By analyzing the structural background,petroleum geological conditions,and typical regional(paleo) oil and gas reservoirs in marine ultra-deep oil and gas regions in China,this paper reveals the evolution processes of...By analyzing the structural background,petroleum geological conditions,and typical regional(paleo) oil and gas reservoirs in marine ultra-deep oil and gas regions in China,this paper reveals the evolution processes of the marine ultra-deep oil and gas reservoirs and the key controlling factors of accumulation.The marine ultra-deep oil and gas resources in China are buried at depth of greater than 6000 m,and are mainly distributed in the Precambrian and Lower Paleozoic strata in the Sichuan,Tarim and Ordos cratonic basins.The development of marine ultra-deep source rocks in China is controlled by cratonic rifts and cratonic depressions with the background of global supercontinent breakup-convergence cycles.The source rocks in Sichuan Basin have the most developed strata,followed by Tarim Basin,and the development strata and scale of Ordos Basin needs to be further confirmed.The marine ultra-deep reservoir in China is dominated by carbonate rocks,and the reservoir performance is controlled by high-energy sedimentary environment in the early stage,superimposed corrosion and fracture in the later stage.The regional caprocks are dominated by gypsum salt rocks,shale,and tight carbonate rock.The ultra-deep oil and gas fields in China have generally experienced two stages of oil-reservoir forming,cracking(or partial cracking) of paleo-oil reservoirs,and late finalization of cracked gas(or highly mature to over mature oil and gas).The oil and gas accumulation is controlled by static and dynamic geological elements jointly.Major hydrocarbon generation center,high quality and large-scale reservoir resulted from karstification of high energy facies belt,thick gypsum rock or shale caprock,and stable trapping and preservation conditions are the key factors for accumulation of ultra-deep oil and gas.We propose three favorable exploration directions,i.e.the areas around intracratonic rift and intracratonic depression,and craton margin.展开更多
Hyperpycnal deposits has gradually emerged as a current research hotspot,with a special focus on lacustrine hyperpycnal deposits.However,our understanding of the formation mechanism and distribution of high-quality re...Hyperpycnal deposits has gradually emerged as a current research hotspot,with a special focus on lacustrine hyperpycnal deposits.However,our understanding of the formation mechanism and distribution of high-quality reservoirs in hyperpycnal deposits remains insufficient.In this study,the formation mechanism and distribution of high-quality reservoirs in the second member of the Sangonghe Formation are studied through sedimentology,petrology,and geochemistry,and 10 types of lithofacies were identified in the depositional sequences of the hyperpycnal flow.These can be summarized as gravelly bed to suspended load lithofacies association(GBS),gravelly reverse to normal compound-graded(GNR),coarse-grained sandy suspended load(CSS),and fine-grained sandy suspended load(FSS)lithofacies associations.The hyperpycnal system can be divided into four individual units:restricted channel,unrestricted channel,lobe,and levee.The reservoir quality varies with lithofacies.Gravelly bed load lithofacies has coarse grain sizes,high content of rigid minerals,and soluble components,such as magmatic rock fragments.Therefore,the gravelly bed load lithofacies reservoir has developed dissolution pores and well-preserved pore throats.Its reservoir quality is good.GBS and GNR are the main lithofacies associations in the restricted channel,where type I and type II reservoirs developed.The unrestricted channel is dominated by the CSS lithofacies association,with type III reservoirs developed.The lobe is dominated by the CSS and FSS lithofacies associations,with type III and type IV reservoirs developed.High-quality reservoirs mainly develop in the restricted and unrestricted channels,whereas reservoirs in the lobe have poor quality.The levees are dominated by siltstone and gray mudstone and are generally nonreservoirs.展开更多
Due to the continuous water percolation and soaking during development of the oilfields, the dynamic balance of a reservoir is altered by the fluid; and the rock framework, pores and throats will be reformed and destr...Due to the continuous water percolation and soaking during development of the oilfields, the dynamic balance of a reservoir is altered by the fluid; and the rock framework, pores and throats will be reformed and destroyed. The interaction between the fluid and the rock leads to a series of micro geological processes, such as clastation, denudation, dissolution and deposition, in the small spaces connected by pores or throats, which control the accumulation and distribution of the remaining oil. These micro geological processes are the essential factors for the evolution of the reservoirs during development. This evolution makes the recovery of the remaining oil more complex.展开更多
Based on comprehensive analyses of occurrence,petrological observation,pore structure and geochemistry,the different reservoir characteristics and reservoir evolutionary pathways between different oolitic shoal reserv...Based on comprehensive analyses of occurrence,petrological observation,pore structure and geochemistry,the different reservoir characteristics and reservoir evolutionary pathways between different oolitic shoal reservoir types of the Feixianguan Formation on the west side of the Kaijiang-Liangping Trough have been studied.There exist three stages of high-energy slope break belts in the Feixianguan period,the corresponding three stages of oolitic shoals gradually migrating in the direction of the trough.Three types of oolitic shoal reservoirs,namely,residual-oolitic dolomite,mold-oolitic dolomite and sparry oolitic limestone,were formed during sedimentary-diagenetic evolution,the pore types being intergranular dissolved pore,mold pore(or intragranular dissolved pore)and residual intergranular pore,respectively.The petrology,physical properties and pore structure of the different types of oolitic shoal reservoirs are quite different.Residual-oolitic dolomite reservoirs have the best quality,while sparry oolitic limestone reservoirs have the poorest.Combined with analyses of trace elements,rare earth elements and carbon-oxygen isotopes,it is suggested that the formation of residual-oolitic dolomite reservoirs is jointly controlled by penesaline seawater seepage-reflux dolomitization and hydrothermal dolomitization.Mold-pore oolitic dolomite reservoirs are controlled by penesaline seawater seepage-reflux dolomitization and meteoric water solution.The burial dissolution of organic acid not only further improves the reservoir qualities of previously formed oolitic dolomite reservoirs,but also preserves residual intergranular pores in the sparry oolitic limestone reservoirs.展开更多
In the Xihu Sag,the reservoirs of the Paleogene Huagang formation have entered the middle diagenetic stage A and the rock physical properties of the water layer are considerably more suitable for the gas migration and...In the Xihu Sag,the reservoirs of the Paleogene Huagang formation have entered the middle diagenetic stage A and the rock physical properties of the water layer are considerably more suitable for the gas migration and storage than those of the present gas layer,indicating the inversion of the physical properties.In this study,core samples were collected from the corresponding reservoir to conduct water-rock reaction experiments in acidic,alkaline,and neutral systems under the specific temperature and pressure.The reasons for the inversion of physical properties were investigated based on the experiment results in reservoir diagenetic environments.The inversion of physical properties can be attributed to the fact that the diagenetic environment around the gas-water interface controls the water-rock reaction effect.With different types of acidic substances,two different situations corresponding to inverted physical properties were analyzed along with the corresponding mechanisms.When the pore fluid is acidic,the physical properties make the overall water layer a better reservoir space than the gas layer,which can be referred to as the overall inversion of physical properties.When the fluid were generally neutral or weakly alkaline and the gas layer was rich in CO2,only the physical properties of the water layer adjacent to the gas-water interface were more favorable for the gas migration than those of the gas layer.This phenomenon can be referred to as the near-interface inversion of physical properties.展开更多
There are various types of natural gas resources in coal measures,making them major targets for natural gas exploration and development in China.In view of the particularity of the whole petroleum system of coal measu...There are various types of natural gas resources in coal measures,making them major targets for natural gas exploration and development in China.In view of the particularity of the whole petroleum system of coal measures and the reservoir-forming evolution of natural gas in coal,this study reveals the formation,enrichment characteristics and distribution laws of coal-rock gas by systematically reviewing the main types and geological characteristics of natural gas in the whole petroleum system of coal measures.First,natural gas in the whole petroleum system of coal measures is divided into two types,conventional gas and unconventional gas,according to its occurrence characteristics and accumulation mechanism,and into six types,distal detrital rock gas,special rock gas,distal/proximal tight sandstone gas,inner-source tight sandstone gas,shale gas,and coal-rock gas,according to its source and reservoir lithology.The natural gas present in coal-rock reservoirs is collectively referred to as coal-rock gas.Existing data indicate significant differences in the geological characteristics of coal-rock gas exploration and development between shallow and deep layers in the same area,with the transition depth boundary generally 1500-2000 m.Based on the current understanding of coal-rock gas and respecting the historical usage conventions of coalbed methane terminology,coal-rock gas can be divided into deep coal-rock gas and shallow coalbed methane according to burial depth.Second,according to the research concept of“full-process reservoir formation”in the theory of the whole petroleum system of coal measures,based on the formation and evolution of typical coal-rock gas reservoirs,coal-rock gas is further divided into four types:primary coal-rock gas,regenerated coal-rock gas,residual coal-rock gas,and bio coal-rock gas.The first two belong to deep coal-rock gas,while the latter two belong to shallow coal-rock gas.Third,research on the coal-rock gas reservoir formation and evolution shows that shallow coal-rock gas is mainly residual coal-rock gas or bio coal-rock gas formed after geological transformation of primary coal-rock gas,with the reservoir characteristics such as low reservoir pressure,low gas saturation,adsorbed gas in dominance,and gas production by drainage and depressurization,while deep coal-rock gas is mainly primary coal-rock gas and regenerated coal-rock gas,with the reservoir characteristics such as high reservoir pressure,high gas saturation,abundant free gas,and no or little water.In particular,the primary coal-rock gas is wide in distribution,large in resource quantity,and good in reservoir quality,making it the most favorable type of coal-rock gas for exploration and development.展开更多
Halimeda is one of the major reef-building algas in the middle Miocene of Xisha, and one of the significant reef-building algas in the algal reef oil and gas field of the South China Sea. However, there have been few ...Halimeda is one of the major reef-building algas in the middle Miocene of Xisha, and one of the significant reef-building algas in the algal reef oil and gas field of the South China Sea. However, there have been few reports regarding the characteristics of mineral rocks, reservoir porosity and permeability layers, and sedimentation-diagenetic-evolution of fossil Halimeda systems. The present paper briefly introduces the relevant studies on chlorophyta Halimeda and the research status of oil and gas exploration. Through the 1 043 m core of the Xichen-1 well, we studied the characteristics of the mineral rocks and porosity and permeability of the middle Miocene Halimeda of the Yongle Atoll, identified and described the segments of fossil Halimeda, and pointed out that most of the segment slides are vertical sections in ovular, irregular or long strips. The overwhelming majority of these fossil Halimeda found and studied are vertical sections instead of cross sections. In this paper, knowledge regarding the cross sections of fossil Halimeda is reported and proven to be similar with the microscopic characteristics of modern living Halimeda;fossil Halimeda are buried in superposition;it is shown that there are different structures present, including typical bio-segment structure, and due to its feature of coexisting with red alga, tying structure, twining structure and encrusting structure are all present;and finally, it is suggested to classify the fossil Halimeda into segment algal reef dolomites. In addition, all of the studied intervals are moderately dolomitized. Secondary microcrystalline-dolosparite dominates the original aragonite raphide zones, and aphanitic-micrite dolomite plays the leading role in the cortexes and medullas;in the aragonite raphide zones between medulla and cysts, secondary dissolved pores and intercrystalline pores are formed inside the segments, and algal frame holes are formed between segments;therefore, a pore space network system （dissolved pores＋intragranular dissolved pores—intercrystalline pores＋algal frame holes） is established. Segment Halimeda dolomite has a porosity of 16.2%–46.1%, a permeability of 0.203×10^–3–2 641×10^–3μm^2, and a throat radius of 23.42–90.43μm, therefore it is shown to be a good oil and gas reservoir. For the reasons mentioned above, we suggest building the neogene organic reef-modern reef sedimentation-diagenetic-evolution models for the Xisha Islands.展开更多
The deeply buried(>4500 m) Cambrian Xixiangchi Formation in the Sichuan Basin, southwestern China, hosts significant reserves of natural gas. A comprehensive analysis combining petrographic, paleo-thermometric, geo...The deeply buried(>4500 m) Cambrian Xixiangchi Formation in the Sichuan Basin, southwestern China, hosts significant reserves of natural gas. A comprehensive analysis combining petrographic, paleo-thermometric, geochemical, and petrophysical materials of the dolostone from the Xixiangchi Formation was conducted to provide insight into deeply buried carbonate reservoirs and decipher the complex diagenetic history. Dolomite-mudstone, fine-crystalline dolostone, and fine-crystalline dolomite cement of the Xixiangchi Formation underwent sabkha and reflux dolomitization. Medium-to coarse-crystalline dolostone, dolo-grainstone, and medium-to coarse-crystalline dolomite cements were then formed by burial dolomitization. These dolomites display δ13C ratios and REE patterns comparable to seawater, with progressively depleted δ18O ratios at greater burial depths. Dolo-grainstone originating from the platform shoal facies exhibits higher primary porosities and well-developed inter-particle pores compared to dolo-mudstone and crystalline dolostone lithologies, which are typically associated with the low-energy tidal flat and/or restricted platform environments. The initial spatial heterogeneity of primary porosity was subsequently modified by meteoric alteration and repeated episodes of dolomitization, which contributed to the development of secondary porosity. These processes increased the resistivity to compaction, and open fractures increased reservoir permeability. During the deep burial regime, saddle dolomite and calcite cements were precipitated at high fluid temperatures(up to 220℃). Thermochemical sulfate reduction is characterized by the occurrence of anhydrite, hydrocarbon, and high homogenization temperatures and significantly low δ13C ratios(av.=-23.7‰) of calcite cements. Deep burial dissolution is significantly constrained by: corrosion of late diagenetic minerals, and the occurrence of bitumen in the center of pores. Mechanisms for the deep-burial dissolution include hydrothermal alteration and thermochemical sulfate reduction. This study indicates the complex diagenetic evolution of Cambrian Xixiangchi Formation, providing significant insights into global deep-burial carbonate reservoir potential.展开更多
Based on objective data collected from interviews in typical villages of the Three Gorges Reservoir Area, the present study devised three livelihood scenarios related to rural transformation development： agricultural...Based on objective data collected from interviews in typical villages of the Three Gorges Reservoir Area, the present study devised three livelihood scenarios related to rural transformation development： agriculturally dominant livelihood, multiple-type livelihood and non-agriculturally dominant livelihood. Moreover, the present study reports the trend characteristics of nonpoint source pollution load of crop farming in relation to the transformation of dominant livelihood types, and discussed the primary factors which affect livelihood type transformations. Results indicated the following：（1） The current farmland pattern shows a trend of diversification as self-cultivation, cropland transfer and fallow in the sample region. Dynamic characteristics of cultivated land present a special feature that is more ＂transfer-into＂ than ＂transfer-out＂. Various scales of planting are represented among the various households, according to the following decreasing order： half-labor household ＆gt; non-labor household ＆gt; adequate labor household.（2） The highest pollution loading produced by crop farming occurs in half-labor households while the lowest occurs in non-labor households. With increasing labor, the pollution load per unit area tends to first increase and then decrease within families with enough labor.（3） As the type of livelihood transitions from agriculturally dominant to non-agriculturally dominant, the maximum reduction of total pollution loading produced by the agricultural industry can reach 72.01%. Compared to agriculturally dominant livelihoods, multiple-type livelihoods produce a pollution load reduction yield of 19.61%-29.85%, and non-agriculturally dominant livelihoods reduce the pollution load yield by 35.20%-72.01%. However, the rate of reduction of total nitrogen is not the same as total phosphorus.（4） The non-agricultural characteristics of labor allocation and income promote the transformation from dominant livelihood types to non-agricultural livelihoods, while potential revenue conversion follows a similar trend. In addition, different household types do not display identical conversion rates, according to the following decreasing order： enough labor household ＆gt; half-labor household ＆gt; non-labor household.（5） During rapid urbanization and the building of new industrial systems, the livelihood types of rural households have been further transformed to off-farm household types in the mountainous region; this process will lead to the further reduction of pollution load generated by planting and agriculture. Hence, significant decreases in the planting pollution load necessitate the development of control measures to enhance transformations from agricultural to off-farm livelihoods.展开更多
The southern Junggar Basin has enormous hydrocarbon mainly from the Jurassic and Permian source rocks,which indicated the importance of exploration of the deeply buried Jurassic reservoirs,therefore,the study of the d...The southern Junggar Basin has enormous hydrocarbon mainly from the Jurassic and Permian source rocks,which indicated the importance of exploration of the deeply buried Jurassic reservoirs,therefore,the study of the deeply buried Upper Jurassic Qigu Formation(J_(3)q)reservoirs in Well DS-1 in the Dushanzi anticline was carried out through microscopic observation and measurement,nuclear magnetic resonance(NMR),scanning electron microscopy(SEM)and high pressure mercury injection.Results showed that the main reservoir storage spaces in the deeply buried Upper Jurassic Qigu Formation reservoirs were fractures and dissolved pores.The J_(3)q reservoirs with low porosity and permeability values of 0e12%and(0e5)×10^(-3)mm^(2) respectively,were generally tight.According to the mercury injection data,heterogeneity existed in the deeply buried Qigu Formation reservoirs with inhomogeneous pores and changeable sizes of pores throats.Pores and pore throats in the silt-fine sandstones of the lower Qigu Formation(J_(3)q^(1))were more big and wide respectively than that in the argillaceous siltstones of the upper Qigu Formation(J_(3)q^(3)).Reservoirs in J_(3)q^(1) had more mobile fluid and better conductivities than reservoirs in J_(3)q^(3).The strong compaction and multistage diagenesis resulted in the tight J_(3)q reservoirs.Anhydrite and quartz cementation,and various authigenetic minerals(e.g.hematite,kaolinite,illite/smectite formation,illite,chlorite and zeolite)filled in the pores.The homogenization temperature of brine inclusions(63.1e161.7℃)in quartz overgrowth indicated the quartz had grown since the late Eocene.Due to the Tian Shan reactivity in the Late Cenozoic,the structure fractures were developed and promoted dissolution by oil and formation water in the reservoirs of J3q1.展开更多
Commercial exploration and development of deep buried coalbed methane (CBM) in Daning-Jixian Block, eastern margin of Ordos Basin, have rapidly increased in recent decades. Gas content, saturation and well productivit...Commercial exploration and development of deep buried coalbed methane (CBM) in Daning-Jixian Block, eastern margin of Ordos Basin, have rapidly increased in recent decades. Gas content, saturation and well productivity show significant heterogeneity in this area. To better understand the geological controlling mechanism on gas distribution heterogeneity, the burial history, hydrocarbon generation history and tectonic evolution history were studied by numerical simulation and experimental simulation, which could provide guidance for further development of CBM in this area. The burial history of coal reservoir can be classified into six stages, i.e., shallowly buried stage, deeply burial stage, uplifting stage, short-term tectonic subsidence stage, large-scale uplifting stage, sustaining uplifting and structural inversion stage. The organic matter in coal reservoir experienced twice hydrocarbon generation. Primary and secondary hydrocarbon generation processes were formed by the Early and Middle Triassic plutonic metamorphism and Early Cretaceous regional magmatic thermal metamorphism, respectively. Five critical tectonic events of the Indosinian, Yanshanian and Himalayan orogenies affect different stages of the CBM reservoir accumulation process. The Indosinian orogeny mainly controls the primary CBM generation. The Yanshanian Orogeny dominates the second gas generation and migration processes. The Himalayan orogeny mainly affects the gas dissipation process and current CBM distribution heterogeneity.展开更多
基金Supported by the National Key R&D Program (2017YFC0603106)。
文摘By analyzing the structural background,petroleum geological conditions,and typical regional(paleo) oil and gas reservoirs in marine ultra-deep oil and gas regions in China,this paper reveals the evolution processes of the marine ultra-deep oil and gas reservoirs and the key controlling factors of accumulation.The marine ultra-deep oil and gas resources in China are buried at depth of greater than 6000 m,and are mainly distributed in the Precambrian and Lower Paleozoic strata in the Sichuan,Tarim and Ordos cratonic basins.The development of marine ultra-deep source rocks in China is controlled by cratonic rifts and cratonic depressions with the background of global supercontinent breakup-convergence cycles.The source rocks in Sichuan Basin have the most developed strata,followed by Tarim Basin,and the development strata and scale of Ordos Basin needs to be further confirmed.The marine ultra-deep reservoir in China is dominated by carbonate rocks,and the reservoir performance is controlled by high-energy sedimentary environment in the early stage,superimposed corrosion and fracture in the later stage.The regional caprocks are dominated by gypsum salt rocks,shale,and tight carbonate rock.The ultra-deep oil and gas fields in China have generally experienced two stages of oil-reservoir forming,cracking(or partial cracking) of paleo-oil reservoirs,and late finalization of cracked gas(or highly mature to over mature oil and gas).The oil and gas accumulation is controlled by static and dynamic geological elements jointly.Major hydrocarbon generation center,high quality and large-scale reservoir resulted from karstification of high energy facies belt,thick gypsum rock or shale caprock,and stable trapping and preservation conditions are the key factors for accumulation of ultra-deep oil and gas.We propose three favorable exploration directions,i.e.the areas around intracratonic rift and intracratonic depression,and craton margin.
基金supported by the State Key Laboratory of Petroleum Resources and Engineering,China University of Petroleum(Beijing).
文摘Hyperpycnal deposits has gradually emerged as a current research hotspot,with a special focus on lacustrine hyperpycnal deposits.However,our understanding of the formation mechanism and distribution of high-quality reservoirs in hyperpycnal deposits remains insufficient.In this study,the formation mechanism and distribution of high-quality reservoirs in the second member of the Sangonghe Formation are studied through sedimentology,petrology,and geochemistry,and 10 types of lithofacies were identified in the depositional sequences of the hyperpycnal flow.These can be summarized as gravelly bed to suspended load lithofacies association(GBS),gravelly reverse to normal compound-graded(GNR),coarse-grained sandy suspended load(CSS),and fine-grained sandy suspended load(FSS)lithofacies associations.The hyperpycnal system can be divided into four individual units:restricted channel,unrestricted channel,lobe,and levee.The reservoir quality varies with lithofacies.Gravelly bed load lithofacies has coarse grain sizes,high content of rigid minerals,and soluble components,such as magmatic rock fragments.Therefore,the gravelly bed load lithofacies reservoir has developed dissolution pores and well-preserved pore throats.Its reservoir quality is good.GBS and GNR are the main lithofacies associations in the restricted channel,where type I and type II reservoirs developed.The unrestricted channel is dominated by the CSS lithofacies association,with type III reservoirs developed.The lobe is dominated by the CSS and FSS lithofacies associations,with type III and type IV reservoirs developed.High-quality reservoirs mainly develop in the restricted and unrestricted channels,whereas reservoirs in the lobe have poor quality.The levees are dominated by siltstone and gray mudstone and are generally nonreservoirs.
文摘Due to the continuous water percolation and soaking during development of the oilfields, the dynamic balance of a reservoir is altered by the fluid; and the rock framework, pores and throats will be reformed and destroyed. The interaction between the fluid and the rock leads to a series of micro geological processes, such as clastation, denudation, dissolution and deposition, in the small spaces connected by pores or throats, which control the accumulation and distribution of the remaining oil. These micro geological processes are the essential factors for the evolution of the reservoirs during development. This evolution makes the recovery of the remaining oil more complex.
基金This research was supported jointly by the National Natural Science Foundation of China(Grant No.41972165)National Science and Technology Major Project(Grant No.2017ZX05008-004-008)National Science and Technology Major Project(Grant No.2016E-0607).
文摘Based on comprehensive analyses of occurrence,petrological observation,pore structure and geochemistry,the different reservoir characteristics and reservoir evolutionary pathways between different oolitic shoal reservoir types of the Feixianguan Formation on the west side of the Kaijiang-Liangping Trough have been studied.There exist three stages of high-energy slope break belts in the Feixianguan period,the corresponding three stages of oolitic shoals gradually migrating in the direction of the trough.Three types of oolitic shoal reservoirs,namely,residual-oolitic dolomite,mold-oolitic dolomite and sparry oolitic limestone,were formed during sedimentary-diagenetic evolution,the pore types being intergranular dissolved pore,mold pore(or intragranular dissolved pore)and residual intergranular pore,respectively.The petrology,physical properties and pore structure of the different types of oolitic shoal reservoirs are quite different.Residual-oolitic dolomite reservoirs have the best quality,while sparry oolitic limestone reservoirs have the poorest.Combined with analyses of trace elements,rare earth elements and carbon-oxygen isotopes,it is suggested that the formation of residual-oolitic dolomite reservoirs is jointly controlled by penesaline seawater seepage-reflux dolomitization and hydrothermal dolomitization.Mold-pore oolitic dolomite reservoirs are controlled by penesaline seawater seepage-reflux dolomitization and meteoric water solution.The burial dissolution of organic acid not only further improves the reservoir qualities of previously formed oolitic dolomite reservoirs,but also preserves residual intergranular pores in the sparry oolitic limestone reservoirs.
基金This research was supported financially by the National Key Technology Research and Development Program of China during the‘13th Five-Year Plan’(No.2016ZX05027-002-006).
文摘In the Xihu Sag,the reservoirs of the Paleogene Huagang formation have entered the middle diagenetic stage A and the rock physical properties of the water layer are considerably more suitable for the gas migration and storage than those of the present gas layer,indicating the inversion of the physical properties.In this study,core samples were collected from the corresponding reservoir to conduct water-rock reaction experiments in acidic,alkaline,and neutral systems under the specific temperature and pressure.The reasons for the inversion of physical properties were investigated based on the experiment results in reservoir diagenetic environments.The inversion of physical properties can be attributed to the fact that the diagenetic environment around the gas-water interface controls the water-rock reaction effect.With different types of acidic substances,two different situations corresponding to inverted physical properties were analyzed along with the corresponding mechanisms.When the pore fluid is acidic,the physical properties make the overall water layer a better reservoir space than the gas layer,which can be referred to as the overall inversion of physical properties.When the fluid were generally neutral or weakly alkaline and the gas layer was rich in CO2,only the physical properties of the water layer adjacent to the gas-water interface were more favorable for the gas migration than those of the gas layer.This phenomenon can be referred to as the near-interface inversion of physical properties.
基金Supported by the National Science and Technology Major Project for New Oil and Gas Exploration and Development(2025ZD1404200)Forward-looking and Fundamental Project of PetroChina Company Limited(2024DJ23)Scientific Research and Technology Development Project of PetroChina Research Institute of Petroleum Exploration&Development(2024vzz).
文摘There are various types of natural gas resources in coal measures,making them major targets for natural gas exploration and development in China.In view of the particularity of the whole petroleum system of coal measures and the reservoir-forming evolution of natural gas in coal,this study reveals the formation,enrichment characteristics and distribution laws of coal-rock gas by systematically reviewing the main types and geological characteristics of natural gas in the whole petroleum system of coal measures.First,natural gas in the whole petroleum system of coal measures is divided into two types,conventional gas and unconventional gas,according to its occurrence characteristics and accumulation mechanism,and into six types,distal detrital rock gas,special rock gas,distal/proximal tight sandstone gas,inner-source tight sandstone gas,shale gas,and coal-rock gas,according to its source and reservoir lithology.The natural gas present in coal-rock reservoirs is collectively referred to as coal-rock gas.Existing data indicate significant differences in the geological characteristics of coal-rock gas exploration and development between shallow and deep layers in the same area,with the transition depth boundary generally 1500-2000 m.Based on the current understanding of coal-rock gas and respecting the historical usage conventions of coalbed methane terminology,coal-rock gas can be divided into deep coal-rock gas and shallow coalbed methane according to burial depth.Second,according to the research concept of“full-process reservoir formation”in the theory of the whole petroleum system of coal measures,based on the formation and evolution of typical coal-rock gas reservoirs,coal-rock gas is further divided into four types:primary coal-rock gas,regenerated coal-rock gas,residual coal-rock gas,and bio coal-rock gas.The first two belong to deep coal-rock gas,while the latter two belong to shallow coal-rock gas.Third,research on the coal-rock gas reservoir formation and evolution shows that shallow coal-rock gas is mainly residual coal-rock gas or bio coal-rock gas formed after geological transformation of primary coal-rock gas,with the reservoir characteristics such as low reservoir pressure,low gas saturation,adsorbed gas in dominance,and gas production by drainage and depressurization,while deep coal-rock gas is mainly primary coal-rock gas and regenerated coal-rock gas,with the reservoir characteristics such as high reservoir pressure,high gas saturation,abundant free gas,and no or little water.In particular,the primary coal-rock gas is wide in distribution,large in resource quantity,and good in reservoir quality,making it the most favorable type of coal-rock gas for exploration and development.
基金The National Science and Technology Major Project for Large Oil-Gas Fields and Coal-formed Gas Development under contract Nos 2008ZX05023 and 2011ZX05025-002the National Natural Science Foundation of China under contract Nos 49206061 and 41106064the National Basic Research Program(973 Program) of China under contract Nos 2012CB956004 and 2009CB219406
文摘Halimeda is one of the major reef-building algas in the middle Miocene of Xisha, and one of the significant reef-building algas in the algal reef oil and gas field of the South China Sea. However, there have been few reports regarding the characteristics of mineral rocks, reservoir porosity and permeability layers, and sedimentation-diagenetic-evolution of fossil Halimeda systems. The present paper briefly introduces the relevant studies on chlorophyta Halimeda and the research status of oil and gas exploration. Through the 1 043 m core of the Xichen-1 well, we studied the characteristics of the mineral rocks and porosity and permeability of the middle Miocene Halimeda of the Yongle Atoll, identified and described the segments of fossil Halimeda, and pointed out that most of the segment slides are vertical sections in ovular, irregular or long strips. The overwhelming majority of these fossil Halimeda found and studied are vertical sections instead of cross sections. In this paper, knowledge regarding the cross sections of fossil Halimeda is reported and proven to be similar with the microscopic characteristics of modern living Halimeda;fossil Halimeda are buried in superposition;it is shown that there are different structures present, including typical bio-segment structure, and due to its feature of coexisting with red alga, tying structure, twining structure and encrusting structure are all present;and finally, it is suggested to classify the fossil Halimeda into segment algal reef dolomites. In addition, all of the studied intervals are moderately dolomitized. Secondary microcrystalline-dolosparite dominates the original aragonite raphide zones, and aphanitic-micrite dolomite plays the leading role in the cortexes and medullas;in the aragonite raphide zones between medulla and cysts, secondary dissolved pores and intercrystalline pores are formed inside the segments, and algal frame holes are formed between segments;therefore, a pore space network system （dissolved pores＋intragranular dissolved pores—intercrystalline pores＋algal frame holes） is established. Segment Halimeda dolomite has a porosity of 16.2%–46.1%, a permeability of 0.203×10^–3–2 641×10^–3μm^2, and a throat radius of 23.42–90.43μm, therefore it is shown to be a good oil and gas reservoir. For the reasons mentioned above, we suggest building the neogene organic reef-modern reef sedimentation-diagenetic-evolution models for the Xisha Islands.
基金funded by the National Natural Science Foundation Project of China(U22B6002)the Major Science&Technology Project of PetroChina(No.2023ZZ02)the Prospective Basic Technology Research Project of PetroChina(2021DJ0605).
文摘The deeply buried(>4500 m) Cambrian Xixiangchi Formation in the Sichuan Basin, southwestern China, hosts significant reserves of natural gas. A comprehensive analysis combining petrographic, paleo-thermometric, geochemical, and petrophysical materials of the dolostone from the Xixiangchi Formation was conducted to provide insight into deeply buried carbonate reservoirs and decipher the complex diagenetic history. Dolomite-mudstone, fine-crystalline dolostone, and fine-crystalline dolomite cement of the Xixiangchi Formation underwent sabkha and reflux dolomitization. Medium-to coarse-crystalline dolostone, dolo-grainstone, and medium-to coarse-crystalline dolomite cements were then formed by burial dolomitization. These dolomites display δ13C ratios and REE patterns comparable to seawater, with progressively depleted δ18O ratios at greater burial depths. Dolo-grainstone originating from the platform shoal facies exhibits higher primary porosities and well-developed inter-particle pores compared to dolo-mudstone and crystalline dolostone lithologies, which are typically associated with the low-energy tidal flat and/or restricted platform environments. The initial spatial heterogeneity of primary porosity was subsequently modified by meteoric alteration and repeated episodes of dolomitization, which contributed to the development of secondary porosity. These processes increased the resistivity to compaction, and open fractures increased reservoir permeability. During the deep burial regime, saddle dolomite and calcite cements were precipitated at high fluid temperatures(up to 220℃). Thermochemical sulfate reduction is characterized by the occurrence of anhydrite, hydrocarbon, and high homogenization temperatures and significantly low δ13C ratios(av.=-23.7‰) of calcite cements. Deep burial dissolution is significantly constrained by: corrosion of late diagenetic minerals, and the occurrence of bitumen in the center of pores. Mechanisms for the deep-burial dissolution include hydrothermal alteration and thermochemical sulfate reduction. This study indicates the complex diagenetic evolution of Cambrian Xixiangchi Formation, providing significant insights into global deep-burial carbonate reservoir potential.
基金Chongqing University Innovation Team for 2016,No.CXTDX201601017Chongqing Research Program of Basic Research and Frontier Technology,No.cstc2017jcyj BX0024
文摘Based on objective data collected from interviews in typical villages of the Three Gorges Reservoir Area, the present study devised three livelihood scenarios related to rural transformation development： agriculturally dominant livelihood, multiple-type livelihood and non-agriculturally dominant livelihood. Moreover, the present study reports the trend characteristics of nonpoint source pollution load of crop farming in relation to the transformation of dominant livelihood types, and discussed the primary factors which affect livelihood type transformations. Results indicated the following：（1） The current farmland pattern shows a trend of diversification as self-cultivation, cropland transfer and fallow in the sample region. Dynamic characteristics of cultivated land present a special feature that is more ＂transfer-into＂ than ＂transfer-out＂. Various scales of planting are represented among the various households, according to the following decreasing order： half-labor household ＆gt; non-labor household ＆gt; adequate labor household.（2） The highest pollution loading produced by crop farming occurs in half-labor households while the lowest occurs in non-labor households. With increasing labor, the pollution load per unit area tends to first increase and then decrease within families with enough labor.（3） As the type of livelihood transitions from agriculturally dominant to non-agriculturally dominant, the maximum reduction of total pollution loading produced by the agricultural industry can reach 72.01%. Compared to agriculturally dominant livelihoods, multiple-type livelihoods produce a pollution load reduction yield of 19.61%-29.85%, and non-agriculturally dominant livelihoods reduce the pollution load yield by 35.20%-72.01%. However, the rate of reduction of total nitrogen is not the same as total phosphorus.（4） The non-agricultural characteristics of labor allocation and income promote the transformation from dominant livelihood types to non-agricultural livelihoods, while potential revenue conversion follows a similar trend. In addition, different household types do not display identical conversion rates, according to the following decreasing order： enough labor household ＆gt; half-labor household ＆gt; non-labor household.（5） During rapid urbanization and the building of new industrial systems, the livelihood types of rural households have been further transformed to off-farm household types in the mountainous region; this process will lead to the further reduction of pollution load generated by planting and agriculture. Hence, significant decreases in the planting pollution load necessitate the development of control measures to enhance transformations from agricultural to off-farm livelihoods.
基金The work was supported by the National Science and Technology Major Project of China(No.2017ZX05008-001,No.2016ZX05003-002)the 13th Five-year Program of PetroChina(2016B-0502).
文摘The southern Junggar Basin has enormous hydrocarbon mainly from the Jurassic and Permian source rocks,which indicated the importance of exploration of the deeply buried Jurassic reservoirs,therefore,the study of the deeply buried Upper Jurassic Qigu Formation(J_(3)q)reservoirs in Well DS-1 in the Dushanzi anticline was carried out through microscopic observation and measurement,nuclear magnetic resonance(NMR),scanning electron microscopy(SEM)and high pressure mercury injection.Results showed that the main reservoir storage spaces in the deeply buried Upper Jurassic Qigu Formation reservoirs were fractures and dissolved pores.The J_(3)q reservoirs with low porosity and permeability values of 0e12%and(0e5)×10^(-3)mm^(2) respectively,were generally tight.According to the mercury injection data,heterogeneity existed in the deeply buried Qigu Formation reservoirs with inhomogeneous pores and changeable sizes of pores throats.Pores and pore throats in the silt-fine sandstones of the lower Qigu Formation(J_(3)q^(1))were more big and wide respectively than that in the argillaceous siltstones of the upper Qigu Formation(J_(3)q^(3)).Reservoirs in J_(3)q^(1) had more mobile fluid and better conductivities than reservoirs in J_(3)q^(3).The strong compaction and multistage diagenesis resulted in the tight J_(3)q reservoirs.Anhydrite and quartz cementation,and various authigenetic minerals(e.g.hematite,kaolinite,illite/smectite formation,illite,chlorite and zeolite)filled in the pores.The homogenization temperature of brine inclusions(63.1e161.7℃)in quartz overgrowth indicated the quartz had grown since the late Eocene.Due to the Tian Shan reactivity in the Late Cenozoic,the structure fractures were developed and promoted dissolution by oil and formation water in the reservoirs of J3q1.
基金This research was funded by the National Natural Science Foundation of China (Grant No. 41902178)National Science and Technology Major Project (Oil & Gas) (No. 2016ZX05065)+1 种基金Natural Science Foundation of Shanxi Province, China (No. 20210302123165)Open Fund of Beijing Key Laboratory of Unconventional Natural Gas Geological Evaluation and Development Engineering, China University of Geosciences (Beijing) (No. 2019BJ02001).
文摘Commercial exploration and development of deep buried coalbed methane (CBM) in Daning-Jixian Block, eastern margin of Ordos Basin, have rapidly increased in recent decades. Gas content, saturation and well productivity show significant heterogeneity in this area. To better understand the geological controlling mechanism on gas distribution heterogeneity, the burial history, hydrocarbon generation history and tectonic evolution history were studied by numerical simulation and experimental simulation, which could provide guidance for further development of CBM in this area. The burial history of coal reservoir can be classified into six stages, i.e., shallowly buried stage, deeply burial stage, uplifting stage, short-term tectonic subsidence stage, large-scale uplifting stage, sustaining uplifting and structural inversion stage. The organic matter in coal reservoir experienced twice hydrocarbon generation. Primary and secondary hydrocarbon generation processes were formed by the Early and Middle Triassic plutonic metamorphism and Early Cretaceous regional magmatic thermal metamorphism, respectively. Five critical tectonic events of the Indosinian, Yanshanian and Himalayan orogenies affect different stages of the CBM reservoir accumulation process. The Indosinian orogeny mainly controls the primary CBM generation. The Yanshanian Orogeny dominates the second gas generation and migration processes. The Himalayan orogeny mainly affects the gas dissipation process and current CBM distribution heterogeneity.
