Lacustrine groundwater discharge(LGD)plays an important role in water resources management.Previous studies have focused on LGD process in a single lake,but the differences in LGD process within the same region have n...Lacustrine groundwater discharge(LGD)plays an important role in water resources management.Previous studies have focused on LGD process in a single lake,but the differences in LGD process within the same region have not been thoroughly investigated.In this study,multiple tracers(hydrochemistry,𝛿D,𝛿18O and 222Rn)were used to compare mechanisms of LGD in Daihai and Ulansuhai Lake in Inner Mongoli1,Northwest China.The hydrochemical types showed a trend from groundwater to lake water,indicating a hydraulic connection between them.In addition,the𝛿D and𝛿18O values of sediment pore water were between the groundwater and lake water,indicating the LGD processes.The radon mass balance model was used to estimate the average groundwater discharge rates of Daihai and Ulansuhai Lake,which were 2.79 mm/day and 3.02 mm/day,respectively.The total nitrogen(TN),total phosphorus(TP),and fluoride inputs associated with LGD in Daihai Lake accounted for 97.52%,96.59%,and 95.84%of the total inputs,respectively.In contrast,TN,TP and fluoride inputs in Ulansuhai Lake were 53.56%,40.98%,and 36.25%,respectively.This indicates that the pollutant inputs associated with LGD posed a potential threat to the ecological stability of Daihai and Ulansuhai Lake.By comparison,the differences of LGD process and associated pollutant flux were controlled by hydrogeological conditions,lakebed permeability and human activities.This study provides a reference for water resources management in Daihai and Ulansuhai Lake basins while improving the understanding of LGD in the Yellow River basin.展开更多
Alkaline lacustrine shale is highly heterogeneous,and the complex relationship between the organicinorganic porosity network and hydrocarbon occurrence restricts the effectiveness of shale oil exploration and developm...Alkaline lacustrine shale is highly heterogeneous,and the complex relationship between the organicinorganic porosity network and hydrocarbon occurrence restricts the effectiveness of shale oil exploration and development.Herein,we investigated the Fengcheng Formation(P_(1)f)in Mahu Sag.This study integrated geochemistry,Soxhlet extraction,scanning electron microscopy,gas adsorption,and nuclear magnetic resonance T_(1)-T_(2)spectroscopy to elucidate the microscopic oil occurrence mechanisms in shales.Results indicate the presence of felsic shale,dolomitic shale,lime shale,and mixed shale within the P_(1)f.Matrix pores and microfractures associated with inorganic minerals are the predominant pore types in P_(1)f.Adsorbed oil primarily resides on the surfaces of organic matter and clay minerals,while free oil predominantly occupies inorganic pores and microfractures with larger pore sizes.Variations exist in the quantity and distribution of shale oil accumulation across different scales,where free oil and adsorbed oil are governed by dominant pores with diameters exceeding 10 nm and ineffective pores with diameters below 10 nm,respectively.Shale oil occurrence characteristics are influenced by organic matter,pore structure,and mineral composition.Felsic shale exhibits a high abundance of dominant pores,possesses the highest oil content,predominantly harbors free oil within these dominant pores,and demonstrates good mobility.Fluid occurrence in dolomitic shale and lime shale is intricate,with low oil content and a free oil to adsorbed oil ratio of 1:1.Mixed shale exhibits elevated clay mineral content and a scarcity of dominant pores.Moreover,ineffective pores contain increased bound water,resulting in medium oil content and limited mobility predominantly due to adsorption.Presently,shale oil mainly occurs in the dominant pores with a diameter larger than 10 nm in a free state.During the exploration and development of alkaline lacustrine shale oil resources,emphasis should be placed on identifying sweet spots within the felsic shale characterized by dominant pores.展开更多
In addition to the organic matter type,abundance,thermal maturity,and shale reservoir space,the preservation conditions of source rocks play a key factor in affecting the quantity and quality of retained hydrocarbons ...In addition to the organic matter type,abundance,thermal maturity,and shale reservoir space,the preservation conditions of source rocks play a key factor in affecting the quantity and quality of retained hydrocarbons in source rocks of lacustrine shale,yet this aspect has received little attention.This paper,based on the case analysis,explores how preservation conditions influence the enrichment of mobile hydrocarbons in shale oil.Research showns that good preservation conditions play three key roles.(1)Ensure the retention of sufficient light hydrocarbons(C_(1)–C_(13)),medium hydrocarbons(C_(14)–C_(25))and small molecular aromatics(including 1–2 benzene rings)in the formation,which enhances the fluidity and flow of shale oil;(2)Maintain a high energy field(abnormally high pressure),thus facilitating the maximum outflow of shale oil;(3)Ensure that the retained hydrocarbons have the miscible flow condition of multi-component hydrocarbons(light hydrocarbons,medium hydrocarbons,heavy hydrocarbons,and heteroatomic compounds),so that the heavy hydrocarbons(C_(25+))and heavy components(non-hydrocarbons and asphaltenes)have improved fluidity and maximum flow capacity.In conclusion,in addition to the advantages of organic matter type,abundance,thermal maturity,and reservoir space,good preservation conditions of shale layers are essential for the formation of economically viable shale oil reservoirs,which should be incorporated into the evaluation criteria of shale oil-rich areas/segments and considered a necessary factor when selecting favorable exploration targets.展开更多
Lacustrine rift basins in China are characterized by pronounced structural segmentation,strong sedimentary heterogeneity,extensive fault-fracture development,and significant variability in thermal maturity and mobilit...Lacustrine rift basins in China are characterized by pronounced structural segmentation,strong sedimentary heterogeneity,extensive fault-fracture development,and significant variability in thermal maturity and mobility of shale oil.This study reviews the current status of exploration and development of shale oil in such basins and examines theoretical frameworks such as“binary enrichment”and source-reservoir configuration,with a focus on five key subjects:(1)sedimentation-diagenesis coupling mechanisms of fine-grained shale reservoir formation;(2)dynamic diagenetic evolution and hydrocarbon occurrence mechanisms of organic-rich shale;(3)dominant controls and evaluation methods for shale oil enrichment;(4)fracturing mechanisms of organic-rich shale and simulation of artificial fracture networks;and(5)flow mechanisms and effective development strategies for shale oil.Integrated analysis suggests that two major scientific challenges must be addressed:the coupled evolution of fine-grained sedimentation,differential diagenesis,and hydrocarbon generation under tectonic influence and its control on shale oil occurrence and enrichment;and multi-scale,multiphase flow mechanisms and three-dimensional development strategies for lacustrine shale oil in complex fault blocks.In response to current exploration and development bottlenecks,future research will be conducted primarily to:(1)deeply understand organic-inorganic interactions and reservoir formation mechanisms in organic-rich shales,and clarify the influence of high-frequency sequence evolution and diagenetic fluids on reservoir space;(2)elucidate the dynamic processes of hydrocarbon generation,expulsion,and retention across different lithofacies,and quantify their relationship with thermal maturity,including the conditions for the formation of self-sealing systems;(3)develop a geologically adaptive,data-and intelligence-driven shale oil classification and grading evaluation system of shale oil;(4)reveal artificial fracture propagation pattern and optimize physical field coupled fracturing technologies for complex lithofacies assemblages;and(5)overcome challenges in multi-scale geological modeling and multiphase flow characterization,and establish advanced numerical simulation methodologies.展开更多
The relationship between marine transgression and the distribution of lacustrine organic matter has restricted shale oil and gas exploration for decades.In this study,the research objective is to analyze the sedimenta...The relationship between marine transgression and the distribution of lacustrine organic matter has restricted shale oil and gas exploration for decades.In this study,the research objective is to analyze the sedimentary environment and evaluate its influence on organic matter in transgressive lacustrine shale.The study uses various analyses including total organic carbon(TOC),Rock-Eval pyrolysis,gas chromatography-mass spectrometry(GC-MS),trace element and isotope analysis.Finally,the study proposes an enrichment model for organic matter.The lacustrine shale of the second member of the Funing Formation(E_(1)f^(2))is divided into three sequences.The results indicate that the depositional environment of the organic matter during this period was an arid and humid,reduced,closed,rift lake basin.In the first sequence,high salinity resulted from increased evaporation,leading to low primary biological productivity.At this time,the lake basin belonged to a salinized closed lake basin.Intermittent transgressions began in the second sequence,with the deep lake area still being dominated by a reducing environment.The third sequence saw the environment evolve into a closed lake basin characterized by a warm and humid freshwater environment with high primary productivity.Marine transgressions introduce a substantial amount of marine plankton,nutrient elements,as well as more CO_(2) and CO_(3)^(2−)into the lake,leading to increased primary productivity.The sedimentary model for transgressive lacustrine source rocks proposed here serves as an example for similar transgressive lake basins.展开更多
China's lacustrine shale oil reserves are abundant,making it a key area for future exploration and development.Most lacustrine shales feature a mix of mineral compositions and interlayer sedimentary structures.Hig...China's lacustrine shale oil reserves are abundant,making it a key area for future exploration and development.Most lacustrine shales feature a mix of mineral compositions and interlayer sedimentary structures.High-quality reservoirs exhibit significant heterogeneity,which influences the stress distribution during fracturing,leading to complex fracture network patterns.This complexity presents challenges for the comprehensive well logging evaluation of the geological-engineering"double sweet spots"in shale oil,severely restricting efficient development.This study focuses on the impact of shale sedimentary layering on the radial slowness of dipole shear waves.It employs rock physics experiments combined with advanced well logging techniques to explore the relationship between reservoir anisotropy caused by sedimentary layering and reservoir quality,thereby establishing a logging evaluation method for vertical identification of"sweet spots"in lacustrine shale oil.The shales in the Fengcheng Formation of the Mahu Sag into three types according to sedimentary structure scale:laminated,interlayer,and massive.Each type has different mineral compositions,affecting reservoir quality and fracturing potential.Laminated shales develop more fractures under stress along the beddings,showing moderate anisotropy,with reservoir capacity dependent on intercrystalline porosity within carbonate layers.Interlayer shales easily form complex fracture networks,exhibiting significant anisotropy,and their reservoir capacity depends on the porosity within sandy bands.Massive mudstones have the fewest fractures under stress,appearing isotropic with reservoir capacity dependent on matrix pore size.The intensity of reservoir anisotropy correlates positively with storage capacity and the propensity to form irregular and complex fracture networks during hydraulic fracturing.In sections without natural fractures,a larger difference between fast and slow shear waves corresponds to a radial profile shift towards warm tones,indicating stronger anisotropy and better reservoir quality,thus forming complex fracture networks during fracturing.Conversely,a smaller difference leads to a profile energy shift towards cooler tones,indicating stronger isotropy and poorer reservoir quality,hindering the formation of complex fracture networks during hydraulic fracturing.In sections with natural fractures,the difference between fast and slow shear waves exhibits erratic behavior,showing a cross-pattern in radial profiles,indicating strong anisotropy.The presence of natural fractures can synergize with induced fracture networks to form more complex systems,significantly enhancing reservoir productivity.展开更多
Pore structure directly affects the occurrence and migration of shale hydrocarbon,and the lack of research on the mechanism of the pore structure is an important reason for the hindrance of shale hydrocarbon explorati...Pore structure directly affects the occurrence and migration of shale hydrocarbon,and the lack of research on the mechanism of the pore structure is an important reason for the hindrance of shale hydrocarbon exploration.By analysing the geochemistry and reservoir characteristics of Jurassic lacustrine shales in Sichuan Basin,this study recovers their paleoenvironments and further discusses paleoenvironmental constraints on pore structure.The results show that the Lower Jurassic lacustrine shales in the Sichuan Basin are in a warm and humid semi-anoxic to anoxic lake environment with high productivity,a strong stagnant environment,and a rapid sedimentation rate,with water depths ranging from about 11.54-55.22 m,and a mixture of type Ⅱ/Ⅲ kerogen is developed.In terms of reservoir characteristics,they are dominated by open-slit pores,and the pores are relatively complex.The percentage of mesopores is the highest,while the percentage of macropores is the lowest.Further analysis shows that paleoclimate controls the overall pore complexity and surface relaxation of shales by influencing the weathering rate of mother rocks.Paleoredox conditions control the proportion and complexity of shale pores by influencing TOC content.The research results will provide theoretical basis for improving the exploration efficiency of lacustrine shale resources and expanding exploration target areas.展开更多
Lacustrine shale oil reservoirs of the Upper Triassic Chang 7 Member in the Ordos Basin have demonstrated significant potential for hydrocarbon resources.Natural fractures play a crucial role in hydrocarbon enrichment...Lacustrine shale oil reservoirs of the Upper Triassic Chang 7 Member in the Ordos Basin have demonstrated significant potential for hydrocarbon resources.Natural fractures play a crucial role in hydrocarbon enrichment and production.Outcrops,cores,borehole image logs,thin sections,and FE-SEM images were used to investigate the types and characteristics of natural fractures in the Chang 7 Member.The factors controlling fracture development and the mechanisms of bedding-parallel fracture formation were revealed by integrating TOC analysis,XRD analysis,and rock pyrolysis.Results show that natural fractures in the study area include high-angle tectonic fractures and nearly horizontal bedding-parallel fractures.Brittle minerals and bed thickness control the occurrence and attributes of tectonic fractures.High TOC content and thermal maturity positively affect the development of bedding-parallel fractures,formed through the conversion of organic matter to hydrocarbons or the smectite-to-illite transformation.Additionally,the dominant orientations of tectonic fractures intersect the present-day maximum horizontal principal stress at a small angle,resulting in large apertures and good effectiveness.Bedding-parallel fractures contribute to enhance porosity and provide favorable pathways for lateral hydrocarbon migration.Collectively,this study could provide valuable insights for finding promising exploration areas in lacustrine shale oil reservoirs in the Ordos Basin and worldwide.展开更多
Taking the shale oil of the first member of the Cretaceous Qingshankou Formation of Changling Sag in southern Songliao Basin as an example,this paper establishes a saturation model of lacustrine shale oil considering ...Taking the shale oil of the first member of the Cretaceous Qingshankou Formation of Changling Sag in southern Songliao Basin as an example,this paper establishes a saturation model of lacustrine shale oil considering the influence of organic matter on clay-bound water conductivity.Based on the fluid characterization results of sealed samples and two-dimensional nuclear magnetic resonance,the differential influence of organic matter on clay-bound water conductivity was quantitatively revealed,and the conductivity mechanism and rock-electrical relationships of lacustrine shale were systematically analyzed.The results show that there are two conductive networks for lacustrine shales,i.e.the matrix free water and the clay-bound water.The bound water cementation index msh was introduced to reflect the impact of organic matter on clay-bound water conductivity,and it is positively correlated with the effective porosity.When there is sufficient rigid framework support and well-developed pores,organic matter is more likely to fill or adsorb onto clay interlayers.This reduces the ion exchange capacity of the electrical double layer,leading to an increase in msh and a decrease in the conductivity of clay-bound water.The overall conductivity of shale is controlled by the clay-bound water conductivity,and the relative contributions of the mentioned two conductive networks to formation conductivity are affected by the effective porosity and msh.The larger the effective porosity and msh,the more the contribution of the matrix free water to formation conductivity.According to the experimental results,the proposed saturation model yields a significantly higher interpretation accuracy in oil saturation than the Archie model and the Total-shale model.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
Based on the analysis of typical lacustrine shale oil zones in China and their geological characteristics,this study elucidates the fundamental differences between the enrichment patterns of shale oil sweet spots and ...Based on the analysis of typical lacustrine shale oil zones in China and their geological characteristics,this study elucidates the fundamental differences between the enrichment patterns of shale oil sweet spots and conventional oil and gas.The key parameters and evaluation methods for assessing the large-scale production potential of lacustrine shale oil are proposed.The results show that shale oil is a petroleum resource that exists in organic-rich shale formations,in other words,it is preserved in its source bed,following a different process of generation-accumulation-enrichment from conventional oil and gas.Thus,the concept of“reservoir”seems to be inapplicable to shale oil.In China,lacustrine shale oil is distributed widely,but the geological characteristics and sweet spots enrichment patterns of shale oil vary significantly in lacustrine basins where the water environment and the tectonic evolution and diagenetic transformation frameworks are distinct.The core of the evaluation of lacustrine shale oil is“sweet spot volume”.The key factors for evaluating the large-scale production of continental shale oil are the oil storage capacity,oil-bearing capacity and oil producing capacity.The key parameters for evaluating these capacities are total porosity,oil content,and free oil content,respectively.It is recommended to determine the total porosity of shale by combining helium porosity measurement with nuclear magnetic resonance(NMR)method,the oil content of key layers by using organic solvent extraction,NMR method and high pressure mercury intrusion methods,and the free oil content by using NMR fluid distribution secondary spectral stripping decomposition and logging.The research results contribute supplemental insights on continental shale oil deliverability in China,and provide a scientific basis for the rapid exploration and large-scale production of lacustrine shale oil.展开更多
To clarify the mechanism of differential enrichment of intrasource shale oil,taking the third of seventh member of the Triassic Yanchang Formation(Chang 7_(3)submember for short)in the Ordos Basin,NW China as an examp...To clarify the mechanism of differential enrichment of intrasource shale oil,taking the third of seventh member of the Triassic Yanchang Formation(Chang 7_(3)submember for short)in the Ordos Basin,NW China as an example,we integrated high-resolution scanning electron microscopy(SEM),optical microscopy,laser Raman spectroscopy,rock pyrolysis,and organic solvent extraction experiments to identify solid bitumen of varying origins,obtain direct evidence of intrasource micro-migration of shale oil,and establish the coupling between the shale nano/micro-fabric and the oil generation,migration and accumulation.The Chang 7_(3)shale with rich alginite in laminae has the highest hydrocarbon generation potential but a low thermal transformation ratio.Frequent alternations of micron-scale argillaceous-felsic laminae enhance the hydrocarbon expulsion efficiency,yielding consistent aromaticity between in-situ and migrated solid bitumen.Mudstone laminae rich in terrestrial organic matter(OM)and clay minerals exhibit lower hydrocarbon generation threshold but stronger hydrocarbon retention capacity,with a certain amount of light oil/bitumen preserved to differentiate the chemical structure of in-situ versus migrated bitumen.Tuffaceous and sandy laminae contain abundant felsic minerals and migrated bitumen.Tuffaceous laminae develop high-angle microfractures under shale overpressure,facilitating oil charging into rigid mineral intergranular pores of sandy laminae.Fractionation during micro-migration progressively decreases the aromatization of solid bitumen from shale,through tuffaceous and mudstone,to sandy laminae,while increasing light hydrocarbon components and enhancing OM-hosted pore development.The intrasource micro-migration and enrichment of the Chang 7_(3)shale oil result from synergistic organic-inorganic diagenesis,with crude oil component fractionation being a key mechanism for forming sweet spots in laminated shale oil reservoirs.展开更多
Based on the technological demands for significantly enhancing oil recovery and long-term CO_(2)sequestration in the lacustrine oil reservoirs of China,this study systematically reviews the progress and practices of C...Based on the technological demands for significantly enhancing oil recovery and long-term CO_(2)sequestration in the lacustrine oil reservoirs of China,this study systematically reviews the progress and practices of CO_(2)flooding and storage technologies in recent years.It addresses the key technological needs and challenges faced in scaling up the application of CO_(2)flooding and storage to mature,developed oil fields,and analyzes future development directions.During the pilot test phase(2006-2019),continuous development and application practices led to the establishment of the first-generation CO_(2)flooding and storage technology system for lacustrine reservoirs.In the industrialization phase(since 2020),significant advances and insights have been achieved in terms of confined phase behavior,storage mechanisms,reservoir engineering,sweep control,engineering process and storage monitoring,enabling the maturation of the second-generation CO_(2)flooding and storage theories and technologies to effectively support the demonstration projects of Carbon Capture,Utilization and Storage(CCUS).To overcome key technical issues such as low miscibility,difficulty in gas channeling control,high process requirements,limited application scenarios,and coordination challenges in CO_(2)flooding and storage,and to support the large-scale application of CCUS,it is necessary to strengthen research on key technologies for establishing the third-generation CO_(2)flooding and storage technological system incorporating miscibility enhancement and transformation,comprehensive regulation for sweep enhancement,whole-process engineering techniques and equipment,long-term storage monitoring safety,and synergistic optimization of flooding and storage.展开更多
Whether clay-rich shale reservoirs with low-medium maturity can serve as primary exploration targets remains a focal point of debate in the academic community.Clarifying the exploration potential of clayrich shale res...Whether clay-rich shale reservoirs with low-medium maturity can serve as primary exploration targets remains a focal point of debate in the academic community.Clarifying the exploration potential of clayrich shale reservoirs is crucial for the future exploration and development of lacustrine shale.The Triassic Yanchang Formation in the Ordos Basin has been one of most productive lacustrine shale oil systems in China,with substantial oil production capacity already established.While the primary productive layers are currently fine-grained siltstone interbeds,however,it remains a highly debated issue whether the volumetrically more significant clay-rich reservoirs can become viable exploration targets in the near future.To address this issue,we examined the exploration potential of different lithofacies assemblages in Member 7(Mbr 7)of the Triassic Yanchang Formation,using a borehole in the Tongchuan area of the southern Ordos Basin as an example.We identified favorable exploration targets and assessed whether clay-rich reservoirs formed predominantly-freshwater conditions can become viable exploration targets.The results indicate the presence of six lithofacies in clay-rich reservoirs of Mbr 7 of the Yanchang Formation,with two main lithofacies assemblages:laminated organic-rich shale and massive mudstone.From the perspective of sandstone distribution,the sandstone interlayers within laminated organic-rich shale are primarily formed by gravity(hyperpycnal)flows,while sandstones deposited in delta front environments are typically associated with massive mudstone.Laminated organic-rich shale deposition occurred in an anoxic,deep-water environment characterized by high primary productivity,whereas massive mudstone formed in environments with high sedimentation rates and substantial terrigenous debris influx.Currently,the exploration potential of sandstone interlayers exceeds that of clay-rich reservoirs,with the greatest potential observed in the sandstone interlayers associated with laminated organic-rich shale formed by gravity(hyperpycnal)flows.Comparative analysis reveals that clay-rich reservoirs with low to medium maturity present great challenges for exploitation,making interlayer-type reservoirs the main focus of exploration at this stage.Nevertheless,clay-rich reservoirs in closed systems with high thermal maturity and organic matter content also hold considerable potential.展开更多
To accurately investigate the evolution characteristics and generation mechanism of retained oil,the study analyzed organic-rich lacustrine shale samples from the Paleogene Kongdian Formation in Cangdong Sag,Bohai Bay...To accurately investigate the evolution characteristics and generation mechanism of retained oil,the study analyzed organic-rich lacustrine shale samples from the Paleogene Kongdian Formation in Cangdong Sag,Bohai Bay Basin.This analysis involves Rock-Eval pyrolysis,pyrolysis simulation experiments,Gas Chromatograph Mass Spectrometer(GC-MS),and reactive molecular dynamics simulations(ReaxFF).The results revealed the retained oil primarily consisted of n-alkanes with carbon numbers ranging from C14 to C36.The generation of retained oil occurred through three stages.A slow growth stage of production rate was observed before reaching the peak of oil production in Stage Ⅰ.Stage Ⅱ involved a rapid increase in oil retention,with C12-C17 and C24-C32 serving as the primary components,increasing continuously during the pyrolysis process.The generation process involved the cleavage of weak bonds,including bridging bonds(hydroxyl,oxy,peroxy,imino,amino,and nitro),ether bonds,and acid amides in the first stage(Ro=0.50%-0.75%).The carbon chains in aromatic ring structures with heteroatomic functional groups breaks in the second stage(R_(o)=0.75%-1.20%).In the third stage(R_(o)=1.20%-2.50%),the ring structures underwent ring-opening reactions to synthesize iso-short-chain olefins and radicals,while further breakdown of aliphatic chains occurred.By coupling pyrolysis simu-lation experiments and molecular simulation technology,the evolution characteristics and bond breaking mechanism of retained oil in three stages were revealed,providing a reference for the for-mation and evolution mechanism of retained oil.展开更多
To elucidate the mechanism by which supercritical CO_(2)(SCCO_(2))-water-shale interactions during CO_(2)energized fracturing influence proppant embedment in lacustrine shale,shale samples from the Bohai Bay Basin wer...To elucidate the mechanism by which supercritical CO_(2)(SCCO_(2))-water-shale interactions during CO_(2)energized fracturing influence proppant embedment in lacustrine shale,shale samples from the Bohai Bay Basin were selected for SCCO_(2)-water-shale interaction experiments.X-ray diffraction(XRD),SEM large-area high-resolution imaging,automated mineral identification and characterization system(AMICS),and nanoindentation tests were employed to examine the micro-mechanical damage mechanisms of fracture surfaces and the evolving patterns of proppant embedment characteristics.The results reveal that:Prolonged interaction time reduces the contents of dolomite,feldspar,and clay minerals,while quartz content increases,with dolomite showing the most pronounced dissolution effect.As interaction time increases,the hardness and elasticity modulus of shale follow a power-law decay pattern,with the peak degradation rate occurring at 1 d,followed by a gradual decline of degradation velocity.Increasing interaction time results in growth in both the number and depth of embedment pits on the sample surface.After more than 3 d of interaction,clustered proppant embedment is observed,accompanied by the formation of deep embedment pits on the surface.展开更多
Organic-rich lacustrine shales are widely distributed in China and have significant potential for unconventional shale gas and oil production although the primary factors controlling the deposition of lacustrine shale...Organic-rich lacustrine shales are widely distributed in China and have significant potential for unconventional shale gas and oil production although the primary factors controlling the deposition of lacustrine shale are disputed. This work clarifies the different characteristics of tectonic evolution and shale among sub-basins in the Bohai Bay Basin in eastern China as a case study by studying basal subsidence, tectonic subsidence rate, basin extensional proportions and shale chemical characteristics. The paper summarizes the correlation between structure and shale deposition, and concludes that tectonic activity is the primary controlling factor for shale development. Episodic tectonic activity controls not only the timing of shale deposition（with the greatest shale deposition occurring primarily during the peak period of basin tectonic activity） but also the spatial distribution of shale（located mainly in areas of maximum subsidence）, the migration pattern of shale（conforming to that of the basin subsidence center）, and shale strata thickness. Tectonic activity also affects the total organic carbon content and organic matter type in shale. When the tectonic activity was the most active and basal subsidence was the maximum, the total organic carbon content of the shale reached its highest value with organic matter type mainly Type I. As tectonic activity weakened, the total organic carbon content decreased, and the organic matter type changed from Type I to Type I-III.展开更多
Taking the mixed pre-salt carbonate rocks in the upper member of Eocene Xiaganchaigou Formation(E_(3)^(2))of Yingxi area in the Qaidam Basin as an example,the lithofacies and controlling mechanisms of reservoir format...Taking the mixed pre-salt carbonate rocks in the upper member of Eocene Xiaganchaigou Formation(E_(3)^(2))of Yingxi area in the Qaidam Basin as an example,the lithofacies and controlling mechanisms of reservoir formation are analyzed based on a large dataset of cores,thin sections and geochemical analysis.The reservoirs in E_(3)^(2)pre-salt layers have five types of lithofacies,of them,mixed granular calcareous dolostone,massive calcareous dolostone,plaque calcareous dolostone,and laminated dolomtic limestone are of sedimentary origin,and breccia calcareous dolostone is of tectonic origin.The four types of sedimentary lithofacies are divided into two types of saline sedimentary sequence lithofacies combinations,low-energy type in the sag area and low to high-energy type in the slope and paleo-uplift zone in the depression.Affected by high-frequency supply of continental clastic material,the two types of salty sedimentary sequences are mostly incomplete subtypes of lithofacies.Lithofacies have strong impacts on pre-salt reservoirs in E_(3)^(2):(1)Lithofacies type and sedimentary sequence controlled the formation and distribution of dolomite intercrystalline pores and dissolved pores during the pene-sedimentary period.(2)The structure of laminated dolomitic limestone controlled the formation of large-scale laminated fractures and high permeability channels during the diagenetic period.(3)Granular,massive,plaque calcareous dolostones have low mud content and strong brittleness,in the late tectonic reactivation period,the distribution of the three types of lithofacies,together with their distance from the top large slip faults and secondary faults,controlled the formation and distribution of high-efficiency fracture-cave brecciaed calcareous dolostone reservoirs.The above research led to the composite lithofacies-tectonic formation model of pre-salt reservoir in E_(3)^(2)of Yingxi area.The tempo-spatial distribution of tectonic breccia calcareous dolostone reservoirs,laminated dolomitic limestone shale oil reservoirs and granular,massive calcareous dolostone dissolved-intercrystalline pore tight reservoirs in various structural belts of the studied area have been figured out.These findings gave new insights into tight-shale oil accumulation theory in mixed carbonate successions from saline lacustrine basins,aiding in high efficient exploration and development of petroleum in the studied area.展开更多
Overlapping gravity accumulation bodies were formed on the northwestern steep slope of the Shuangyang Formation in the Moliqing fault depression of northeast China.This study analyzed in detail the spatial distributio...Overlapping gravity accumulation bodies were formed on the northwestern steep slope of the Shuangyang Formation in the Moliqing fault depression of northeast China.This study analyzed in detail the spatial distribution of the lithofacies and lithofacies associations of these accumulation bodies based on more than 600 m of core sections,and summarized 12 major types of lithofacies and three types of lithofacies associations：（1） the proximal zone consists of gravelly debris flows dominated by alluvial channel conglomerates;（2） the middle zone is dominated by various gravity flow deposits and traction flow deposits;and（3） the distal zone is dominated by mudstones with intercalations of sandy debris and turbidites.Combining with the grain size cumulative probability curves analysis,we determined the transformation of debris flows to sandy debris flows and to turbidity currents in the slope zone of the basin margin,and further proposed a lacustrine slope apron model that is characterized by（1） an inconstant multiple source（line source）,（2） an alternation of gravity flow deposits and traction flow deposits dominated by periodical changes in a source flood flow system,and（3） the transformation of sandy debris flow deposits into distal turbidity current deposits.This sedimentary model may be applicable to other fault depressions for predicting reservoir distribution.展开更多
High-yielding oil wells were recently found in the first member of Paleogene Shahejie Formation,the Binhai area of Qikou Sag,providing an example of medium-and deep-buried high-quality reservoirs in the central part o...High-yielding oil wells were recently found in the first member of Paleogene Shahejie Formation,the Binhai area of Qikou Sag,providing an example of medium-and deep-buried high-quality reservoirs in the central part of a faulted lacustrine basin.By using data of cores,cast thin sections,scanning electron microscope and physical property tests,the sedimentary facies,physical properties and main control factors of the high-quality reservoirs were analyzed.The reservoirs are identified as deposits of slump-type sub-lacustrine fans,which are marked by muddy fragments,slump deformation structure and Bouma sequences in sandstones.They present mostly medium porosity and low permeability,and slightly medium porosity and high permeability.They have primary intergranular pores,intergranular and intragranular dissolution pores in feldspar and detritus grains,and structural microcracks as storage space.The main factors controlling the high quality reservoirs are as follows:(1)Favorable sedimentary microfacies of main and proximal distributary gravity flow channels.The microfacies with coarse sediment were dominated by transportation and deposition of sandy debris flow,and the effect of deposition on reservoir properties decreases with the increase of depth.(2)Medium texture maturity.It is shown by medium-sorted sandstones that were formed by beach bar sediment collapsing and redepositing,and was good for the formation of the primary intergranular pores.(3)High content of intermediate-acid volcanic rock detritus.The reservoir sandstone has high content of detritus of various components,especially intermediate-acid volcanic rock detritus,which is good for the formation of dissolution pores.(4)Organic acid corrosion.It was attributed to hydrocarbon maturity during mesodiagenetic A substage.(5)Early-forming and long lasting overpressure.A large-scale overpressure compartment was caused by under-compaction and hydrocarbon generation pressurization related to thick deep-lacustrine mudstone,and is responsible for the preservation of abundant primary pores.(6)Regional transtensional tectonic action.It resulted in the structural microcracks.展开更多
基金supported by the Natural Science Foundation of Inner Mongolia Autonomous Region of China(No.2023QN04011)the National Natural Science Foundation of China(Nos.42307092 and 52279067)+1 种基金Ordos Science and Technology Major Project(No.ZD20232303)Project of Key Laboratory of River and Lake in Inner Mongolia Autonomous Region(No.2022QZBZ0003).
文摘Lacustrine groundwater discharge(LGD)plays an important role in water resources management.Previous studies have focused on LGD process in a single lake,but the differences in LGD process within the same region have not been thoroughly investigated.In this study,multiple tracers(hydrochemistry,𝛿D,𝛿18O and 222Rn)were used to compare mechanisms of LGD in Daihai and Ulansuhai Lake in Inner Mongoli1,Northwest China.The hydrochemical types showed a trend from groundwater to lake water,indicating a hydraulic connection between them.In addition,the𝛿D and𝛿18O values of sediment pore water were between the groundwater and lake water,indicating the LGD processes.The radon mass balance model was used to estimate the average groundwater discharge rates of Daihai and Ulansuhai Lake,which were 2.79 mm/day and 3.02 mm/day,respectively.The total nitrogen(TN),total phosphorus(TP),and fluoride inputs associated with LGD in Daihai Lake accounted for 97.52%,96.59%,and 95.84%of the total inputs,respectively.In contrast,TN,TP and fluoride inputs in Ulansuhai Lake were 53.56%,40.98%,and 36.25%,respectively.This indicates that the pollutant inputs associated with LGD posed a potential threat to the ecological stability of Daihai and Ulansuhai Lake.By comparison,the differences of LGD process and associated pollutant flux were controlled by hydrogeological conditions,lakebed permeability and human activities.This study provides a reference for water resources management in Daihai and Ulansuhai Lake basins while improving the understanding of LGD in the Yellow River basin.
基金financially supported by the State Key Laboratory of Shale Oil and Gas Enrichment Mechanisms and Efficient Development(33550000-22-ZC0613-0006)National Natural Science Foundation of China(42202133)+2 种基金CNPC Innovation Fund(2022DQ02-0106)Strategic Cooperation Technology Projects of the CNPC and CUPB(ZLZX2020-01-05)Key Laboratory of Tectonics and Petroleum Resources(China University of Geosciences),Ministry of Education,China(TPR-2023-05)。
文摘Alkaline lacustrine shale is highly heterogeneous,and the complex relationship between the organicinorganic porosity network and hydrocarbon occurrence restricts the effectiveness of shale oil exploration and development.Herein,we investigated the Fengcheng Formation(P_(1)f)in Mahu Sag.This study integrated geochemistry,Soxhlet extraction,scanning electron microscopy,gas adsorption,and nuclear magnetic resonance T_(1)-T_(2)spectroscopy to elucidate the microscopic oil occurrence mechanisms in shales.Results indicate the presence of felsic shale,dolomitic shale,lime shale,and mixed shale within the P_(1)f.Matrix pores and microfractures associated with inorganic minerals are the predominant pore types in P_(1)f.Adsorbed oil primarily resides on the surfaces of organic matter and clay minerals,while free oil predominantly occupies inorganic pores and microfractures with larger pore sizes.Variations exist in the quantity and distribution of shale oil accumulation across different scales,where free oil and adsorbed oil are governed by dominant pores with diameters exceeding 10 nm and ineffective pores with diameters below 10 nm,respectively.Shale oil occurrence characteristics are influenced by organic matter,pore structure,and mineral composition.Felsic shale exhibits a high abundance of dominant pores,possesses the highest oil content,predominantly harbors free oil within these dominant pores,and demonstrates good mobility.Fluid occurrence in dolomitic shale and lime shale is intricate,with low oil content and a free oil to adsorbed oil ratio of 1:1.Mixed shale exhibits elevated clay mineral content and a scarcity of dominant pores.Moreover,ineffective pores contain increased bound water,resulting in medium oil content and limited mobility predominantly due to adsorption.Presently,shale oil mainly occurs in the dominant pores with a diameter larger than 10 nm in a free state.During the exploration and development of alkaline lacustrine shale oil resources,emphasis should be placed on identifying sweet spots within the felsic shale characterized by dominant pores.
基金Supported by the National Natural Science Foundation of China(U22B6004)Project of PetroChina Research Institute of Petroleum Exploration and Development(2022yjcq03)Core Technology Key Project of China Petroleum Changqing Oilfield Company(KJZX2023-01).
文摘In addition to the organic matter type,abundance,thermal maturity,and shale reservoir space,the preservation conditions of source rocks play a key factor in affecting the quantity and quality of retained hydrocarbons in source rocks of lacustrine shale,yet this aspect has received little attention.This paper,based on the case analysis,explores how preservation conditions influence the enrichment of mobile hydrocarbons in shale oil.Research showns that good preservation conditions play three key roles.(1)Ensure the retention of sufficient light hydrocarbons(C_(1)–C_(13)),medium hydrocarbons(C_(14)–C_(25))and small molecular aromatics(including 1–2 benzene rings)in the formation,which enhances the fluidity and flow of shale oil;(2)Maintain a high energy field(abnormally high pressure),thus facilitating the maximum outflow of shale oil;(3)Ensure that the retained hydrocarbons have the miscible flow condition of multi-component hydrocarbons(light hydrocarbons,medium hydrocarbons,heavy hydrocarbons,and heteroatomic compounds),so that the heavy hydrocarbons(C_(25+))and heavy components(non-hydrocarbons and asphaltenes)have improved fluidity and maximum flow capacity.In conclusion,in addition to the advantages of organic matter type,abundance,thermal maturity,and reservoir space,good preservation conditions of shale layers are essential for the formation of economically viable shale oil reservoirs,which should be incorporated into the evaluation criteria of shale oil-rich areas/segments and considered a necessary factor when selecting favorable exploration targets.
基金Supported by the National Natural Science Foundation of China(U24B6002)National Science and Technology Major Project(2024ZD14001)Project of the Sinopec Science and Technology Department(P25196,P24207).
文摘Lacustrine rift basins in China are characterized by pronounced structural segmentation,strong sedimentary heterogeneity,extensive fault-fracture development,and significant variability in thermal maturity and mobility of shale oil.This study reviews the current status of exploration and development of shale oil in such basins and examines theoretical frameworks such as“binary enrichment”and source-reservoir configuration,with a focus on five key subjects:(1)sedimentation-diagenesis coupling mechanisms of fine-grained shale reservoir formation;(2)dynamic diagenetic evolution and hydrocarbon occurrence mechanisms of organic-rich shale;(3)dominant controls and evaluation methods for shale oil enrichment;(4)fracturing mechanisms of organic-rich shale and simulation of artificial fracture networks;and(5)flow mechanisms and effective development strategies for shale oil.Integrated analysis suggests that two major scientific challenges must be addressed:the coupled evolution of fine-grained sedimentation,differential diagenesis,and hydrocarbon generation under tectonic influence and its control on shale oil occurrence and enrichment;and multi-scale,multiphase flow mechanisms and three-dimensional development strategies for lacustrine shale oil in complex fault blocks.In response to current exploration and development bottlenecks,future research will be conducted primarily to:(1)deeply understand organic-inorganic interactions and reservoir formation mechanisms in organic-rich shales,and clarify the influence of high-frequency sequence evolution and diagenetic fluids on reservoir space;(2)elucidate the dynamic processes of hydrocarbon generation,expulsion,and retention across different lithofacies,and quantify their relationship with thermal maturity,including the conditions for the formation of self-sealing systems;(3)develop a geologically adaptive,data-and intelligence-driven shale oil classification and grading evaluation system of shale oil;(4)reveal artificial fracture propagation pattern and optimize physical field coupled fracturing technologies for complex lithofacies assemblages;and(5)overcome challenges in multi-scale geological modeling and multiphase flow characterization,and establish advanced numerical simulation methodologies.
基金financially supported by the National Natural Science Foundation of China(Grant No.42072150)and we thank the sponsors of these projects.
文摘The relationship between marine transgression and the distribution of lacustrine organic matter has restricted shale oil and gas exploration for decades.In this study,the research objective is to analyze the sedimentary environment and evaluate its influence on organic matter in transgressive lacustrine shale.The study uses various analyses including total organic carbon(TOC),Rock-Eval pyrolysis,gas chromatography-mass spectrometry(GC-MS),trace element and isotope analysis.Finally,the study proposes an enrichment model for organic matter.The lacustrine shale of the second member of the Funing Formation(E_(1)f^(2))is divided into three sequences.The results indicate that the depositional environment of the organic matter during this period was an arid and humid,reduced,closed,rift lake basin.In the first sequence,high salinity resulted from increased evaporation,leading to low primary biological productivity.At this time,the lake basin belonged to a salinized closed lake basin.Intermittent transgressions began in the second sequence,with the deep lake area still being dominated by a reducing environment.The third sequence saw the environment evolve into a closed lake basin characterized by a warm and humid freshwater environment with high primary productivity.Marine transgressions introduce a substantial amount of marine plankton,nutrient elements,as well as more CO_(2) and CO_(3)^(2−)into the lake,leading to increased primary productivity.The sedimentary model for transgressive lacustrine source rocks proposed here serves as an example for similar transgressive lake basins.
基金supported by supportedby the China Postdoctoral Science Foundation under Grant Nos.2024M753612 and GZC20233101Supported by the Strategic Cooperation Technology Projects of CNPC and CUPB(ZLZX2020-05)the Science Foundation of China University of Petroleum,Beijing(No.2462023XKBH012).
文摘China's lacustrine shale oil reserves are abundant,making it a key area for future exploration and development.Most lacustrine shales feature a mix of mineral compositions and interlayer sedimentary structures.High-quality reservoirs exhibit significant heterogeneity,which influences the stress distribution during fracturing,leading to complex fracture network patterns.This complexity presents challenges for the comprehensive well logging evaluation of the geological-engineering"double sweet spots"in shale oil,severely restricting efficient development.This study focuses on the impact of shale sedimentary layering on the radial slowness of dipole shear waves.It employs rock physics experiments combined with advanced well logging techniques to explore the relationship between reservoir anisotropy caused by sedimentary layering and reservoir quality,thereby establishing a logging evaluation method for vertical identification of"sweet spots"in lacustrine shale oil.The shales in the Fengcheng Formation of the Mahu Sag into three types according to sedimentary structure scale:laminated,interlayer,and massive.Each type has different mineral compositions,affecting reservoir quality and fracturing potential.Laminated shales develop more fractures under stress along the beddings,showing moderate anisotropy,with reservoir capacity dependent on intercrystalline porosity within carbonate layers.Interlayer shales easily form complex fracture networks,exhibiting significant anisotropy,and their reservoir capacity depends on the porosity within sandy bands.Massive mudstones have the fewest fractures under stress,appearing isotropic with reservoir capacity dependent on matrix pore size.The intensity of reservoir anisotropy correlates positively with storage capacity and the propensity to form irregular and complex fracture networks during hydraulic fracturing.In sections without natural fractures,a larger difference between fast and slow shear waves corresponds to a radial profile shift towards warm tones,indicating stronger anisotropy and better reservoir quality,thus forming complex fracture networks during fracturing.Conversely,a smaller difference leads to a profile energy shift towards cooler tones,indicating stronger isotropy and poorer reservoir quality,hindering the formation of complex fracture networks during hydraulic fracturing.In sections with natural fractures,the difference between fast and slow shear waves exhibits erratic behavior,showing a cross-pattern in radial profiles,indicating strong anisotropy.The presence of natural fractures can synergize with induced fracture networks to form more complex systems,significantly enhancing reservoir productivity.
基金supported from the Opening fund of State Key Laboratory of Shale Oil and Gas Enrichment Mechanisms and Effective Development(33550000-22-ZC0613-0297)National Natural Science Foundation of China(42102196)the Natural Science Basis Research Plan in Shaanxi Province of China(2022JM-147).
文摘Pore structure directly affects the occurrence and migration of shale hydrocarbon,and the lack of research on the mechanism of the pore structure is an important reason for the hindrance of shale hydrocarbon exploration.By analysing the geochemistry and reservoir characteristics of Jurassic lacustrine shales in Sichuan Basin,this study recovers their paleoenvironments and further discusses paleoenvironmental constraints on pore structure.The results show that the Lower Jurassic lacustrine shales in the Sichuan Basin are in a warm and humid semi-anoxic to anoxic lake environment with high productivity,a strong stagnant environment,and a rapid sedimentation rate,with water depths ranging from about 11.54-55.22 m,and a mixture of type Ⅱ/Ⅲ kerogen is developed.In terms of reservoir characteristics,they are dominated by open-slit pores,and the pores are relatively complex.The percentage of mesopores is the highest,while the percentage of macropores is the lowest.Further analysis shows that paleoclimate controls the overall pore complexity and surface relaxation of shales by influencing the weathering rate of mother rocks.Paleoredox conditions control the proportion and complexity of shale pores by influencing TOC content.The research results will provide theoretical basis for improving the exploration efficiency of lacustrine shale resources and expanding exploration target areas.
基金supported by the National Natural Science Foundation of China(42090025,42302148)State Key Laboratory of Shale Oil and Gas Enrichment Mechanisms and Effective Development(33550000-22-ZC0613-0336)CNPC Innovation Found(2023DQ02-0103)。
文摘Lacustrine shale oil reservoirs of the Upper Triassic Chang 7 Member in the Ordos Basin have demonstrated significant potential for hydrocarbon resources.Natural fractures play a crucial role in hydrocarbon enrichment and production.Outcrops,cores,borehole image logs,thin sections,and FE-SEM images were used to investigate the types and characteristics of natural fractures in the Chang 7 Member.The factors controlling fracture development and the mechanisms of bedding-parallel fracture formation were revealed by integrating TOC analysis,XRD analysis,and rock pyrolysis.Results show that natural fractures in the study area include high-angle tectonic fractures and nearly horizontal bedding-parallel fractures.Brittle minerals and bed thickness control the occurrence and attributes of tectonic fractures.High TOC content and thermal maturity positively affect the development of bedding-parallel fractures,formed through the conversion of organic matter to hydrocarbons or the smectite-to-illite transformation.Additionally,the dominant orientations of tectonic fractures intersect the present-day maximum horizontal principal stress at a small angle,resulting in large apertures and good effectiveness.Bedding-parallel fractures contribute to enhance porosity and provide favorable pathways for lateral hydrocarbon migration.Collectively,this study could provide valuable insights for finding promising exploration areas in lacustrine shale oil reservoirs in the Ordos Basin and worldwide.
基金Supported by National Natural Science Foundation of China(42472217).
文摘Taking the shale oil of the first member of the Cretaceous Qingshankou Formation of Changling Sag in southern Songliao Basin as an example,this paper establishes a saturation model of lacustrine shale oil considering the influence of organic matter on clay-bound water conductivity.Based on the fluid characterization results of sealed samples and two-dimensional nuclear magnetic resonance,the differential influence of organic matter on clay-bound water conductivity was quantitatively revealed,and the conductivity mechanism and rock-electrical relationships of lacustrine shale were systematically analyzed.The results show that there are two conductive networks for lacustrine shales,i.e.the matrix free water and the clay-bound water.The bound water cementation index msh was introduced to reflect the impact of organic matter on clay-bound water conductivity,and it is positively correlated with the effective porosity.When there is sufficient rigid framework support and well-developed pores,organic matter is more likely to fill or adsorb onto clay interlayers.This reduces the ion exchange capacity of the electrical double layer,leading to an increase in msh and a decrease in the conductivity of clay-bound water.The overall conductivity of shale is controlled by the clay-bound water conductivity,and the relative contributions of the mentioned two conductive networks to formation conductivity are affected by the effective porosity and msh.The larger the effective porosity and msh,the more the contribution of the matrix free water to formation conductivity.According to the experimental results,the proposed saturation model yields a significantly higher interpretation accuracy in oil saturation than the Archie model and the Total-shale model.
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 National Key R&D Program of China(2024YFE0114000)Science and Technology Project of China National Petroleum Corporation(2024DJ8702).
文摘Based on the analysis of typical lacustrine shale oil zones in China and their geological characteristics,this study elucidates the fundamental differences between the enrichment patterns of shale oil sweet spots and conventional oil and gas.The key parameters and evaluation methods for assessing the large-scale production potential of lacustrine shale oil are proposed.The results show that shale oil is a petroleum resource that exists in organic-rich shale formations,in other words,it is preserved in its source bed,following a different process of generation-accumulation-enrichment from conventional oil and gas.Thus,the concept of“reservoir”seems to be inapplicable to shale oil.In China,lacustrine shale oil is distributed widely,but the geological characteristics and sweet spots enrichment patterns of shale oil vary significantly in lacustrine basins where the water environment and the tectonic evolution and diagenetic transformation frameworks are distinct.The core of the evaluation of lacustrine shale oil is“sweet spot volume”.The key factors for evaluating the large-scale production of continental shale oil are the oil storage capacity,oil-bearing capacity and oil producing capacity.The key parameters for evaluating these capacities are total porosity,oil content,and free oil content,respectively.It is recommended to determine the total porosity of shale by combining helium porosity measurement with nuclear magnetic resonance(NMR)method,the oil content of key layers by using organic solvent extraction,NMR method and high pressure mercury intrusion methods,and the free oil content by using NMR fluid distribution secondary spectral stripping decomposition and logging.The research results contribute supplemental insights on continental shale oil deliverability in China,and provide a scientific basis for the rapid exploration and large-scale production of lacustrine shale oil.
基金Supported by the National Science and Technology Major Project(2024ZD1404901,2017ZX05035)Strategic Priority Research Program(Category B)of the Chinese Academy of Sciences(XDB10050100).
文摘To clarify the mechanism of differential enrichment of intrasource shale oil,taking the third of seventh member of the Triassic Yanchang Formation(Chang 7_(3)submember for short)in the Ordos Basin,NW China as an example,we integrated high-resolution scanning electron microscopy(SEM),optical microscopy,laser Raman spectroscopy,rock pyrolysis,and organic solvent extraction experiments to identify solid bitumen of varying origins,obtain direct evidence of intrasource micro-migration of shale oil,and establish the coupling between the shale nano/micro-fabric and the oil generation,migration and accumulation.The Chang 7_(3)shale with rich alginite in laminae has the highest hydrocarbon generation potential but a low thermal transformation ratio.Frequent alternations of micron-scale argillaceous-felsic laminae enhance the hydrocarbon expulsion efficiency,yielding consistent aromaticity between in-situ and migrated solid bitumen.Mudstone laminae rich in terrestrial organic matter(OM)and clay minerals exhibit lower hydrocarbon generation threshold but stronger hydrocarbon retention capacity,with a certain amount of light oil/bitumen preserved to differentiate the chemical structure of in-situ versus migrated bitumen.Tuffaceous and sandy laminae contain abundant felsic minerals and migrated bitumen.Tuffaceous laminae develop high-angle microfractures under shale overpressure,facilitating oil charging into rigid mineral intergranular pores of sandy laminae.Fractionation during micro-migration progressively decreases the aromatization of solid bitumen from shale,through tuffaceous and mudstone,to sandy laminae,while increasing light hydrocarbon components and enhancing OM-hosted pore development.The intrasource micro-migration and enrichment of the Chang 7_(3)shale oil result from synergistic organic-inorganic diagenesis,with crude oil component fractionation being a key mechanism for forming sweet spots in laminated shale oil reservoirs.
基金Supported by the China National Key R&D Program(2023YFF0614100)National Science and Technology Major Project of China(2024ZD14066)+1 种基金Major Project of PetroChina Company Limited(2021ZZ01)Key R&D Project of Xinjiang Uygur Autonomous Region of China(2024B03001).
文摘Based on the technological demands for significantly enhancing oil recovery and long-term CO_(2)sequestration in the lacustrine oil reservoirs of China,this study systematically reviews the progress and practices of CO_(2)flooding and storage technologies in recent years.It addresses the key technological needs and challenges faced in scaling up the application of CO_(2)flooding and storage to mature,developed oil fields,and analyzes future development directions.During the pilot test phase(2006-2019),continuous development and application practices led to the establishment of the first-generation CO_(2)flooding and storage technology system for lacustrine reservoirs.In the industrialization phase(since 2020),significant advances and insights have been achieved in terms of confined phase behavior,storage mechanisms,reservoir engineering,sweep control,engineering process and storage monitoring,enabling the maturation of the second-generation CO_(2)flooding and storage theories and technologies to effectively support the demonstration projects of Carbon Capture,Utilization and Storage(CCUS).To overcome key technical issues such as low miscibility,difficulty in gas channeling control,high process requirements,limited application scenarios,and coordination challenges in CO_(2)flooding and storage,and to support the large-scale application of CCUS,it is necessary to strengthen research on key technologies for establishing the third-generation CO_(2)flooding and storage technological system incorporating miscibility enhancement and transformation,comprehensive regulation for sweep enhancement,whole-process engineering techniques and equipment,long-term storage monitoring safety,and synergistic optimization of flooding and storage.
基金supported by the National Natural Science Foundation of China(Projects 42090022)。
文摘Whether clay-rich shale reservoirs with low-medium maturity can serve as primary exploration targets remains a focal point of debate in the academic community.Clarifying the exploration potential of clayrich shale reservoirs is crucial for the future exploration and development of lacustrine shale.The Triassic Yanchang Formation in the Ordos Basin has been one of most productive lacustrine shale oil systems in China,with substantial oil production capacity already established.While the primary productive layers are currently fine-grained siltstone interbeds,however,it remains a highly debated issue whether the volumetrically more significant clay-rich reservoirs can become viable exploration targets in the near future.To address this issue,we examined the exploration potential of different lithofacies assemblages in Member 7(Mbr 7)of the Triassic Yanchang Formation,using a borehole in the Tongchuan area of the southern Ordos Basin as an example.We identified favorable exploration targets and assessed whether clay-rich reservoirs formed predominantly-freshwater conditions can become viable exploration targets.The results indicate the presence of six lithofacies in clay-rich reservoirs of Mbr 7 of the Yanchang Formation,with two main lithofacies assemblages:laminated organic-rich shale and massive mudstone.From the perspective of sandstone distribution,the sandstone interlayers within laminated organic-rich shale are primarily formed by gravity(hyperpycnal)flows,while sandstones deposited in delta front environments are typically associated with massive mudstone.Laminated organic-rich shale deposition occurred in an anoxic,deep-water environment characterized by high primary productivity,whereas massive mudstone formed in environments with high sedimentation rates and substantial terrigenous debris influx.Currently,the exploration potential of sandstone interlayers exceeds that of clay-rich reservoirs,with the greatest potential observed in the sandstone interlayers associated with laminated organic-rich shale formed by gravity(hyperpycnal)flows.Comparative analysis reveals that clay-rich reservoirs with low to medium maturity present great challenges for exploitation,making interlayer-type reservoirs the main focus of exploration at this stage.Nevertheless,clay-rich reservoirs in closed systems with high thermal maturity and organic matter content also hold considerable potential.
基金financially supported by the National Natural Science Foundation of China (Grant No. 42072150)
文摘To accurately investigate the evolution characteristics and generation mechanism of retained oil,the study analyzed organic-rich lacustrine shale samples from the Paleogene Kongdian Formation in Cangdong Sag,Bohai Bay Basin.This analysis involves Rock-Eval pyrolysis,pyrolysis simulation experiments,Gas Chromatograph Mass Spectrometer(GC-MS),and reactive molecular dynamics simulations(ReaxFF).The results revealed the retained oil primarily consisted of n-alkanes with carbon numbers ranging from C14 to C36.The generation of retained oil occurred through three stages.A slow growth stage of production rate was observed before reaching the peak of oil production in Stage Ⅰ.Stage Ⅱ involved a rapid increase in oil retention,with C12-C17 and C24-C32 serving as the primary components,increasing continuously during the pyrolysis process.The generation process involved the cleavage of weak bonds,including bridging bonds(hydroxyl,oxy,peroxy,imino,amino,and nitro),ether bonds,and acid amides in the first stage(Ro=0.50%-0.75%).The carbon chains in aromatic ring structures with heteroatomic functional groups breaks in the second stage(R_(o)=0.75%-1.20%).In the third stage(R_(o)=1.20%-2.50%),the ring structures underwent ring-opening reactions to synthesize iso-short-chain olefins and radicals,while further breakdown of aliphatic chains occurred.By coupling pyrolysis simu-lation experiments and molecular simulation technology,the evolution characteristics and bond breaking mechanism of retained oil in three stages were revealed,providing a reference for the for-mation and evolution mechanism of retained oil.
基金Supported by the National Natural Science Foundation of China(52425402,52204021,52404038)Scientific Research Fund of China University of Petroleum(Beijing)(2462022BJRC002).
文摘To elucidate the mechanism by which supercritical CO_(2)(SCCO_(2))-water-shale interactions during CO_(2)energized fracturing influence proppant embedment in lacustrine shale,shale samples from the Bohai Bay Basin were selected for SCCO_(2)-water-shale interaction experiments.X-ray diffraction(XRD),SEM large-area high-resolution imaging,automated mineral identification and characterization system(AMICS),and nanoindentation tests were employed to examine the micro-mechanical damage mechanisms of fracture surfaces and the evolving patterns of proppant embedment characteristics.The results reveal that:Prolonged interaction time reduces the contents of dolomite,feldspar,and clay minerals,while quartz content increases,with dolomite showing the most pronounced dissolution effect.As interaction time increases,the hardness and elasticity modulus of shale follow a power-law decay pattern,with the peak degradation rate occurring at 1 d,followed by a gradual decline of degradation velocity.Increasing interaction time results in growth in both the number and depth of embedment pits on the sample surface.After more than 3 d of interaction,clustered proppant embedment is observed,accompanied by the formation of deep embedment pits on the surface.
基金supported by China Postdoctoral Science Foundation (No. 2013M530680)the foundation of the Key Laboratory of Tectonics and Petroleum Resources (China University of Geosciences, Wuhan) of the Ministry of Education (No.TPR-2010-12)
文摘Organic-rich lacustrine shales are widely distributed in China and have significant potential for unconventional shale gas and oil production although the primary factors controlling the deposition of lacustrine shale are disputed. This work clarifies the different characteristics of tectonic evolution and shale among sub-basins in the Bohai Bay Basin in eastern China as a case study by studying basal subsidence, tectonic subsidence rate, basin extensional proportions and shale chemical characteristics. The paper summarizes the correlation between structure and shale deposition, and concludes that tectonic activity is the primary controlling factor for shale development. Episodic tectonic activity controls not only the timing of shale deposition（with the greatest shale deposition occurring primarily during the peak period of basin tectonic activity） but also the spatial distribution of shale（located mainly in areas of maximum subsidence）, the migration pattern of shale（conforming to that of the basin subsidence center）, and shale strata thickness. Tectonic activity also affects the total organic carbon content and organic matter type in shale. When the tectonic activity was the most active and basal subsidence was the maximum, the total organic carbon content of the shale reached its highest value with organic matter type mainly Type I. As tectonic activity weakened, the total organic carbon content decreased, and the organic matter type changed from Type I to Type I-III.
基金Supported by the China National Science and Technology Major Project(2017ZX05001-002,2016ZX05046-006)Petro China Science and Technology Major Project(2019B-0309)。
文摘Taking the mixed pre-salt carbonate rocks in the upper member of Eocene Xiaganchaigou Formation(E_(3)^(2))of Yingxi area in the Qaidam Basin as an example,the lithofacies and controlling mechanisms of reservoir formation are analyzed based on a large dataset of cores,thin sections and geochemical analysis.The reservoirs in E_(3)^(2)pre-salt layers have five types of lithofacies,of them,mixed granular calcareous dolostone,massive calcareous dolostone,plaque calcareous dolostone,and laminated dolomtic limestone are of sedimentary origin,and breccia calcareous dolostone is of tectonic origin.The four types of sedimentary lithofacies are divided into two types of saline sedimentary sequence lithofacies combinations,low-energy type in the sag area and low to high-energy type in the slope and paleo-uplift zone in the depression.Affected by high-frequency supply of continental clastic material,the two types of salty sedimentary sequences are mostly incomplete subtypes of lithofacies.Lithofacies have strong impacts on pre-salt reservoirs in E_(3)^(2):(1)Lithofacies type and sedimentary sequence controlled the formation and distribution of dolomite intercrystalline pores and dissolved pores during the pene-sedimentary period.(2)The structure of laminated dolomitic limestone controlled the formation of large-scale laminated fractures and high permeability channels during the diagenetic period.(3)Granular,massive,plaque calcareous dolostones have low mud content and strong brittleness,in the late tectonic reactivation period,the distribution of the three types of lithofacies,together with their distance from the top large slip faults and secondary faults,controlled the formation and distribution of high-efficiency fracture-cave brecciaed calcareous dolostone reservoirs.The above research led to the composite lithofacies-tectonic formation model of pre-salt reservoir in E_(3)^(2)of Yingxi area.The tempo-spatial distribution of tectonic breccia calcareous dolostone reservoirs,laminated dolomitic limestone shale oil reservoirs and granular,massive calcareous dolostone dissolved-intercrystalline pore tight reservoirs in various structural belts of the studied area have been figured out.These findings gave new insights into tight-shale oil accumulation theory in mixed carbonate successions from saline lacustrine basins,aiding in high efficient exploration and development of petroleum in the studied area.
基金supported by the Natural Science Foundation of China(grant No.41502100)the Shandong Province Postdoctoral Innovation Project Special Fund(grant No.201306069)
文摘Overlapping gravity accumulation bodies were formed on the northwestern steep slope of the Shuangyang Formation in the Moliqing fault depression of northeast China.This study analyzed in detail the spatial distribution of the lithofacies and lithofacies associations of these accumulation bodies based on more than 600 m of core sections,and summarized 12 major types of lithofacies and three types of lithofacies associations：（1） the proximal zone consists of gravelly debris flows dominated by alluvial channel conglomerates;（2） the middle zone is dominated by various gravity flow deposits and traction flow deposits;and（3） the distal zone is dominated by mudstones with intercalations of sandy debris and turbidites.Combining with the grain size cumulative probability curves analysis,we determined the transformation of debris flows to sandy debris flows and to turbidity currents in the slope zone of the basin margin,and further proposed a lacustrine slope apron model that is characterized by（1） an inconstant multiple source（line source）,（2） an alternation of gravity flow deposits and traction flow deposits dominated by periodical changes in a source flood flow system,and（3） the transformation of sandy debris flow deposits into distal turbidity current deposits.This sedimentary model may be applicable to other fault depressions for predicting reservoir distribution.
基金Supported by the CNPC Science and Technology Major Project(2018E-11)
文摘High-yielding oil wells were recently found in the first member of Paleogene Shahejie Formation,the Binhai area of Qikou Sag,providing an example of medium-and deep-buried high-quality reservoirs in the central part of a faulted lacustrine basin.By using data of cores,cast thin sections,scanning electron microscope and physical property tests,the sedimentary facies,physical properties and main control factors of the high-quality reservoirs were analyzed.The reservoirs are identified as deposits of slump-type sub-lacustrine fans,which are marked by muddy fragments,slump deformation structure and Bouma sequences in sandstones.They present mostly medium porosity and low permeability,and slightly medium porosity and high permeability.They have primary intergranular pores,intergranular and intragranular dissolution pores in feldspar and detritus grains,and structural microcracks as storage space.The main factors controlling the high quality reservoirs are as follows:(1)Favorable sedimentary microfacies of main and proximal distributary gravity flow channels.The microfacies with coarse sediment were dominated by transportation and deposition of sandy debris flow,and the effect of deposition on reservoir properties decreases with the increase of depth.(2)Medium texture maturity.It is shown by medium-sorted sandstones that were formed by beach bar sediment collapsing and redepositing,and was good for the formation of the primary intergranular pores.(3)High content of intermediate-acid volcanic rock detritus.The reservoir sandstone has high content of detritus of various components,especially intermediate-acid volcanic rock detritus,which is good for the formation of dissolution pores.(4)Organic acid corrosion.It was attributed to hydrocarbon maturity during mesodiagenetic A substage.(5)Early-forming and long lasting overpressure.A large-scale overpressure compartment was caused by under-compaction and hydrocarbon generation pressurization related to thick deep-lacustrine mudstone,and is responsible for the preservation of abundant primary pores.(6)Regional transtensional tectonic action.It resulted in the structural microcracks.
