the west continental shelf of Yinggehai basin, South China Sea, we do attempt not only to know the CO 2 origins, but also to make an understanding of the degassing processes from the mantle and crust. Based on the stable carbon isotope ratios of CO 2 alone, the organic and inorganic CO 2 can be successively distinguished, but the formation conditions and mixing processes for inorganic CO 2 are still not clear. The relationships between lg[R(= 3He/ 4He)/R a(=1.386×10 -6)] and CO 2 content (%), CO 2/ 3He and δ 13C CO 2 have been employed, respectively, to obtain that the CO 2 gases in the reservoirs can be classified into three categories: (1) organic CO 2 with very low contents but contaminated by mantle-derived helium; (2) inorganic CO 2 gases with lower to higher contents being mixtures of crustal CO 2 with mantle-derived CO 2, the mantle- contributed percentage being in the range of 0 %-27 %, and (3) mainly crust-derived inorganic CO 2 gases being characterized by high contents (more than 50 %) and indicating the crustal addition by metamorphism of rich-in carbon rocks in basement. Nevertheless, some CO 2/ 3He ratios of organic CO 2 fall into the range 10 8-10 10, which made us inquire whether the CO 2/ 3He=(1-10)×10 9 can be the unique signature of magmatic CO 2 or not. All the observation of plutonic activities, fluid inclusion measurements in gas reservoirs, pre-stack depth/time seismic sections and the satellite infrared remote photography taken from Yinggehai basin, South China Sea, during Chichi earthquake in Taiwan on September 21, 1999, supports that the degassing processes are in a discontinuous mode, which may be triggered by igneous intrusion or extrusion, or earthquakes. In the central diapir zone of the basin, at least 3 to 4 orders of discharge of across-formational thermal fluid flows through fractures can be determined in different scales. The mantle degassing process may have a strong effect on overpressured system forming and outgassing in crust. However, it is very difficult to estimate the transferring rates for a special fractured zone at a specific time interval.
文摘Overpressure developed throughout most of the Yinggehai basin. The burial depth to top overpressure varied from about 1 600 m to 4 500 m, with the shallowest top overpressure occurring in the depocenter. The main cause of the overpressure was disequilibrium compaction resulting from rapid sedimentation of fine grained sediments. The overpressure was strengthened by the retention of fluids including gases due to lack of faults before diapir development. The diapirism in the Yinggehai basin was a combined result of the strong overpressure and the tensile stress field caused by the right lateral slip of the boundary fault. The diapirism, a product of the movement of overpressured fluids and plastic shales, shaped the vertical conduits from source to traps that would be absent without overpressured fluid release. Natural gas accumulation in traps in the diapir structure zones was also intermittent, which can be inferred from the inter reservoir compositional heterogeneity, transient thermal effect of fluid flow and migration fractionation.
基金Supported by the Research on Exploration and Development Technology and New Exploration Field of High Temperature and Pressure Gas Reservoir in Western South China Sea(CNOOC-KJ135ZDXM38ZJ02ZJ)National Natural Science Foundation of China(41972129)National Science and Technology Key Project(2016ZX05024-005,2016ZX05026-003-005)。
文摘The characteristics of reservoir heterogeneity of the marine gravity flow tight sandstone from the Miocene Huangliu Formation under abnormally high pressure setting at LD10 area in Yinggehai Basin are studied,and the influencing factors on reservoir heterogeneity are discussed,based on modular formation dynamics test,thin sections,XRD analysis of clay minerals,scanning electron microscopy,measurement of pore throat image,porosity and permeability,and high pressure Hg injection,as well as the stimulation of burial thermal history.The aim is to elucidate characteristics of the heterogeneity and the evolution process of heterogeneity of the reservoir,and predict the favorable reservoirs distribution.(1)The heterogeneity of the reservoir is mainly controlled by the cement heterogeneity,pore throat heterogeneity,quality of the reservoir heterogeneity,and the diagenesis under an abnormally high pressure setting.(2)The differences in pore-throat structure caused by diagenetic evolution affected the intergranular material heterogeneity and the pore throat heterogeneity,and finally controlled the heterogeneity of reservoir quality.(3)Compared with the reservoir under normal pressure,abnormally high pressure restrains strength of the compaction and cementation and enhances the dissolution of the reservoir to some extent,and abnormally high pressure thus weakening the heterogeneity of the reservoir to a certain degree.The favorable reservoirs are mainly distributed in the gravity flow sand body under the strong overpressure zone in the middle and lower part of Huangliu Formation.
文摘The characteristics, origin and injection history of the Dongfang gas field, the largest gas field found in the Yinggehai basin, are studied by integrated geological, geothermal and geochemical data. The gas field shows considerable variation in hydrocarbon gas, nitrogen and carbon dioxide content, aud has been filled by at least four stage fluids. A strong thermal anomaIy caused by hydrothermal fluid flows occurs in the gas field, as evidenced rrom drill-stem test and fluid iuclusion homogenization temperatures, rock-eval tmax,vitrinite reflectance as well as clay-mineral transformation profiles. Such a thermal anomaly suggests focused, rapid flow of deeply-sourced hydrothermal rluids. The inter-reservoir heterogeneities, the strong migotion rractionation related to abrupt changes in pressure and temperature and tbe short-lived, transient nature of the thermal effect of fluid flow are evidences of episodic rluid injections from the overpressured systems into the reservoirs.
基金The National Natural Science Foundation of China’s Major Project“Research on Geophysical Theories and Methods of Unconventional Oil and Gas Exploration and Development”,Task I:“China’s Tight Oil and Gas Reservoir Geological Characteristics,Classification and Typical Geological Model Establishment”under contract No.41390451。
文摘The Dongfang1-1 gas field(DF1-1)in the Yinggehai Basin is currently the largest offshore self-developed gas field in China and is rich in oil and gas resources.The second member of the Pliocene Yinggehai Formation(YGHF)is the main gas-producing formation and is composed of various sedimentary types;however,a clear understanding of the sedimentary types and development patterns is lacking.Here,typical lithofacies,logging facies and seismic facies types and characteristics of the YGHF are identified based on high-precision 3D seismic data combined with drilling,logging,analysis and testing data.Based on 3D seismic interpretation and attribute analysis,the origin of high-amplitude reflections is clarified,and the main types and evolution characteristics of sedimentary facies are identified.Taking gas formation upper II(IIU)as an example,the plane distribution of the delta front and bottom current channel is determined;finally,a comprehensive sedimentary model of the YGHF second member is established.This second member is a shallowly buried“bright spot”gas reservoir with weak compaction.The velocity of sandstone is slightly lower than that of mudstone,and the reflection has medium amplitude when there is no gas.The velocity of sandstone decreases considerably after gas accumulation,resulting in an increase in the wave impedance difference and high-amplitude(bright spot)reflection between sandstone and mudstone;the range of high amplitudes is consistent with that of gas-bearing traps.The distribution of gas reservoirs is obviously controlled by dome-shaped diapir structural traps,and diapir faults are channels through which natural gas from underlying Miocene source rocks can enter traps.The study area is a delta front deposit developed on a shallow sea shelf.The lithologies of the reservoir are mainly composed of very fine sand and coarse silt,and a variety of sedimentary structural types reflect a shallow sea delta environment;upward thickening funnel type,strong toothed bell type and toothed funnel type logging facies are developed.In total,4 stages of delta front sand bodies(corresponding to progradational reflection seismic facies)derived from the Red River and Blue River in Vietnam have developed in the second member of the YGHF;these sand bodies are dated to 1.5 Ma and correspond to four gas formations.During sedimentation,many bottom current channels(corresponding to channel fill seismic facies)formed,which interacted with the superposed progradational reflections.When the provenance supply was strong in the northwest,the area was dominated by a large set of delta front deposits.In the period of relative sea level rise,surface bottom currents parallel to the coastline were dominant,and undercutting erosion was obvious,forming multistage superimposed erosion troughs.Three large bottom current channels that developed in the late sedimentary period of gas formation IIU are the most typical.
基金supported by Major National Science and Technology Project(Grant No.2016ZX05024-005)。
文摘Various deep-water deposits developed in the Yinggehai Basin and Qiongdongnan Basin(Ying-Qiong Basin)in the northern South China Sea,making the two basins significantly hydrocarbon-producing areas and ideal for studying the genetic mechanism and sedimentary characteristics of deep-water clastic rocks.Using cores,image well logging,heavy mineral assemblages,and seismic data,we thoroughly studied the geometry,tectonic background,driving mechanism and source-to-sink process of deep-water deposits in the study area.The results showed that:(1)there were five genetic mechanisms of deep-water clastic rock,i.e.,slides,slumps,debris flows,turbidity currents,and bottom currents.(2)The sliding deposits were distributed from the delta front to the continental slope toe.The slumping deposits were mainly distributed at the continental slope toe or the basin’s central area,far from the delta front The turbidity deposits were widely developed in the deep-water area,but with huge differences in thickness.The bottom currents mainly reworked previous deposits far from the slope.(3)Slip and extension along the preexisting fault zone were the main structural factors that drive the axial channel formation at the slope foot.(4)The sand-rich gravity sediment flows in the Ying-Qiong basin were primarily caused by the direct supply of terrigenous debris into the marine environment over the slope break.
文摘The characteristics and distribution of faults in Yinggehai basin discussed in this paper reveal the structural effects of the overpressure fluid expulsion. The rapid subsidence and mud rich intervals of the marine rocks dominate the formation of the overpressure systems and the enormous volumes of the overpressure fluids in the basin. Triggered by some faults, the overpressure fluids were expulsed rapidly from the overpressure compartments to form a series of diapirs in the basin, resulting in the dense fractures or faults and folds in the limbs of diapirs. These fractures and faults provided the migration pathway for the vertical flow of hydrocarbons, so that the gas fields arising from this process might migrate upwards to the sandstone reservoir. Therefore, the hydrocarbon accumulations are usually located in the upper parts of diapiric structures.
文摘The accurate prediction of overpressure is one of the key issues that restrict the effective development of oil and gas resources in the Yinggehai Basin. In this paper, the formation mechanism of overpressure in Yinggehai Basin is studied. Based on this mechanism, the quantitative prediction model and empirical parameters of overpressure are optimized in Yinggehai Basin and applied in engineering. The results show that the formation mechanism of overpressure in the Yinggehai Basin is complicated, and the causes of overpressure in different blocks of basin are different. The eastern block mainly develops loading-type overpressure, while the Ledong block is dominated by unloading high pressure. Different blocks should employ different abnormal high-pressure prediction models. The East block mainly adopts the Eaton method, and the Ledong block mainly utilizes the Bowers method. The empirical parameters of different models can be determined according to the actual drilling conditions. The practical application demonstrates that the abnormal high-pressure prediction error is within 2%, and it is able to satisfy the requirements of on-site engineering.
基金Supported by the China National Science and Technology Major Project(2016ZX05024-005)
文摘The subtle strike-slip tectonic deformation and its relationship to deposition, overpressure and hydrocarbon migration were studied on the basis of systematic sorting of tectonic data.(1) The local T(tension) fractures derived from sinistral strike-slip process were formed before 10.5 Ma, large in number in the nose structure of the eastern slope, and reactivated episodically under the effect of fluid overpressure in the late stage, they served as dominant vertical hydrocarbon migration paths in the slope area of basin.(2) The dextral strike-slip extension was conducive to the increase of depositional rate and formation of regional under-compacted seal, and induced generation of local T fractures which triggered the development of diapirs; in turn, the development of diapirs made T fractures grow in size further.(3) The sinistral strike-slip process weakened after 10.5 Ma, causing tectonic movement characterized by compression in the north and rotational extension in the south, and the uplift and erosion of strata in Hanoi sag and a surge in clastics supply for south Yinggehai sag. Finally, migrating slope channelized submarine fans and superimposed basin floor fans were developed respectively on the asymmetrical east and west slopes of the Yinggehai sag.
