The connectivity of shale pores and the occurrence of movable oil in shales have long been the focus of research.In this study,samples from wells BX7 and BYY2 in the Eq3^4-10 cyclothem of Qianjiang Formation in the Qi...The connectivity of shale pores and the occurrence of movable oil in shales have long been the focus of research.In this study,samples from wells BX7 and BYY2 in the Eq3^4-10 cyclothem of Qianjiang Formation in the Qianjiang depression,were analyzed.A double mercury injection method was used to distinguish between invalid and effective connected pores.The pore characteristics for occurrence of retained hydrocarbons and movable shale oil were identified by comparing pore changes in low temperature nitrogen adsorption and high pressure mercury injection experiments before and after extraction and the change in the mercury injection amounts in the pores between two separate mercury injections.The results show that less than 50%of the total connected pores in the Eq34-10 cyclothem samples are effective.The development of effective connected pores affects the mobility of shale oil but varies with different lithofacies.The main factor limiting shale oil mobility in Well BX7 is the presence of pores with throat sizes less than 15 nm.In Well BYY2,residual mercury in injection testing of lamellar dolomitic mudstone facies was mainly concentrated in pores with throats of 10-200 nm,and in bulk argillaceous dolomite facies,it was mainly concentrated at 60-300 nm.The throats of hydrocarbon-retaining pores can be 5 nm or even smaller,but pores with movable shale oil in the well were found to have throat sizes greater than 40 nm.Excluding the influence of differences in wettability,the movability of shale oil is mainly affected by differences in lithofacies,the degree of pore deformation caused by diagenesis,the complexity of pore structures,and the connectivity of pore throats.Dissolution and reprecipitation of halite also inhibit the mobility of shale oil.展开更多
The Tarim Basin has revealed numerous tight sandstone oil and gas reservoirs.The tidal fl at zone in the Shunbei area is currently in the detailed exploration stage,requiring a comprehensive description of the sand bo...The Tarim Basin has revealed numerous tight sandstone oil and gas reservoirs.The tidal fl at zone in the Shunbei area is currently in the detailed exploration stage,requiring a comprehensive description of the sand body distribution characteristics for rational exploration well deployment.However,using a single method for sand body prediction has yielded poor results.Seismic facies analysis can eff ectively predict the macro-development characteristics of sedimentary sand bodies but lacks the resolution to capture fine details.In contrast,single-well sedimentary facies analysis can describe detailed sand body development but struggles to reveal broader trends.Therefore,this study proposes a method that combines seismic facies analysis with single-well sedimentary microfacies analysis,using the lower section of the Kepingtage Formation in the Shunbei area as a case study.First,seismic facies were obtained through unsupervised vector quantization to control the macro-distribution characteristics of sand bodies,while principal component analysis(PCA)was applied to improve the depiction of fine sand body details from seismic attributes.Based on 3D seismic data,well-logging data,and geological interpretation results,a detailed structural interpretation was performed to establish a high-precision stratigraphic framework,thereby enhancing the accuracy of sand body prediction.Seismic facies analysis was then conducted to obtain the macro-distribution characteristics of the sand bodies.Subsequently,core data and logging curves from individual wells were used to clarify the vertical development characteristics of tidal channels and sandbars.Next,PCA was employed to select the seismic attributes most sensitive to sand bodies in diff erent sedimentary facies.Results indicate that RMS amplitude in the subtidal zone and instantaneous phase in the intertidal zone are the most sensitive to sand bodies.A comparative analysis of individual seismic attributes for sand body characterization revealed that facies-based delineation improved the accuracy of sand body identification,eff ectively capturing their contours and shapes.This method,which integrates seismic facies,single-well sedimentary microfacies,and machine learning techniques,enhances the precision of sand body characterization and off ers a novel approach to sand body prediction.展开更多
Shale gas is an important unconventional resource,and shale reservoirs typically contain both water and gas fluids.Water can occupy the shale gas storage space,reduce the flow capacity of shale gas,and even completely...Shale gas is an important unconventional resource,and shale reservoirs typically contain both water and gas fluids.Water can occupy the shale gas storage space,reduce the flow capacity of shale gas,and even completely seal off the shale gas.When the shale develops an effective sealing capacity,the water saturation of the shale reaches a threshold value which can be measured using physical simulation experiments.However,limited research has been conducted on the quantitative calculation of critical water saturation.In order to obtain the critical water saturation of shale,this paper proposes a theoretical calculation method to estimate the critical water saturation of shale based on DLvo(Derjaguin-Landau-Verwey-Overbeek)theory.Two shale samples from the Longmaxi Formation in the Sichuan Basin with different total organic carbon(TOC)were selected for gas adsorption experiments to characterize the pore structure of the organic matter and inorganic matter of the shale.Based on the established theoretical and geological models,the critical water film thickness and critical water saturation of pores with different pore sizes were calculated.Taking the boundary conditions into account,the critical water saturation of the two shale samples was ultimately determined.The results showed that inorganic pores occupied 81.0%of the pores of the shale with a ToC of 0.89%,and their dominant pore sizes were dominated by mesopores around 40 nm;inorganic pores occupied 48.7%of the pores of the shale with a TOC of 4.27%,and their dominant pore sizes were dominated by micropores and mesopores around 0-20 nm and 40 nm.As the pore size increased,the corresponding critical water film thickness also increased,and the critical water saturation was normally distributed in the pore size range centered at about 10 nm.The distribution of critical water saturation in inorganic pores with different pore sizes was in the range of about 63%-76%,and the critical water saturation of shale with a TOC of 0.89%and shale with a TOC of 4.27%were calculated to be 41.7%and 32.7%,respectively.The method proposed in this study accurately calculates the critical water saturation of shale and effectively distinguishes the differences critical water saturation between shales with different TOc.Further,shale gas reservoirs can be finely characterized by comparing with the original water saturation of shale layers.This study is of great scientific significance to shale gas exploration and development,and even to the field of cO2 geological storage.展开更多
Occurrence and abundance of molecular hydrogen in natural geologic reservoirs are enigmatic,due to its various sources,diverse migration pathways and complicated biological and chemical reactions.Natural gas samples c...Occurrence and abundance of molecular hydrogen in natural geologic reservoirs are enigmatic,due to its various sources,diverse migration pathways and complicated biological and chemical reactions.Natural gas samples containing hydrogen from producing wells in several sedimentary basins in China were collected in this study,and gas abundances and isotopic compositions of these gases were compared with those in global petroliferous basins and deep intrusive rocks.Several geochemical indicators were suggested for identifying sources,migration and accumulation mechanisms of hydrogen in the subsurface environment.Hydrogen contents in natural gas deposits have contributions from various sources with the following high-to-low order:microbial degradation>serpentinization>deep mantle volatile release>radiation-induced water decomposition>thermal cracking of organic matter.A hydrogen-rich reservoir in Kansas,USA,is specifically analyzed to determine its formation mechanism.This study suggests that future exploration of geological hydrogen resources may focus on the igneous rock bodies with overlying dense sedimentary rocks in the continental rift systems.展开更多
The deep-water systems in different types of sedimentary basins exhibit significant variability.Current knowledge of deep-water deposition is mainly derived from deep-marine turbidite systems.However,the characteristi...The deep-water systems in different types of sedimentary basins exhibit significant variability.Current knowledge of deep-water deposition is mainly derived from deep-marine turbidite systems.However,the characteristics and differences of sub-lacustrine gravity flow deposition systems have been a research focus in the fields of sedimentology and petroleum geology.This study investigates the facies archi-tecture,depositional processes,and sediment distribution patterns of a sub-lacustrine debrite system in the Eocene Dongying Rift of the Bohai Bay Basin,China,through the analysis of integrated core data,3-D seismic data,and well-log data.Nine facies have been identified within the debrite system,representing various depositional processes such as sandy debris flow,muddy debris flow,turbidity currents,sandy slide,sandy slide/slump,and mud flow.Our research indicates that the sub-lacustrine system is primarily influenced by debris flow rather than turbidity currents,as supported by facies quantification,inter-pretation,and flow rheology analysis.Additionally,we have identified five basic facies building blocks in debrite systems,including slide masses,slump masses,debrite channels,debrite lobes,and turbidite sheets.We have also elucidated and proposed detailed sedimentary processes,flow transport,and transformation within the sub-lacustrine system through analysis of flow origins,facies sequences,and distribution characteristics.Our findings highlight the evolutionary progression from delta-front collapse to sandy slide/slump,sandy debris flow,and finally muddy debris flow.The efficient generation of turbidity currents from parental landslides on sand-prone slopes is deemed unlikely due to rift-basin morphology and transport distances.The formation of the five basic facies building blocks is closely linked to depositional processes and dominant flow types.Consequently,we present a deep-water depositional model for sub-lacustrine debrite systems,focusing on flow dynamics,sediment distribu-tion patterns,and basin morphology within deep lacustrine rifts.This model offers valuable insights into the variability of deep-water deposition in diverse basin settings and aids in predicting lithologic res-ervoirs during deep-water hydrocarbon exploration.展开更多
This paper summarizes the important progress in the field of oil and gas production engineering during the"Thirteenth Five-Year Plan"period of China,analyzes the challenges faced by the current oil and gas p...This paper summarizes the important progress in the field of oil and gas production engineering during the"Thirteenth Five-Year Plan"period of China,analyzes the challenges faced by the current oil and gas production engineering in terms of technological adaptability,digital construction,energy-saving and emission reduction,and points out the future development direction.During the"Thirteenth Five-Year Plan"period,series of important progresses have been made in five major technologies,including separated-layer injection,artificial lift,reservoir stimulation,gas well de-watering,and workover,which provide key technical support for continuous potential tapping of mature oilfields and profitable production of new oilfields.Under the current complex international political and economic situation,oil and gas production engineering is facing severe challenges in three aspects:technical difficulty increases in oil and gas production,insignificant improvements in digital transformation,and lack of core technical support for energy-saving and emission reduction.This paper establishes three major strategic directions and implementation paths,including oil stabilization and gas enhancement,digital transformation,and green and low-carbon development.Five key research areas are listed including fine separated-layer injection technology,high efficiency artificial lift technology,fine reservoir stimulation technology,long term gas well de-watering technology and intelligent workover technology,so as to provide engineering technical support for the transformation,upgrading and high-quality development of China’s oil and gas industry.展开更多
The Upper Ordovician Wufeng-Lower Silurian Longmaxi shale is widely distributed in the Sichuan Basin and its periphery,which is the key stratum for marine shale gas exploration and development(E&D)in China.Based o...The Upper Ordovician Wufeng-Lower Silurian Longmaxi shale is widely distributed in the Sichuan Basin and its periphery,which is the key stratum for marine shale gas exploration and development(E&D)in China.Based on sedimentary environment,material basis,storage space,fracability and reservoir evolution data,the reservoir characteristics of the Wufeng-Longmaxi shale and their significance for shale gas E&D are systematically compared and analyzed in this paper.The results show that(1)the depocenter of the Wufeng(WF)-Longmaxi(LM)shale gradually migrates from east to west.The high-quality shale reservoirs in the eastern Sichuan Basin are mainly siliceous shales,which are primarily distributed in the graptolite shale interval of WF2-LM5.The high-quality reservoirs in the southern Sichuan Basin are mainly calcareous-siliceous and organic-rich argillaceous shales,which are distributed in the graptolite shale interval of WF2-LM7.(2)Deep shale gas(the burial depth>3500 m)in the Sichuan Basin has high-ultrahigh pressure and superior physical properties.The organic-rich siliceous,calcareous-siliceous and organic-rich argillaceous shales have suitable reservoir properties.The marginal area of the Sichuan Basin has a higher degree of pressure relief,which leads to the argillaceous and silty shales evolving into direct cap rocks with poor reservoir/good sealing capacity.(3)Combining shale gas exploration practices and impacts of lithofacies,depth,pressure coefficient and brittle-ductile transition on the reservoir properties,it is concluded that the favorable depth interval of the Wufeng-Longmaxi shale gas is 2200~4000 m under current technical conditions.(4)Aiming at the differential reservoir properties of the Wufeng-Longmaxi shale in the Sichuan Basin and its periphery,several suggestions for future research directions and E&D of shale gas are formulated.展开更多
Geological conditions and main controlling factors of gas accumulation in subsalt Ma 4 Member of Ordovician Majiagou Formation are examined based on large amounts of drilling,logging and seismic data.The new understan...Geological conditions and main controlling factors of gas accumulation in subsalt Ma 4 Member of Ordovician Majiagou Formation are examined based on large amounts of drilling,logging and seismic data.The new understandings on the control of paleo-uplift over facies,reservoirs and accumulations are reached:(1)During the sedimentary period of Majiagou Formation,the central paleo-uplift divided the North China Sea in central-eastern of the basin from the Qinqi Sea at southwest margin of the basin,and controlled the deposition of the thick hummocky grain beach facies dolomite on platform margin of Ma 4 Member.Under the influence of the evolution of the central paleo-uplift,the frame of two uplifts alternate with two sags was formed in the central-eastern part of the basin,dolomite of inner-platform beach facies developed in the underwater low-uplift zones,and marl developed in the low-lying areas between uplifts.(2)From the central paleo-uplift to the east margin of the basin,the dolomite in the Ma 4 Member gradually becomes thinner and turns into limestone.The lateral sealing of the limestone sedimentary facies transition zone gives rise to a large dolomite lithological trap.(3)During the late Caledonian,the basin was uplifted as a whole,and the central paleo-uplift was exposed and denuded to various degrees;high-quality Upper Paleozoic Carboniferous-Permian coal measures source rocks deposited on the paleo-uplift in an area of 60000 km^(2),providing large-scale hydrocarbon for the dolomite lithological traps in the underlying Ma 4 Member.(4)During the Indosinian-Yanshanian stage,the basin tilted westwards,and central paleo-uplift depressed into an efficient hydrocarbon supply window.The gas from the Upper Paleozoic source rock migrated through the high porosity and permeability dolomite in the central paleo-uplift to and accumulated in the updip high part;meanwhile,the subsalt marine source rock supplied gas through the Caledonian faults and micro-fractures as a significant supplementary.Under the guidance of the above new understandings,two favorable exploration areas in the Ma 4 Member in the central-eastern basin were sorted out.Two risk exploration wells were deployed,both revealed thick gas-bearing layer in Ma 4 Member,and one of them tapped high production gas flow.The study has brought a historic breakthrough in the gas exploration of subsalt Ma 4 Member of Ordovician,and opened up a new frontier of gas exploration in the Ordos Basin.展开更多
Based on field outcrop investigation,interpretation and analysis of drilling and seismic data,and consulting on a large number of previous research results,the characteristics of ancient marine hydrocarbon source rock...Based on field outcrop investigation,interpretation and analysis of drilling and seismic data,and consulting on a large number of previous research results,the characteristics of ancient marine hydrocarbon source rocks,favorable reservoir facies belts,hydrocarbon migration direction and reservoir-forming law in the Ordos Basin have been studied from the viewpoints of North China Craton breakup and Qilian-Qinling oceanic basin opening and closing.Four main results are obtained:(1)Controlled by deep-water shelf-rift,there are three suites of source rocks in the Ordos Basin and its periphery:Mesoproterozoic,Lower Cambrian and Middle-Upper Ordovician.(2)Controlled by littoral environment,paleo-uplift and platform margin,four types of reservoirs are developed in the area:Mesoproterozoic-Lower Cambrian littoral shallow sea quartz sandstone,Middle-Upper Cambrian–Ordovician weathering crust and dolomitized reservoir,and Ordovician L-shape platform margin reef and beach bodies.(3)Reservoir-forming assemblages vary greatly in the study area,with"upper generation and lower storage"as the main pattern in the platform,followed by"self-generation and self-storage".There are both"upper generation and lower storage"and"self-generation and self-storage"in the platform margin zone.In addition,in the case of communication between deep-large faults and the Changchengian system paleo-rift trough,there may also exist a"lower generation and upper reservoir"combination between the platform and the margin.(4)There are four new exploration fields including Qingyang paleo-uplift pre-Carboniferous weathering crust,L-shape platform margin zone in southwestern margin of the basin,Ordovician subsalt assemblage in central and eastern parts of the basin,and Mesoproterozoic–Cambrian.Among them,pre-Carboniferous weathering crust and L-shape platform margin facies zone are more realistic replacement areas,and Ordovician subsalt assemblage and the Proterozoic-Cambrian have certain potential and are worth exploring.展开更多
The Fuling shale gas field in China is the largest shale gas field as well as the largest of its type discovered in any Lower Paleozoic formation.In this study,the geology and production of the upper and lower gas lay...The Fuling shale gas field in China is the largest shale gas field as well as the largest of its type discovered in any Lower Paleozoic formation.In this study,the geology and production of the upper and lower gas layers in the Fuling shale gas field are evaluated in terms of structure,shale quality,fault,initial production,and estimated ultimate recovery(EUR).The shale in the lower gas layer of the Jiaoshiba anticline is a high-quality reservoir,where the space is dominated by organic pores in kerogen,and the gas content is high.The shale gas wells reveal relatively high initial production and EUR.However,the shale in the upper gas layer of the Jiaoshiba anticline has reservoir space mainly composed of clay mineral pores and organic pores within bitumen,and the gas content is low.In terms of structure,primary gas migration may occur in the upper gas layer,resulting in free gas accumulation in the structural high,where the development effects are generally better than those in the structural low.The lower gas layer in the Pingqiao anticline,is the main interval for shale gas accumulation and development due to the high-quality shale.Under the influence of faults,the efficiency of exploration wells emplaced on top of the anticline is much lower a compared with those in the flanks.The residual synclines close to the Sichuan Basin,including the Baima and Baitao anticlines,are characterized by more recent uplifts,larger area,greater distance from the deep and large faults,and early fracture closure.Therefore,we recommend that the shale gas exploration and development should be carried out preferentially in areas close to the center of the residual synclines,featuring relatively high-pressure coefficient and moderate burial depth.展开更多
The mechanism of formation of lacustrine deposits within stable orogenic belts and their potential for shale oil and gas exploration are frontier themes of challenge in the fields of sedimentology and petroleum explor...The mechanism of formation of lacustrine deposits within stable orogenic belts and their potential for shale oil and gas exploration are frontier themes of challenge in the fields of sedimentology and petroleum exploration. Orogenic belts witness strong tectonic activities and normally cannot host stable lacustrine basins and deep shale formations. Therefore, basins in orogenic belts are considered to have no potential to form shale hydrocarbon reservoirs. Here we investigate the Luanping Basin located in the Yanshan orogenic belt where previous studies regarded rivers and fan deltas as the major main Mesozoic deposits. Based on detailed field exploration and scientific drilling, we report the finding of a large number of lacustrine shale continental deep-water deposits in the Mesozoic strata. Our finding of the occurrence of active shale oil and gas also in this basin also subvert the previous perceptions.We report SHRIMP zircon U-Pb age that define the bottom boundary of the target interval as 127.6 ± 1.7 Ma belonging to the early Cretaceous strata. Tectonics and climate are considered to be the main factors that controlled the deep-water sedimentation during this period. The drill cores revealed evidence of shale gas and the TOC of shale is 0.33%–3.60%, with an average value of 1.39% and Ro is 0.84%–1.21%, with an average value of 1.002%. The brittleness index of shale is between 52.7% and 100%. After vertical well fracturing, the daily gas production is more than 1000 m^(3). Our findings show that the basin has considerable potential for shale oil and gas. The geological resources of the shale gas in the Xiguayuan Fm. are estimated as 1110.12 × 10^(8) m^(3), with shale oil geological resources of 3340.152 × 10^(4) t. Our findings indicate that the Yanshan orogenic belt has potential exploration prospect. This work not only redefines the Luanping Basin as a rift deep-water Mesozoic Lake Basin, but also rules out the previous notion that the basin is dominated by shallow water sediments. The discovery of shale oil and gas also provides an important reference for subsequent petroleum exploration and development in this basin. Our study shows that shale oil and gas reservoirs can be found in the lacustrine basins of orogenic belts which were strongly influenced by volcanism. These results have significant implications for the sedimentology and oil exploration in the Qinling and Xingmeng Orogenic Belts of China, as well as those in other terranes of the world including the New England Orogenic Belt in Australia.展开更多
For extra-low permeability reservoirs, with a permeability of about 0.3×10?3 μm2, fluid flow and production performance in cores were studied. A long core holder with a multi-location piezometric measurement was...For extra-low permeability reservoirs, with a permeability of about 0.3×10?3 μm2, fluid flow and production performance in cores were studied. A long core holder with a multi-location piezometric measurement was specially designed. An artificial long core, about 700 mm long and with a cross section of 45mm×45mm, was used. In the experiment, pressure distribution along the core can be measured in real time. Single phase flow in the core was investigated. Different modes of production in long cores were also simulated including natural depletion, water flooding, and advanced water flooding. Through physical simulation, flow parameters were collected and production characteristics in extra-low permeability cores were studied. From experimental results, it can be seen that fluid flow in extra-low permeability cores is different from that in high permeability cores. Transmission of pressure in extra-low permeability cores is very slow, and it needs a long time for the pressure to become stable. The distribution curve of pressure along the core is nonlinear and the production rate in extra-low permeability reservoirs decreases sharply. The development effects of different production modes in extra-low permeability cores were compared with one another. Among the production modes, advanced water flooding has much potential for effective development of extra-low permeability reservoirs. Natural depletion and conventional water flooding can also be used in early production periods. In addition, the countermeasures and some ideas especially for the potential development of extra-low permeability reservoirs are suggested.展开更多
No breakthrough has been made in petroleum exploration of the Sinian Dengying Formation in the southeastern Sichuan Basin as the major factors controlling the hydrocarbon accumulation of the Dengying Formation have no...No breakthrough has been made in petroleum exploration of the Sinian Dengying Formation in the southeastern Sichuan Basin as the major factors controlling the hydrocarbon accumulation of the Dengying Formation have not been well established,including the development period and distribution of the platform margin,the effectiveness of the source-reservoir combination and the reliability of the Cambrian pre-salt structural trap.Based on the interpretation of seismic data and hydrocarbon-source correlation,the distribution of the platform margin of the Sinian Dengying Formation in the southeastern Sichuan Basin was mapped.Moreover,the gas source rocks of the Dengying Formation were clarified according to geochemical characteristics of fluid inclusions,and the pre-salt structures were further confirmed by seismic forward modeling and experiments of prestack depth migration.Results showed that the sedimentary facies of the 4th member of Dengying Formation in the southeastern Sichuan Basin was platform margin of gentle slope type.The platform margin reservoir of the Dengying Formation and the Lower Cambrian source rocks constitute a favorable source-reservoir combination.The carbon isotope characteristics of gas in fluid inclusions indicate that some of the oil/gas in the Dengying Formation were contributed by the Doushantuo Formation source rocks.As the difference in seismic velocities between carbonate rocks and gypsum/salt beds may cause a reduction in the amplitude of pre-salt structures,the low-amplitude structures identified on current seismic profiles are underestimated instead of overestimated.Accordingly,the Sinian structural traps are confirmed to develop in the deep pre-salt sequences in the low-steep anticline belt,southeastern Sichuan Basin.On the basis of the above new understanding,we propose two types of hydrocarbon migration modes for the Sinian Dengying Formation in southeastern Sichuan Basin,including lateral migration of hydrocarbons generated from the Cambrian Qiongzusi Formation and vertical migration of hydrocarbons derived from the Sinian Doushantuo Formation.Lithologic traps at the platform margin and pre-salt structural traps within the platform are favorable targets for natural gas exploration.展开更多
The Sichuan Basin is a major target for shale gas exploration in present China because of its rich gas stored in abundant black shales with multiple bed series.For further guidance or reference,field exploration and d...The Sichuan Basin is a major target for shale gas exploration in present China because of its rich gas stored in abundant black shales with multiple bed series.For further guidance or reference,field exploration and development practices in the shale reservoirs Upper Ordovician WufengeLower Silurian Longmaxi shale reservoirs were studied in terms of development stages and progress,favorable conditions for shale gas accumulation,bottlenecking issues on theories and technologies related to shale gas development,and so on.The following findings were obtained.(1)Shale with rich organic matters originated from the deep shelf has a good quality and great thickness in the continuous beds.The relatively stable wide buffer zones in synclines(anticlines)provides favorable conditions for shale gas accumulation and preservation with well developed micro-fractures and overpressure as necessary factors for a great potential of high shale gas productivity.(2)The bottlenecking technical issues restricting the shale gas industrial development in this study area include the following aspects:understandings of rich-organic matter shale sedimentary facies and modes,shale reservoir diagenetic process and evaluation systems,shale gas generation and accumulation mechanism,geophysical logging identification and prediction of shale gas layers,low resource utilization rate,great uncertainty of shale gas development,no technological breakthrough in the exploration of shale gas reservoirs buried deeper than 3500 m.In conclusion,this study area will be the major target for the shale gas exploration and development in China in a rather long period in the future.展开更多
It was previously deemed that volcanic rocks in the western Sichuan Basin were not developed,which restricted the exploration of volcanic gas reservoirs in this area.Recently,however,Sinopec's wildcat well,Well YS...It was previously deemed that volcanic rocks in the western Sichuan Basin were not developed,which restricted the exploration of volcanic gas reservoirs in this area.Recently,however,Sinopec's wildcat well,Well YS1 encounters Upper Permian volcanic rocks about 300 m thick in the western Sichuan Basin,the reservoir physical properties of which are good with strong gas shows.In order to evaluate the exploration prospect of volcanic gas reservoirs in western Sichuan Basin,we studied the Permian volcanic rocks in this area from the aspects of formation and development characteristics,reservoir characteristics,gas genesis and plays based on the new understandings on exploration wells,com-bined with the analysis on tectonic evolution and its controlling effect on volcanism.Then,the volcanic eruption mechanism,the distribution mode of volcanic edifice and the hydrocarbon accumulation pattern of volcanic gas reservoir were figured out.Finally,the exploration potential of natural gas was evaluated.The following research results were obtained:(1)the Permian volcanic rocks in western Sichuan Basin are well developed and its tectonic setting is consistent with that of Emeishan basalt,which is the product of the Emeishan mantle plume.(2)Under the control of vertical faults,a great number of volcanic edifices are developed and there are many eruption cycles.Volcanic rocks are superimposed vertically and connected laterally.(3)The volcanic rocks in western Sichuan Basin are different to some extent from those in southwestern Sichuan Basin in terms of lithology,lithofacies and reservoir characteristics.In the western Sichuan Basin,the tuff of explosive facies is dominant with some basalt of effusive facies,and the reservoir space of volcanic rocks is mainly acted by inter-breccia skeletal pores,dissolved pores and matrix micro-pores.In conclusion,multiple sets of effective source rocks are developed around the volcanic intervals in western Sichuan Basin,and together they constitute effective natural gas plays.Therefore,it has a better natural gas exploration prospect,and it is a new field worthy of attention.展开更多
Based on the analysis of the production composition of reservoirs developed by the second&tertiary recovery combination(STRC),the relationship between the overall output of the STRC project and the production leve...Based on the analysis of the production composition of reservoirs developed by the second&tertiary recovery combination(STRC),the relationship between the overall output of the STRC project and the production level during the blank water flooding stage is proposed.According to the basic principle of reservoir engineering that the“recovery factor is equal to sweeping coefficient multiplied by oil displacement efficiency”,the formula for calculating the ultimate oil recovery factor of chemical combination flooding reservoir was established.By dividing the reservoir into a series of grids according to differen-tial calculus thinking,the relationship between the ultimate recovery factor of a certain number of grids and the recovery de-gree of the reservoir was established,and then the variation law of oil production rate of the STRC reservoir was obtained.The concept of“oil rate enlargement factor of chemical combination flooding”was defined,and a production calculation method of reservoir developed by STRC was put forward based on practical oilfield development experience.The study shows that the oil production enhancing effect of STRC increases evenly with the in crease of the ratio of STRC displacement efficiency to water displacement efficiency,and increases rapidly with the increase of the ratio of recovery degree at flooding mode conversion to the water displacement efficiency.STRC is more effective in increasing oil production of reservoir with high recovery degree.Through practical tests of the alkali free binary flooding(polymer/surfactant)projects,the relative error of the oil production calculation method of STRC reservoir is about±10%,which meets the requirements of reservoir engineering.展开更多
By using core,logging curves,and experiment data,favorable lithofacies types in the 2 nd Member of Triassic Xujiahe Formation in the Xinchang area,Sichuan Basin were classified,standard of the favorable lithofacies wa...By using core,logging curves,and experiment data,favorable lithofacies types in the 2 nd Member of Triassic Xujiahe Formation in the Xinchang area,Sichuan Basin were classified,standard of the favorable lithofacies was established,planar distribution regularities of the favorable lithofacies were identified,and forming mechanisms of the favorable lithofacies and their control effect on production were examined.(1)The 2 nd Member of Xujiahe Formation has twelve types of lithofacies,among which multiple layer medium-coarse grain sandstone lithofacies,parallel bedding medium-coarse grain sandstone lithofacies,massive bedding medium-coarse grain sandstone lithofacies,inclined bedding medium-coarse grain sandstone lithofacies,and charcoal-bearing medium-coarse grain sandstone lithofacies with better physical properties and higher gas content are favorable lithofacies;they feature low gamma,low neutron porosity,low resistivity,and high acoustic travel time on logging curves.(2)The sedimentary process controls spatial distribution of sand bodies which are the material basis of the favorable lithofacies;post diagenetic fluids would differentially reconstruct the favorable lithofacies;tectonic activities and abnormal formation pressure made strata slide along the weakness plane,giving rise to fractures in different types of rocks,which can enhance the reservoir permeability significantly.(3)The development degree of favorable lithofacies is a major factor affecting stable production of gas well.展开更多
One-dimensional gas injection storage building and one-cycle injection-production modeling experiment,and two-dimensional flat core storage building and multi-cycle injection-production modeling experiment were carrie...One-dimensional gas injection storage building and one-cycle injection-production modeling experiment,and two-dimensional flat core storage building and multi-cycle injection-production modeling experiment were carried out using one-dimensional long core and large two-dimensional flat physical models to find out the effects of reservoir physical properties and injection-production balance time on reservoir pore utilization efficiency,effective reservoir capacity formation and capacity-reaching cycle.The results show that reservoir physical properties and formation water saturation are the main factors affecting the construction and operation of gas-reservoir type underground gas storage.During the construction and operation of gas-reservoir type gas storage,the reservoir space can be divided into three types of working zones:high efficiency,low efficiency and ineffective ones.The higher the reservoir permeability,the higher the pore utilization efficiency is,the smaller the ineffective working zone is,or there is no ineffective working zone;the smaller the loss of injected gas is,and the higher the utilization rate of pores is.The better the reservoir physical properties,the larger the reservoir space and the larger the final gas storage capacity is.The higher the water saturation of the reservoir,the more the gas loss during gas storage capacity building and operation is.Optimizing injection-production regime to discharge water and reduce water saturation is an effective way to reduce gas loss in gas storage.In the process of multiple cycles of injection and production,there is a reasonable injection-production balance time,further extending the injection-production balance period after reaching the reasonable time has little contribution to the expansion of gas storage capacity.展开更多
The Lower Cambrian is one of the important exploration strata of marine shale gas reservoirs in the Upper Yangtze region,but its exploration is geologically impacted by multiple factors such as deep burial depth,fewer...The Lower Cambrian is one of the important exploration strata of marine shale gas reservoirs in the Upper Yangtze region,but its exploration is geologically impacted by multiple factors such as deep burial depth,fewer wells and unsatisfactory exploration results.In this paper,the mineral composition of the Lower Cambrian black shale in the Upper Yangtze region was investigated using the data of X-ray diffraction,rock thin section,scanning electron microscope(SEM)and argon ion polishing-electron microscope,and its significance in oil and gas exploration was also analyzed.The followingfindings were made.First,shale in this region is mainly composed of clay minerals and quartz,and secondarily of carbonate minerals and feldspar.The average content of quartz in shale is 44.6%,and two types of quartz are developed,i.e.terrigenous quartz and biogenic silica.The average content of clay minerals is 33.32%,with illite(I)content being the highest,illite/smectite(I/S)layer content uneven,the mixed layer ratio lower,generally 5%,and chlorite(C)and kaolinite(K)locally distributed.Second,four types of clay mineral assemblages are identified,including I+I/S+C,transition from I+I/S+C to I+C,I+C,and I,indicating that diagenetic environments of shale are different in different areas.Third,the disordered arrangement of mineral grains is favorable for the survival of intergranular pores,indicating that in the diagenetic alteration process of feldspar into clay minerals,linear pores can be generated.It is concluded that the brittleness index of shale in this region is generally above 40%,indicating a good fragility.The fragility of shale in SE Guizhou is better than that in SW Sichuan Basin.展开更多
Fine identification and division of lithofacies types of continental shale strata is an important basis for the evaluation of shale gas exploration and development potential.At present,however,there is no consensus on...Fine identification and division of lithofacies types of continental shale strata is an important basis for the evaluation of shale gas exploration and development potential.At present,however,there is no consensus on the identification standard and division scheme of shale lithofacies.Taking the continental shale strata of theMiddleeLower Jurassic in the SichuanBasin as an example,this paper established a lithofacies division method bymeans of core observation,whole-rockmineral X-ray diffraction analysis,thin section analysis,total organic carbon(TOC)measurement and heliumporosity measurement after analyzing whole-rock mineral composition and shale characteristics.Then lithofacies types of shale strata were identified and divided,and characteristics of lithofacies assemblages in different scales were investigated.Finally,their significance for shale gas exploration was discussed.The following research results were obtained.First,20 shale lithofacies types of 6 categories are totally identified in this continental shale strata using the newly established three-step lithofacies divisionmethod(whole-rock mineral composition partitione-TOC classification-correction and improvement of mineral texture and sedimentary structure).Among them,mediumehigh TOC clay shale lithofacies,laminaethin layer clay shale lithofacies and lowemedium TOC silty shale lithofacies are dominant,followed by lowemedium TOC shell limy clay shale lithofacies,and TOC bearing and low TOC silty clay shale lithofacies.Second,the average TOC and the average porosity of clay shale lithofacies and shell limestone clay shale lithofacies are higher than those of silty and silty clay shale lithofacies.It is indicated thatmineral composition and lithofacies types of shale have a certain impact on gas source and reservoir performance.Third,three types of assemblages are identified in the continental shale strata,including mudstoneelimestone assemblage,mudstoneesandstone assemblage and mudstoneelimestoneesandstone mixed assemblage,which reflect the sedimentary characteristics of distal region,proximal region and transitional region in the lacustrine environment,respectively;and that the characterization of different lithofacies assemblages is conducive to recognizing the differences between different shale sedimentary environments.Fourth,fine identification and statistic of the number and frequency of limy shell laminae and thin layers in the terrestrial organic-rich shale with high claymineral content can provide a basis for the fracturability evaluation of gas-rich zones and the optimization of optimum exploration and development intervals.展开更多
基金supported by the National Natural Science Foundation of China(No.U19B6003)。
文摘The connectivity of shale pores and the occurrence of movable oil in shales have long been the focus of research.In this study,samples from wells BX7 and BYY2 in the Eq3^4-10 cyclothem of Qianjiang Formation in the Qianjiang depression,were analyzed.A double mercury injection method was used to distinguish between invalid and effective connected pores.The pore characteristics for occurrence of retained hydrocarbons and movable shale oil were identified by comparing pore changes in low temperature nitrogen adsorption and high pressure mercury injection experiments before and after extraction and the change in the mercury injection amounts in the pores between two separate mercury injections.The results show that less than 50%of the total connected pores in the Eq34-10 cyclothem samples are effective.The development of effective connected pores affects the mobility of shale oil but varies with different lithofacies.The main factor limiting shale oil mobility in Well BX7 is the presence of pores with throat sizes less than 15 nm.In Well BYY2,residual mercury in injection testing of lamellar dolomitic mudstone facies was mainly concentrated in pores with throats of 10-200 nm,and in bulk argillaceous dolomite facies,it was mainly concentrated at 60-300 nm.The throats of hydrocarbon-retaining pores can be 5 nm or even smaller,but pores with movable shale oil in the well were found to have throat sizes greater than 40 nm.Excluding the influence of differences in wettability,the movability of shale oil is mainly affected by differences in lithofacies,the degree of pore deformation caused by diagenesis,the complexity of pore structures,and the connectivity of pore throats.Dissolution and reprecipitation of halite also inhibit the mobility of shale oil.
基金Collaborative Project Grant from the Exploration and Development Research Institute of SINOPEC Northwest Oilfi eld Company(Grant No.KY2021-S-104).
文摘The Tarim Basin has revealed numerous tight sandstone oil and gas reservoirs.The tidal fl at zone in the Shunbei area is currently in the detailed exploration stage,requiring a comprehensive description of the sand body distribution characteristics for rational exploration well deployment.However,using a single method for sand body prediction has yielded poor results.Seismic facies analysis can eff ectively predict the macro-development characteristics of sedimentary sand bodies but lacks the resolution to capture fine details.In contrast,single-well sedimentary facies analysis can describe detailed sand body development but struggles to reveal broader trends.Therefore,this study proposes a method that combines seismic facies analysis with single-well sedimentary microfacies analysis,using the lower section of the Kepingtage Formation in the Shunbei area as a case study.First,seismic facies were obtained through unsupervised vector quantization to control the macro-distribution characteristics of sand bodies,while principal component analysis(PCA)was applied to improve the depiction of fine sand body details from seismic attributes.Based on 3D seismic data,well-logging data,and geological interpretation results,a detailed structural interpretation was performed to establish a high-precision stratigraphic framework,thereby enhancing the accuracy of sand body prediction.Seismic facies analysis was then conducted to obtain the macro-distribution characteristics of the sand bodies.Subsequently,core data and logging curves from individual wells were used to clarify the vertical development characteristics of tidal channels and sandbars.Next,PCA was employed to select the seismic attributes most sensitive to sand bodies in diff erent sedimentary facies.Results indicate that RMS amplitude in the subtidal zone and instantaneous phase in the intertidal zone are the most sensitive to sand bodies.A comparative analysis of individual seismic attributes for sand body characterization revealed that facies-based delineation improved the accuracy of sand body identification,eff ectively capturing their contours and shapes.This method,which integrates seismic facies,single-well sedimentary microfacies,and machine learning techniques,enhances the precision of sand body characterization and off ers a novel approach to sand body prediction.
基金the Sinopec Ministry of Science and Technology Research Project of Experimental study and application of key parameters for self-sealing evaluation of deep shale(KLP25015)Research on stress in complex tectonic zones and its impact on shale gas enrichment and high yield(P24181)+1 种基金Quantitative characterization technology and application of fluid properties in veins of shale of eastern fault basins(KLP24017)Evolution and differential enrichment mechanism of deep-ultra deep shale gas in southeastern Sichuan(P23132).
文摘Shale gas is an important unconventional resource,and shale reservoirs typically contain both water and gas fluids.Water can occupy the shale gas storage space,reduce the flow capacity of shale gas,and even completely seal off the shale gas.When the shale develops an effective sealing capacity,the water saturation of the shale reaches a threshold value which can be measured using physical simulation experiments.However,limited research has been conducted on the quantitative calculation of critical water saturation.In order to obtain the critical water saturation of shale,this paper proposes a theoretical calculation method to estimate the critical water saturation of shale based on DLvo(Derjaguin-Landau-Verwey-Overbeek)theory.Two shale samples from the Longmaxi Formation in the Sichuan Basin with different total organic carbon(TOC)were selected for gas adsorption experiments to characterize the pore structure of the organic matter and inorganic matter of the shale.Based on the established theoretical and geological models,the critical water film thickness and critical water saturation of pores with different pore sizes were calculated.Taking the boundary conditions into account,the critical water saturation of the two shale samples was ultimately determined.The results showed that inorganic pores occupied 81.0%of the pores of the shale with a ToC of 0.89%,and their dominant pore sizes were dominated by mesopores around 40 nm;inorganic pores occupied 48.7%of the pores of the shale with a TOC of 4.27%,and their dominant pore sizes were dominated by micropores and mesopores around 0-20 nm and 40 nm.As the pore size increased,the corresponding critical water film thickness also increased,and the critical water saturation was normally distributed in the pore size range centered at about 10 nm.The distribution of critical water saturation in inorganic pores with different pore sizes was in the range of about 63%-76%,and the critical water saturation of shale with a TOC of 0.89%and shale with a TOC of 4.27%were calculated to be 41.7%and 32.7%,respectively.The method proposed in this study accurately calculates the critical water saturation of shale and effectively distinguishes the differences critical water saturation between shales with different TOc.Further,shale gas reservoirs can be finely characterized by comparing with the original water saturation of shale layers.This study is of great scientific significance to shale gas exploration and development,and even to the field of cO2 geological storage.
基金supported by the National Natural Science Foundation of China(Nos.42488101,42141021,42172149,42172168,U2244209)the Tencent Foundation through the XPLORER PRIZE。
文摘Occurrence and abundance of molecular hydrogen in natural geologic reservoirs are enigmatic,due to its various sources,diverse migration pathways and complicated biological and chemical reactions.Natural gas samples containing hydrogen from producing wells in several sedimentary basins in China were collected in this study,and gas abundances and isotopic compositions of these gases were compared with those in global petroliferous basins and deep intrusive rocks.Several geochemical indicators were suggested for identifying sources,migration and accumulation mechanisms of hydrogen in the subsurface environment.Hydrogen contents in natural gas deposits have contributions from various sources with the following high-to-low order:microbial degradation>serpentinization>deep mantle volatile release>radiation-induced water decomposition>thermal cracking of organic matter.A hydrogen-rich reservoir in Kansas,USA,is specifically analyzed to determine its formation mechanism.This study suggests that future exploration of geological hydrogen resources may focus on the igneous rock bodies with overlying dense sedimentary rocks in the continental rift systems.
基金supported by the National Natural Science Foundation of China(No.42202170,42172109,42072140,42102133,42202122)the Natural Science Foundation of Chongqing(CSTB2022NSCQ-MSX1166,CSTB2022NSCQ-JQX0031)+1 种基金the Science and Technology Research Program of Chongqing Municipal Education Commission(KJQN202201511,KJZD-M202101502)Project of Chongqing University of Science&Technology(ckrc2022028,YKJCX2320109).
文摘The deep-water systems in different types of sedimentary basins exhibit significant variability.Current knowledge of deep-water deposition is mainly derived from deep-marine turbidite systems.However,the characteristics and differences of sub-lacustrine gravity flow deposition systems have been a research focus in the fields of sedimentology and petroleum geology.This study investigates the facies archi-tecture,depositional processes,and sediment distribution patterns of a sub-lacustrine debrite system in the Eocene Dongying Rift of the Bohai Bay Basin,China,through the analysis of integrated core data,3-D seismic data,and well-log data.Nine facies have been identified within the debrite system,representing various depositional processes such as sandy debris flow,muddy debris flow,turbidity currents,sandy slide,sandy slide/slump,and mud flow.Our research indicates that the sub-lacustrine system is primarily influenced by debris flow rather than turbidity currents,as supported by facies quantification,inter-pretation,and flow rheology analysis.Additionally,we have identified five basic facies building blocks in debrite systems,including slide masses,slump masses,debrite channels,debrite lobes,and turbidite sheets.We have also elucidated and proposed detailed sedimentary processes,flow transport,and transformation within the sub-lacustrine system through analysis of flow origins,facies sequences,and distribution characteristics.Our findings highlight the evolutionary progression from delta-front collapse to sandy slide/slump,sandy debris flow,and finally muddy debris flow.The efficient generation of turbidity currents from parental landslides on sand-prone slopes is deemed unlikely due to rift-basin morphology and transport distances.The formation of the five basic facies building blocks is closely linked to depositional processes and dominant flow types.Consequently,we present a deep-water depositional model for sub-lacustrine debrite systems,focusing on flow dynamics,sediment distribu-tion patterns,and basin morphology within deep lacustrine rifts.This model offers valuable insights into the variability of deep-water deposition in diverse basin settings and aids in predicting lithologic res-ervoirs during deep-water hydrocarbon exploration.
基金Supported by the Basic Science Center Project of National Natural Science Foundation of China(72088101)National Natural Science Funded Project(52074345)CNPC Scientific Research and Technology Development Project(2020D-5001-21)。
文摘This paper summarizes the important progress in the field of oil and gas production engineering during the"Thirteenth Five-Year Plan"period of China,analyzes the challenges faced by the current oil and gas production engineering in terms of technological adaptability,digital construction,energy-saving and emission reduction,and points out the future development direction.During the"Thirteenth Five-Year Plan"period,series of important progresses have been made in five major technologies,including separated-layer injection,artificial lift,reservoir stimulation,gas well de-watering,and workover,which provide key technical support for continuous potential tapping of mature oilfields and profitable production of new oilfields.Under the current complex international political and economic situation,oil and gas production engineering is facing severe challenges in three aspects:technical difficulty increases in oil and gas production,insignificant improvements in digital transformation,and lack of core technical support for energy-saving and emission reduction.This paper establishes three major strategic directions and implementation paths,including oil stabilization and gas enhancement,digital transformation,and green and low-carbon development.Five key research areas are listed including fine separated-layer injection technology,high efficiency artificial lift technology,fine reservoir stimulation technology,long term gas well de-watering technology and intelligent workover technology,so as to provide engineering technical support for the transformation,upgrading and high-quality development of China’s oil and gas industry.
基金granted by the National Science and Technology Major Project of the Ministry of Science and Technology of China (Grant No. 2017ZX05036002–001)National Natural Science Foundation of China (No. 41202103, 41872124)SINOPEC Ministry of Science and Technology Project (Grant No. P17027–2)
文摘The Upper Ordovician Wufeng-Lower Silurian Longmaxi shale is widely distributed in the Sichuan Basin and its periphery,which is the key stratum for marine shale gas exploration and development(E&D)in China.Based on sedimentary environment,material basis,storage space,fracability and reservoir evolution data,the reservoir characteristics of the Wufeng-Longmaxi shale and their significance for shale gas E&D are systematically compared and analyzed in this paper.The results show that(1)the depocenter of the Wufeng(WF)-Longmaxi(LM)shale gradually migrates from east to west.The high-quality shale reservoirs in the eastern Sichuan Basin are mainly siliceous shales,which are primarily distributed in the graptolite shale interval of WF2-LM5.The high-quality reservoirs in the southern Sichuan Basin are mainly calcareous-siliceous and organic-rich argillaceous shales,which are distributed in the graptolite shale interval of WF2-LM7.(2)Deep shale gas(the burial depth>3500 m)in the Sichuan Basin has high-ultrahigh pressure and superior physical properties.The organic-rich siliceous,calcareous-siliceous and organic-rich argillaceous shales have suitable reservoir properties.The marginal area of the Sichuan Basin has a higher degree of pressure relief,which leads to the argillaceous and silty shales evolving into direct cap rocks with poor reservoir/good sealing capacity.(3)Combining shale gas exploration practices and impacts of lithofacies,depth,pressure coefficient and brittle-ductile transition on the reservoir properties,it is concluded that the favorable depth interval of the Wufeng-Longmaxi shale gas is 2200~4000 m under current technical conditions.(4)Aiming at the differential reservoir properties of the Wufeng-Longmaxi shale in the Sichuan Basin and its periphery,several suggestions for future research directions and E&D of shale gas are formulated.
基金Supported by the Scientific Research and Technology Development Project of PetroChina。
文摘Geological conditions and main controlling factors of gas accumulation in subsalt Ma 4 Member of Ordovician Majiagou Formation are examined based on large amounts of drilling,logging and seismic data.The new understandings on the control of paleo-uplift over facies,reservoirs and accumulations are reached:(1)During the sedimentary period of Majiagou Formation,the central paleo-uplift divided the North China Sea in central-eastern of the basin from the Qinqi Sea at southwest margin of the basin,and controlled the deposition of the thick hummocky grain beach facies dolomite on platform margin of Ma 4 Member.Under the influence of the evolution of the central paleo-uplift,the frame of two uplifts alternate with two sags was formed in the central-eastern part of the basin,dolomite of inner-platform beach facies developed in the underwater low-uplift zones,and marl developed in the low-lying areas between uplifts.(2)From the central paleo-uplift to the east margin of the basin,the dolomite in the Ma 4 Member gradually becomes thinner and turns into limestone.The lateral sealing of the limestone sedimentary facies transition zone gives rise to a large dolomite lithological trap.(3)During the late Caledonian,the basin was uplifted as a whole,and the central paleo-uplift was exposed and denuded to various degrees;high-quality Upper Paleozoic Carboniferous-Permian coal measures source rocks deposited on the paleo-uplift in an area of 60000 km^(2),providing large-scale hydrocarbon for the dolomite lithological traps in the underlying Ma 4 Member.(4)During the Indosinian-Yanshanian stage,the basin tilted westwards,and central paleo-uplift depressed into an efficient hydrocarbon supply window.The gas from the Upper Paleozoic source rock migrated through the high porosity and permeability dolomite in the central paleo-uplift to and accumulated in the updip high part;meanwhile,the subsalt marine source rock supplied gas through the Caledonian faults and micro-fractures as a significant supplementary.Under the guidance of the above new understandings,two favorable exploration areas in the Ma 4 Member in the central-eastern basin were sorted out.Two risk exploration wells were deployed,both revealed thick gas-bearing layer in Ma 4 Member,and one of them tapped high production gas flow.The study has brought a historic breakthrough in the gas exploration of subsalt Ma 4 Member of Ordovician,and opened up a new frontier of gas exploration in the Ordos Basin.
基金Supported by the PetroChina Special S&T Project(2016E-0502)National Natural Science Foundation of China(41772099,41872116).
文摘Based on field outcrop investigation,interpretation and analysis of drilling and seismic data,and consulting on a large number of previous research results,the characteristics of ancient marine hydrocarbon source rocks,favorable reservoir facies belts,hydrocarbon migration direction and reservoir-forming law in the Ordos Basin have been studied from the viewpoints of North China Craton breakup and Qilian-Qinling oceanic basin opening and closing.Four main results are obtained:(1)Controlled by deep-water shelf-rift,there are three suites of source rocks in the Ordos Basin and its periphery:Mesoproterozoic,Lower Cambrian and Middle-Upper Ordovician.(2)Controlled by littoral environment,paleo-uplift and platform margin,four types of reservoirs are developed in the area:Mesoproterozoic-Lower Cambrian littoral shallow sea quartz sandstone,Middle-Upper Cambrian–Ordovician weathering crust and dolomitized reservoir,and Ordovician L-shape platform margin reef and beach bodies.(3)Reservoir-forming assemblages vary greatly in the study area,with"upper generation and lower storage"as the main pattern in the platform,followed by"self-generation and self-storage".There are both"upper generation and lower storage"and"self-generation and self-storage"in the platform margin zone.In addition,in the case of communication between deep-large faults and the Changchengian system paleo-rift trough,there may also exist a"lower generation and upper reservoir"combination between the platform and the margin.(4)There are four new exploration fields including Qingyang paleo-uplift pre-Carboniferous weathering crust,L-shape platform margin zone in southwestern margin of the basin,Ordovician subsalt assemblage in central and eastern parts of the basin,and Mesoproterozoic–Cambrian.Among them,pre-Carboniferous weathering crust and L-shape platform margin facies zone are more realistic replacement areas,and Ordovician subsalt assemblage and the Proterozoic-Cambrian have certain potential and are worth exploring.
基金supported by the National Natural Science Foundation of China(Grant No.41872124 and 91755211)and several Sinopec in-house projects.We thank Sinopec Petroleum Exploration and Production Research Institute,Sinopec Exploration Company,Sinopec Jianghan Oilfield,and Sinopec East China Petroleum Company for valuable data and information.
文摘The Fuling shale gas field in China is the largest shale gas field as well as the largest of its type discovered in any Lower Paleozoic formation.In this study,the geology and production of the upper and lower gas layers in the Fuling shale gas field are evaluated in terms of structure,shale quality,fault,initial production,and estimated ultimate recovery(EUR).The shale in the lower gas layer of the Jiaoshiba anticline is a high-quality reservoir,where the space is dominated by organic pores in kerogen,and the gas content is high.The shale gas wells reveal relatively high initial production and EUR.However,the shale in the upper gas layer of the Jiaoshiba anticline has reservoir space mainly composed of clay mineral pores and organic pores within bitumen,and the gas content is low.In terms of structure,primary gas migration may occur in the upper gas layer,resulting in free gas accumulation in the structural high,where the development effects are generally better than those in the structural low.The lower gas layer in the Pingqiao anticline,is the main interval for shale gas accumulation and development due to the high-quality shale.Under the influence of faults,the efficiency of exploration wells emplaced on top of the anticline is much lower a compared with those in the flanks.The residual synclines close to the Sichuan Basin,including the Baima and Baitao anticlines,are characterized by more recent uplifts,larger area,greater distance from the deep and large faults,and early fracture closure.Therefore,we recommend that the shale gas exploration and development should be carried out preferentially in areas close to the center of the residual synclines,featuring relatively high-pressure coefficient and moderate burial depth.
基金In the process of writing this paper,we received the financial support of the National Science and Technology Major Project(Grant No.2017ZX05009-002)the support from Wuxi Branch of SINOPEC Petroleum Exploration&Production Research Institute。
文摘The mechanism of formation of lacustrine deposits within stable orogenic belts and their potential for shale oil and gas exploration are frontier themes of challenge in the fields of sedimentology and petroleum exploration. Orogenic belts witness strong tectonic activities and normally cannot host stable lacustrine basins and deep shale formations. Therefore, basins in orogenic belts are considered to have no potential to form shale hydrocarbon reservoirs. Here we investigate the Luanping Basin located in the Yanshan orogenic belt where previous studies regarded rivers and fan deltas as the major main Mesozoic deposits. Based on detailed field exploration and scientific drilling, we report the finding of a large number of lacustrine shale continental deep-water deposits in the Mesozoic strata. Our finding of the occurrence of active shale oil and gas also in this basin also subvert the previous perceptions.We report SHRIMP zircon U-Pb age that define the bottom boundary of the target interval as 127.6 ± 1.7 Ma belonging to the early Cretaceous strata. Tectonics and climate are considered to be the main factors that controlled the deep-water sedimentation during this period. The drill cores revealed evidence of shale gas and the TOC of shale is 0.33%–3.60%, with an average value of 1.39% and Ro is 0.84%–1.21%, with an average value of 1.002%. The brittleness index of shale is between 52.7% and 100%. After vertical well fracturing, the daily gas production is more than 1000 m^(3). Our findings show that the basin has considerable potential for shale oil and gas. The geological resources of the shale gas in the Xiguayuan Fm. are estimated as 1110.12 × 10^(8) m^(3), with shale oil geological resources of 3340.152 × 10^(4) t. Our findings indicate that the Yanshan orogenic belt has potential exploration prospect. This work not only redefines the Luanping Basin as a rift deep-water Mesozoic Lake Basin, but also rules out the previous notion that the basin is dominated by shallow water sediments. The discovery of shale oil and gas also provides an important reference for subsequent petroleum exploration and development in this basin. Our study shows that shale oil and gas reservoirs can be found in the lacustrine basins of orogenic belts which were strongly influenced by volcanism. These results have significant implications for the sedimentology and oil exploration in the Qinling and Xingmeng Orogenic Belts of China, as well as those in other terranes of the world including the New England Orogenic Belt in Australia.
基金supported by China National Program on Key Basic Research Project (973 Program) (Grant No. 2006CB705805)National Key Scientific and Technological Project (Grant No. 2008ZX05009-004)
文摘For extra-low permeability reservoirs, with a permeability of about 0.3×10?3 μm2, fluid flow and production performance in cores were studied. A long core holder with a multi-location piezometric measurement was specially designed. An artificial long core, about 700 mm long and with a cross section of 45mm×45mm, was used. In the experiment, pressure distribution along the core can be measured in real time. Single phase flow in the core was investigated. Different modes of production in long cores were also simulated including natural depletion, water flooding, and advanced water flooding. Through physical simulation, flow parameters were collected and production characteristics in extra-low permeability cores were studied. From experimental results, it can be seen that fluid flow in extra-low permeability cores is different from that in high permeability cores. Transmission of pressure in extra-low permeability cores is very slow, and it needs a long time for the pressure to become stable. The distribution curve of pressure along the core is nonlinear and the production rate in extra-low permeability reservoirs decreases sharply. The development effects of different production modes in extra-low permeability cores were compared with one another. Among the production modes, advanced water flooding has much potential for effective development of extra-low permeability reservoirs. Natural depletion and conventional water flooding can also be used in early production periods. In addition, the countermeasures and some ideas especially for the potential development of extra-low permeability reservoirs are suggested.
基金the National Natural Science Foundation of China(No.U19B6003U20B6001)the Chinese Academy of Sciences(No.XDA14000000).
文摘No breakthrough has been made in petroleum exploration of the Sinian Dengying Formation in the southeastern Sichuan Basin as the major factors controlling the hydrocarbon accumulation of the Dengying Formation have not been well established,including the development period and distribution of the platform margin,the effectiveness of the source-reservoir combination and the reliability of the Cambrian pre-salt structural trap.Based on the interpretation of seismic data and hydrocarbon-source correlation,the distribution of the platform margin of the Sinian Dengying Formation in the southeastern Sichuan Basin was mapped.Moreover,the gas source rocks of the Dengying Formation were clarified according to geochemical characteristics of fluid inclusions,and the pre-salt structures were further confirmed by seismic forward modeling and experiments of prestack depth migration.Results showed that the sedimentary facies of the 4th member of Dengying Formation in the southeastern Sichuan Basin was platform margin of gentle slope type.The platform margin reservoir of the Dengying Formation and the Lower Cambrian source rocks constitute a favorable source-reservoir combination.The carbon isotope characteristics of gas in fluid inclusions indicate that some of the oil/gas in the Dengying Formation were contributed by the Doushantuo Formation source rocks.As the difference in seismic velocities between carbonate rocks and gypsum/salt beds may cause a reduction in the amplitude of pre-salt structures,the low-amplitude structures identified on current seismic profiles are underestimated instead of overestimated.Accordingly,the Sinian structural traps are confirmed to develop in the deep pre-salt sequences in the low-steep anticline belt,southeastern Sichuan Basin.On the basis of the above new understanding,we propose two types of hydrocarbon migration modes for the Sinian Dengying Formation in southeastern Sichuan Basin,including lateral migration of hydrocarbons generated from the Cambrian Qiongzusi Formation and vertical migration of hydrocarbons derived from the Sinian Doushantuo Formation.Lithologic traps at the platform margin and pre-salt structural traps within the platform are favorable targets for natural gas exploration.
基金supported by the National Major Science and Technology Project“A Study on Formation and Enrichment Law,Selection Evaluation Technology and Application of Shale Gas in the Sichuan Basin and Its Periphery”(No.2017ZX05035).
文摘The Sichuan Basin is a major target for shale gas exploration in present China because of its rich gas stored in abundant black shales with multiple bed series.For further guidance or reference,field exploration and development practices in the shale reservoirs Upper Ordovician WufengeLower Silurian Longmaxi shale reservoirs were studied in terms of development stages and progress,favorable conditions for shale gas accumulation,bottlenecking issues on theories and technologies related to shale gas development,and so on.The following findings were obtained.(1)Shale with rich organic matters originated from the deep shelf has a good quality and great thickness in the continuous beds.The relatively stable wide buffer zones in synclines(anticlines)provides favorable conditions for shale gas accumulation and preservation with well developed micro-fractures and overpressure as necessary factors for a great potential of high shale gas productivity.(2)The bottlenecking technical issues restricting the shale gas industrial development in this study area include the following aspects:understandings of rich-organic matter shale sedimentary facies and modes,shale reservoir diagenetic process and evaluation systems,shale gas generation and accumulation mechanism,geophysical logging identification and prediction of shale gas layers,low resource utilization rate,great uncertainty of shale gas development,no technological breakthrough in the exploration of shale gas reservoirs buried deeper than 3500 m.In conclusion,this study area will be the major target for the shale gas exploration and development in China in a rather long period in the future.
基金Project supported by Sinopec Science and Technology Special Project“Evaluation of Hydrocarbon Formation Conditions and Targets of Permian Volcanic Rocks in Western Sichuan”(No.P18069-3)National Science and Technology Major Special Project“Evaluation and Strategic zone selection of Hydrocarbon Resources Potential of Marine Carbonate Strata”(No.2017ZX05005001-004).
文摘It was previously deemed that volcanic rocks in the western Sichuan Basin were not developed,which restricted the exploration of volcanic gas reservoirs in this area.Recently,however,Sinopec's wildcat well,Well YS1 encounters Upper Permian volcanic rocks about 300 m thick in the western Sichuan Basin,the reservoir physical properties of which are good with strong gas shows.In order to evaluate the exploration prospect of volcanic gas reservoirs in western Sichuan Basin,we studied the Permian volcanic rocks in this area from the aspects of formation and development characteristics,reservoir characteristics,gas genesis and plays based on the new understandings on exploration wells,com-bined with the analysis on tectonic evolution and its controlling effect on volcanism.Then,the volcanic eruption mechanism,the distribution mode of volcanic edifice and the hydrocarbon accumulation pattern of volcanic gas reservoir were figured out.Finally,the exploration potential of natural gas was evaluated.The following research results were obtained:(1)the Permian volcanic rocks in western Sichuan Basin are well developed and its tectonic setting is consistent with that of Emeishan basalt,which is the product of the Emeishan mantle plume.(2)Under the control of vertical faults,a great number of volcanic edifices are developed and there are many eruption cycles.Volcanic rocks are superimposed vertically and connected laterally.(3)The volcanic rocks in western Sichuan Basin are different to some extent from those in southwestern Sichuan Basin in terms of lithology,lithofacies and reservoir characteristics.In the western Sichuan Basin,the tuff of explosive facies is dominant with some basalt of effusive facies,and the reservoir space of volcanic rocks is mainly acted by inter-breccia skeletal pores,dissolved pores and matrix micro-pores.In conclusion,multiple sets of effective source rocks are developed around the volcanic intervals in western Sichuan Basin,and together they constitute effective natural gas plays.Therefore,it has a better natural gas exploration prospect,and it is a new field worthy of attention.
基金Supported by the National Science and Technology Major Project of China (2016ZX05010).
文摘Based on the analysis of the production composition of reservoirs developed by the second&tertiary recovery combination(STRC),the relationship between the overall output of the STRC project and the production level during the blank water flooding stage is proposed.According to the basic principle of reservoir engineering that the“recovery factor is equal to sweeping coefficient multiplied by oil displacement efficiency”,the formula for calculating the ultimate oil recovery factor of chemical combination flooding reservoir was established.By dividing the reservoir into a series of grids according to differen-tial calculus thinking,the relationship between the ultimate recovery factor of a certain number of grids and the recovery de-gree of the reservoir was established,and then the variation law of oil production rate of the STRC reservoir was obtained.The concept of“oil rate enlargement factor of chemical combination flooding”was defined,and a production calculation method of reservoir developed by STRC was put forward based on practical oilfield development experience.The study shows that the oil production enhancing effect of STRC increases evenly with the in crease of the ratio of STRC displacement efficiency to water displacement efficiency,and increases rapidly with the increase of the ratio of recovery degree at flooding mode conversion to the water displacement efficiency.STRC is more effective in increasing oil production of reservoir with high recovery degree.Through practical tests of the alkali free binary flooding(polymer/surfactant)projects,the relative error of the oil production calculation method of STRC reservoir is about±10%,which meets the requirements of reservoir engineering.
基金Supported by the China National Science and Technology Major Project(2016ZX05002-006)Sinopec Science and Technology Department Project(P18089-4)
文摘By using core,logging curves,and experiment data,favorable lithofacies types in the 2 nd Member of Triassic Xujiahe Formation in the Xinchang area,Sichuan Basin were classified,standard of the favorable lithofacies was established,planar distribution regularities of the favorable lithofacies were identified,and forming mechanisms of the favorable lithofacies and their control effect on production were examined.(1)The 2 nd Member of Xujiahe Formation has twelve types of lithofacies,among which multiple layer medium-coarse grain sandstone lithofacies,parallel bedding medium-coarse grain sandstone lithofacies,massive bedding medium-coarse grain sandstone lithofacies,inclined bedding medium-coarse grain sandstone lithofacies,and charcoal-bearing medium-coarse grain sandstone lithofacies with better physical properties and higher gas content are favorable lithofacies;they feature low gamma,low neutron porosity,low resistivity,and high acoustic travel time on logging curves.(2)The sedimentary process controls spatial distribution of sand bodies which are the material basis of the favorable lithofacies;post diagenetic fluids would differentially reconstruct the favorable lithofacies;tectonic activities and abnormal formation pressure made strata slide along the weakness plane,giving rise to fractures in different types of rocks,which can enhance the reservoir permeability significantly.(3)The development degree of favorable lithofacies is a major factor affecting stable production of gas well.
基金Supported by the the National Natural Science Foundation of China(No.52074318)PetroChina Company Limited Key Program for Science and Technology Development(kt2020-16-01).
文摘One-dimensional gas injection storage building and one-cycle injection-production modeling experiment,and two-dimensional flat core storage building and multi-cycle injection-production modeling experiment were carried out using one-dimensional long core and large two-dimensional flat physical models to find out the effects of reservoir physical properties and injection-production balance time on reservoir pore utilization efficiency,effective reservoir capacity formation and capacity-reaching cycle.The results show that reservoir physical properties and formation water saturation are the main factors affecting the construction and operation of gas-reservoir type underground gas storage.During the construction and operation of gas-reservoir type gas storage,the reservoir space can be divided into three types of working zones:high efficiency,low efficiency and ineffective ones.The higher the reservoir permeability,the higher the pore utilization efficiency is,the smaller the ineffective working zone is,or there is no ineffective working zone;the smaller the loss of injected gas is,and the higher the utilization rate of pores is.The better the reservoir physical properties,the larger the reservoir space and the larger the final gas storage capacity is.The higher the water saturation of the reservoir,the more the gas loss during gas storage capacity building and operation is.Optimizing injection-production regime to discharge water and reduce water saturation is an effective way to reduce gas loss in gas storage.In the process of multiple cycles of injection and production,there is a reasonable injection-production balance time,further extending the injection-production balance period after reaching the reasonable time has little contribution to the expansion of gas storage capacity.
文摘The Lower Cambrian is one of the important exploration strata of marine shale gas reservoirs in the Upper Yangtze region,but its exploration is geologically impacted by multiple factors such as deep burial depth,fewer wells and unsatisfactory exploration results.In this paper,the mineral composition of the Lower Cambrian black shale in the Upper Yangtze region was investigated using the data of X-ray diffraction,rock thin section,scanning electron microscope(SEM)and argon ion polishing-electron microscope,and its significance in oil and gas exploration was also analyzed.The followingfindings were made.First,shale in this region is mainly composed of clay minerals and quartz,and secondarily of carbonate minerals and feldspar.The average content of quartz in shale is 44.6%,and two types of quartz are developed,i.e.terrigenous quartz and biogenic silica.The average content of clay minerals is 33.32%,with illite(I)content being the highest,illite/smectite(I/S)layer content uneven,the mixed layer ratio lower,generally 5%,and chlorite(C)and kaolinite(K)locally distributed.Second,four types of clay mineral assemblages are identified,including I+I/S+C,transition from I+I/S+C to I+C,I+C,and I,indicating that diagenetic environments of shale are different in different areas.Third,the disordered arrangement of mineral grains is favorable for the survival of intergranular pores,indicating that in the diagenetic alteration process of feldspar into clay minerals,linear pores can be generated.It is concluded that the brittleness index of shale in this region is generally above 40%,indicating a good fragility.The fragility of shale in SE Guizhou is better than that in SW Sichuan Basin.
基金supported by the National Major Science and Technology Project“Evaluation of shale gas exploration potential in continental strata”(No.:2017ZX05036004)Sinopec Technology Development Project“Main control factors of shale gas enrichment and favorable targets in Ziliujing Formation in Northeast Sichuan”(No.:P19017-2).
文摘Fine identification and division of lithofacies types of continental shale strata is an important basis for the evaluation of shale gas exploration and development potential.At present,however,there is no consensus on the identification standard and division scheme of shale lithofacies.Taking the continental shale strata of theMiddleeLower Jurassic in the SichuanBasin as an example,this paper established a lithofacies division method bymeans of core observation,whole-rockmineral X-ray diffraction analysis,thin section analysis,total organic carbon(TOC)measurement and heliumporosity measurement after analyzing whole-rock mineral composition and shale characteristics.Then lithofacies types of shale strata were identified and divided,and characteristics of lithofacies assemblages in different scales were investigated.Finally,their significance for shale gas exploration was discussed.The following research results were obtained.First,20 shale lithofacies types of 6 categories are totally identified in this continental shale strata using the newly established three-step lithofacies divisionmethod(whole-rock mineral composition partitione-TOC classification-correction and improvement of mineral texture and sedimentary structure).Among them,mediumehigh TOC clay shale lithofacies,laminaethin layer clay shale lithofacies and lowemedium TOC silty shale lithofacies are dominant,followed by lowemedium TOC shell limy clay shale lithofacies,and TOC bearing and low TOC silty clay shale lithofacies.Second,the average TOC and the average porosity of clay shale lithofacies and shell limestone clay shale lithofacies are higher than those of silty and silty clay shale lithofacies.It is indicated thatmineral composition and lithofacies types of shale have a certain impact on gas source and reservoir performance.Third,three types of assemblages are identified in the continental shale strata,including mudstoneelimestone assemblage,mudstoneesandstone assemblage and mudstoneelimestoneesandstone mixed assemblage,which reflect the sedimentary characteristics of distal region,proximal region and transitional region in the lacustrine environment,respectively;and that the characterization of different lithofacies assemblages is conducive to recognizing the differences between different shale sedimentary environments.Fourth,fine identification and statistic of the number and frequency of limy shell laminae and thin layers in the terrestrial organic-rich shale with high claymineral content can provide a basis for the fracturability evaluation of gas-rich zones and the optimization of optimum exploration and development intervals.
