By reviewing the research progress and exploration practices of shale gas geology in China,analyzing and summarizing the geological characteristics,enrichment laws,and resource potential of different types of shale ga...By reviewing the research progress and exploration practices of shale gas geology in China,analyzing and summarizing the geological characteristics,enrichment laws,and resource potential of different types of shale gas,the following understandings have been obtained:(1)Marine,transitional,and lacustrine shales in China are distributed from old to new in geological age,and the complexity of tectonic reworking and hydrocarbon generation evolution processes gradually decreases.(2)The sedimentary environment controls the type of source-reservoir configuration,which is the basis of“hydrocarbon generation and reservoir formation”.The types of source-reservoir configuration in marine and lacustrine shales are mainly source-reservoir integration,with occasional source-reservoir separation.The configuration types of transitional shale are mainly source-reservoir integration and source-reservoir symbiosis.(3)The resistance of rigid minerals to compression for pore preservation and the overpressure facilitate the enrichment of source-reservoir integrated shale gas.Good source reservoir coupling and preservation conditions are crucial for the shale gas enrichment of source-reservoir symbiosis and source-reservoir separation types.(4)Marine shale remains the main battlefield for increasing shale gas reserves and production in China,while transitional and lacustrine shales are expected to become important replacement areas.It is recommended to carry out the shale gas exploration at three levels:Accelerate the exploration of Silurian,Cambrian,and Permian marine shales in the Upper-Middle Yangtze region;make key exploration breakthroughs in ultra-deep marine shales of the Upper-Middle Yangtze region,the new Ordovician marine shale strata in the North China region,the transitional shales of the Carboniferous and Permian,as well as the Mesozoic lacustrine shale gas in basins such as Sichuan,Ordos and Songliao;explore and prepare for new shale gas exploration areas such as South China and Northwest China,providing technology and resource reserves for the sustainable development of shale gas in China.展开更多
Shales, the most abundant of sedimentary rocks, are valued as the source-rocks and seals to porous petroleum reservoirs. Over the past-twenty years, organic-rich shales have also emerged as valuable petroleum systems ...Shales, the most abundant of sedimentary rocks, are valued as the source-rocks and seals to porous petroleum reservoirs. Over the past-twenty years, organic-rich shales have also emerged as valuable petroleum systems （reservoir, seal, and source rocks contained in the same for- mation）. As such they have become primary targets for petroleum exploration and exploitation. This Part 1 of a three-part review addresses the bulk properties, multi-scale geometry and gas adsorption characteristics of these diverse and complex rocks. Shales display extremely low permeability, and their porosity is also low, but multi-scale. Characterizing the geometry and interconnectivity of the pore-structure frameworks with the natural-fracture networks within shales is essential for establish- ing their petroleum exploitation potential. Organic-rich shales typically contain two distinct types of porosity： matrix porosity and fracture porosity. In addition to inter-granular porosity, the matrix po- rosity includes two types of mineral-hosted porosity： inorganic-mineral-hosted porosity （1P）; and, organic-matter-hosted （within the kerogen） porosity （OP）. Whereas, the fracture porosity and per- meability is crucial for petroleum production from shales, it is within the OP where, typically, much of the in-situ oil and gas resources resides, and from where it needs to be mobilized. OP increases signifi- cantly as shales become more thermally mature （i.e., within the gas generation zones）, and plays a key role in the ultimate recovery from shale-gas systems. Shales＇ methane sorption capacities （MSC） tends to be positively correlated with their total organic carbon content （TOC）, thermal maturation, and mi- cropore volume. Clay minerals also significantly influence key physical properties of shale related to fluid flow （permeability） and response to stress （fracability） that determine their prospectivity for pe- troleum exploitation. Clay minerals can also adsorb gas, some much better than others. The surface area of the pore structure of shales can be positively or negatively correlated with TOC content, de- pending upon mineralogy and thermal maturity, and can influence its gas adsorption capacity. Part 2 of this three-part review considers, in a separate article, the geochemistry and thermal maturity cha- racteristics of shale; whereas Part 3, addresses the geomechanical attributes of shales, including their complex wettability, adsorption, water imbibition and ＂fracability＂ characteristics. The objectives of this Part 1 of the review is to identify important distinguishing characteristics related to the bulk properties of the most-prospective, petroleum-rich shales.展开更多
0 INTRODUCTION Shale oil has become a significant component of unconventional oil and gas exploration worldwide,dramatically transforming the global energy landscape over the past two decades(Xu et al.,2024;Guo et al....0 INTRODUCTION Shale oil has become a significant component of unconventional oil and gas exploration worldwide,dramatically transforming the global energy landscape over the past two decades(Xu et al.,2024;Guo et al.,2023;Wan et al.,2023;Zou et al.,2020).The successful commercial development of shale oil resources in North America has triggered a global surge in unconventional petroleum exploration,with many countries now actively pursuing their own shale resource development programs(Yang and Jin,2019).展开更多
Pore structure characteristics,gas content,and micro-scale gas occurrence mechanisms were investigated in the Shan_(2)^(3)sub-member marine-continental transitional shale of the southeastern margin of the Ordos Basin ...Pore structure characteristics,gas content,and micro-scale gas occurrence mechanisms were investigated in the Shan_(2)^(3)sub-member marine-continental transitional shale of the southeastern margin of the Ordos Basin using scanning electron microscope images,lowtemperature N_(2)/CO_(2)adsorption and high-pressure mercury intrusion,methane isothermal adsorption experiments,and CH4-saturated nuclear magnetic resonance(NMR).Two distinct shale types were identified:organic pore-rich shale(Type OP)and microfracture-rich shale(Type M).The Type OP shale exhibited relatively well-developed organic matter pores,while the Type M shale was primarily characterized by a high degree of microfracture development.An experimental method combining methane isothermal adsorption on crushed samples and CH4-saturated NMR of plug samples was proposed to determine the adsorbed gas,free gas,and total gas content under high temperature and pressure conditions.There were four main research findings.(1)Marine-continental transitional shale exhibited substantial total gas content in situ,ranging from 2.58 to 5.73 cm^(3)/g,with an average of 4.35 cm^(3)/g.The adsorbed gas primarily resided in organic matter pores through micropore filling and multilayer adsorption,followed by multilayer adsorption in clay pores.(2)The changes in adsorbed and free pore volumes can be divided into four stages.Pores of<5 nm exclusively contain adsorbed gas,while those of 5-20 nm have a high proportion of adsorbed gas alongside free gas.Pores ranging from 20 to 100 nm have a high proportion of free gas and few adsorbed gas,while pores of>100 nm and microfractures are almost predominantly free gas.(3)The proportion of adsorbed gas in Type OP shale exceeds that in Type M,reaching 66%.(4)Methane adsorbed in Type OP shale demonstrates greater desorption capability,suggesting a potential for enhanced stable production,which finds support in existing production well data.However,it must be emphasized that high-gas-bearing intervals in both types present valuable opportunities for exploration and development.These data may support future model validations and enhance confidence in exploring and developing marine-continental transitional shale gas.展开更多
As shale exploitation is still in its infancy outside North America much research effort is being channelled into various aspects of geochemical characterization of shales to identify the most prospective basins, form...As shale exploitation is still in its infancy outside North America much research effort is being channelled into various aspects of geochemical characterization of shales to identify the most prospective basins, formations and map their petroleum generation capabilities across local, regional and basin-wide scales. The measurement of total organic carbon, distinguishing and categorizing the kerogen types in terms oil-prone versus gas-prone, and using vitrinite reflectance and Rock-Eval data to estimate thermal maturity are standard practice in the industry and applied to samples from most wellbores drilled. It is the trends of stable isotopes ratios, particularly those of carbon, the wetness ra- tio （C1/~＇（C2＋C3））, and certain chemical biomarkers that have proved to be most informative about the status of shales as a petroleum system. These data make it possible to identify production ＂sweet- spots＂, discriminate oil-, gas-liquid- and gas-prone shales from kerogen compositions and thermal ma- turities. Rollovers and reversals of ethane and propane carbon isotope ratios are particularly indica- tive of high thermal maturity exposure of an organic-rich shale. Comparisons of hopane, strerane and terpane biomarkers with vitrinite reflectance （Ro） measurements of thermal maturity highlight dis- crepancies suggesting that Ro is not always a reliable indicator of thermal maturity. Major and trace element inorganic geochemistry data and ratios provides useful information regarding provenance, paleoenvironments, and stratigraphic-layer discrimination. This review considers the data measure- ment, analysis and interpretation of techniques associated with kerogen typing, thermal maturity, sta- ble and non-stable isotopic ratios for rocks and gases derived from them, production sweet-spot identi- fication, geochemical biomarkers and inorganic chemical indicators. It also highlights uncertainties and discrepancies observed in their practical application, and the numerous outstanding questions as- sociated with them.展开更多
Modeling geomechanical properties of shales to make sense of their complex properties is at the forefront of petroleum exploration and exploitation application and has received much re- search attention in recent year...Modeling geomechanical properties of shales to make sense of their complex properties is at the forefront of petroleum exploration and exploitation application and has received much re- search attention in recent years. A shale＇s key geomechanical properties help to identify its ＂fracibility＂ its fluid flow patterns and rates, and its in-place petroleum resources and potential commercial re- serves. The models and the information they provide, in turn, enable engineers to design drilling pat- terns, fracture-stimulation programs and materials selection that will avoid formation damage and op- timize recovery of petroleum. A wide-range of tools, technologies, experiments and mathematical techniques are deployed to achieve this. Characterizing the interconnected fracture, permeability and porosity network is an essential step in understanding a shales highly-anisotropic features on multiple scales （nano to macro）. Weli-log data, and its petrophysical interpretation to calibrate many geome- chanical metrics to those measured in rock samples by laboratory techniques plays a key role in pro- viding affordable tools that can be deployed cost-effectively in multiple well bores. Likewise, micro- seismic data helps to match fracture density and propagation observed on a reservoir scale with pre- dictions from simulations and laboratory tests conducted on idealised/simplified discrete fracture net- work models. Shales complex wettability, adsorption and water imbibition characteristics have a sig- nificant influence on potential formation damage during stimulation and the short-term and long-term flow of petroleum achievable. Many gas flow mechanisms and models are proposed taking into ac- count the multiple flow mechanisms involved （e.g., desorption, diffusion, slippage and viscous flow op- erating at multiple porosity levels from nano- to macro-scales）. Fitting historical production data and well decline curves to model predictions helps to verify whether model＇s geomechanical assumptions are realistic or not. This review discusses the techniques applied and the models developed that are relevant to applied geomechanics, highlighting examples of their application and the numerous out- standin~ questions associated with them.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
The global energy demand is increasing rapidly,and it is imperative to develop shale hydrocarbon re-sources vigorously.The prerequisite for enhancing the exploitation efficiency of shale reservoirs is the systematic e...The global energy demand is increasing rapidly,and it is imperative to develop shale hydrocarbon re-sources vigorously.The prerequisite for enhancing the exploitation efficiency of shale reservoirs is the systematic elucidation of the occurrence characteristics,flow behavior,and enhanced oil recovery(EOR)mechanisms of shale oil within commonly developed nanopores.Molecular dynamics(MD)technique can simulate the occurrence,flow,and extraction processes of shale oil at the nanoscale,and then quantitatively characterize various fluid properties,flow characteristics,and action mechanisms under different reservoir conditions by calculating and analyzing a series of MD parameters.However,the existing review on the application of MD simulation in shale oil reservoirs is not systematic enough and lacks a summary of technical challenges and solutions.Therefore,recent MD studies on shale oil res-ervoirs were summarized and analyzed.Firstly,the applicability of force fields and ensembles of MD in shale reservoirs with different reservoir conditions and fluid properties was discussed.Subsequently,the calculation methods and application examples of MD parameters characterizing various properties of fluids at the microscale were summarized.Then,the application of MD simulation in the study of shale oil occurrence characteristics,flow behavior,and EOR mechanisms was reviewed,along with the elucidation of corresponding micro-mechanisms.Moreover,influencing factors of pore structure,wall properties,reservoir conditions,fluid components,injection/production parameters,formation water,and inorganic salt ions were analyzed,and some new conclusions were obtained.Finally,the main challenges associated with the application of MD simulations to shale oil reservoirs were discussed,and reasonable prospects for future MD research directions were proposed.The purpose of this review is to provide theoretical basis and methodological support for applying MD simulation to study shale oil reservoirs.展开更多
Gas-bearing shales have become a major source of future natural gas production worldwide.It has become increasingly urgent to develop a reliable prediction model and corresponding workflow for identifying shale gas sw...Gas-bearing shales have become a major source of future natural gas production worldwide.It has become increasingly urgent to develop a reliable prediction model and corresponding workflow for identifying shale gas sweet spots.The formation of gas-bearing shales is closely linked to relative sealevel changes,providing an important approach to predicting sweet spots in the Wufeng-Longmaxi shale in the southern Sichuan Basin,China.Three types of marine shale gas sweet spots are identified in the shale based on their formation stages combined with relative sea-level changes:early,middle,and late transgression types.This study develops a prediction model and workflow for identifying shale gas sweet spots by analyzing relative sea-level changes and facies sequences.Predicting shale gas sweet spots in an explored block using this model and workflow can provide a valuable guide for well design and hydraulic fracturing,significantly enhancing the efficiency of shale gas exploration and development.Notably,the new prediction model and workflow can be utilized for the rapid evaluation of the potential for shale gas development in new shale gas blocks or those with low exploratory maturity.展开更多
Research on the distribution and development of black shales in the Lianggaoshan Formation has been deficient,which has hindered exploration for lacustrine shale oil in the Sichuan Basin.Our study characterized the we...Research on the distribution and development of black shales in the Lianggaoshan Formation has been deficient,which has hindered exploration for lacustrine shale oil in the Sichuan Basin.Our study characterized the well logging data,core samples,outcrops,and geochemistry of black shales in the Lianggaoshan Formation in the Sichuan Basin.Our analysis focused on the lake basin evolution and the migration characteristics,paleoenvironmental features,formation mechanisms,and developmental model of the black shales.The results indicated that black shales in the Lianggaoshan Formation exhibited significant lateral migration,with an overall thickening trend from east to west.Within the 1st Member of the formation,black shale occurred as a single thick layer in the eastern region that gradually thinned toward the central region.Multiple sets of shale developed within the 2nd and 3rd members,and these had lower thicknesses than the 1st Member and migrated toward central Sichuan.Paleoproductivity and terrigenous input were the main factors controlling the deposition of black shales.A semi-humid climate influenced the deposition of black shales,bringing abundant freshwater,terrigenous debris,and nutrients into the basin.Decomposition of organic matter consumed oxygen in sediment and bottom water,causing localized oxygen deficiency in the strata.展开更多
Based on the basic data of drilling,logging,testing and geological experiments,the geological characteristics of the Permian Dalong Formation marine shales in the northern Sichuan Basin and the factors controlling sha...Based on the basic data of drilling,logging,testing and geological experiments,the geological characteristics of the Permian Dalong Formation marine shales in the northern Sichuan Basin and the factors controlling shale gas enrichment and high yield are studied.The results are obtained in four aspects.First,the high-quality shale of the Dalong Formation was formed after the deposition of the Permian Wujiaping Formation,and it is developed in the Kaijiang-Liangping trough in the northern part of Sichuan Basin,where deep-water continental shelf facies and deep-water reduction environment with thriving siliceous organisms have formed the black siliceous shale rich in organic matter.Second,the Dalong Formation shale contains both organic and inorganic pores,with stratification of alternated brittle and plastic minerals.In addition to organic pores,a large number of inorganic pores are developed even in ultra-deep(deeper than 4500 m)layers,contributing a total porosity of more than 5%,which significantly expands the storage space for shale gas.Third,the limestone at the roof and floor of the Dalong Formation acted as seal rock in the early burial and hydrocarbon generation stage,providing favorable conditions for the continuous hydrocarbon generation and rich gas preservation in shale interval.In the later reservoir stimulation process,it was beneficial to the lateral extension of the fractures,so as to achieve the optimal stimulation performance and increase the well-controlled resources.Combining the geological,engineering and economic conditions,the favorable area with depth less than 5500 m is determined to be 1800 km2,with resources of 5400×10^(8) m^(3).Fourth,the shale reservoirs of the Dalong Formation are thin but rich in shale gas.The syncline zone far away from the main faults in the high and steep tectonic zone,eastern Sichuan Basin,with depth less than 5500 m,is the most favorable target for producing the Permian shale gas under the current engineering and technical conditions.It mainly includes the Nanya syncline,Tanmuchang syncline and Liangping syncline.展开更多
The black shale samples from the Niutitang Formation in the Yangtze Block were sequentially treated using organic solvent extraction and wet chemical oxidation.The organic matter(OM)in the shales includes physically m...The black shale samples from the Niutitang Formation in the Yangtze Block were sequentially treated using organic solvent extraction and wet chemical oxidation.The organic matter(OM)in the shales includes physically mobile OM(PmOM),chemically mobile OM(CmOM),and stable OM(StOM).The CmOM has the strongest CH_(4)adsorption capacity because it has the largest volume of micropores and mesopores.In contrast,the PmOM has a very negative effect on the CH_(4)adsorption because it is poreless.The XD shale is a siliceous shale,in which the quartz particles wrap partly OM,preventing extraction and oxidation.The SL shale is an argillaceous shale,in which most of the OM is combined with clay minerals to form organo-clay composites.In both the SL and XD shales,the OM that is extractable via organic solvents is distributed among the mineral particles and is interconnected.The conceptual model of marine black shale in different environments needs to be perfected in the future because quantitative and qualitative methods should be combined to clarify the relationship between the known OM types(e.g.,pyrobitumen,solid bitumen,and solid kerogen)and the OM types identified in this study.展开更多
Based on large-field rock thin section scanning,high-resolution field emission-scanning electron microscopy(FE-SEM),fluorescence spectroscopy,and rock pyrolysis experiments of the Mesoproterozoic Jixianian Hongshuizhu...Based on large-field rock thin section scanning,high-resolution field emission-scanning electron microscopy(FE-SEM),fluorescence spectroscopy,and rock pyrolysis experiments of the Mesoproterozoic Jixianian Hongshuizhuang Formation shale samples from the Yanliao Basin in northern China,combined with sedimentary forward modeling,a systematic petrological and organic geochemical study was conducted on the reservoir quality,oil-bearing potential,distribution,and resource potential of the Hongshuizhuang Formation shale in Well Yuanji-2.The results indicate that:(1)The original organic carbon content of the Hongshuizhuang Formation shale averages up to 6.24%,and the original hydrocarbon generation potential is as high as 44.09 mg/g,demonstrating a strong oil generation potential.(2)The rock type is primarily siliceous shale containing low clay mineral content,characterized by the development of shale bedding fractures and organic shrinkage fractures,resulting in good compressibility and reservoir quality.(3)The fifth and fourth members of the Hongshuizhuang Formation serve as shale oil sweet spots,contributing more than 60%of shale oil production with their total thickness as only 40%of the target formation.(4)The Kuancheng-Laozhuanghu area is the most prospective shale oil exploration option in the Yanliao Basin and covers approximately 7200 km^(2).Its original total hydrocarbon generation potential reaches about 74.11 billion tons,with current estimated retained shale oil resources exceeding 1.148 billion tons(lower limit)–comparable to the geological resources of the Permian Lucaogou Formation shale oil in the Jimsar Sag of the Junggar Basin.These findings demonstrate the robust exploration potential of the Hongshuizhuang Formation shale oil in the Yanliao Basin.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
Shale gas serves as a significant strategic successor resource for future oil and gas reserves and production in China.Thus,a profound understanding of the adsorption mechanism of shale gas in shale reservoirs is cruc...Shale gas serves as a significant strategic successor resource for future oil and gas reserves and production in China.Thus,a profound understanding of the adsorption mechanism of shale gas in shale reservoirs is crucial to accurately predict and evaluate shale gas reserves.In this study,we utilized two simulation methods,molecular dynamics simulation and Giant Canonical Monte Carlo simulation to examine the adsorption characteristics of kerogen under varying temperature and pressure conditions.We compared the results under identical temperature and pressure conditions for different mineral-kerogen composite models.Moreover,we examined the effects of temperature,pressure,and mineral species on the kerogen adsorption mechanism.The results indicate that shale formations with high organic matter content and a substantial proportion of non-clay inorganic minerals,as well as those subjected to higher temperature and pressure conditions than the shallow layer,possess a greater capacity to accommodate shale gas.This study examined the adsorption mechanism of methane in shale gas using different mineral-kerogen composite models.The findings of this study provide more accurate guidance and support for efficient development of shale gas.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 lamina(combination)types,reservoir characteristics and shale oil occurrence states of organic-rich shale in the Triassic Yanchang Formation Chang 73 sub-member in the Ordos Basin were systematically investigated t...The lamina(combination)types,reservoir characteristics and shale oil occurrence states of organic-rich shale in the Triassic Yanchang Formation Chang 73 sub-member in the Ordos Basin were systematically investigated to reveal the main controlling factors of shale oil occurrence under different lamina combinations.The differential enrichment mechanisms and patterns of shale oil were discussed using the shale oil micro-migration characterization and evaluation methods from the perspectives of relay hydrocarbon supply,stepwise migration,and multi-stage differentiation.The results are obtained in five aspects.First,Chang 73 shale mainly develops five types of lamina combination,i.e.non-laminated shale,sandy laminated shale,tuffaceous laminated shale,mixed laminated shale,and organic-rich laminated shale.Second,shales with different lamina combinations are obviously different in the reservoir space.Specifically,shales with sandy laminae and tuffaceous laminae have a large number of intergranular pores,dissolution pores and hydrocarbon generation-induced fractures.The multi-scale pore and fracture system constitutes the main place for liquid hydrocarbon occurrence.Third,the occurrence and distribution of shale oil in shale with different lamina combinations are jointly controlled by organic matter abundance,reservoir property,thermal evolution degree,mineral composition and laminae scale.The micro-nano-scale pore-fracture networks within shales containing rigid laminae,particularly sandy and tuffaceous laminations,primarily contain free-state light hydrocarbon components.In contrast,adsorption-phase heavy hydrocarbon components predominantly occupy surfaces of organic matter assemblages,clay mineral matrices,and framework mineral particulates.Fourth,there is obvious shale oil micro-migration between shales with different lamina combinations in Chang 73.Generally,such micro-migration is stepwise in a sequence of organic-rich laminated shale→tuffaceous laminated shale→mixed laminated shale→sandy lamiated shale→non-laminated shale.Fifth,the relay hydrocarbon supply of organic matter under the control of the spatial superposition of shales with various laminae,the stepwise migration via multi-scale pore and fracture network,and the multi-differentiation in shales with different lamina combinations under the control of organic-inorganic interactions fundamentally decide the differences of shale oil components between shales with different lamina combinations.展开更多
The marine-continental transitional shale of the Upper Permian Longtan Formation is widely distributed in Hunan and shows significant exploration potential.Frequent changes in lithofacies have however notably influenc...The marine-continental transitional shale of the Upper Permian Longtan Formation is widely distributed in Hunan and shows significant exploration potential.Frequent changes in lithofacies have however notably influenced the shale gas enrichment.The strata of the Longtan Formation in the Shaoyang Depression,central Hunan,were taken as the study object for this project.Three lithofacies assemblages were identified:shale interbedded with sandstone layer(SAL),sandstone interbedded with shale layer(ASL)and laminated shale layer(LSL).The SAL shale shows significant variability in hydrocarbon generation potential,which leads to shale gas characterized by'hydrocarbon generation in high total organic carbon(TOC)shale,retention in low TOC shale and accumulation in sandstone'.The ASL shale,influenced by the redox conditions of the depositional environment,shows a lower concentration of organic matter.This results in an enrichment model of'hydrocarbon generation and accumulation in shale,with sealing by sandstone'.The laminar structure of LSL shale causes both quartz and clay minerals to control the reservoir.Shale gas is characterized by'hydrocarbon generation in mud laminae,retention and accumulation in silty laminae,with multiple intra-source migration paths'.In the marine-continental transitional shale gas system,the enrichment intervals of different types of shale gas reservoirs exhibit significant variability.展开更多
The evolution of cracks in shale directly affects the efficient production of shale gas.However,there is a lack of research on the characteristics of crack initiation in deep dense shale under different stress conditi...The evolution of cracks in shale directly affects the efficient production of shale gas.However,there is a lack of research on the characteristics of crack initiation in deep dense shale under different stress conditions.In this work,considering the different combinations of confining pressure and bedding plane inclination angle(α),biaxial mechanical loading experiments were conducted on shale containing circular holes.The research results indicate that the confining pressure and inclination angle of the bedding planes significantly influence the failure patterns of shale containing circular holes.The instability of shale containing circular holes can be classified into five types:tensile failure along the bedding planes,tensile failure through the bedding planes,shear slip along the bedding planes,shear failure through the bedding planes,and block instability failure.Furthermore,the evolution of strain and stress fields around the circular holes was found to be the fundamental cause of variations in the initiation characteristics and locations of shale cracks.The crack initiation criterion for shale containing circular hole was established,providing a new method for evaluating the trajectory of shale hole wall fractures.This study holds significant importance for evaluating the evolution and stability of fracture networks within shale reservoirs.展开更多
Shale gas is abundant in the Paleozoic of the Yangtze Platform,and several high-yield shale gas fields have been built in the Upper Yangtze Platform,China.The Permian of the South Yellow Sea Basin(SYSB)in the Lower Ya...Shale gas is abundant in the Paleozoic of the Yangtze Platform,and several high-yield shale gas fields have been built in the Upper Yangtze Platform,China.The Permian of the South Yellow Sea Basin(SYSB)in the Lower Yangtze area is considered a potential target for shale gas exploration;however,the fundamental geological conditions of shale gas have not been studied.Based on the first whole-cored scientific drilling borehole(CSDP-2)in the SYSB,detailed tests involving petrology,organic geochemistry,and reservoir physical properties were conducted to evaluate the shale gas potential of the Lower Permian.The Lower Permian is dominated by organic-rich siliceous,clay,and clay-mixed shales.The average total organic carbon content is 5.99%,and the organic matter is mainly type Ⅱ_(1)−Ⅱ_(2),which has entered the high-over mature evolution stage.The pore types of organic-rich shales mainly include organic pores,dissolution pores,and intergranular pores,of which the meso-/macropores are well developed.The average porosity is 3.04%,and the total specific surface area and pore volume are 3.47 m^(2)/g and 7.21×10^(−3) cm^(3)/g,respectively.The average Langmuir volume obtained from the methane adsorption isotherms is 2.70 cm^(3)/g,and methane is mainly adsorbed in the meso-/macropores.The lower Permian shales are rich in methane as indicated by gas logging results,with an average content of 7.3%,which can reach up to 65.9%.A comparison of the study area with typical shale gas fields shows that the Lower Permian is brittle and shallowly buried and has a high potential for shale gas exploration and low-cost development.The depression areas of the SYSB are overlain by thick Mesozoic-Cenozoic sediments,show higher organic matter maturity,and may have greater shale gas potential.The shale gas exploration breakthrough of the study area is of great significance to ensure the energy supply of economically developed areas on the east China.展开更多
基金Supported by the National Natural Science Foundation of China(42172165,42272143)Project of SINOPEC Science and Technology Department(P24181,KLP24017).
文摘By reviewing the research progress and exploration practices of shale gas geology in China,analyzing and summarizing the geological characteristics,enrichment laws,and resource potential of different types of shale gas,the following understandings have been obtained:(1)Marine,transitional,and lacustrine shales in China are distributed from old to new in geological age,and the complexity of tectonic reworking and hydrocarbon generation evolution processes gradually decreases.(2)The sedimentary environment controls the type of source-reservoir configuration,which is the basis of“hydrocarbon generation and reservoir formation”.The types of source-reservoir configuration in marine and lacustrine shales are mainly source-reservoir integration,with occasional source-reservoir separation.The configuration types of transitional shale are mainly source-reservoir integration and source-reservoir symbiosis.(3)The resistance of rigid minerals to compression for pore preservation and the overpressure facilitate the enrichment of source-reservoir integrated shale gas.Good source reservoir coupling and preservation conditions are crucial for the shale gas enrichment of source-reservoir symbiosis and source-reservoir separation types.(4)Marine shale remains the main battlefield for increasing shale gas reserves and production in China,while transitional and lacustrine shales are expected to become important replacement areas.It is recommended to carry out the shale gas exploration at three levels:Accelerate the exploration of Silurian,Cambrian,and Permian marine shales in the Upper-Middle Yangtze region;make key exploration breakthroughs in ultra-deep marine shales of the Upper-Middle Yangtze region,the new Ordovician marine shale strata in the North China region,the transitional shales of the Carboniferous and Permian,as well as the Mesozoic lacustrine shale gas in basins such as Sichuan,Ordos and Songliao;explore and prepare for new shale gas exploration areas such as South China and Northwest China,providing technology and resource reserves for the sustainable development of shale gas in China.
基金the Department of Science and Technology (DST Ministry of Science and Technology, Government of India), for providing funding for his research through the DST-Inspire Assured Opportunity of Research Career (AORC) scheme
文摘Shales, the most abundant of sedimentary rocks, are valued as the source-rocks and seals to porous petroleum reservoirs. Over the past-twenty years, organic-rich shales have also emerged as valuable petroleum systems （reservoir, seal, and source rocks contained in the same for- mation）. As such they have become primary targets for petroleum exploration and exploitation. This Part 1 of a three-part review addresses the bulk properties, multi-scale geometry and gas adsorption characteristics of these diverse and complex rocks. Shales display extremely low permeability, and their porosity is also low, but multi-scale. Characterizing the geometry and interconnectivity of the pore-structure frameworks with the natural-fracture networks within shales is essential for establish- ing their petroleum exploitation potential. Organic-rich shales typically contain two distinct types of porosity： matrix porosity and fracture porosity. In addition to inter-granular porosity, the matrix po- rosity includes two types of mineral-hosted porosity： inorganic-mineral-hosted porosity （1P）; and, organic-matter-hosted （within the kerogen） porosity （OP）. Whereas, the fracture porosity and per- meability is crucial for petroleum production from shales, it is within the OP where, typically, much of the in-situ oil and gas resources resides, and from where it needs to be mobilized. OP increases signifi- cantly as shales become more thermally mature （i.e., within the gas generation zones）, and plays a key role in the ultimate recovery from shale-gas systems. Shales＇ methane sorption capacities （MSC） tends to be positively correlated with their total organic carbon content （TOC）, thermal maturation, and mi- cropore volume. Clay minerals also significantly influence key physical properties of shale related to fluid flow （permeability） and response to stress （fracability） that determine their prospectivity for pe- troleum exploitation. Clay minerals can also adsorb gas, some much better than others. The surface area of the pore structure of shales can be positively or negatively correlated with TOC content, de- pending upon mineralogy and thermal maturity, and can influence its gas adsorption capacity. Part 2 of this three-part review considers, in a separate article, the geochemistry and thermal maturity cha- racteristics of shale; whereas Part 3, addresses the geomechanical attributes of shales, including their complex wettability, adsorption, water imbibition and ＂fracability＂ characteristics. The objectives of this Part 1 of the review is to identify important distinguishing characteristics related to the bulk properties of the most-prospective, petroleum-rich shales.
基金supported by the State Key Laboratory of Petroleum Resources and Engineering,China University of Petroleum(Beijing)(No.PRE/open-2501)。
文摘0 INTRODUCTION Shale oil has become a significant component of unconventional oil and gas exploration worldwide,dramatically transforming the global energy landscape over the past two decades(Xu et al.,2024;Guo et al.,2023;Wan et al.,2023;Zou et al.,2020).The successful commercial development of shale oil resources in North America has triggered a global surge in unconventional petroleum exploration,with many countries now actively pursuing their own shale resource development programs(Yang and Jin,2019).
基金the Science and Technology Cooperation Project of the CNPC-SWPU Innovation Alliance,China(No.2020CX030101)the National Natural Science Foundation of China(No.42222209)the Scientific Research and Technological Development Program of CNPC,China(No.2023ZZ0801).
文摘Pore structure characteristics,gas content,and micro-scale gas occurrence mechanisms were investigated in the Shan_(2)^(3)sub-member marine-continental transitional shale of the southeastern margin of the Ordos Basin using scanning electron microscope images,lowtemperature N_(2)/CO_(2)adsorption and high-pressure mercury intrusion,methane isothermal adsorption experiments,and CH4-saturated nuclear magnetic resonance(NMR).Two distinct shale types were identified:organic pore-rich shale(Type OP)and microfracture-rich shale(Type M).The Type OP shale exhibited relatively well-developed organic matter pores,while the Type M shale was primarily characterized by a high degree of microfracture development.An experimental method combining methane isothermal adsorption on crushed samples and CH4-saturated NMR of plug samples was proposed to determine the adsorbed gas,free gas,and total gas content under high temperature and pressure conditions.There were four main research findings.(1)Marine-continental transitional shale exhibited substantial total gas content in situ,ranging from 2.58 to 5.73 cm^(3)/g,with an average of 4.35 cm^(3)/g.The adsorbed gas primarily resided in organic matter pores through micropore filling and multilayer adsorption,followed by multilayer adsorption in clay pores.(2)The changes in adsorbed and free pore volumes can be divided into four stages.Pores of<5 nm exclusively contain adsorbed gas,while those of 5-20 nm have a high proportion of adsorbed gas alongside free gas.Pores ranging from 20 to 100 nm have a high proportion of free gas and few adsorbed gas,while pores of>100 nm and microfractures are almost predominantly free gas.(3)The proportion of adsorbed gas in Type OP shale exceeds that in Type M,reaching 66%.(4)Methane adsorbed in Type OP shale demonstrates greater desorption capability,suggesting a potential for enhanced stable production,which finds support in existing production well data.However,it must be emphasized that high-gas-bearing intervals in both types present valuable opportunities for exploration and development.These data may support future model validations and enhance confidence in exploring and developing marine-continental transitional shale gas.
基金the Department of Science & Technology (DST Ministry of Science & Technology, Government of India), for providing funding for his research through the DST-Inspire Assured Opportunity of Research Career (AORC) scheme
文摘As shale exploitation is still in its infancy outside North America much research effort is being channelled into various aspects of geochemical characterization of shales to identify the most prospective basins, formations and map their petroleum generation capabilities across local, regional and basin-wide scales. The measurement of total organic carbon, distinguishing and categorizing the kerogen types in terms oil-prone versus gas-prone, and using vitrinite reflectance and Rock-Eval data to estimate thermal maturity are standard practice in the industry and applied to samples from most wellbores drilled. It is the trends of stable isotopes ratios, particularly those of carbon, the wetness ra- tio （C1/~＇（C2＋C3））, and certain chemical biomarkers that have proved to be most informative about the status of shales as a petroleum system. These data make it possible to identify production ＂sweet- spots＂, discriminate oil-, gas-liquid- and gas-prone shales from kerogen compositions and thermal ma- turities. Rollovers and reversals of ethane and propane carbon isotope ratios are particularly indica- tive of high thermal maturity exposure of an organic-rich shale. Comparisons of hopane, strerane and terpane biomarkers with vitrinite reflectance （Ro） measurements of thermal maturity highlight dis- crepancies suggesting that Ro is not always a reliable indicator of thermal maturity. Major and trace element inorganic geochemistry data and ratios provides useful information regarding provenance, paleoenvironments, and stratigraphic-layer discrimination. This review considers the data measure- ment, analysis and interpretation of techniques associated with kerogen typing, thermal maturity, sta- ble and non-stable isotopic ratios for rocks and gases derived from them, production sweet-spot identi- fication, geochemical biomarkers and inorganic chemical indicators. It also highlights uncertainties and discrepancies observed in their practical application, and the numerous outstanding questions as- sociated with them.
基金the Department of Science & Technology (DST Ministry of Science & Technology, Government of India), for providing funding for his research through the DST-Inspire Assured Opportunity of Research Career (AORC) scheme
文摘Modeling geomechanical properties of shales to make sense of their complex properties is at the forefront of petroleum exploration and exploitation application and has received much re- search attention in recent years. A shale＇s key geomechanical properties help to identify its ＂fracibility＂ its fluid flow patterns and rates, and its in-place petroleum resources and potential commercial re- serves. The models and the information they provide, in turn, enable engineers to design drilling pat- terns, fracture-stimulation programs and materials selection that will avoid formation damage and op- timize recovery of petroleum. A wide-range of tools, technologies, experiments and mathematical techniques are deployed to achieve this. Characterizing the interconnected fracture, permeability and porosity network is an essential step in understanding a shales highly-anisotropic features on multiple scales （nano to macro）. Weli-log data, and its petrophysical interpretation to calibrate many geome- chanical metrics to those measured in rock samples by laboratory techniques plays a key role in pro- viding affordable tools that can be deployed cost-effectively in multiple well bores. Likewise, micro- seismic data helps to match fracture density and propagation observed on a reservoir scale with pre- dictions from simulations and laboratory tests conducted on idealised/simplified discrete fracture net- work models. Shales complex wettability, adsorption and water imbibition characteristics have a sig- nificant influence on potential formation damage during stimulation and the short-term and long-term flow of petroleum achievable. Many gas flow mechanisms and models are proposed taking into ac- count the multiple flow mechanisms involved （e.g., desorption, diffusion, slippage and viscous flow op- erating at multiple porosity levels from nano- to macro-scales）. Fitting historical production data and well decline curves to model predictions helps to verify whether model＇s geomechanical assumptions are realistic or not. This review discusses the techniques applied and the models developed that are relevant to applied geomechanics, highlighting examples of their application and the numerous out- standin~ questions associated with them.
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(52304021,52104022,52204031)the Natural Science Foundation of Sichuan Province(2022NSFSC0205,2024NSFSC0201,2023NSFSC0947)the National Science and Technology Major Projects of China(2017ZX05049006-010).
文摘The global energy demand is increasing rapidly,and it is imperative to develop shale hydrocarbon re-sources vigorously.The prerequisite for enhancing the exploitation efficiency of shale reservoirs is the systematic elucidation of the occurrence characteristics,flow behavior,and enhanced oil recovery(EOR)mechanisms of shale oil within commonly developed nanopores.Molecular dynamics(MD)technique can simulate the occurrence,flow,and extraction processes of shale oil at the nanoscale,and then quantitatively characterize various fluid properties,flow characteristics,and action mechanisms under different reservoir conditions by calculating and analyzing a series of MD parameters.However,the existing review on the application of MD simulation in shale oil reservoirs is not systematic enough and lacks a summary of technical challenges and solutions.Therefore,recent MD studies on shale oil res-ervoirs were summarized and analyzed.Firstly,the applicability of force fields and ensembles of MD in shale reservoirs with different reservoir conditions and fluid properties was discussed.Subsequently,the calculation methods and application examples of MD parameters characterizing various properties of fluids at the microscale were summarized.Then,the application of MD simulation in the study of shale oil occurrence characteristics,flow behavior,and EOR mechanisms was reviewed,along with the elucidation of corresponding micro-mechanisms.Moreover,influencing factors of pore structure,wall properties,reservoir conditions,fluid components,injection/production parameters,formation water,and inorganic salt ions were analyzed,and some new conclusions were obtained.Finally,the main challenges associated with the application of MD simulations to shale oil reservoirs were discussed,and reasonable prospects for future MD research directions were proposed.The purpose of this review is to provide theoretical basis and methodological support for applying MD simulation to study shale oil reservoirs.
文摘Gas-bearing shales have become a major source of future natural gas production worldwide.It has become increasingly urgent to develop a reliable prediction model and corresponding workflow for identifying shale gas sweet spots.The formation of gas-bearing shales is closely linked to relative sealevel changes,providing an important approach to predicting sweet spots in the Wufeng-Longmaxi shale in the southern Sichuan Basin,China.Three types of marine shale gas sweet spots are identified in the shale based on their formation stages combined with relative sea-level changes:early,middle,and late transgression types.This study develops a prediction model and workflow for identifying shale gas sweet spots by analyzing relative sea-level changes and facies sequences.Predicting shale gas sweet spots in an explored block using this model and workflow can provide a valuable guide for well design and hydraulic fracturing,significantly enhancing the efficiency of shale gas exploration and development.Notably,the new prediction model and workflow can be utilized for the rapid evaluation of the potential for shale gas development in new shale gas blocks or those with low exploratory maturity.
基金funded by Science and Technology Cooperation Project of the CNPC-SWPU Innovation Alliance(2020CX050103).
文摘Research on the distribution and development of black shales in the Lianggaoshan Formation has been deficient,which has hindered exploration for lacustrine shale oil in the Sichuan Basin.Our study characterized the well logging data,core samples,outcrops,and geochemistry of black shales in the Lianggaoshan Formation in the Sichuan Basin.Our analysis focused on the lake basin evolution and the migration characteristics,paleoenvironmental features,formation mechanisms,and developmental model of the black shales.The results indicated that black shales in the Lianggaoshan Formation exhibited significant lateral migration,with an overall thickening trend from east to west.Within the 1st Member of the formation,black shale occurred as a single thick layer in the eastern region that gradually thinned toward the central region.Multiple sets of shale developed within the 2nd and 3rd members,and these had lower thicknesses than the 1st Member and migrated toward central Sichuan.Paleoproductivity and terrigenous input were the main factors controlling the deposition of black shales.A semi-humid climate influenced the deposition of black shales,bringing abundant freshwater,terrigenous debris,and nutrients into the basin.Decomposition of organic matter consumed oxygen in sediment and bottom water,causing localized oxygen deficiency in the strata.
基金Supported by the PetroChina Science&Technology Special Project(2023ZZ21YJ04)PetroChina Gas Reservoir Evaluation Project(20230304-08)。
文摘Based on the basic data of drilling,logging,testing and geological experiments,the geological characteristics of the Permian Dalong Formation marine shales in the northern Sichuan Basin and the factors controlling shale gas enrichment and high yield are studied.The results are obtained in four aspects.First,the high-quality shale of the Dalong Formation was formed after the deposition of the Permian Wujiaping Formation,and it is developed in the Kaijiang-Liangping trough in the northern part of Sichuan Basin,where deep-water continental shelf facies and deep-water reduction environment with thriving siliceous organisms have formed the black siliceous shale rich in organic matter.Second,the Dalong Formation shale contains both organic and inorganic pores,with stratification of alternated brittle and plastic minerals.In addition to organic pores,a large number of inorganic pores are developed even in ultra-deep(deeper than 4500 m)layers,contributing a total porosity of more than 5%,which significantly expands the storage space for shale gas.Third,the limestone at the roof and floor of the Dalong Formation acted as seal rock in the early burial and hydrocarbon generation stage,providing favorable conditions for the continuous hydrocarbon generation and rich gas preservation in shale interval.In the later reservoir stimulation process,it was beneficial to the lateral extension of the fractures,so as to achieve the optimal stimulation performance and increase the well-controlled resources.Combining the geological,engineering and economic conditions,the favorable area with depth less than 5500 m is determined to be 1800 km2,with resources of 5400×10^(8) m^(3).Fourth,the shale reservoirs of the Dalong Formation are thin but rich in shale gas.The syncline zone far away from the main faults in the high and steep tectonic zone,eastern Sichuan Basin,with depth less than 5500 m,is the most favorable target for producing the Permian shale gas under the current engineering and technical conditions.It mainly includes the Nanya syncline,Tanmuchang syncline and Liangping syncline.
基金financially supported by the National Natural Science Fund of China(Nos.42002166,41690134,42162016)the Guizhou Provincial Fund Project(Nos.[2020]1Y161,ZK[2021]199,ZK[2022]106)。
文摘The black shale samples from the Niutitang Formation in the Yangtze Block were sequentially treated using organic solvent extraction and wet chemical oxidation.The organic matter(OM)in the shales includes physically mobile OM(PmOM),chemically mobile OM(CmOM),and stable OM(StOM).The CmOM has the strongest CH_(4)adsorption capacity because it has the largest volume of micropores and mesopores.In contrast,the PmOM has a very negative effect on the CH_(4)adsorption because it is poreless.The XD shale is a siliceous shale,in which the quartz particles wrap partly OM,preventing extraction and oxidation.The SL shale is an argillaceous shale,in which most of the OM is combined with clay minerals to form organo-clay composites.In both the SL and XD shales,the OM that is extractable via organic solvents is distributed among the mineral particles and is interconnected.The conceptual model of marine black shale in different environments needs to be perfected in the future because quantitative and qualitative methods should be combined to clarify the relationship between the known OM types(e.g.,pyrobitumen,solid bitumen,and solid kerogen)and the OM types identified in this study.
基金Supported by the National Key R&D Program of China(2022YFF0800304)PetroChina Science and Technology Project(2023ZZ0203)。
文摘Based on large-field rock thin section scanning,high-resolution field emission-scanning electron microscopy(FE-SEM),fluorescence spectroscopy,and rock pyrolysis experiments of the Mesoproterozoic Jixianian Hongshuizhuang Formation shale samples from the Yanliao Basin in northern China,combined with sedimentary forward modeling,a systematic petrological and organic geochemical study was conducted on the reservoir quality,oil-bearing potential,distribution,and resource potential of the Hongshuizhuang Formation shale in Well Yuanji-2.The results indicate that:(1)The original organic carbon content of the Hongshuizhuang Formation shale averages up to 6.24%,and the original hydrocarbon generation potential is as high as 44.09 mg/g,demonstrating a strong oil generation potential.(2)The rock type is primarily siliceous shale containing low clay mineral content,characterized by the development of shale bedding fractures and organic shrinkage fractures,resulting in good compressibility and reservoir quality.(3)The fifth and fourth members of the Hongshuizhuang Formation serve as shale oil sweet spots,contributing more than 60%of shale oil production with their total thickness as only 40%of the target formation.(4)The Kuancheng-Laozhuanghu area is the most prospective shale oil exploration option in the Yanliao Basin and covers approximately 7200 km^(2).Its original total hydrocarbon generation potential reaches about 74.11 billion tons,with current estimated retained shale oil resources exceeding 1.148 billion tons(lower limit)–comparable to the geological resources of the Permian Lucaogou Formation shale oil in the Jimsar Sag of the Junggar Basin.These findings demonstrate the robust exploration potential of the Hongshuizhuang Formation shale oil in the Yanliao Basin.
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(Grant No.42102145)the Science Foundation of China University of Petroleum,Beijing(Grant No.2462022YXZZ007)。
文摘Shale gas serves as a significant strategic successor resource for future oil and gas reserves and production in China.Thus,a profound understanding of the adsorption mechanism of shale gas in shale reservoirs is crucial to accurately predict and evaluate shale gas reserves.In this study,we utilized two simulation methods,molecular dynamics simulation and Giant Canonical Monte Carlo simulation to examine the adsorption characteristics of kerogen under varying temperature and pressure conditions.We compared the results under identical temperature and pressure conditions for different mineral-kerogen composite models.Moreover,we examined the effects of temperature,pressure,and mineral species on the kerogen adsorption mechanism.The results indicate that shale formations with high organic matter content and a substantial proportion of non-clay inorganic minerals,as well as those subjected to higher temperature and pressure conditions than the shallow layer,possess a greater capacity to accommodate shale gas.This study examined the adsorption mechanism of methane in shale gas using different mineral-kerogen composite models.The findings of this study provide more accurate guidance and support for efficient development of shale gas.
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(42302184)Innovation Group Project of Basic Research in Gansu Province,China(22JR5RA045)。
文摘The lamina(combination)types,reservoir characteristics and shale oil occurrence states of organic-rich shale in the Triassic Yanchang Formation Chang 73 sub-member in the Ordos Basin were systematically investigated to reveal the main controlling factors of shale oil occurrence under different lamina combinations.The differential enrichment mechanisms and patterns of shale oil were discussed using the shale oil micro-migration characterization and evaluation methods from the perspectives of relay hydrocarbon supply,stepwise migration,and multi-stage differentiation.The results are obtained in five aspects.First,Chang 73 shale mainly develops five types of lamina combination,i.e.non-laminated shale,sandy laminated shale,tuffaceous laminated shale,mixed laminated shale,and organic-rich laminated shale.Second,shales with different lamina combinations are obviously different in the reservoir space.Specifically,shales with sandy laminae and tuffaceous laminae have a large number of intergranular pores,dissolution pores and hydrocarbon generation-induced fractures.The multi-scale pore and fracture system constitutes the main place for liquid hydrocarbon occurrence.Third,the occurrence and distribution of shale oil in shale with different lamina combinations are jointly controlled by organic matter abundance,reservoir property,thermal evolution degree,mineral composition and laminae scale.The micro-nano-scale pore-fracture networks within shales containing rigid laminae,particularly sandy and tuffaceous laminations,primarily contain free-state light hydrocarbon components.In contrast,adsorption-phase heavy hydrocarbon components predominantly occupy surfaces of organic matter assemblages,clay mineral matrices,and framework mineral particulates.Fourth,there is obvious shale oil micro-migration between shales with different lamina combinations in Chang 73.Generally,such micro-migration is stepwise in a sequence of organic-rich laminated shale→tuffaceous laminated shale→mixed laminated shale→sandy lamiated shale→non-laminated shale.Fifth,the relay hydrocarbon supply of organic matter under the control of the spatial superposition of shales with various laminae,the stepwise migration via multi-scale pore and fracture network,and the multi-differentiation in shales with different lamina combinations under the control of organic-inorganic interactions fundamentally decide the differences of shale oil components between shales with different lamina combinations.
基金financial support from the National Natural Science Foundation of China(Grant Nos.U23B20155 and 42202140)the Science and Technology Innovation Program of Hunan Province(2023RC1021)+1 种基金the China Geological Survey(DD20221659)the Science and Technology Bureau,Changsha,China(kq2208261)。
文摘The marine-continental transitional shale of the Upper Permian Longtan Formation is widely distributed in Hunan and shows significant exploration potential.Frequent changes in lithofacies have however notably influenced the shale gas enrichment.The strata of the Longtan Formation in the Shaoyang Depression,central Hunan,were taken as the study object for this project.Three lithofacies assemblages were identified:shale interbedded with sandstone layer(SAL),sandstone interbedded with shale layer(ASL)and laminated shale layer(LSL).The SAL shale shows significant variability in hydrocarbon generation potential,which leads to shale gas characterized by'hydrocarbon generation in high total organic carbon(TOC)shale,retention in low TOC shale and accumulation in sandstone'.The ASL shale,influenced by the redox conditions of the depositional environment,shows a lower concentration of organic matter.This results in an enrichment model of'hydrocarbon generation and accumulation in shale,with sealing by sandstone'.The laminar structure of LSL shale causes both quartz and clay minerals to control the reservoir.Shale gas is characterized by'hydrocarbon generation in mud laminae,retention and accumulation in silty laminae,with multiple intra-source migration paths'.In the marine-continental transitional shale gas system,the enrichment intervals of different types of shale gas reservoirs exhibit significant variability.
基金Projects(52104143,52109135,52374099)supported by the National Natural Science Foundation of ChinaProject(2025YFHZ0323)supported by the Natural Science Foundation of Sichuan Province,China。
文摘The evolution of cracks in shale directly affects the efficient production of shale gas.However,there is a lack of research on the characteristics of crack initiation in deep dense shale under different stress conditions.In this work,considering the different combinations of confining pressure and bedding plane inclination angle(α),biaxial mechanical loading experiments were conducted on shale containing circular holes.The research results indicate that the confining pressure and inclination angle of the bedding planes significantly influence the failure patterns of shale containing circular holes.The instability of shale containing circular holes can be classified into five types:tensile failure along the bedding planes,tensile failure through the bedding planes,shear slip along the bedding planes,shear failure through the bedding planes,and block instability failure.Furthermore,the evolution of strain and stress fields around the circular holes was found to be the fundamental cause of variations in the initiation characteristics and locations of shale cracks.The crack initiation criterion for shale containing circular hole was established,providing a new method for evaluating the trajectory of shale hole wall fractures.This study holds significant importance for evaluating the evolution and stability of fracture networks within shale reservoirs.
基金supported by the Natural Science Foundation of Shandong Province(ZR2023MD112)financially supported by Laoshan Laboratory(LSKJ202203401).
文摘Shale gas is abundant in the Paleozoic of the Yangtze Platform,and several high-yield shale gas fields have been built in the Upper Yangtze Platform,China.The Permian of the South Yellow Sea Basin(SYSB)in the Lower Yangtze area is considered a potential target for shale gas exploration;however,the fundamental geological conditions of shale gas have not been studied.Based on the first whole-cored scientific drilling borehole(CSDP-2)in the SYSB,detailed tests involving petrology,organic geochemistry,and reservoir physical properties were conducted to evaluate the shale gas potential of the Lower Permian.The Lower Permian is dominated by organic-rich siliceous,clay,and clay-mixed shales.The average total organic carbon content is 5.99%,and the organic matter is mainly type Ⅱ_(1)−Ⅱ_(2),which has entered the high-over mature evolution stage.The pore types of organic-rich shales mainly include organic pores,dissolution pores,and intergranular pores,of which the meso-/macropores are well developed.The average porosity is 3.04%,and the total specific surface area and pore volume are 3.47 m^(2)/g and 7.21×10^(−3) cm^(3)/g,respectively.The average Langmuir volume obtained from the methane adsorption isotherms is 2.70 cm^(3)/g,and methane is mainly adsorbed in the meso-/macropores.The lower Permian shales are rich in methane as indicated by gas logging results,with an average content of 7.3%,which can reach up to 65.9%.A comparison of the study area with typical shale gas fields shows that the Lower Permian is brittle and shallowly buried and has a high potential for shale gas exploration and low-cost development.The depression areas of the SYSB are overlain by thick Mesozoic-Cenozoic sediments,show higher organic matter maturity,and may have greater shale gas potential.The shale gas exploration breakthrough of the study area is of great significance to ensure the energy supply of economically developed areas on the east China.
