This study examines the characteristics and pore evolution of the Baikouquan conglomerate reservoir in the Mahu sag of the Junggar Basin from original sedimentation and diagenesis.Analysis is based on core observation...This study examines the characteristics and pore evolution of the Baikouquan conglomerate reservoir in the Mahu sag of the Junggar Basin from original sedimentation and diagenesis.Analysis is based on core observation,thin section,X-ray diffraction,cathodoluminescence and image analysis,and combined with physical property and well log data.The results show that conglomerate reservoir in the Baikouquan Formation can be divided into three lithofacies types:TypeⅠis argillaceous filling conglomerate facies,in which cementation and dissolution are not developed,and the interstitial material is mainly argillaceous;TypeⅡis tuffaceous filling in fine conglomerate facies,in which volcanic rock debris,illite and dissolution are developed;TypeⅢis sandstone filling conglomerate facies,in which cementation and dissolution are developed.The reservoir undergoes complex diagenesis,and the diagenetic sequence is:compaction→early chlorite film→early calcite cementation→detritus,feldspar and tuffaceous dissolution→quartz secondary enlargement→late calcite cementation→oil invasion→forming illite.Quantitative study of pore evolution shows that dissolution and calcite cementation are relatively developed in lithofacies Type III,and that compaction has a great influence on lithofacies TypeⅠand II.According to comprehensive evaluation of lithofacies,diagenesis and pore structure characteristics,the reservoir space type is mainly the dissolution pore.It is mainly primarily mainly composed of lithofacies Type III,thickness of the gravel body is more than 25 m,porosity is generally more than 12%,which represents favorable conditions for the distribution of favorable reservoir.展开更多
The evolution of shale reservoirs is mainly related to two functions:mechanical compaction controlled by ground stress and chemical compaction controlled by thermal effect.Thermal simulation experiments were conducted...The evolution of shale reservoirs is mainly related to two functions:mechanical compaction controlled by ground stress and chemical compaction controlled by thermal effect.Thermal simulation experiments were conducted to simulate the chemical compaction of marine-continental transitional shale,and X-ray diffraction(XRD),CO2 adsorption,N2 adsorption and high-pressure mercury injection(MIP)were then used to characterize shale diagenesis and porosity.Moreover,simulations of mechanical compaction adhering to mathematical models were performed,and a shale compaction model was proposed considering clay content and kaolinite proportions.The advantage of this model is that the change in shale compressibility,which is caused by the transformation of clay minerals during thermal evolution,may be considered.The combination of the thermal simulation and compaction model may depict the interactions between chemical and mechanical compaction.Such interactions may then express the pore evolution of shale in actual conditions of formation.Accordingly,the obtained results demonstrated that shales having low kaolinite possess higher porosity at the same burial depth and clay mineral content,proving that other clay minerals such as illite-smectite mixed layers(I/S)and illite are conducive to the development of pores.Shales possessing a high clay mineral content have a higher porosity in shallow layers(<3500 m)and a lower porosity in deep layers(>3500 m).Both the amount and location of the increase in porosity differ at different geothermal gradients.High geothermal gradients favor the preservation of high porosity in shale at an appropriate Ro.The pore evolution of the marine-continental transitional shale is divided into five stages.Stage 2 possesses an Ro of 1.0%-1.6%and has high porosity along with a high specific surface area.Stage 3 has an Ro of 1.6%-2.0%and contains a higher porosity with a low specific surface area.Finally,Stage 4 has an Ro of 2.0%-2.9%with a low porosity and high specific surface area.展开更多
The relationship between hydrocarbon generation and the evolution of shale pore structure and its heterogeneity of continental shale from the Ordos Basin,China was quantitatively studied based on thermal simulation ex...The relationship between hydrocarbon generation and the evolution of shale pore structure and its heterogeneity of continental shale from the Ordos Basin,China was quantitatively studied based on thermal simulation experiment,mercury injection capillary pressure(MICP),gas adsorption,vitrinite reflectance(R_(o))analysis,and hydrocarbon generation test combined with Frenkel-Halsey-Hill(FHH)fractal model.The result shows that the pore volume(PV)and specific surface area(SSA)of pores with different pore sizes show a trend of decreasing first and then increasing as the maturity increases in general,R_(o)>1.59%is initially defined as a favorable stage for pore development in continental shale.Hydrocarbon generation has different effects on pore heterogeneity of different scales.For the N_(2)adsorption,the roughness of small pore surface(D_(1))decreases in the oil window;the complexity of large pore structure(D_(2))increases in the oil window but decreases in the gas window.For the MICP,the heterogeneity of small pore(D_(1))increases in the oil window and increases first and then decreases in the gas window;D_(2)remains basically constant during the whole stage and is close to 3,indicating that the heterogeneity of large pores is extremely strong and is not affected by hydrocarbon generation.展开更多
From observing cores of 18 wells,identifying 175 ordinary thin sections and 61 thin casting sections,energy spectrum analyses of 37 samples,homogenization temperature measurement of fluid inclusions of 11 samples,we d...From observing cores of 18 wells,identifying 175 ordinary thin sections and 61 thin casting sections,energy spectrum analyses of 37 samples,homogenization temperature measurement of fluid inclusions of 11 samples,we determine the types of diagenesis and pores of the Fuyu oil reservoir in the north Qijia region.We classified the pores and measured their plane porosity using CIA 2000,the software of rock image analysis,calculated the effect of different kinds of diagenesis on porosity,studied the controlling actions of diagenesis to pore evolution quantitatively,combined with burial history,thermal history and their diagenetic environments.Our results show that mechanical compaction and carbonate cementation are the major destructive diagenesed,developed during early diagenesis stages.The reduction in porosity by mechanical compaction and carbonate cementation are about 25% and 8%,while the destructive intensity of siliceous cementation and clay mineral cementation is relatively much smaller,i.e.,the reduction of porosity is about 2% and 0.2% Dissolution is constructive diagenesis,the increment of porosity is about 6%.There are four diagenesis evolution stages,during which the porosity reduced from 30%～38% to 2%～20%.Mechanical compaction and early cementation are the main diageneses in the early diagenesis stages,when porosity was reduced to 2%～10%.Dissolution is the main diagenesis of an A I substage of the middle diagenesis stage,when porosity increased 1%～8%.The dissolution of the A Ⅱ substage of the middle diagenesis stage affected by late cementation,raised porosity 1%～5%.The porosity varied slightly during the middle stage B.展开更多
The Upper Ediacaran microbial carbonates of the Tarim Basin are potential reservoir geobodies for future hydrocarbon exploration with rising interest in exploration for deeply-buried reserves.However,little knowledge ...The Upper Ediacaran microbial carbonates of the Tarim Basin are potential reservoir geobodies for future hydrocarbon exploration with rising interest in exploration for deeply-buried reserves.However,little knowledge has been acquired on the types of microbial carbonates that are present,the properties of the reservoir and the pore evolution,hampering predictions of high-quality reservoirs in these carbonates.Integrated with petrography and in-situ U-Pb dating geochronology analyses,this study aims to clarify the types of microbial carbonates present and to reconstruct the pore evolution processes of the potential reservoir rocks.The Upper Ediacaran microbial carbonates of the Tarim Basin can be divided into four types,based on their features in terms of different scales(macro-to micro-):microbial laminite,stromatolite,spongiomicrobialite and microbial-peloidal wackestone/mudstone.Petrophysical properties show that all these microbial carbonates have low porosity and very low permeability with poor connectivity.These carbonates were subject to long-term and complex diagenetic processes,mainly consisting of dissolution,compaction,pervasive dolomitization,cementation and fracturing.The most important reservoir spaces are contributed by vugs and dissolution-enlarged pores,which are likely to have been associated with the widespread uplift of the Aksu area in the terminal Ediacaran.In contrast,the cementation of the fine-to-medium crystalline dolomite greatly reduced the pre-existing pores.Pore types are closely related to different microbial fabrics,which played an important role in the pore evolution of the microbial carbonates.展开更多
The Chang-63 reservoir in the Huaqing area has widely developed tight sandstone ＂thick sand layers, but not reservoirs characterized by rich in oil＂, and it is thus necessary to further study its oil and gas enrichm...The Chang-63 reservoir in the Huaqing area has widely developed tight sandstone ＂thick sand layers, but not reservoirs characterized by rich in oil＂, and it is thus necessary to further study its oil and gas enrichment law. This study builds porosity and fracture development and evolution models in different deposition environments, through core observation, casting thin section, SEM, porosity and permeability analysis, burial history analysis, and ＂four-property-relationships＂ analysis.展开更多
At present,simulation on reservoir evolution under normal pressure is common while that under abnormal pressure is rare.In this paper,the Miocene“high-temperature and overpressure”reservoir in the LedongeLingshui Sa...At present,simulation on reservoir evolution under normal pressure is common while that under abnormal pressure is rare.In this paper,the Miocene“high-temperature and overpressure”reservoir in the LedongeLingshui Sag of the Qiongdongnan Basin was taken as the research object to quantitatively define the effects of high pressure and overpressure on the evolution of reservoir pores.After the temperature and pressure field in this area was divided in the setting of sedimentation and diagenesis,the evolution characteristics of pores in different temperature and pressure field were analyzed by means of natural analogy and physical simulation experiment.Then,the effects of overpressure and fluids on the evolution of reservoir pores were discussed.Finally,the main factors controlling the development of high-quality reservoirs were determined.And the following research results were obtained.First,the temperature and pressure field of the Miocene reservoir in the LedongeLingshui Sag can be divided into three zones,i.e.,high temperature and normal pressure zone,high temperature and overpressure zone,and high temperature and super overpressure zone.Second,overpressure and super overpressure can provide some preservation on primary pores.In the same diagenetic stage,the plane porosity of overpressure and super overpressure reservoirs is 1.23e6.74%higher than that of normal pressure reservoirs.Once the reservoir pressure in overpressure and super overpressure areas is higher than hydrostatic pressure by 8 MPa and 4 MPa,respectively,about 1%primary pores are preserved.Third,the dissolution of organic acid makes greater contribution to the secondary pores in reservoirs and its plane porosity is 0.96-7.38%higher than that of normal compaction reservoirs.Fourth,the leaching effect of meteorological water on reservoir physical properties is slight,and its plane porosity is only 0.19%higher than that of normal compaction reservoirs.In conclusion,the dissolution of organic acid is the most constructive effect for the reservoirs in high temperature and normal pressure.In addition,preservation of primary pores by overpressure is the most constructive effect for the reservoirs in high temperature and(super)overpressure,and the higher the overpressure is,the more preservation effect it provides on pores.展开更多
Marine organic-rich marl is not only a high-quality hydrocarbon source of conventional oil and gas,but also a new type and field of unconventional oil and gas exploration.An understanding of its pore structure evoluti...Marine organic-rich marl is not only a high-quality hydrocarbon source of conventional oil and gas,but also a new type and field of unconventional oil and gas exploration.An understanding of its pore structure evolution characteristics during a hydrocarbon generation process is theoretically significant and has application prospects for the exploration and development of this special type of natural gas reservoirs.This study conducted thermal simulation of hydrocarbon generation under near-geological conditions during a whole process for cylinder samples of low mature marine organic-rich marl in the Middle Devonian of Luquan,Yunnan Province,China.During this process,hydrocarbon products at different evolution stages were quantified and corresponding geochemical properties were analyzed.Simultaneously,field emission scanning electron microscopy(FE-SEM)and low-pressure gas adsorption(CO_(2),N_(2))tests were applied to the corresponding cylinder residue samples to reveal the mechanisms of different types of pore formation and evolution,and clarify the dynamic evolution processes of their pore systems.The results show that with an increase in temperature and pressure,the total oil yield peaks at an equivalent vitrinite reflectance(VR_(o))of 1.03%and is at the maximum retention stage of liquid hydrocarbons,which are 367.51 mg/g TOC and 211.67 mg/g TOC,respectively.The hydrocarbon gas yield increases continuously with an increase in maturity.The high retained oil rate at the peak of oil generation provides an abundant material basis for gas formation at high maturity and over-maturity stage.The lower limit of VR_(o)for organic matter(OM)pore mass development is about 1.6%,and bitumen pores,organic-clay complex pores together with intergranular pores,grain edge seams and dissolution pores constitute a complicated pore-seam-network system,which is the main reservoir space for unconventional carbonate gas.Pore formation and evolution are controlled synergistically by hydrocarbon generation,diagenesis and organic-inorganic interactions,and the pattern of pore structure evolution can be divided into four stages.A pore volume(PV)and a specific surface area(SSA)are at their highest values within the maturity range of 1.9%to 2.5%,which is conducive to exploring unconventional natural gas.展开更多
In recent years,fueled by significant advancements in oil exploration technologies within the Ordos Basin,an increasing number of low-permeability or ultra-low-permeability reservoirs have been identified.Elucidating ...In recent years,fueled by significant advancements in oil exploration technologies within the Ordos Basin,an increasing number of low-permeability or ultra-low-permeability reservoirs have been identified.Elucidating their reservoir characteristics and formation mechanisms has become a critical priority for sustainable hydrocarbon development.The study focused on the Chang 6 Member of the Upper Triassic Yanchang Formation in the Heshui area of the Ordos Basin,systematically investigating its petrological features,porosity and permeability characteristics,diagenesis,and diagenetic evolution sequence.By integrating core observation,thin-section identification,and physical property measurements,a comprehensive quantitative evaluation of reservoir pore evolution was performed.These analytical outcomes were subsequently applied to simulate hydrocarbon migration and accumulation.These research results will provide a scientific basis for in-depth quantitative study of the pore evolution in ultra-low-permeability oil reservoirs and accurately constructing basin models.As indicated,the reservoir lithology in the study area predominantly comprises siltstone interbedded with mudstone or argillaceous siltstone,characterized by low porosity and permeability.Through diagenetic characteristics-based reconstruction constrained by the existing porosity data,pore evolution during diagenesis was quantitatively modeled.The simulated pore evolution aligns with actual geological observations,validating the reliability of the methodology.Furthermore,the quantified pore evolution results were applied to simulate hydrocarbon migration using PetroMod software,showing that hydrocarbon charging in the basin began at the end of the Late Jurassic(J3),peaking in hydrocarbon generation,expulsion,and accumulation by the end of the Early Cretaceous(K1)and maintaining high accumulation rates until the late Cretaceous,though significantly decreasing at the present stage.The simulation results were verified by comparison with actual drilling data,which confirms their reliability and applicability to other analogous oilfields.展开更多
As the cornerstone for evaluating the storage capacity of shale reservoirs and assessing the viability of shale gas exploitation,shale pores play a very important role in shale reservoirs.Based on drilling well and te...As the cornerstone for evaluating the storage capacity of shale reservoirs and assessing the viability of shale gas exploitation,shale pores play a very important role in shale reservoirs.Based on drilling well and test data,deep learning,and artificial intelligence for image analysis,the types,characteristics,structures,and vertical heterogeneity of shale pores were studied.Additionally,we conducted a comprehensive investigation into the sedimentary environment characteristics and their influence on the heterogeneity of shale reservoir pores in the Longmaxi Formation using associated geochemical analyses.The results revealed that the sedimentary environment underwent significant changes in the Longmaxi Formation,characterized by a sea level fall,accelerated sedimentation rates,weakened reducing conditions,decreased palaeoproductivity,and increased terrigenous influx,which led to a decrease in the frequency of organic matter(OM)pores,paralleled by a gradual increase in inorganic pores.In the S_(1)1_(1)^(1-1),S_(1)1_(1)^(1-2),S_(1)1_(1)^(1-3) sections of the Long11 sub-member,OM pores constitute the primary pore type.Conversely,in the S_(1)1_(1)^(1-4) section and the Long12 sub-member,inorganic pores prevail as the primary pore type.Furthermore,the strongly anoxic sections are also pay zones that are not only enriched in OM but also concentrated with OM pores.The S_(1)1_(1)^(1-1) and S_(1)1_(1)^(1-2) sections are characterized by anoxic conditions,with total organic carbon(TOC)content exceeding 4%and abundant biogenic silica.Notably,an increased terrigenous influx adversely impacts the development and preservation of pores in the Long11 sub-member while exerting a dual effect in the Long12 sub-member.The increased terrigenous influx dilutes the OM and decreases the probability of intergranular pores and intragranular pores filled by OM.Moreover,more brittle mineral particles were deposited,which promotes the development and preservation of intergranular and intragranular pores.展开更多
For exploration and potential evaluation of deep shale reservoirs with high maturity,hydrocarbon generation and pore evolution of muddy shale in deep high evolution stage were investigated by the high-temperature high...For exploration and potential evaluation of deep shale reservoirs with high maturity,hydrocarbon generation and pore evolution of muddy shale in deep high evolution stage were investigated by the high-temperature high-pressure simulation experiment.Results indicated that under high pressure condition,nano-scale micropores in organic matter-rich muddy shale constantly increased as rise of temperature and pressure,leading to increase of shale porosity.However,in the high mature-overmature stage,shale porosity decreased with further increase of temperature and pressure.In contrast to micropores,micro-scale capillary pores and megapores in shale constantly decreased as rise of simulation temperature or pressure,indicating that deep-burial reservoirs was not favorable for free-gas storage;but significant increase of micropores and surface area during this stage could make up for a loss of adsorbed natural gas in shale due to decrease of adsorption capacity which was induced by increase of temperature and pressure,thus leading to high shale gas potential in deep layers.A large number of secondary micropores were developed in the simulated samples such as pyrite and dolomite,demonstrating that shale clasts and mineral matrix could also form abundant secondary micropores during the deep evolution stage;during the evolution process,shale as hydrocarbon source rock could generate a large amount of acidic fluid which was favorable for development of secondary porosity.展开更多
The majority of oil and gas resources in the world are related to saline sediments, which mainly occur in sedimentary strata in the form of cap rocks or salt-associated shales. A large number of shale oil resources ha...The majority of oil and gas resources in the world are related to saline sediments, which mainly occur in sedimentary strata in the form of cap rocks or salt-associated shales. A large number of shale oil resources have been discovered in the saline shale sediments of the Cenozoic terrestrial lake basin in China. The hydrocarbon generation ability and the reservoir capacity of shale control the oil and gas generation. The reservoir capacity is mainly characterized by pore type, structure and porosity. Most of China’s shale oil and gas resources belong to salt-bearing formations. The role of gypsum-salt rocks in the formation and evolution of organic matter (OM) in such formations has received extensive attention. However, systematic understanding is lacking. Research on the pore formation and evolution in shale under the action of gypsum-salt rock sediments is especially weak. Taking the shales in the third member of the Shahejie Formation (Es_(3)) of the Bohai Bay Basin as an example, the influence of halite on the formation and evolution process of pores was studied in this paper. The results show that halite and gypsum minerals were associated with OM, which made them more likely to develop OM pores. The samples with a high halite mineral content (HC) are more developed regarding the pore volume and specific surface area than those with a low HC. The formation of thick salt rocks is influenced by factors of deep thermal brine upwelling, sea erosion and arid environments. The frequent alternation between humid and arid environments led to the outbreak and death of organisms and the precipitation of gypsum-salt rock, which formed the simultaneous deposition of OM and halite minerals. Finally, we have established a model of shale pore evolution under the participation of the gypsum-salt rock, and halite minerals contribute to pore development in both Stage II and Stage IV. This study provides strong microscopic evidence for the pore system formation and evolution in salt-bearing reservoirs.展开更多
At present,researches on the pore evolution of shale reservoir and its evolution mechanism are still at such a groping stage that a consensus has not yet reached.Based on core analysis and thermal simulation experimen...At present,researches on the pore evolution of shale reservoir and its evolution mechanism are still at such a groping stage that a consensus has not yet reached.Based on core analysis and thermal simulation experiments,the pore types,pore structures and pore-size change rules of shale gas reservoirs of Upper Ordovician Wufeng-Lower Silurian Longmaxi Fms in the southeastern(SE)Sichuan Basin and its basin-margin transition zone(hereinafter referred to as the basin-margin transition zone of SE Chongqing)were studied by means of argon ion polishing-scanning electron microscopy(SEM)and atomic force microscopy.Then,the evolution characteristics of organic pores were discussed,and the influence of associated minerals on pore evolution was analyzed.Finally,a pore evolution model for the shale gas reservoirs in this area was established.And the following research results were obtained.First,three types of reservoir spaces are mainly developed in the high-quality shale reservoirs of Wufeng-Longmaxi Fms in this area,including fracture,inorganic pore and organic pore.And the organic pores provide the primary reservoir space of shale gas,which can be divided into four categories,i.e.,amorphous kerogen pores,structured kerogen pores,asphaltene pores and paleontology fossil pores.Second,organic contracted fractures are related to the contraction of organic matters,first appearing on one side of the organic matters and then becomes wider and wider with the increase of temperatures.Third,organic pores are mostly the“spongy”pores distributed densely inside the organic matters.When Ro is in the range of 1.56-3.50%,macropores and mesopores are dominant.And when Ro exceeds 3.50%,macropores decrease while mesopores and micropores increase.Fourth,the types of organic matters and the content of associated minerals(e.g.clay minerals,siliceous particles and pyrite)play an important role in the development of pores.In conclusion,the pore evolution law of Wufeng-Longmaxi shale in the basin-margin transition zone of SE Chongqing is that with the increase of burial depth,inorganic porosity decreases significantly,organic porosity increases first and then decreases,and the total porosity shows a change trend of decreasing first,then increasing and finally decreasing continuously.展开更多
Pyrolysis experiments were conducted on lacustrine organic-rich shale from Cangdong Sag in Bohai Bay Basin,China,to investigate the impact of hydrocarbon generation on shale pore structure evolution.Thermal evolution ...Pyrolysis experiments were conducted on lacustrine organic-rich shale from Cangdong Sag in Bohai Bay Basin,China,to investigate the impact of hydrocarbon generation on shale pore structure evolution.Thermal evolution is found to control the transformation of organic matter,hydrocarbon products characteristics,and pore structure changes.Furthermore,pore volume and specific surface area increase with increasing maturity.In low-mature stage,the retained oil content begins to increase,pore volumes show slight changes,and primary pores are occluded by the generated crude oil of high molecular weight and density.In the oil-window stage,the retained oil content rapidly increases and reaches maximum,and pore volumes gradually increase with increasing thermal maturity.At high mature stage,the retained oil content begins to decrease,and the pore volume increases considerably owing to the expulsion of liquid hydrocarbon.In over mature stage,natural gas content significantly increases and kerogen transforms to asphalt.Numerous organic pores are formed and the pore size gradually increases,resulting from the connection of organic pores caused the increasing thermal stress.This study lays a foundation for understanding variation of hydrocarbon products during the thermal evolution of lacustrine shales and its relationship with the evolution of shale reservoirs.展开更多
The Upper Ordovician Wufeng-Lower Silurian Longmaxi and the Lower Cambrian Qiongzhusi shales are the major targets for shale gas exploration and development in China.Although the two organic-rich shales share similar ...The Upper Ordovician Wufeng-Lower Silurian Longmaxi and the Lower Cambrian Qiongzhusi shales are the major targets for shale gas exploration and development in China.Although the two organic-rich shales share similar distribution ranges and thicknesses,they exhibit substantially different exploration and development results.This work analyzed the nanopore structures of the shale reservoirs in this region.Pore development of 51 shale samples collected from various formations and locations was compared using the petromineralogical,geochemical,structural geological and reservoir geological methods.The results indicate that the reservoir space in these shales is dominated by organic pores and the total pore volume of micropores,mesopores,macropores in different tectonic areas and formations show different trends with the increase of TOC.It is suggested that organic pores of shale can be well preserved in areas with simple structure and suitable preservation conditions,and the shale with smaller maximum ancient burial depth and later hydrocarbongeneration-end-time is also more conducive to pore preservation.Organic pore evolution models are established,and they are as follows:①Organic matter pore development stage,②Early stage of organic matter pore destruction,and③late stage of organic matter pore destruction.The areas conducive to pore development are favorable for shale gas development.Research results can effectively guide the optimization and evaluation of favorable areas of shale gas.展开更多
The lacustrine shale of deep Shahezi Formation in the Songliao basin has great gas potential,but its pore evolution,heterogeneity,and connectivity characteristics remain unclear.In this work,total organic carbon analy...The lacustrine shale of deep Shahezi Formation in the Songliao basin has great gas potential,but its pore evolution,heterogeneity,and connectivity characteristics remain unclear.In this work,total organic carbon analysis,rock pyrolysis,X-ray diffraction field emission scanning electron microscopy,the particle and crack analysis system software,low-temperature nitrogen adsorption experiment,fractal theory,high-pressure mercury injection experiment and nuclear magnetic resonance experiment were used to study the Shahezi shale from Well SK-2.The result indicated that the organic pores in Shahezi shale are not developed,and the intergranular and intragranular pores are mainly formed by illitedominated clay.As the burial depth increases,the pore size and slit-shaped pores formed by clay decrease,and dissolved pores in the feldspar and carbonate minerals and dissolved fractures in the quartz increase.The pore evolution is affected by clay,compaction,and high-temperature corrosion.Based on the pore structure characteristics reflected by the pore size distribution and pore structure parameters obtained by multiple experimental methods,the pore development and evolution are divided into three stages.During stageⅠandⅡ,the pore heterogeneity of the shale reservoirs increases with the depth,the physical properties and pore connectivity deteriorate,but the gas-bearing property is good.In stageⅢ,the pore heterogeneity is the highest,its gas generation and storage capacity are low,but the increase of micro-fractures makes pore connectivity and gas-bearing better.展开更多
The evolution of pore structure in shales is affected by both the thermal evolution of organic matter(OM)and by inorganic diagenesis,resulting in a wide variety of pore structures.This paper examines the OM distributi...The evolution of pore structure in shales is affected by both the thermal evolution of organic matter(OM)and by inorganic diagenesis,resulting in a wide variety of pore structures.This paper examines the OM distribution in lacustrine shales and its influence on pore structure,and describes the process of porosity development.The principal findings are:(i)Three distribution patterns of OM in lacustrine shales are distinguished;laminated continuous distribution,clumped distribution,and stellate scattered distribution.The differences in total organic carbon(TOC)content,free hydrocarbon content(S_(1)),and OM porosity among these distribution patterns are discussed.(ii)Porosity is negatively correlated with TOC and plagioclase content and positively correlated with quartz,dolomite,and clay mineral content.(iii)Pore evolution in lacustrine shales is characterized by a sequence of decreasing-increasing-decreasing porosity,followed by continuously increasing porosity until a relatively stable condition is reached.(iv)A new model for evaluating porosity in lacustrine shales is proposed.Using this model,the organic and inorganic porosity of shales in the Permian Lucaogou Formation are calculated to be 2.5%-5%and 1%-6.3%,respectively,which correlate closely with measured data.These findings may provide a scientific basis and technical support for the sweet spotting in lacustrine shales in China.展开更多
Aiming at the complicated problem of the genesis of high-quality hybrid sedimentary rocks,the pore-throat systems,controlling factors and fluid mobility of hybrid sedimentary rocks in the Permian Lucaogou Formation in...Aiming at the complicated problem of the genesis of high-quality hybrid sedimentary rocks,the pore-throat systems,controlling factors and fluid mobility of hybrid sedimentary rocks in the Permian Lucaogou Formation in Jimusar Sag were examined.The results show that the hybrid sedimentary rocks contain 5 types of pore-throat system,intergranular(Type A),mixed intergranular-dissolved-intercrystalline(Type B),dissolved(Type C),mixed dissolved-intercrystalline(Type D)and intercrystalline(Type E)ones.The pore-throat systems are controlled by 3 major factors,the component content and arrangement(CCA)of hybrid sedimentary rocks,sedimentary environment and diagenesis.CCA controls the matrix support mode of hybrid sedimentary rocks,and therefore controls the types and changes of pore-throat system.The sedimentary environment mainly controls the macroscopic distribution of pore-throat system,i.e.,hybrid sedimentary rocks deposited in the near source and high-energy environment are characterized by high content of coarse-grained component,granular/interbedded-support mode,and development of Type A and Type B pore-throat systems.Hybrid sedimentary rocks deposited in the medium-energy environment far from source are characterized by dolomitic/mud support mode and Type C and Type D pore-throat systems.Hybrid sedimentary rocks deposited in low-energy environment far from source have mainly Type E and Type D pore-throat systems.Diagenetic processes such as compaction and calcite cementation make the proportions of Type A and Type C pore-throat systems decrease further.In the hybrid sedimentary process of sandy-mud,pore-throat system types show a change of"A→B→C→D",in that of dolomite-sand,pore-throat system types show a change of"A→C→D→E"or"B→D→E",and in that of dolomite-mud,pore-throat system types show a change of"D→E",which are affected in details by the contents of coarse-grain component,feldspar and dolomite.The reservoir with Type A pore-throats has the best physical properties and fluid mobility,and the reservoirs with Type D and Type E pore-throats have the poorest.The movable fluid distribution is related to the matrix support mode,and the larger pores in hybrid sedimentary rocks of dolomite/mud support mode have no obvious advantage in fluid mobility.The findings of this study provide a geological basis for evaluating and building reasonable interpretation model of hybrid sedimentary rocks sweet spot.展开更多
To investigate the macroscopic fatigue properties and the mesoscopic pore evolution characteristics of salt rock under cyclic loading,fatigue tests under different upper-limit stresses were carried out on salt rock,an...To investigate the macroscopic fatigue properties and the mesoscopic pore evolution characteristics of salt rock under cyclic loading,fatigue tests under different upper-limit stresses were carried out on salt rock,and the mesoscopic pore structures of salt rock before and after fatigue tests and under different cycle numbers were measured using CT scanning instrument.Based on the test results,the effects of the cycle number and the upper-limit stress on the evolution of cracks,pore morphology,pore number,pore volume,pore size,plane porosity,and volume porosity of salt rock were analyzed.The failure path of salt rock specimens under cyclic loading was analyzed using the distribution law of plane porosity.The damage variable of salt rock under cyclic loading was defined on basis of the variation of volume porosity with cycle number.In order to describe the fatigue deformation behavior of salt rock under cyclic loading,the nonlinear Burgers damage constitutive model was further established.The results show that the model established can better reflect the whole development process of fatigue deformation of salt rock under cyclic loading.展开更多
Coal gasification fly ash(CGFA)is an industrial solid waste from the coal circulating fluidized bed(CFB)gasification process,and it needs to be effectively disposed to achieve sustainable development of the environmen...Coal gasification fly ash(CGFA)is an industrial solid waste from the coal circulating fluidized bed(CFB)gasification process,and it needs to be effectively disposed to achieve sustainable development of the environment.To realize the application of CGFA as a precursor of porous carbon materials,the physicochemical properties of three kinds of CGFA from industrial CFB gasifiers are analyzed.Then,the activation potential of CGFA is acquired via steam activation experiments in a tube furnace reactor.Finally,the fluidization activation technology of CGFA is practiced in a bench-scale CFB test rig,and its advantages are highlighted.The results show that CGFA is characterized by a high carbon content in the range of 54.06%–74.09%,an ultrafine particle size(d50:16.3–26.1 μm),and a relatively developed pore structure(specific surface area SSA:139.29–551.97 m^(2)·g^(-1)).The proportion of micropores in CGFA increases gradually with the coal rank.Steam activation experiments show that the pore development of CGFA mainly includes three stages:initial pore development,dynamic equilibrium between micropores and mesopores and pore collapse.The SSA of lignite fly ash(LFA),subbituminous fly ash(SBFA)and anthracite fly ash(AFA)is maximally increased by 105%,13%and 72%after steam activation;the order of the largest carbon reaction rate and decomposition ratio of steam among the three kinds of CGFA is SBFA>LFA>AFA.As the ratio of oxygen to carbon during the fluidization activation of LFA is from 0.09 to 0.19,the carbon conversion ratio increases from 14.4%to 26.8%and the cold gas efficiency increases from 6.8%to 10.2%.The SSA of LFA increases by up to 53.9%during the fluidization activation process,which is mainly due to the mesoporous development.Relative to steam activation in a tube furnace reactor,fluidization activation takes an extremely short time(seconds)to achieve the same activation effect.It is expected to further improve the activation effect of LFA by regulating the carbon conversion ratio range of 27%–35%to create pores in the initial development stage.展开更多
基金supported by the China National Science and Technology Major Projects(No.2017ZX05001)the PetroChina Science and Technology Major Projects(No.2016B-0304)China Postdoctoral Science Foundation(No.2020M680819).
文摘This study examines the characteristics and pore evolution of the Baikouquan conglomerate reservoir in the Mahu sag of the Junggar Basin from original sedimentation and diagenesis.Analysis is based on core observation,thin section,X-ray diffraction,cathodoluminescence and image analysis,and combined with physical property and well log data.The results show that conglomerate reservoir in the Baikouquan Formation can be divided into three lithofacies types:TypeⅠis argillaceous filling conglomerate facies,in which cementation and dissolution are not developed,and the interstitial material is mainly argillaceous;TypeⅡis tuffaceous filling in fine conglomerate facies,in which volcanic rock debris,illite and dissolution are developed;TypeⅢis sandstone filling conglomerate facies,in which cementation and dissolution are developed.The reservoir undergoes complex diagenesis,and the diagenetic sequence is:compaction→early chlorite film→early calcite cementation→detritus,feldspar and tuffaceous dissolution→quartz secondary enlargement→late calcite cementation→oil invasion→forming illite.Quantitative study of pore evolution shows that dissolution and calcite cementation are relatively developed in lithofacies Type III,and that compaction has a great influence on lithofacies TypeⅠand II.According to comprehensive evaluation of lithofacies,diagenesis and pore structure characteristics,the reservoir space type is mainly the dissolution pore.It is mainly primarily mainly composed of lithofacies Type III,thickness of the gravel body is more than 25 m,porosity is generally more than 12%,which represents favorable conditions for the distribution of favorable reservoir.
文摘The evolution of shale reservoirs is mainly related to two functions:mechanical compaction controlled by ground stress and chemical compaction controlled by thermal effect.Thermal simulation experiments were conducted to simulate the chemical compaction of marine-continental transitional shale,and X-ray diffraction(XRD),CO2 adsorption,N2 adsorption and high-pressure mercury injection(MIP)were then used to characterize shale diagenesis and porosity.Moreover,simulations of mechanical compaction adhering to mathematical models were performed,and a shale compaction model was proposed considering clay content and kaolinite proportions.The advantage of this model is that the change in shale compressibility,which is caused by the transformation of clay minerals during thermal evolution,may be considered.The combination of the thermal simulation and compaction model may depict the interactions between chemical and mechanical compaction.Such interactions may then express the pore evolution of shale in actual conditions of formation.Accordingly,the obtained results demonstrated that shales having low kaolinite possess higher porosity at the same burial depth and clay mineral content,proving that other clay minerals such as illite-smectite mixed layers(I/S)and illite are conducive to the development of pores.Shales possessing a high clay mineral content have a higher porosity in shallow layers(<3500 m)and a lower porosity in deep layers(>3500 m).Both the amount and location of the increase in porosity differ at different geothermal gradients.High geothermal gradients favor the preservation of high porosity in shale at an appropriate Ro.The pore evolution of the marine-continental transitional shale is divided into five stages.Stage 2 possesses an Ro of 1.0%-1.6%and has high porosity along with a high specific surface area.Stage 3 has an Ro of 1.6%-2.0%and contains a higher porosity with a low specific surface area.Finally,Stage 4 has an Ro of 2.0%-2.9%with a low porosity and high specific surface area.
基金supported by the National Science and Technology Major Project of the Ministry of Science and Technology of China"Study on Formation Mechanism and Enrichment Regularity of Different Types of Shale Gas"(2016ZX05034)the Oil&Gas Survey,China Geological Survey for their support of this research。
文摘The relationship between hydrocarbon generation and the evolution of shale pore structure and its heterogeneity of continental shale from the Ordos Basin,China was quantitatively studied based on thermal simulation experiment,mercury injection capillary pressure(MICP),gas adsorption,vitrinite reflectance(R_(o))analysis,and hydrocarbon generation test combined with Frenkel-Halsey-Hill(FHH)fractal model.The result shows that the pore volume(PV)and specific surface area(SSA)of pores with different pore sizes show a trend of decreasing first and then increasing as the maturity increases in general,R_(o)>1.59%is initially defined as a favorable stage for pore development in continental shale.Hydrocarbon generation has different effects on pore heterogeneity of different scales.For the N_(2)adsorption,the roughness of small pore surface(D_(1))decreases in the oil window;the complexity of large pore structure(D_(2))increases in the oil window but decreases in the gas window.For the MICP,the heterogeneity of small pore(D_(1))increases in the oil window and increases first and then decreases in the gas window;D_(2)remains basically constant during the whole stage and is close to 3,indicating that the heterogeneity of large pores is extremely strong and is not affected by hydrocarbon generation.
基金the National Basic Research Program of China (No.2009 CB219306)the Important National Science & Technology Specific Projects (No.2009GYXQ14)
文摘From observing cores of 18 wells,identifying 175 ordinary thin sections and 61 thin casting sections,energy spectrum analyses of 37 samples,homogenization temperature measurement of fluid inclusions of 11 samples,we determine the types of diagenesis and pores of the Fuyu oil reservoir in the north Qijia region.We classified the pores and measured their plane porosity using CIA 2000,the software of rock image analysis,calculated the effect of different kinds of diagenesis on porosity,studied the controlling actions of diagenesis to pore evolution quantitatively,combined with burial history,thermal history and their diagenetic environments.Our results show that mechanical compaction and carbonate cementation are the major destructive diagenesed,developed during early diagenesis stages.The reduction in porosity by mechanical compaction and carbonate cementation are about 25% and 8%,while the destructive intensity of siliceous cementation and clay mineral cementation is relatively much smaller,i.e.,the reduction of porosity is about 2% and 0.2% Dissolution is constructive diagenesis,the increment of porosity is about 6%.There are four diagenesis evolution stages,during which the porosity reduced from 30%～38% to 2%～20%.Mechanical compaction and early cementation are the main diageneses in the early diagenesis stages,when porosity was reduced to 2%～10%.Dissolution is the main diagenesis of an A I substage of the middle diagenesis stage,when porosity increased 1%～8%.The dissolution of the A Ⅱ substage of the middle diagenesis stage affected by late cementation,raised porosity 1%～5%.The porosity varied slightly during the middle stage B.
基金financially supported by the National Key Research and Development(R&D)Program of China(2017YFC0603103)the National Natural Science Foundation of China(U19B6003)。
文摘The Upper Ediacaran microbial carbonates of the Tarim Basin are potential reservoir geobodies for future hydrocarbon exploration with rising interest in exploration for deeply-buried reserves.However,little knowledge has been acquired on the types of microbial carbonates that are present,the properties of the reservoir and the pore evolution,hampering predictions of high-quality reservoirs in these carbonates.Integrated with petrography and in-situ U-Pb dating geochronology analyses,this study aims to clarify the types of microbial carbonates present and to reconstruct the pore evolution processes of the potential reservoir rocks.The Upper Ediacaran microbial carbonates of the Tarim Basin can be divided into four types,based on their features in terms of different scales(macro-to micro-):microbial laminite,stromatolite,spongiomicrobialite and microbial-peloidal wackestone/mudstone.Petrophysical properties show that all these microbial carbonates have low porosity and very low permeability with poor connectivity.These carbonates were subject to long-term and complex diagenetic processes,mainly consisting of dissolution,compaction,pervasive dolomitization,cementation and fracturing.The most important reservoir spaces are contributed by vugs and dissolution-enlarged pores,which are likely to have been associated with the widespread uplift of the Aksu area in the terminal Ediacaran.In contrast,the cementation of the fine-to-medium crystalline dolomite greatly reduced the pre-existing pores.Pore types are closely related to different microbial fabrics,which played an important role in the pore evolution of the microbial carbonates.
文摘The Chang-63 reservoir in the Huaqing area has widely developed tight sandstone ＂thick sand layers, but not reservoirs characterized by rich in oil＂, and it is thus necessary to further study its oil and gas enrichment law. This study builds porosity and fracture development and evolution models in different deposition environments, through core observation, casting thin section, SEM, porosity and permeability analysis, burial history analysis, and ＂four-property-relationships＂ analysis.
基金supported by the National Major Science and Technology Project under the 13th Five-Year Plan“Forming Conditions of Large to Medium Gas Fields in Deepwater Area of Qiongdongnan Basin and Key Exploration Technologies”(No.:2016ZX05026-002)the Science and Technology Project of CNOOC“A Study on ReservoireCaprock Joint Control Mechanism and Effective ReservoireCaprock Distribution under Differential Rock-Field Coupling”(No.:ZYKY-2018-ZJ-01).
文摘At present,simulation on reservoir evolution under normal pressure is common while that under abnormal pressure is rare.In this paper,the Miocene“high-temperature and overpressure”reservoir in the LedongeLingshui Sag of the Qiongdongnan Basin was taken as the research object to quantitatively define the effects of high pressure and overpressure on the evolution of reservoir pores.After the temperature and pressure field in this area was divided in the setting of sedimentation and diagenesis,the evolution characteristics of pores in different temperature and pressure field were analyzed by means of natural analogy and physical simulation experiment.Then,the effects of overpressure and fluids on the evolution of reservoir pores were discussed.Finally,the main factors controlling the development of high-quality reservoirs were determined.And the following research results were obtained.First,the temperature and pressure field of the Miocene reservoir in the LedongeLingshui Sag can be divided into three zones,i.e.,high temperature and normal pressure zone,high temperature and overpressure zone,and high temperature and super overpressure zone.Second,overpressure and super overpressure can provide some preservation on primary pores.In the same diagenetic stage,the plane porosity of overpressure and super overpressure reservoirs is 1.23e6.74%higher than that of normal pressure reservoirs.Once the reservoir pressure in overpressure and super overpressure areas is higher than hydrostatic pressure by 8 MPa and 4 MPa,respectively,about 1%primary pores are preserved.Third,the dissolution of organic acid makes greater contribution to the secondary pores in reservoirs and its plane porosity is 0.96-7.38%higher than that of normal compaction reservoirs.Fourth,the leaching effect of meteorological water on reservoir physical properties is slight,and its plane porosity is only 0.19%higher than that of normal compaction reservoirs.In conclusion,the dissolution of organic acid is the most constructive effect for the reservoirs in high temperature and normal pressure.In addition,preservation of primary pores by overpressure is the most constructive effect for the reservoirs in high temperature and(super)overpressure,and the higher the overpressure is,the more preservation effect it provides on pores.
基金supported by the National Natural Science Foundation of China(Grant No.41930426)。
文摘Marine organic-rich marl is not only a high-quality hydrocarbon source of conventional oil and gas,but also a new type and field of unconventional oil and gas exploration.An understanding of its pore structure evolution characteristics during a hydrocarbon generation process is theoretically significant and has application prospects for the exploration and development of this special type of natural gas reservoirs.This study conducted thermal simulation of hydrocarbon generation under near-geological conditions during a whole process for cylinder samples of low mature marine organic-rich marl in the Middle Devonian of Luquan,Yunnan Province,China.During this process,hydrocarbon products at different evolution stages were quantified and corresponding geochemical properties were analyzed.Simultaneously,field emission scanning electron microscopy(FE-SEM)and low-pressure gas adsorption(CO_(2),N_(2))tests were applied to the corresponding cylinder residue samples to reveal the mechanisms of different types of pore formation and evolution,and clarify the dynamic evolution processes of their pore systems.The results show that with an increase in temperature and pressure,the total oil yield peaks at an equivalent vitrinite reflectance(VR_(o))of 1.03%and is at the maximum retention stage of liquid hydrocarbons,which are 367.51 mg/g TOC and 211.67 mg/g TOC,respectively.The hydrocarbon gas yield increases continuously with an increase in maturity.The high retained oil rate at the peak of oil generation provides an abundant material basis for gas formation at high maturity and over-maturity stage.The lower limit of VR_(o)for organic matter(OM)pore mass development is about 1.6%,and bitumen pores,organic-clay complex pores together with intergranular pores,grain edge seams and dissolution pores constitute a complicated pore-seam-network system,which is the main reservoir space for unconventional carbonate gas.Pore formation and evolution are controlled synergistically by hydrocarbon generation,diagenesis and organic-inorganic interactions,and the pattern of pore structure evolution can be divided into four stages.A pore volume(PV)and a specific surface area(SSA)are at their highest values within the maturity range of 1.9%to 2.5%,which is conducive to exploring unconventional natural gas.
基金funded by National Science and Technology Major Projects(Grant No.2016ZX05050,2017ZX05001002-008)China National Petroleum Corporation Major Projects(No.2021DJ2203)Key Laboratory of Petroleum Resources Exploration and Evaluation,Gansu Province(No.KLPREEGS-2024-22)。
文摘In recent years,fueled by significant advancements in oil exploration technologies within the Ordos Basin,an increasing number of low-permeability or ultra-low-permeability reservoirs have been identified.Elucidating their reservoir characteristics and formation mechanisms has become a critical priority for sustainable hydrocarbon development.The study focused on the Chang 6 Member of the Upper Triassic Yanchang Formation in the Heshui area of the Ordos Basin,systematically investigating its petrological features,porosity and permeability characteristics,diagenesis,and diagenetic evolution sequence.By integrating core observation,thin-section identification,and physical property measurements,a comprehensive quantitative evaluation of reservoir pore evolution was performed.These analytical outcomes were subsequently applied to simulate hydrocarbon migration and accumulation.These research results will provide a scientific basis for in-depth quantitative study of the pore evolution in ultra-low-permeability oil reservoirs and accurately constructing basin models.As indicated,the reservoir lithology in the study area predominantly comprises siltstone interbedded with mudstone or argillaceous siltstone,characterized by low porosity and permeability.Through diagenetic characteristics-based reconstruction constrained by the existing porosity data,pore evolution during diagenesis was quantitatively modeled.The simulated pore evolution aligns with actual geological observations,validating the reliability of the methodology.Furthermore,the quantified pore evolution results were applied to simulate hydrocarbon migration using PetroMod software,showing that hydrocarbon charging in the basin began at the end of the Late Jurassic(J3),peaking in hydrocarbon generation,expulsion,and accumulation by the end of the Early Cretaceous(K1)and maintaining high accumulation rates until the late Cretaceous,though significantly decreasing at the present stage.The simulation results were verified by comparison with actual drilling data,which confirms their reliability and applicability to other analogous oilfields.
基金supported by the National Natural Science Foundation of China(Grant No.42372173)the Science and Technology Cooperation Project of the CNPC-SWPU Innovation Alliance,China(Grant No.2020CX020000).
文摘As the cornerstone for evaluating the storage capacity of shale reservoirs and assessing the viability of shale gas exploitation,shale pores play a very important role in shale reservoirs.Based on drilling well and test data,deep learning,and artificial intelligence for image analysis,the types,characteristics,structures,and vertical heterogeneity of shale pores were studied.Additionally,we conducted a comprehensive investigation into the sedimentary environment characteristics and their influence on the heterogeneity of shale reservoir pores in the Longmaxi Formation using associated geochemical analyses.The results revealed that the sedimentary environment underwent significant changes in the Longmaxi Formation,characterized by a sea level fall,accelerated sedimentation rates,weakened reducing conditions,decreased palaeoproductivity,and increased terrigenous influx,which led to a decrease in the frequency of organic matter(OM)pores,paralleled by a gradual increase in inorganic pores.In the S_(1)1_(1)^(1-1),S_(1)1_(1)^(1-2),S_(1)1_(1)^(1-3) sections of the Long11 sub-member,OM pores constitute the primary pore type.Conversely,in the S_(1)1_(1)^(1-4) section and the Long12 sub-member,inorganic pores prevail as the primary pore type.Furthermore,the strongly anoxic sections are also pay zones that are not only enriched in OM but also concentrated with OM pores.The S_(1)1_(1)^(1-1) and S_(1)1_(1)^(1-2) sections are characterized by anoxic conditions,with total organic carbon(TOC)content exceeding 4%and abundant biogenic silica.Notably,an increased terrigenous influx adversely impacts the development and preservation of pores in the Long11 sub-member while exerting a dual effect in the Long12 sub-member.The increased terrigenous influx dilutes the OM and decreases the probability of intergranular pores and intragranular pores filled by OM.Moreover,more brittle mineral particles were deposited,which promotes the development and preservation of intergranular and intragranular pores.
基金This work was supported by National Key Basic Research Program of China(973 Program)(No.2012CB214704-02)National Science and Technology Major Project of China(No.2011ZX05008-002)and Key Laboratory Project of Gansu(No.1309RTSA041).
文摘For exploration and potential evaluation of deep shale reservoirs with high maturity,hydrocarbon generation and pore evolution of muddy shale in deep high evolution stage were investigated by the high-temperature high-pressure simulation experiment.Results indicated that under high pressure condition,nano-scale micropores in organic matter-rich muddy shale constantly increased as rise of temperature and pressure,leading to increase of shale porosity.However,in the high mature-overmature stage,shale porosity decreased with further increase of temperature and pressure.In contrast to micropores,micro-scale capillary pores and megapores in shale constantly decreased as rise of simulation temperature or pressure,indicating that deep-burial reservoirs was not favorable for free-gas storage;but significant increase of micropores and surface area during this stage could make up for a loss of adsorbed natural gas in shale due to decrease of adsorption capacity which was induced by increase of temperature and pressure,thus leading to high shale gas potential in deep layers.A large number of secondary micropores were developed in the simulated samples such as pyrite and dolomite,demonstrating that shale clasts and mineral matrix could also form abundant secondary micropores during the deep evolution stage;during the evolution process,shale as hydrocarbon source rock could generate a large amount of acidic fluid which was favorable for development of secondary porosity.
基金funded by the National Natural Science Foundation of China(41872128)Postdoctoral Foundation of China University of Petroleum(Beijing)(ZX20220102).
文摘The majority of oil and gas resources in the world are related to saline sediments, which mainly occur in sedimentary strata in the form of cap rocks or salt-associated shales. A large number of shale oil resources have been discovered in the saline shale sediments of the Cenozoic terrestrial lake basin in China. The hydrocarbon generation ability and the reservoir capacity of shale control the oil and gas generation. The reservoir capacity is mainly characterized by pore type, structure and porosity. Most of China’s shale oil and gas resources belong to salt-bearing formations. The role of gypsum-salt rocks in the formation and evolution of organic matter (OM) in such formations has received extensive attention. However, systematic understanding is lacking. Research on the pore formation and evolution in shale under the action of gypsum-salt rock sediments is especially weak. Taking the shales in the third member of the Shahejie Formation (Es_(3)) of the Bohai Bay Basin as an example, the influence of halite on the formation and evolution process of pores was studied in this paper. The results show that halite and gypsum minerals were associated with OM, which made them more likely to develop OM pores. The samples with a high halite mineral content (HC) are more developed regarding the pore volume and specific surface area than those with a low HC. The formation of thick salt rocks is influenced by factors of deep thermal brine upwelling, sea erosion and arid environments. The frequent alternation between humid and arid environments led to the outbreak and death of organisms and the precipitation of gypsum-salt rock, which formed the simultaneous deposition of OM and halite minerals. Finally, we have established a model of shale pore evolution under the participation of the gypsum-salt rock, and halite minerals contribute to pore development in both Stage II and Stage IV. This study provides strong microscopic evidence for the pore system formation and evolution in salt-bearing reservoirs.
基金supported by the National Major Science and Technology Project“Demonstration project of normal-pressure shale gas exploration and development in the Pengshui area”(No.2016ZX05061)the Sinopec Science and Technology Development Department Project“Study on main controlling factors of shale gas enrichment in the basin-margin transition zone of SE Chongqing”(No.P18057-2).
文摘At present,researches on the pore evolution of shale reservoir and its evolution mechanism are still at such a groping stage that a consensus has not yet reached.Based on core analysis and thermal simulation experiments,the pore types,pore structures and pore-size change rules of shale gas reservoirs of Upper Ordovician Wufeng-Lower Silurian Longmaxi Fms in the southeastern(SE)Sichuan Basin and its basin-margin transition zone(hereinafter referred to as the basin-margin transition zone of SE Chongqing)were studied by means of argon ion polishing-scanning electron microscopy(SEM)and atomic force microscopy.Then,the evolution characteristics of organic pores were discussed,and the influence of associated minerals on pore evolution was analyzed.Finally,a pore evolution model for the shale gas reservoirs in this area was established.And the following research results were obtained.First,three types of reservoir spaces are mainly developed in the high-quality shale reservoirs of Wufeng-Longmaxi Fms in this area,including fracture,inorganic pore and organic pore.And the organic pores provide the primary reservoir space of shale gas,which can be divided into four categories,i.e.,amorphous kerogen pores,structured kerogen pores,asphaltene pores and paleontology fossil pores.Second,organic contracted fractures are related to the contraction of organic matters,first appearing on one side of the organic matters and then becomes wider and wider with the increase of temperatures.Third,organic pores are mostly the“spongy”pores distributed densely inside the organic matters.When Ro is in the range of 1.56-3.50%,macropores and mesopores are dominant.And when Ro exceeds 3.50%,macropores decrease while mesopores and micropores increase.Fourth,the types of organic matters and the content of associated minerals(e.g.clay minerals,siliceous particles and pyrite)play an important role in the development of pores.In conclusion,the pore evolution law of Wufeng-Longmaxi shale in the basin-margin transition zone of SE Chongqing is that with the increase of burial depth,inorganic porosity decreases significantly,organic porosity increases first and then decreases,and the total porosity shows a change trend of decreasing first,then increasing and finally decreasing continuously.
基金supported by the National Natural Science Foundation of China(Grant Nos.42072150,41372144)the State Science and Technology Major Project of China(Grant No.2017ZX05049001-008)
文摘Pyrolysis experiments were conducted on lacustrine organic-rich shale from Cangdong Sag in Bohai Bay Basin,China,to investigate the impact of hydrocarbon generation on shale pore structure evolution.Thermal evolution is found to control the transformation of organic matter,hydrocarbon products characteristics,and pore structure changes.Furthermore,pore volume and specific surface area increase with increasing maturity.In low-mature stage,the retained oil content begins to increase,pore volumes show slight changes,and primary pores are occluded by the generated crude oil of high molecular weight and density.In the oil-window stage,the retained oil content rapidly increases and reaches maximum,and pore volumes gradually increase with increasing thermal maturity.At high mature stage,the retained oil content begins to decrease,and the pore volume increases considerably owing to the expulsion of liquid hydrocarbon.In over mature stage,natural gas content significantly increases and kerogen transforms to asphalt.Numerous organic pores are formed and the pore size gradually increases,resulting from the connection of organic pores caused the increasing thermal stress.This study lays a foundation for understanding variation of hydrocarbon products during the thermal evolution of lacustrine shales and its relationship with the evolution of shale reservoirs.
基金supported by the National Science and Technology Major Project(Grant No.2017ZX05035)
文摘The Upper Ordovician Wufeng-Lower Silurian Longmaxi and the Lower Cambrian Qiongzhusi shales are the major targets for shale gas exploration and development in China.Although the two organic-rich shales share similar distribution ranges and thicknesses,they exhibit substantially different exploration and development results.This work analyzed the nanopore structures of the shale reservoirs in this region.Pore development of 51 shale samples collected from various formations and locations was compared using the petromineralogical,geochemical,structural geological and reservoir geological methods.The results indicate that the reservoir space in these shales is dominated by organic pores and the total pore volume of micropores,mesopores,macropores in different tectonic areas and formations show different trends with the increase of TOC.It is suggested that organic pores of shale can be well preserved in areas with simple structure and suitable preservation conditions,and the shale with smaller maximum ancient burial depth and later hydrocarbongeneration-end-time is also more conducive to pore preservation.Organic pore evolution models are established,and they are as follows:①Organic matter pore development stage,②Early stage of organic matter pore destruction,and③late stage of organic matter pore destruction.The areas conducive to pore development are favorable for shale gas development.Research results can effectively guide the optimization and evaluation of favorable areas of shale gas.
基金supported by the National Natural Science Foundation of China(Grant Nos.42072168 and 41802156)the National Key R&D Program of China(Grant No.2019YFC0605405)the Fundamental Research Funds for the Central Universities(Grant Nos.2023ZKPYDC07 and 2022YQDC06)。
文摘The lacustrine shale of deep Shahezi Formation in the Songliao basin has great gas potential,but its pore evolution,heterogeneity,and connectivity characteristics remain unclear.In this work,total organic carbon analysis,rock pyrolysis,X-ray diffraction field emission scanning electron microscopy,the particle and crack analysis system software,low-temperature nitrogen adsorption experiment,fractal theory,high-pressure mercury injection experiment and nuclear magnetic resonance experiment were used to study the Shahezi shale from Well SK-2.The result indicated that the organic pores in Shahezi shale are not developed,and the intergranular and intragranular pores are mainly formed by illitedominated clay.As the burial depth increases,the pore size and slit-shaped pores formed by clay decrease,and dissolved pores in the feldspar and carbonate minerals and dissolved fractures in the quartz increase.The pore evolution is affected by clay,compaction,and high-temperature corrosion.Based on the pore structure characteristics reflected by the pore size distribution and pore structure parameters obtained by multiple experimental methods,the pore development and evolution are divided into three stages.During stageⅠandⅡ,the pore heterogeneity of the shale reservoirs increases with the depth,the physical properties and pore connectivity deteriorate,but the gas-bearing property is good.In stageⅢ,the pore heterogeneity is the highest,its gas generation and storage capacity are low,but the increase of micro-fractures makes pore connectivity and gas-bearing better.
基金sponsored by the National Natural Science Foundation of China(42072187,42090025)CNPC Key Project of Science and Technology(2021DQ0405)。
文摘The evolution of pore structure in shales is affected by both the thermal evolution of organic matter(OM)and by inorganic diagenesis,resulting in a wide variety of pore structures.This paper examines the OM distribution in lacustrine shales and its influence on pore structure,and describes the process of porosity development.The principal findings are:(i)Three distribution patterns of OM in lacustrine shales are distinguished;laminated continuous distribution,clumped distribution,and stellate scattered distribution.The differences in total organic carbon(TOC)content,free hydrocarbon content(S_(1)),and OM porosity among these distribution patterns are discussed.(ii)Porosity is negatively correlated with TOC and plagioclase content and positively correlated with quartz,dolomite,and clay mineral content.(iii)Pore evolution in lacustrine shales is characterized by a sequence of decreasing-increasing-decreasing porosity,followed by continuously increasing porosity until a relatively stable condition is reached.(iv)A new model for evaluating porosity in lacustrine shales is proposed.Using this model,the organic and inorganic porosity of shales in the Permian Lucaogou Formation are calculated to be 2.5%-5%and 1%-6.3%,respectively,which correlate closely with measured data.These findings may provide a scientific basis and technical support for the sweet spotting in lacustrine shales in China.
基金Supported by the National Key Basic Research and Development Program(2015CB250906)National Natural Science Foundation of China(41972139,41922015)Special Funds for Basic Scientific Research in Central Universities(18CX02069A)。
文摘Aiming at the complicated problem of the genesis of high-quality hybrid sedimentary rocks,the pore-throat systems,controlling factors and fluid mobility of hybrid sedimentary rocks in the Permian Lucaogou Formation in Jimusar Sag were examined.The results show that the hybrid sedimentary rocks contain 5 types of pore-throat system,intergranular(Type A),mixed intergranular-dissolved-intercrystalline(Type B),dissolved(Type C),mixed dissolved-intercrystalline(Type D)and intercrystalline(Type E)ones.The pore-throat systems are controlled by 3 major factors,the component content and arrangement(CCA)of hybrid sedimentary rocks,sedimentary environment and diagenesis.CCA controls the matrix support mode of hybrid sedimentary rocks,and therefore controls the types and changes of pore-throat system.The sedimentary environment mainly controls the macroscopic distribution of pore-throat system,i.e.,hybrid sedimentary rocks deposited in the near source and high-energy environment are characterized by high content of coarse-grained component,granular/interbedded-support mode,and development of Type A and Type B pore-throat systems.Hybrid sedimentary rocks deposited in the medium-energy environment far from source are characterized by dolomitic/mud support mode and Type C and Type D pore-throat systems.Hybrid sedimentary rocks deposited in low-energy environment far from source have mainly Type E and Type D pore-throat systems.Diagenetic processes such as compaction and calcite cementation make the proportions of Type A and Type C pore-throat systems decrease further.In the hybrid sedimentary process of sandy-mud,pore-throat system types show a change of"A→B→C→D",in that of dolomite-sand,pore-throat system types show a change of"A→C→D→E"or"B→D→E",and in that of dolomite-mud,pore-throat system types show a change of"D→E",which are affected in details by the contents of coarse-grain component,feldspar and dolomite.The reservoir with Type A pore-throats has the best physical properties and fluid mobility,and the reservoirs with Type D and Type E pore-throats have the poorest.The movable fluid distribution is related to the matrix support mode,and the larger pores in hybrid sedimentary rocks of dolomite/mud support mode have no obvious advantage in fluid mobility.The findings of this study provide a geological basis for evaluating and building reasonable interpretation model of hybrid sedimentary rocks sweet spot.
基金supported by the National Natural Science Foundation of China(No.52178354).
文摘To investigate the macroscopic fatigue properties and the mesoscopic pore evolution characteristics of salt rock under cyclic loading,fatigue tests under different upper-limit stresses were carried out on salt rock,and the mesoscopic pore structures of salt rock before and after fatigue tests and under different cycle numbers were measured using CT scanning instrument.Based on the test results,the effects of the cycle number and the upper-limit stress on the evolution of cracks,pore morphology,pore number,pore volume,pore size,plane porosity,and volume porosity of salt rock were analyzed.The failure path of salt rock specimens under cyclic loading was analyzed using the distribution law of plane porosity.The damage variable of salt rock under cyclic loading was defined on basis of the variation of volume porosity with cycle number.In order to describe the fatigue deformation behavior of salt rock under cyclic loading,the nonlinear Burgers damage constitutive model was further established.The results show that the model established can better reflect the whole development process of fatigue deformation of salt rock under cyclic loading.
基金financially supported by the Special Research Assistant Fund Project of Chinese Academy of Sciences.
文摘Coal gasification fly ash(CGFA)is an industrial solid waste from the coal circulating fluidized bed(CFB)gasification process,and it needs to be effectively disposed to achieve sustainable development of the environment.To realize the application of CGFA as a precursor of porous carbon materials,the physicochemical properties of three kinds of CGFA from industrial CFB gasifiers are analyzed.Then,the activation potential of CGFA is acquired via steam activation experiments in a tube furnace reactor.Finally,the fluidization activation technology of CGFA is practiced in a bench-scale CFB test rig,and its advantages are highlighted.The results show that CGFA is characterized by a high carbon content in the range of 54.06%–74.09%,an ultrafine particle size(d50:16.3–26.1 μm),and a relatively developed pore structure(specific surface area SSA:139.29–551.97 m^(2)·g^(-1)).The proportion of micropores in CGFA increases gradually with the coal rank.Steam activation experiments show that the pore development of CGFA mainly includes three stages:initial pore development,dynamic equilibrium between micropores and mesopores and pore collapse.The SSA of lignite fly ash(LFA),subbituminous fly ash(SBFA)and anthracite fly ash(AFA)is maximally increased by 105%,13%and 72%after steam activation;the order of the largest carbon reaction rate and decomposition ratio of steam among the three kinds of CGFA is SBFA>LFA>AFA.As the ratio of oxygen to carbon during the fluidization activation of LFA is from 0.09 to 0.19,the carbon conversion ratio increases from 14.4%to 26.8%and the cold gas efficiency increases from 6.8%to 10.2%.The SSA of LFA increases by up to 53.9%during the fluidization activation process,which is mainly due to the mesoporous development.Relative to steam activation in a tube furnace reactor,fluidization activation takes an extremely short time(seconds)to achieve the same activation effect.It is expected to further improve the activation effect of LFA by regulating the carbon conversion ratio range of 27%–35%to create pores in the initial development stage.
