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
Tectonism is one of the dominant factors affecting the shale pore structure.However,the control of shale pore structure by tectonic movements is still controversial,which limits the research progress of shale gas accu...Tectonism is one of the dominant factors affecting the shale pore structure.However,the control of shale pore structure by tectonic movements is still controversial,which limits the research progress of shale gas accumulation mechanism in the complex tectonic region of southern China.In this study,34 samples were collected from two exploratory wells located in different tectonic locations.Diverse experiments,e.g.,organic geochemistry,XRD analysis,FE-SEM,low-pressure gas adsorption,and high-pressure mercury intrusion,were conducted to fully characterize the shale reservoir.The TOC,Ro,and mineral composition of the shale samples between the two wells are similar,which reflects that the shale samples of the two wells have proximate pores-generating capacity and pores-supporting capacity.However,the pore characteristics of shale samples from two wells are significantly different.Compared with the stabilized zone shale,the porosity,pore volume,and specific surface area of the deformed zone shale were reduced by 60.61%,64.85%,and 27.81%,respectively.Moreover,the macroscopic and fine pores were reduced by 54.01%and 84.95%,respectively.Fault activity and uplift denudation are not conducive to pore preservation,and the rigid basement of Huangling uplift can promote pore preservation.These three factors are important reasons for controlling the difference in pore structure between two wells shales.We established a conceptual model of shale pores evolution under different tectonic preservation conditions.This study is significant to clarify the scale of shale gas formation and enrichment in complex tectonic regions,and helps in the selection of shale sweet spots.展开更多
[Objective] This study aimed to investigate the effect of different short-term preservation conditions on mycelial growth of Morchella conica, and search for opti- mum preservation conditions. [Method] M. conica strai...[Objective] This study aimed to investigate the effect of different short-term preservation conditions on mycelial growth of Morchella conica, and search for opti- mum preservation conditions. [Method] M. conica strains in tubes were preserved at two temperature treatments 10 ℃/5 ℃ （day/night） and 15℃/10 ℃（day/night） in scat- tered light or dark for 30 or 60 d. The strain preserved at 4 ℃ dark for 90 d was the control （CK）. So, a total of nine treatments were prepared in this study. [Result] Mycelial growth of M. conica preserved at 10 ℃/5 ℃ was better than that at 15 ℃/10 ℃ and control. The colony color and aerial hyphae of strains preserved in scattered light was also better than that in dark. Additionally, the preservation time showed no distinct effect on mycelial growth at 10 ℃/5 ℃. So the time could be lengthened. But the maximal preservation time was 60 d at 15 ℃/10 ℃. Therefore, preserved under the appropriate conditions of 10 ℃/5 ℃, scattered light for 30 d, the strain had the neat colony edge, moderate aerial mycelia, dense mycelia, lower sectoral variation, uniform mycelial growth rate and high dry weight of mycelia.展开更多
The Upper Ordovician-Lower Silurian Longmaxi Shale in the Upper Yangtze block represents one of the most important shale gas plays in China. The shale composition, porosity, organic thermal maturity, and methane sorpt...The Upper Ordovician-Lower Silurian Longmaxi Shale in the Upper Yangtze block represents one of the most important shale gas plays in China. The shale composition, porosity, organic thermal maturity, and methane sorption were investigated at the Qilongcun section in the Dingshan area, southeastern Sichuan Basin. The results show that the Upper Ordovician-Lower Silurian Longmaxi Shale contains： （1） sapropelic I organic matter; （2） a 40-m thick bedded sequence where total organic carbon （TOC） content is 〉 2%; （3） a 30-m thick layer at the base of the Longmaxi Shale with a brittle mineral content higher than 50%; and （4） a mean methane adsorption capacity of 1.80 cm3/g （7 MPa pressure）. A positive correlation between TOC and sorbed gas indicates that organic matter content exerts an important control on methane storage capacity. Based on the analysis of the shale reservoir characteristics, the lower member of the Longmaxi Shale can thus be considered a favorable stratum for shale gas exploration and exploitation. It has similar reservoir characteristics with the Longmaxi Shale in the Jiaoshiba area tested with a high-yield industrial gas flow. However, based on tectonic analysis, differences in the level of industrial gas flow between the low-yield study area and the high-yield Jiaoshiba area may result from different tectonic preservation conditions. Evidence from these studies indicates the shale gas potential of the Longmaxi Shale is constrained by the reservoir and preservation conditions.展开更多
Although carbon isotope reversal and its reasons in shale gas reservoirs have been widely recognized,the application of the reversal is yet to be investigated.A study on high-maturity shale from Wufeng and Longmaxi Fo...Although carbon isotope reversal and its reasons in shale gas reservoirs have been widely recognized,the application of the reversal is yet to be investigated.A study on high-maturity shale from Wufeng and Longmaxi Formations in the Sichuan Basin not only reveals the relationship between the degree of isotopes inversion and the production capacity(e.g.,estimated ultimate recovery(EUR))of the gas well but also indicates the preservation conditions of shale gas reservoirs.(1)Although there are differences in gas isotopes in different shale gas reservoirs,the isotope fractionation of shale gas is small during the production stage of gas wells,even when the wellbore pressure drops to zero.The main cause of the difference in carbon isotopes and their inversion degree can be the uplift time during the Yanshan period and the formation pressure relief degree of shale gas reservoirs in distinct structural positions.Thus,carbon isotope inversion is a good indicator of shale gas preservation condition and EUR of shale gas wells.(2)The degree of carbon isotope inversion correlates strongly with shale gas content and EUR.The calculation formula of shale-gas recoverable reserves was established using△δ^(13)C(δC_(1)-δC_(2))and EUR.(3)The gas loss rate and total loss amount can be estimated using the dynamic reserves and isotopic difference values of gas wells in various shale gas fields,which also reflects the current methane loss,thereby demonstrating great potential for evaluating global methane loss in shales.展开更多
^87Sr/^86Sr, δ^18O and δ^13C ratios of calcite, dolomite, gypsum filling vugs and fissures in marine carbonates and their host rocks from the Sinian to the middle Triassic, are employed to trace the possible source ...^87Sr/^86Sr, δ^18O and δ^13C ratios of calcite, dolomite, gypsum filling vugs and fissures in marine carbonates and their host rocks from the Sinian to the middle Triassic, are employed to trace the possible source and migration path of key fluids related to development of hydrocarbon, hydrocarbon preservation condition are then discussed further. Comprehensive research, based on the paleo-fluid, the property of formation water and the deformation intensity etc., indicates that the preservation conditions in the Shizhu synclinorium zone and Fangdoushan anticlinorium zone are the most predominant in the central Yangtze. Three sets of fluid systems in the Shizhu synclinorium zone are identified. Little fluid exchange occurs between the upper-middle fluid system and the lower fluid system, so two independent preservation units have developed. Both the Permian and the Triassic in the upper preservation units and the Dengying Formation of the Sinian and the lower Cambrian in the lower preservation units have good preservation conditions. The preservation condition in the lower association （Z-S） located in the Huaguoping synclinorium zone in the western Hubei and Hunan is better than that in other tectonic units, where the fluids in the lower association migrated vertically across strata when the fluid isolating intervals were destroyed, the regional seals are absent and the conditions for the preservation of hydrocarbon accumulations are totally destroyed. The preservation condition is increasingly more favorable from the western Jiangxi and Hunan to the western Hubei ＆ eastern Chongqing on the whole.展开更多
Complex tectonic movements and high thermal maturity of marine shale dominate South China,where preservation conditions are critical for shale gas enrichment and productivity.Based on the exploration practices of the ...Complex tectonic movements and high thermal maturity of marine shale dominate South China,where preservation conditions are critical for shale gas enrichment and productivity.Based on the exploration practices of the Silurian shale gas at the southeastern margin of the Sichuan Basin in recent years,conventional gas and shale gas were compared in terms of their preservation conditions.The results revealed that superior roof and floor conditions are indispensable to shale gas preservation.Moreover,the self-sealing ability and the huge gap of up to 2–8 times between vertical and lateral permeability of shale gas reservoirs determine the lateral diffusion as the basic pattern of shale gas migration.The unconformity at the bottom of Lower Cambrian leads to worse preservation conditions in the system,and cutting by faults may accelerate the diffusion of shale gas.Major controlling factors for shale gas preservation and their criteria of discrimination were also investigated.It is suggested that:(1)the strength of tectonic modification is the major factor controlling shale gas preservation.Broad and gentle structures with continuous seals and an anticlinal setting are more favorable for the enrichment of shale gas,and a closed evolutionary environment with late uplifting is more favorable for the preservation of shale gas;(2)shale gas can be preserved well in downdip areas without faults or effectively closed or shielded by faults and areas far away from outcrops or zones with stratigraphic hiatus;(3)pressure coefficient is a comprehensive indicator for discriminating preservation conditions.In the study area,the pressure coefficient is in positive correlation with shale gas production and the high or super-high pressure of reservoir is a signal of good preservation condition for shale gas;and(4)in the areas within the southeastern Sichuan Basin,other than those close to erosion zones or hiatus,the Wufeng Fm.of Upper Ordovician and the Longmaxi Fm.of Lower Silurian present high pressure coefficient(up to 2.25)generally,demonstrating good preservation conditions for shale gas,while the pressure coefficient reduces progressively toward or outside the margin of the basin,corresponding to downgrading preservation conditions.展开更多
Lower Paleozoic dark shale is developed in the western Middle Yangtze Block,which lays a material foundation for the enrichment and accumulation of marine shale gas.In order to ascertain the control action of geologic...Lower Paleozoic dark shale is developed in the western Middle Yangtze Block,which lays a material foundation for the enrichment and accumulation of marine shale gas.In order to ascertain the control action of geological structures on the differential preservation of shale gas and reveal the key factors in shale gas preservation,this paperfirstly analyzed the structure characteristics of this area,carried out structure pattern recognition and structural belt division,and studied structural deformation mode and intensity.Based on this,the relationships between different structure styles and shale gas preservation conditions were analyzed.Finally,combined with the structural deformation and the lithofacies paleogeographic characteristics of marine shale,the favorable exploration zones of shale gas were proposed.And the following research results were obtained.First,the western Middle Yangtze Block can be divided into four structural deformation belts,and three types of piggyback structural patterns have been identified,including restricted type,weakly reformed type and strongly reformed type.Second,the restricted type is located in the northwestern part of Hunan and Hubei Provinces.In this pattern,piggyback structure is incomplete and thrust belt and Compressive fold belt are developed.Third,the weakly and strongly reformed types are located in the western parts of Hunan and Hubei,and Wulingshan area,respectively.They both have complete piggyback structures,but the former has lower deformation intensity and has never undergone the late superimposed reformation.Fourth,there are three structural transfer belts in the western Middle Yangtze Block,i.e.the structural transfer belt between the East Sichuan faultefold belt and West HunaneHubei faultefold belt,the structural transfer belt between West HunaneHubei faultefold belt and Wulingshan faultefold belt,and the structural transfer belt between the outcrop and the hinterland of Middle Yangtze Block.Thefirst one is structurally transformed at the Qiyueshan fault.The East Sichuan faultefold belt on the west is an ejective fold with low fault density and formation denudation intensity,where shale gas is enriched in anticlines and slopes;while the West HunaneHubei faultefold belt on the east is a trough-like fold with strong faulting and high formation denudation intensity,where shale gas is enriched in residual synclines.In conclusion,shale gas preservation conditions of Upper Ordovician Wufeng FormationeLower Silurian Longmaxi Formation in this area are the best in Zigui syncline,thrustedetachment zone and western margin of Qiyueshan fault.The favorable exploration areas of shale gas of Lower Cambrian Niutitang Formation are distributed in the westernflank of Yichang Slope,Kaixian thrust zone,compressive fold zone and thrustedetachment zone.展开更多
In the South Yellow Sea Basin,Mesozoic-Paleozoic marine strata are generally well developed with large thickness,and they are characterized by multi-source and multi-stage hydrocarbon accumulation,providing a material...In the South Yellow Sea Basin,Mesozoic-Paleozoic marine strata are generally well developed with large thickness,and they are characterized by multi-source and multi-stage hydrocarbon accumulation,providing a material basis for the formation of large-scale oil and gas fields.However,no substantial breakthrough has been made in this area.Based on previous research results,the complex tectonic pattern of this superimposed basin was formed by multi-stage tectonic movements and the favorable static conditions for hydrocarbon preservation were reworked or destroyed by later superimposition.Therefore,hydrocarbon preservation conditions are the key factors for restricting the breakthrough of marine oil and gas exploration in this area.In this paper,hydrocarbon preservation conditions of marine strata in the South Yellow Sea Basin were comprehensively analyzed from many aspects,such as tectonic movement,source conditions,caprock characteristics,magmatic activities,and hydrogeological and hydrogeochemical characteristics.It is indicated that the complex tectonic pattern of the South Yellow Sea Basin is resulted from tectonic events in multiple stages,and the development and evolution of regional source rocks are mainly controlled by two stages(i.e.,the stable evolution stage of Mesozoic-Paleozoic marine basin and the Mesozoic-Cenozoic tectonic pattern transformation and basin formation stage),so the characteristics of differential oil and gas preservation are presented.Besides,better marine hydrocarbon preservation preconditions in this area are weaker tectonic reworking,development of high-quality thick source rocks,good vertical sealing capacity of caprocks,weaker magmatic activity and confined hydrogeological conditions.It is concluded that the Laoshan Uplift in the central part of the South Yellow Sea Basin is structurally stable with weaker faulting and magmatic activities,so it is better in oil and gas preservation conditions.Besides,several large-scale structural traps with good petroleum geological conditions and complete source-reservoir-caprock assemblages are developed in this area.Therefore,this area is the most promising region for Paleozoic marine oil and gas exploration in this basin.展开更多
The Zhaotong National Shale Gas Demonstration Area along the southern margin of the Sichuan Basin is located in the complex marine tectonic area of South China,where shale deformation and reformation are intense and t...The Zhaotong National Shale Gas Demonstration Area along the southern margin of the Sichuan Basin is located in the complex marine tectonic area of South China,where shale deformation and reformation are intense and the factors controlling sweet spots are complex,so the preservation conditions have an important impact on the enrichment of shale gas.In order to support the selection and evaluation of shale gas sweet spots in this area and improve the success rate of drilling,this paper carried out a geological survey onfield outcrops.Then,based on drilling,mud logging and physical property test data,the structural deformation pattern and the regional deformation characteristics of this demonstration area were analyzed,and the development characteristics of formation joints and fractures,the sealing capacity of shale sur-rounding rock and the distribution characteristics of gas reservoirs were studied.Finally,the preservation conditions of shale gas in the Wufeng Formation of Upper Ordovician and the Longmaxi Formation of Lower Silurian were discussed.And the following research results were ob-tained.First,in the Zhaotong National Shale Gas Demonstration Area,three structural deformation patterns are developed from south to north,including trough type,equal amplitude type and baffle type,which are distributed in three major deformation zones,respectively,i.e.,the shear deformation zone of Central Guizhou Uplift,the compressionetorsion deformation zone of northern YunnaneGuizhou Depression and the compression deformation zone of Southern Sichuan Depression.Second,three types of joints and fractures whose relationships with the di-rection of strata are high angle,middleelow angle and bedding intersection are developed in the WufengeLongmaxi formations and its overlying strata,and their occurrence characteristics are basically consistent with those of the three major deformation zones.Third,the shale of WufengeLongmaxi formations is thick in the north and thin in the south and possesses the preservation conditions of sourceereservoir inte-gration and self-sealing hydrocarbon accumulation.And combined with the sealing ability of the overburden strata and the roof andfloor,its preservation conditions are overall better.Fourth,from the perspective of shale gas component,this area can be divided into three belts,i.e.,methane,methaneþnitrogen mixture and nitrogen from north to south.And the preservation conditions of shale gas are generally better in the north and worse in the south.In conclusion,the shale in the centralenorthern part of Zhaotong National Shale Gas Demonstration Area(compression deformation area and its southern margin)is the most favorable area because of its large shale thickness,weak reformation and deformation,bedding development of joints and fractures,good sealing performance and excellent preservation conditions.The compressionetorsion deformation zone of northern YunnaneGuizhou Depression in the central part is moderate in preservation conditions,and it is the relatively favorable area.The shear deformation zone of Central Guizhou Uplift in the southern part has poor preservation conditions,and it is a prospective area.展开更多
Many scholars carried out large quantity of researches on oil and gas preservative condi-tions of marine carbonate rocks from the aspects of cap rocks,faults,formation water,hydrodynamic,and tectonism.This article giv...Many scholars carried out large quantity of researches on oil and gas preservative condi-tions of marine carbonate rocks from the aspects of cap rocks,faults,formation water,hydrodynamic,and tectonism.This article gives dynamic evaluation on oil and gas preservative conditions of marine stratum in Jianghan（江汉） plain of multiphase tectonic disturbance from the view of paleofluid geo-chemistry.The conclusion shows that there mainly existed fluid filling of two periods in the reservoir of Lower-Middle Triassic to Permian.The fluid filled in the earlier period came from Lower Palaeozoic.The interchange of fluid in Lower-Middle Triassic to Permian suggested the oil and gas in Lower Pa-laeozoic had been broken up.The fluid filled in the later period（Lower-Middle Triassic to Permian） came from the same or adjacent strata and lacked anatectic fluidogenous features coming from Palaeozoic.With good preservative conditions of bulk fluid at the time,the fluid of Lower-Middle Triassic to Permian and that of Lower Palaeozoic did not connect with each other.However,the hydrocarbon generation peak of marine source rocks had passed or the paleo-oil and gas reser-voirs had been destroyed at that time and the marine stratum of Palaeozoic to Triassic in the research area did not put out commercial oil and gas flow.展开更多
Preservation conditions are key to enriching shallow shale gas.Therefore,the veins of two typical wells in the Shixi syncline in northern Guizhou as research objects.Based on core observation,vein thin-section observa...Preservation conditions are key to enriching shallow shale gas.Therefore,the veins of two typical wells in the Shixi syncline in northern Guizhou as research objects.Based on core observation,vein thin-section observation,cathodoluminescence,calcite in situ U-Pb dating,fluid inclusion microthermometry,Raman spectrum shift,single well basin simulation,and C-O isotope geochemical analysis,the researchers clarified the characteristics of the veins and the differences in paleofluid activity,as well as their significance for shale gas preservation.The results showed that:1)a small number of high-angle fractures had developed mainly in the Shixi syncline in northern Guizhou.The width of viens is small and filled primarily with early calcite-quartz and late calcite.The inclusions were mainly methane and brine.The proportion of brine inclusions in the SD1 well was greater than that in the SX1 well.The SD1 well has experienced more intense second-stage uplift and denudation,and the consequent gas loss is serious.2)The results of the C-O isotope analysis showed that most of the vein-forming fluids were derived from marine carbonate rocks.The O_(3)b had obvious negative deviations ofδ^(13)C andδ^(18)O,which were modified by exogenous or deep hydrothermal fluid.The C-O isotope difference between the vein bodies and the surrounding rock of the SX1 well was small,and the preservation conditions were better.3)The difference in gas content in the Shixi syncline depends on the degree of damage to gas reservoir preservation conditions caused by burial depth and other factors.Shixi syncline is a wide and gentle syncline with central retention enrichment mode.Therefore,clarifying the development of shale veins,the characteristics of paleofluid activity,and their significance for shale gas preservation can lay a foundation for studying the enrichment mechanism of shallow shale gas and thus guide further exploration and development.展开更多
Significant breakthroughs of shale gas exploration have been made in Lower Cambrian and Sinian shale in the north margin of the Yangtze Block,South China.The drill wells with industrial gas flow located in the souther...Significant breakthroughs of shale gas exploration have been made in Lower Cambrian and Sinian shale in the north margin of the Yangtze Block,South China.The drill wells with industrial gas flow located in the southern margin of the Huangling dome.Base on the geological survey,2D seismic,geochronological and drill wells data,the tectonic evolution history of Huangling dome was studied,and its control effect on the preservation condition of shale gas was discussed.The result shows that the Huangling dome might undergo four tectonic stages:(1)About 800 Ma,granite intrusion in the Huangling dome basement,primarily of granites replaced metamorphism rocks;(2)800-200 Ma,no significant tectonic movement with slowly buried history;(3)From 200 Ma,multi-phase uplift and the sedimentary rocks was eroded in the core of the Huangling dome.Shale gas in the Cambrian and Sinian strata was well preserved in the margin of the Huangling dome as the following reasons:(1)The Sinian shale was buried about 7.8 km indepth during Middle Jurassic,source rocks have a suitable thermal maturity for shale gas;(2)The rigid basement of the Huangling dome was mainly composed by homogeneity granite,without intensive deformation.As the main challenges of the widely distributed Lower Cambrian and Sinian shale are highmaturity and intensive deformation,a geological unit with a dome probably is a favorable zone for the old age shale gas.Therefore,it indicates that the adjacent zone of the Xuefengshan,Shennongjia and Hannan are the geological units with a dome and probably have potentials for the exploration of shale in the Lower Cambrian and Sinian.展开更多
The studies on the paleo-fluid in the OrdovicianeSilurian detachment zone in the MiddleeUpper Yangtze area focus on the origin of highdensity methane inclusions and the evolution process of formation pressure,but rare...The studies on the paleo-fluid in the OrdovicianeSilurian detachment zone in the MiddleeUpper Yangtze area focus on the origin of highdensity methane inclusions and the evolution process of formation pressure,but rarely deal with the significance of paleo-fluid to shale gas preservation.In this paper,the relationship between fracture formation and detachment zone was analyzed by observing the OrdovicianeSilurian outcrops in western HunaneHubei area and by investigating the geological characteristics of fracture veins in the drilling cores.Then,the significance of paleo-fluid forming environment and detachment zone to shale gas preservation was studied by using inclusion compositions of fracture veins and homogenization temperature test data.Finally,accumulationedispersion modes of shale gas in the detachment zone were established.The following results were obtained.First,the detachment zone is lithologically composed of silicite with intercalated shale at the OrdovicianeSilurian interface.In the detachment zone,rocks are broken and small crumples are developed.The conjugate-vertical joints are relatively developed in the silicite above and below the detachment zone.Second,multi-stage and multi-type inclusions,especially the aqueous inclusions,are developed in the veins of the detachment zone.Third,the infiltration depth of ancient meteoric water along the detachment zone in the study area is over 4000 m.High-density overpressure methane inclusions were captured in the detachment zone during early stage,while normal-pressure methane and nitrogen inclusions were captured during late stage.Fourth,the ionic constituents of inclusions recording the fluid activity during the late stage was characterized by high sodium-chloride coefficient,high desulfurization coefficient and low metamorphic coefficient,and it is indicated that the sealing capacity of the shale in the detachment zone gets worse.Fifth,the accumulation and dispersion of shale gas in the detachment zone within the study area is divided into three modes,i.e.,syncline,broad anticline and closed anticline.In conclusion,the detachment zone in the study area is permeable.Synclines and closed anticlines developed in detachment structures are unfavorable for the accumulation of shale gas,while broad anticlines are favorable.展开更多
As shallow resources are increasingly depleted,the mechanics'theory and testing technology of deep insitu rock has become urgent.Traditional coring technologies obtain rock samples without retaining the in-situ en...As shallow resources are increasingly depleted,the mechanics'theory and testing technology of deep insitu rock has become urgent.Traditional coring technologies obtain rock samples without retaining the in-situ environmental conditions,leading to distortion of the measured parameters.Herein,a coring and testing systems retaining in-situ geological conditions is presented:the coring system that obtains in-situ rock samples,and the transfer and testing system that stores and analyzes the rocks under a reconstructed environment.The ICP-Coring system mainly consists of the pressure controller,active insulated core reactor and insulation layer and sealing film.The ultimate bearing strength of 100 MPa for pressurepreservation,temperature control accuracy of 0.97%for temperature-retained are realized.CH_(4)and CO permeability of the optimized sealing film are as low as 3.85 and 0.33 ppm/min.The average tensile elongation of the film is 152.4%and the light transmittance is reduced to 0%.Additionally,the pressure and steady-state temperature accuracy for reconstructing the in-situ environment of transfer and storage system up to 1%and±0.2 is achieved.The error recorded of the noncontact sensor ring made of lowdensity polymer is less than 6%than that of the contact test.The system can provide technical support for the deep in-situ rock mechanics research,improving deep resource acquisition capabilities and further clarifying deep-earth processes.展开更多
The Lower Silurian Longmaxi Formation is a major horizon for shale gas development in the Changning block in Sichuan Basin.In this study,the fracture features in the Longmaxi Formation in the Changning block were inve...The Lower Silurian Longmaxi Formation is a major horizon for shale gas development in the Changning block in Sichuan Basin.In this study,the fracture features in the Longmaxi Formation in the Changning block were investigated through outcrop observation,core description,inclusion testing,and Fullbore Formation MicroImage logging.The results showed that tectogenetic shear fractures dominated the Longmaxi Formation,with maximum principal stress in the SSW,NW,and NE directions.According to fracture features and stress analysis,three phases of faults were generated by tectonic movements after the buried depth reached a maximum in the study area:phase 1 nearly EW-trending faults formed in the middle-late Yanshanian,phase 2 NE-trending faults formed from the end of the Yanshanian to the early Himalayan,and phase 3 NW-trending faults formed from the middle Himalayan to the present.According to the regression analysis of the tested shale gas production and faults,the faults with a throw of>200 m could have a great effect on gas production,and high-yield wells were generally located over 1 km away from faults.Based on the dissection of tectonic styles and typical wells drilled in the Changning block,three shale gas accumulation models were established:wide gentle syncline+internal smalxl fault,subdued anticline+large fault,and slope+internal fault.The study reveals the mechanism of fault influence on shale gas accumulation in the Longmaxi Formation in the Changning block and provides a reference for efficient shale gas production in the Sichuan Basin.展开更多
Shale fractures are an important factor controlling shale gas enrichment and high-productivity zones in the Longmaxi Formation, Jiaoshiba area in eastern Sichuan. Drilling results have, however, shown that the shale f...Shale fractures are an important factor controlling shale gas enrichment and high-productivity zones in the Longmaxi Formation, Jiaoshiba area in eastern Sichuan. Drilling results have, however, shown that the shale fracture density does not have a straightforward correlation with shale gas productivity. Based on logging data, drilling and seismic data, the relationship between shale fracture and shale gas accumulation is investigated by integrating the results of experiments and geophysical methods. The following conclusions have been drawn：（1） Tracer diffusion tests indicate that zones of fracture act as favorable channels for shale gas migration and high-angle fractures promote gas accumulation.（2） Based on the result of azimuthal anisotropy prediction, a fracture system with anisotropy strength values between 1 and 1.15 represents a moderate development of high-angle fractures, which is considered to be favorable for shale gas accumulation and high productivity, while fracture systems with anisotropy strength values larger than 1.15 indicate over-development of shale fracture, which may result in the destruction of the shale reservoir preservation conditions.展开更多
Coals developed in the Oligocene Yacheng and Lingshui formations in the Qiongdongnan Basin have high organic matter abundance, and the dark mudstones in the two formations have reached a good source rock standard but ...Coals developed in the Oligocene Yacheng and Lingshui formations in the Qiongdongnan Basin have high organic matter abundance, and the dark mudstones in the two formations have reached a good source rock standard but with strong heterogeneity. Through the analysis of trace elements, organic macerals and biomarkers, it is indicated that plankton has made little contribution to Oligocene source rocks compared with the terrestrial higher plants. The organic matter preservation depends on hydrodynamics and the redox environment, and the former is the major factor in the study area. During the sedimentary period of the Yacheng Formation, tidal flats were developed in the central uplift zone, where the hydrodynamic conditions were weak and the input of terrestrial organic matter was abundant. So the Yacheng Salient of the central uplift zone is the most favorable area for the development of source rocks, followed by the central depression zone. During the sedimentary period of the Lingshui Formation, the organic matter input was sufficient in the central depression zone due to multiple sources of sediments. The semi-enclosed environment was favorable for organic matter accumulation, so high quality source rocks could be easily formed in this area, followed by the Yacheng salient of central uplift zone. Source rocks were less developed in the northern depression zone owing to poor preservation conditions,展开更多
The shale gas resources in China have great potential and the geological resources of shale gas is over 100×10^(12)m^(3),which includes about 20×10^(12)m^(3) of recoverable resources.Organic-rich shales can ...The shale gas resources in China have great potential and the geological resources of shale gas is over 100×10^(12)m^(3),which includes about 20×10^(12)m^(3) of recoverable resources.Organic-rich shales can be divided into three types according to their sedimentary environments,namely marine,marine-continental transitional,and continental shales,which are distributed in 13 stratigraphic systems from the Mesoproterozoic to the Cenozoic.The Sichuan Basin and its surrounding areas have the highest geological resources of shale gas,and the commercial development of shale gas has been achieved in the Upper Ordovician Wufeng Formation-Lower Silurian Longmaxi Formation in these areas,with a shale gas production of up to 20×10^(9)m^(3) in 2020.China has seen rapid shale gas exploration and development over the last five years,successively achieving breakthroughs and important findings in many areas and strata.The details are as follows.(1)Large-scale development of middle-shallow shale gas(burial depth:less than 3500 m)has been realized,with the productivity having rapidly increased;(2)breakthroughs have been constantly made in the development of deep shale gas(burial depth:3500-4500 m),and the ultradeep shale gas(burial depth:greater than 4500 m)is under testing;(3)breakthroughs have been made in the development of normal-pressure shale gas,and the assessment of the shale gas in complex tectonic areas is being accelerated;(4)shale gas has been frequently discovered in new areas and new strata,exhibiting a great prospect.Based on the exploration and development practice,three aspects of consensus have been gradually reached on the research progress in the geological theories of shale gas achieved in China.(1)in terms of deep-water fine-grained sediments,organic-rich shales are the base for the formation of shale gas;(2)in terms of high-quality reservoirs,the development of micro-nano organic matter-hosted pores serves as the core of shale gas accumulation;(3)in terms of preservation conditions,weak structural transformation,a moderate degree of thermal evolution,and a high pressure coefficient are the key to shale gas enrichment.As a type of important low-carbon fossil energy,shale gas will play an increasingly important role in achieving the strategic goals of peak carbon dioxide emissions and carbon neutrality.Based on the in-depth study of shale gas geological conditions and current exploration progress,three important directions for shale gas exploration in China in the next five years are put forward.展开更多
Hydrocarbon preservation conditions have restricted exploration in the Middle and Upper Yangtze,and structural deformation and fluid activity have played an important role in the origin and preservation of oil and gas...Hydrocarbon preservation conditions have restricted exploration in the Middle and Upper Yangtze,and structural deformation and fluid activity have played an important role in the origin and preservation of oil and gas.In order to study that how the deformation and fluid activity impact the hydrocarbon preservation,we did some field work and collected some calcite vein samples for analysis of deformation periods using acoustic emission and fluid inclusions.Combined with previous studies,the strata distribution,tectonic deformation and fluid characteristics show that there are three structural belts in the study area：East Sichuan,West Hunan and Hubei and the northwestern periphery of the Xuefeng Uplift,and that their tectonic deformation style,fluid inclusion characteristics and hydrocarbon preservation are different.The breakthrough thrusts were well developed in the anticline core,and a lot of hydrocarbon inclusions were found in calcite veins around the thrusts in East Sichuan.The breakthrough thrusts were only in the syncline core in West Hunan and Hubei,and the brine inclusions did not contain hydrocarbon in calcite veins around the thrusts.Many breakthrough thrusts were found in the northwestern periphery of the Xuefeng Uplift,where there were only rare calcite veins.The deformation and hydrocarbon inclusion indicated that when there was no fault breakthrough in East Sichuan,the Paleozoic covered by the Triassic regional cap was good for hydrocarbon preservation.The strata above the Lower Paleozoic were denuded,and lots of brine inclusions and deep infiltration of surface water were found in the West Hunan and Hubei,so only the part of the syncline area with a well developed Silurian regional cap had good preservation conditions.Intense tectonic movements and denudation were widely developed in the northwestern periphery of the Xuefeng Uplift,where there were only paleo-reservoirs,non-hydrocarbon fluid activity and poor preservation conditions.展开更多
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 (42122017,41821002)the Hubei Provincial Natural Science Foundation of China (2020CFB501)+1 种基金the Shandong Provincial Key Research and Development Program (2020ZLYS08)the Independent innovation research program of China University of Petroleum (East China) (21CX06001A)。
文摘Tectonism is one of the dominant factors affecting the shale pore structure.However,the control of shale pore structure by tectonic movements is still controversial,which limits the research progress of shale gas accumulation mechanism in the complex tectonic region of southern China.In this study,34 samples were collected from two exploratory wells located in different tectonic locations.Diverse experiments,e.g.,organic geochemistry,XRD analysis,FE-SEM,low-pressure gas adsorption,and high-pressure mercury intrusion,were conducted to fully characterize the shale reservoir.The TOC,Ro,and mineral composition of the shale samples between the two wells are similar,which reflects that the shale samples of the two wells have proximate pores-generating capacity and pores-supporting capacity.However,the pore characteristics of shale samples from two wells are significantly different.Compared with the stabilized zone shale,the porosity,pore volume,and specific surface area of the deformed zone shale were reduced by 60.61%,64.85%,and 27.81%,respectively.Moreover,the macroscopic and fine pores were reduced by 54.01%and 84.95%,respectively.Fault activity and uplift denudation are not conducive to pore preservation,and the rigid basement of Huangling uplift can promote pore preservation.These three factors are important reasons for controlling the difference in pore structure between two wells shales.We established a conceptual model of shale pores evolution under different tectonic preservation conditions.This study is significant to clarify the scale of shale gas formation and enrichment in complex tectonic regions,and helps in the selection of shale sweet spots.
文摘[Objective] This study aimed to investigate the effect of different short-term preservation conditions on mycelial growth of Morchella conica, and search for opti- mum preservation conditions. [Method] M. conica strains in tubes were preserved at two temperature treatments 10 ℃/5 ℃ （day/night） and 15℃/10 ℃（day/night） in scat- tered light or dark for 30 or 60 d. The strain preserved at 4 ℃ dark for 90 d was the control （CK）. So, a total of nine treatments were prepared in this study. [Result] Mycelial growth of M. conica preserved at 10 ℃/5 ℃ was better than that at 15 ℃/10 ℃ and control. The colony color and aerial hyphae of strains preserved in scattered light was also better than that in dark. Additionally, the preservation time showed no distinct effect on mycelial growth at 10 ℃/5 ℃. So the time could be lengthened. But the maximal preservation time was 60 d at 15 ℃/10 ℃. Therefore, preserved under the appropriate conditions of 10 ℃/5 ℃, scattered light for 30 d, the strain had the neat colony edge, moderate aerial mycelia, dense mycelia, lower sectoral variation, uniform mycelial growth rate and high dry weight of mycelia.
基金supported by Science and Technology Support Program of Sichuan Province(No.15ZC1390)National Natural Science Foundation of China(No.41102064)
文摘The Upper Ordovician-Lower Silurian Longmaxi Shale in the Upper Yangtze block represents one of the most important shale gas plays in China. The shale composition, porosity, organic thermal maturity, and methane sorption were investigated at the Qilongcun section in the Dingshan area, southeastern Sichuan Basin. The results show that the Upper Ordovician-Lower Silurian Longmaxi Shale contains： （1） sapropelic I organic matter; （2） a 40-m thick bedded sequence where total organic carbon （TOC） content is 〉 2%; （3） a 30-m thick layer at the base of the Longmaxi Shale with a brittle mineral content higher than 50%; and （4） a mean methane adsorption capacity of 1.80 cm3/g （7 MPa pressure）. A positive correlation between TOC and sorbed gas indicates that organic matter content exerts an important control on methane storage capacity. Based on the analysis of the shale reservoir characteristics, the lower member of the Longmaxi Shale can thus be considered a favorable stratum for shale gas exploration and exploitation. It has similar reservoir characteristics with the Longmaxi Shale in the Jiaoshiba area tested with a high-yield industrial gas flow. However, based on tectonic analysis, differences in the level of industrial gas flow between the low-yield study area and the high-yield Jiaoshiba area may result from different tectonic preservation conditions. Evidence from these studies indicates the shale gas potential of the Longmaxi Shale is constrained by the reservoir and preservation conditions.
基金supported by the National Natural Science Foundation of China(Grant No.41872124,42202175&No.42130803)。
文摘Although carbon isotope reversal and its reasons in shale gas reservoirs have been widely recognized,the application of the reversal is yet to be investigated.A study on high-maturity shale from Wufeng and Longmaxi Formations in the Sichuan Basin not only reveals the relationship between the degree of isotopes inversion and the production capacity(e.g.,estimated ultimate recovery(EUR))of the gas well but also indicates the preservation conditions of shale gas reservoirs.(1)Although there are differences in gas isotopes in different shale gas reservoirs,the isotope fractionation of shale gas is small during the production stage of gas wells,even when the wellbore pressure drops to zero.The main cause of the difference in carbon isotopes and their inversion degree can be the uplift time during the Yanshan period and the formation pressure relief degree of shale gas reservoirs in distinct structural positions.Thus,carbon isotope inversion is a good indicator of shale gas preservation condition and EUR of shale gas wells.(2)The degree of carbon isotope inversion correlates strongly with shale gas content and EUR.The calculation formula of shale-gas recoverable reserves was established using△δ^(13)C(δC_(1)-δC_(2))and EUR.(3)The gas loss rate and total loss amount can be estimated using the dynamic reserves and isotopic difference values of gas wells in various shale gas fields,which also reflects the current methane loss,thereby demonstrating great potential for evaluating global methane loss in shales.
基金supported by the National Natural Science Foundation(41072082)National Basic Research Program of China(No.2005CB422106)national key subject constructional item of mineralogy,petrology and mineral deposit(SZD0407)and backup candidate fund of academic and technical senior scholar in Sichuan Province
文摘^87Sr/^86Sr, δ^18O and δ^13C ratios of calcite, dolomite, gypsum filling vugs and fissures in marine carbonates and their host rocks from the Sinian to the middle Triassic, are employed to trace the possible source and migration path of key fluids related to development of hydrocarbon, hydrocarbon preservation condition are then discussed further. Comprehensive research, based on the paleo-fluid, the property of formation water and the deformation intensity etc., indicates that the preservation conditions in the Shizhu synclinorium zone and Fangdoushan anticlinorium zone are the most predominant in the central Yangtze. Three sets of fluid systems in the Shizhu synclinorium zone are identified. Little fluid exchange occurs between the upper-middle fluid system and the lower fluid system, so two independent preservation units have developed. Both the Permian and the Triassic in the upper preservation units and the Dengying Formation of the Sinian and the lower Cambrian in the lower preservation units have good preservation conditions. The preservation condition in the lower association （Z-S） located in the Huaguoping synclinorium zone in the western Hubei and Hunan is better than that in other tectonic units, where the fluids in the lower association migrated vertically across strata when the fluid isolating intervals were destroyed, the regional seals are absent and the conditions for the preservation of hydrocarbon accumulations are totally destroyed. The preservation condition is increasingly more favorable from the western Jiangxi and Hunan to the western Hubei ＆ eastern Chongqing on the whole.
基金Sinopec special and significant project“Formative conditions of shale gas in lower strata association in the periphery of Sichuan Basin and play evaluation”(No.P13129).
文摘Complex tectonic movements and high thermal maturity of marine shale dominate South China,where preservation conditions are critical for shale gas enrichment and productivity.Based on the exploration practices of the Silurian shale gas at the southeastern margin of the Sichuan Basin in recent years,conventional gas and shale gas were compared in terms of their preservation conditions.The results revealed that superior roof and floor conditions are indispensable to shale gas preservation.Moreover,the self-sealing ability and the huge gap of up to 2–8 times between vertical and lateral permeability of shale gas reservoirs determine the lateral diffusion as the basic pattern of shale gas migration.The unconformity at the bottom of Lower Cambrian leads to worse preservation conditions in the system,and cutting by faults may accelerate the diffusion of shale gas.Major controlling factors for shale gas preservation and their criteria of discrimination were also investigated.It is suggested that:(1)the strength of tectonic modification is the major factor controlling shale gas preservation.Broad and gentle structures with continuous seals and an anticlinal setting are more favorable for the enrichment of shale gas,and a closed evolutionary environment with late uplifting is more favorable for the preservation of shale gas;(2)shale gas can be preserved well in downdip areas without faults or effectively closed or shielded by faults and areas far away from outcrops or zones with stratigraphic hiatus;(3)pressure coefficient is a comprehensive indicator for discriminating preservation conditions.In the study area,the pressure coefficient is in positive correlation with shale gas production and the high or super-high pressure of reservoir is a signal of good preservation condition for shale gas;and(4)in the areas within the southeastern Sichuan Basin,other than those close to erosion zones or hiatus,the Wufeng Fm.of Upper Ordovician and the Longmaxi Fm.of Lower Silurian present high pressure coefficient(up to 2.25)generally,demonstrating good preservation conditions for shale gas,while the pressure coefficient reduces progressively toward or outside the margin of the basin,corresponding to downgrading preservation conditions.
基金Project supported by the National Science and Technology Major Special Project“Large Oil and Gas Fields and CBM Development”(No.2016ZX05002)China Petroleum&Chemical Corporation Science and Technology Department Pilot Project“Evolution and Breakthrough Direction of Hydrocarbon Accumulation in the Lower Assemblage of Western Middle Yangtze Block”(No.p16042).
文摘Lower Paleozoic dark shale is developed in the western Middle Yangtze Block,which lays a material foundation for the enrichment and accumulation of marine shale gas.In order to ascertain the control action of geological structures on the differential preservation of shale gas and reveal the key factors in shale gas preservation,this paperfirstly analyzed the structure characteristics of this area,carried out structure pattern recognition and structural belt division,and studied structural deformation mode and intensity.Based on this,the relationships between different structure styles and shale gas preservation conditions were analyzed.Finally,combined with the structural deformation and the lithofacies paleogeographic characteristics of marine shale,the favorable exploration zones of shale gas were proposed.And the following research results were obtained.First,the western Middle Yangtze Block can be divided into four structural deformation belts,and three types of piggyback structural patterns have been identified,including restricted type,weakly reformed type and strongly reformed type.Second,the restricted type is located in the northwestern part of Hunan and Hubei Provinces.In this pattern,piggyback structure is incomplete and thrust belt and Compressive fold belt are developed.Third,the weakly and strongly reformed types are located in the western parts of Hunan and Hubei,and Wulingshan area,respectively.They both have complete piggyback structures,but the former has lower deformation intensity and has never undergone the late superimposed reformation.Fourth,there are three structural transfer belts in the western Middle Yangtze Block,i.e.the structural transfer belt between the East Sichuan faultefold belt and West HunaneHubei faultefold belt,the structural transfer belt between West HunaneHubei faultefold belt and Wulingshan faultefold belt,and the structural transfer belt between the outcrop and the hinterland of Middle Yangtze Block.Thefirst one is structurally transformed at the Qiyueshan fault.The East Sichuan faultefold belt on the west is an ejective fold with low fault density and formation denudation intensity,where shale gas is enriched in anticlines and slopes;while the West HunaneHubei faultefold belt on the east is a trough-like fold with strong faulting and high formation denudation intensity,where shale gas is enriched in residual synclines.In conclusion,shale gas preservation conditions of Upper Ordovician Wufeng FormationeLower Silurian Longmaxi Formation in this area are the best in Zigui syncline,thrustedetachment zone and western margin of Qiyueshan fault.The favorable exploration areas of shale gas of Lower Cambrian Niutitang Formation are distributed in the westernflank of Yichang Slope,Kaixian thrust zone,compressive fold zone and thrustedetachment zone.
文摘In the South Yellow Sea Basin,Mesozoic-Paleozoic marine strata are generally well developed with large thickness,and they are characterized by multi-source and multi-stage hydrocarbon accumulation,providing a material basis for the formation of large-scale oil and gas fields.However,no substantial breakthrough has been made in this area.Based on previous research results,the complex tectonic pattern of this superimposed basin was formed by multi-stage tectonic movements and the favorable static conditions for hydrocarbon preservation were reworked or destroyed by later superimposition.Therefore,hydrocarbon preservation conditions are the key factors for restricting the breakthrough of marine oil and gas exploration in this area.In this paper,hydrocarbon preservation conditions of marine strata in the South Yellow Sea Basin were comprehensively analyzed from many aspects,such as tectonic movement,source conditions,caprock characteristics,magmatic activities,and hydrogeological and hydrogeochemical characteristics.It is indicated that the complex tectonic pattern of the South Yellow Sea Basin is resulted from tectonic events in multiple stages,and the development and evolution of regional source rocks are mainly controlled by two stages(i.e.,the stable evolution stage of Mesozoic-Paleozoic marine basin and the Mesozoic-Cenozoic tectonic pattern transformation and basin formation stage),so the characteristics of differential oil and gas preservation are presented.Besides,better marine hydrocarbon preservation preconditions in this area are weaker tectonic reworking,development of high-quality thick source rocks,good vertical sealing capacity of caprocks,weaker magmatic activity and confined hydrogeological conditions.It is concluded that the Laoshan Uplift in the central part of the South Yellow Sea Basin is structurally stable with weaker faulting and magmatic activities,so it is better in oil and gas preservation conditions.Besides,several large-scale structural traps with good petroleum geological conditions and complete source-reservoir-caprock assemblages are developed in this area.Therefore,this area is the most promising region for Paleozoic marine oil and gas exploration in this basin.
基金supported by the National Major Science and Technology Project"Zhaotong Shale Gas Exploration&Development Demonstration Project"(No.2017ZX05063)CNPC Major Field Test Project"Research and Test of Key Effective Expoitation Techniques of Deep Shale Gas"(No.:2019F-13)。
文摘The Zhaotong National Shale Gas Demonstration Area along the southern margin of the Sichuan Basin is located in the complex marine tectonic area of South China,where shale deformation and reformation are intense and the factors controlling sweet spots are complex,so the preservation conditions have an important impact on the enrichment of shale gas.In order to support the selection and evaluation of shale gas sweet spots in this area and improve the success rate of drilling,this paper carried out a geological survey onfield outcrops.Then,based on drilling,mud logging and physical property test data,the structural deformation pattern and the regional deformation characteristics of this demonstration area were analyzed,and the development characteristics of formation joints and fractures,the sealing capacity of shale sur-rounding rock and the distribution characteristics of gas reservoirs were studied.Finally,the preservation conditions of shale gas in the Wufeng Formation of Upper Ordovician and the Longmaxi Formation of Lower Silurian were discussed.And the following research results were ob-tained.First,in the Zhaotong National Shale Gas Demonstration Area,three structural deformation patterns are developed from south to north,including trough type,equal amplitude type and baffle type,which are distributed in three major deformation zones,respectively,i.e.,the shear deformation zone of Central Guizhou Uplift,the compressionetorsion deformation zone of northern YunnaneGuizhou Depression and the compression deformation zone of Southern Sichuan Depression.Second,three types of joints and fractures whose relationships with the di-rection of strata are high angle,middleelow angle and bedding intersection are developed in the WufengeLongmaxi formations and its overlying strata,and their occurrence characteristics are basically consistent with those of the three major deformation zones.Third,the shale of WufengeLongmaxi formations is thick in the north and thin in the south and possesses the preservation conditions of sourceereservoir inte-gration and self-sealing hydrocarbon accumulation.And combined with the sealing ability of the overburden strata and the roof andfloor,its preservation conditions are overall better.Fourth,from the perspective of shale gas component,this area can be divided into three belts,i.e.,methane,methaneþnitrogen mixture and nitrogen from north to south.And the preservation conditions of shale gas are generally better in the north and worse in the south.In conclusion,the shale in the centralenorthern part of Zhaotong National Shale Gas Demonstration Area(compression deformation area and its southern margin)is the most favorable area because of its large shale thickness,weak reformation and deformation,bedding development of joints and fractures,good sealing performance and excellent preservation conditions.The compressionetorsion deformation zone of northern YunnaneGuizhou Depression in the central part is moderate in preservation conditions,and it is the relatively favorable area.The shear deformation zone of Central Guizhou Uplift in the southern part has poor preservation conditions,and it is a prospective area.
基金supported by the Major Project of Chinese National Programs for Fundamental Research and Development 973 Program (No. 2012CB214805)
文摘Many scholars carried out large quantity of researches on oil and gas preservative condi-tions of marine carbonate rocks from the aspects of cap rocks,faults,formation water,hydrodynamic,and tectonism.This article gives dynamic evaluation on oil and gas preservative conditions of marine stratum in Jianghan（江汉） plain of multiphase tectonic disturbance from the view of paleofluid geo-chemistry.The conclusion shows that there mainly existed fluid filling of two periods in the reservoir of Lower-Middle Triassic to Permian.The fluid filled in the earlier period came from Lower Palaeozoic.The interchange of fluid in Lower-Middle Triassic to Permian suggested the oil and gas in Lower Pa-laeozoic had been broken up.The fluid filled in the later period（Lower-Middle Triassic to Permian） came from the same or adjacent strata and lacked anatectic fluidogenous features coming from Palaeozoic.With good preservative conditions of bulk fluid at the time,the fluid of Lower-Middle Triassic to Permian and that of Lower Palaeozoic did not connect with each other.However,the hydrocarbon generation peak of marine source rocks had passed or the paleo-oil and gas reser-voirs had been destroyed at that time and the marine stratum of Palaeozoic to Triassic in the research area did not put out commercial oil and gas flow.
文摘Preservation conditions are key to enriching shallow shale gas.Therefore,the veins of two typical wells in the Shixi syncline in northern Guizhou as research objects.Based on core observation,vein thin-section observation,cathodoluminescence,calcite in situ U-Pb dating,fluid inclusion microthermometry,Raman spectrum shift,single well basin simulation,and C-O isotope geochemical analysis,the researchers clarified the characteristics of the veins and the differences in paleofluid activity,as well as their significance for shale gas preservation.The results showed that:1)a small number of high-angle fractures had developed mainly in the Shixi syncline in northern Guizhou.The width of viens is small and filled primarily with early calcite-quartz and late calcite.The inclusions were mainly methane and brine.The proportion of brine inclusions in the SD1 well was greater than that in the SX1 well.The SD1 well has experienced more intense second-stage uplift and denudation,and the consequent gas loss is serious.2)The results of the C-O isotope analysis showed that most of the vein-forming fluids were derived from marine carbonate rocks.The O_(3)b had obvious negative deviations ofδ^(13)C andδ^(18)O,which were modified by exogenous or deep hydrothermal fluid.The C-O isotope difference between the vein bodies and the surrounding rock of the SX1 well was small,and the preservation conditions were better.3)The difference in gas content in the Shixi syncline depends on the degree of damage to gas reservoir preservation conditions caused by burial depth and other factors.Shixi syncline is a wide and gentle syncline with central retention enrichment mode.Therefore,clarifying the development of shale veins,the characteristics of paleofluid activity,and their significance for shale gas preservation can lay a foundation for studying the enrichment mechanism of shallow shale gas and thus guide further exploration and development.
基金This research is financially supposed by China Gelogical Survey project(1211302108020,DD20160177,DD20190081)
文摘Significant breakthroughs of shale gas exploration have been made in Lower Cambrian and Sinian shale in the north margin of the Yangtze Block,South China.The drill wells with industrial gas flow located in the southern margin of the Huangling dome.Base on the geological survey,2D seismic,geochronological and drill wells data,the tectonic evolution history of Huangling dome was studied,and its control effect on the preservation condition of shale gas was discussed.The result shows that the Huangling dome might undergo four tectonic stages:(1)About 800 Ma,granite intrusion in the Huangling dome basement,primarily of granites replaced metamorphism rocks;(2)800-200 Ma,no significant tectonic movement with slowly buried history;(3)From 200 Ma,multi-phase uplift and the sedimentary rocks was eroded in the core of the Huangling dome.Shale gas in the Cambrian and Sinian strata was well preserved in the margin of the Huangling dome as the following reasons:(1)The Sinian shale was buried about 7.8 km indepth during Middle Jurassic,source rocks have a suitable thermal maturity for shale gas;(2)The rigid basement of the Huangling dome was mainly composed by homogeneity granite,without intensive deformation.As the main challenges of the widely distributed Lower Cambrian and Sinian shale are highmaturity and intensive deformation,a geological unit with a dome probably is a favorable zone for the old age shale gas.Therefore,it indicates that the adjacent zone of the Xuefengshan,Shennongjia and Hannan are the geological units with a dome and probably have potentials for the exploration of shale in the Lower Cambrian and Sinian.
基金supported by the National Major Science and Technology Project“Study on high-mature shale gas occurrence mechanism and enriching law in Middle Yangtze region”(No.:2016ZX05034-001-002)the Foundation Project of China Geological Survey“Investigation and evaluation of shale gas resources in Wuling and Western Hunan-Hubei area”(No.:12120114049801).
文摘The studies on the paleo-fluid in the OrdovicianeSilurian detachment zone in the MiddleeUpper Yangtze area focus on the origin of highdensity methane inclusions and the evolution process of formation pressure,but rarely deal with the significance of paleo-fluid to shale gas preservation.In this paper,the relationship between fracture formation and detachment zone was analyzed by observing the OrdovicianeSilurian outcrops in western HunaneHubei area and by investigating the geological characteristics of fracture veins in the drilling cores.Then,the significance of paleo-fluid forming environment and detachment zone to shale gas preservation was studied by using inclusion compositions of fracture veins and homogenization temperature test data.Finally,accumulationedispersion modes of shale gas in the detachment zone were established.The following results were obtained.First,the detachment zone is lithologically composed of silicite with intercalated shale at the OrdovicianeSilurian interface.In the detachment zone,rocks are broken and small crumples are developed.The conjugate-vertical joints are relatively developed in the silicite above and below the detachment zone.Second,multi-stage and multi-type inclusions,especially the aqueous inclusions,are developed in the veins of the detachment zone.Third,the infiltration depth of ancient meteoric water along the detachment zone in the study area is over 4000 m.High-density overpressure methane inclusions were captured in the detachment zone during early stage,while normal-pressure methane and nitrogen inclusions were captured during late stage.Fourth,the ionic constituents of inclusions recording the fluid activity during the late stage was characterized by high sodium-chloride coefficient,high desulfurization coefficient and low metamorphic coefficient,and it is indicated that the sealing capacity of the shale in the detachment zone gets worse.Fifth,the accumulation and dispersion of shale gas in the detachment zone within the study area is divided into three modes,i.e.,syncline,broad anticline and closed anticline.In conclusion,the detachment zone in the study area is permeable.Synclines and closed anticlines developed in detachment structures are unfavorable for the accumulation of shale gas,while broad anticlines are favorable.
基金supported by the Program for Guangdong Introducing Innovative and Enterpreneurial Teams(No.2019ZT08G315)National Natural Science Foundation of China(No.51827901,U2013603,and 52004166)。
文摘As shallow resources are increasingly depleted,the mechanics'theory and testing technology of deep insitu rock has become urgent.Traditional coring technologies obtain rock samples without retaining the in-situ environmental conditions,leading to distortion of the measured parameters.Herein,a coring and testing systems retaining in-situ geological conditions is presented:the coring system that obtains in-situ rock samples,and the transfer and testing system that stores and analyzes the rocks under a reconstructed environment.The ICP-Coring system mainly consists of the pressure controller,active insulated core reactor and insulation layer and sealing film.The ultimate bearing strength of 100 MPa for pressurepreservation,temperature control accuracy of 0.97%for temperature-retained are realized.CH_(4)and CO permeability of the optimized sealing film are as low as 3.85 and 0.33 ppm/min.The average tensile elongation of the film is 152.4%and the light transmittance is reduced to 0%.Additionally,the pressure and steady-state temperature accuracy for reconstructing the in-situ environment of transfer and storage system up to 1%and±0.2 is achieved.The error recorded of the noncontact sensor ring made of lowdensity polymer is less than 6%than that of the contact test.The system can provide technical support for the deep in-situ rock mechanics research,improving deep resource acquisition capabilities and further clarifying deep-earth processes.
基金supported by The Science and Technology Project of CNPC,China(Grant No.2023ZZ21)Research Project of PetroChina Southwest Oil&Gas Field Company,China(Grant No.20220304-19)Research Project of PetroChina Southwest Oil&Gas Field Company,China(Grant No.20220304-08).
文摘The Lower Silurian Longmaxi Formation is a major horizon for shale gas development in the Changning block in Sichuan Basin.In this study,the fracture features in the Longmaxi Formation in the Changning block were investigated through outcrop observation,core description,inclusion testing,and Fullbore Formation MicroImage logging.The results showed that tectogenetic shear fractures dominated the Longmaxi Formation,with maximum principal stress in the SSW,NW,and NE directions.According to fracture features and stress analysis,three phases of faults were generated by tectonic movements after the buried depth reached a maximum in the study area:phase 1 nearly EW-trending faults formed in the middle-late Yanshanian,phase 2 NE-trending faults formed from the end of the Yanshanian to the early Himalayan,and phase 3 NW-trending faults formed from the middle Himalayan to the present.According to the regression analysis of the tested shale gas production and faults,the faults with a throw of>200 m could have a great effect on gas production,and high-yield wells were generally located over 1 km away from faults.Based on the dissection of tectonic styles and typical wells drilled in the Changning block,three shale gas accumulation models were established:wide gentle syncline+internal smalxl fault,subdued anticline+large fault,and slope+internal fault.The study reveals the mechanism of fault influence on shale gas accumulation in the Longmaxi Formation in the Changning block and provides a reference for efficient shale gas production in the Sichuan Basin.
基金supported by the National Key Basic Research Program of China (973 Program, No. 2014CB239104)National Science and Technology Major Project (No. 2017ZX05049002-005)+1 种基金Sinopec Basic Prospect Project (No. G5800-16-ZS-KJB043)NSFC-Sinopec Joint Key Project (No. U1663207)
文摘Shale fractures are an important factor controlling shale gas enrichment and high-productivity zones in the Longmaxi Formation, Jiaoshiba area in eastern Sichuan. Drilling results have, however, shown that the shale fracture density does not have a straightforward correlation with shale gas productivity. Based on logging data, drilling and seismic data, the relationship between shale fracture and shale gas accumulation is investigated by integrating the results of experiments and geophysical methods. The following conclusions have been drawn：（1） Tracer diffusion tests indicate that zones of fracture act as favorable channels for shale gas migration and high-angle fractures promote gas accumulation.（2） Based on the result of azimuthal anisotropy prediction, a fracture system with anisotropy strength values between 1 and 1.15 represents a moderate development of high-angle fractures, which is considered to be favorable for shale gas accumulation and high productivity, while fracture systems with anisotropy strength values larger than 1.15 indicate over-development of shale fracture, which may result in the destruction of the shale reservoir preservation conditions.
基金financially supported by the Major State Basic Research Development Program(973 Program)(Grant No.2009CB219402)
文摘Coals developed in the Oligocene Yacheng and Lingshui formations in the Qiongdongnan Basin have high organic matter abundance, and the dark mudstones in the two formations have reached a good source rock standard but with strong heterogeneity. Through the analysis of trace elements, organic macerals and biomarkers, it is indicated that plankton has made little contribution to Oligocene source rocks compared with the terrestrial higher plants. The organic matter preservation depends on hydrodynamics and the redox environment, and the former is the major factor in the study area. During the sedimentary period of the Yacheng Formation, tidal flats were developed in the central uplift zone, where the hydrodynamic conditions were weak and the input of terrestrial organic matter was abundant. So the Yacheng Salient of the central uplift zone is the most favorable area for the development of source rocks, followed by the central depression zone. During the sedimentary period of the Lingshui Formation, the organic matter input was sufficient in the central depression zone due to multiple sources of sediments. The semi-enclosed environment was favorable for organic matter accumulation, so high quality source rocks could be easily formed in this area, followed by the Yacheng salient of central uplift zone. Source rocks were less developed in the northern depression zone owing to poor preservation conditions,
基金supported by a project of shale gas in Southern China(DD20190561)initiated by the China Geological Surveythe project for High-level Innovative Talents in Science and Technology,Ministry of Natural Resources(12110600000018003918)。
文摘The shale gas resources in China have great potential and the geological resources of shale gas is over 100×10^(12)m^(3),which includes about 20×10^(12)m^(3) of recoverable resources.Organic-rich shales can be divided into three types according to their sedimentary environments,namely marine,marine-continental transitional,and continental shales,which are distributed in 13 stratigraphic systems from the Mesoproterozoic to the Cenozoic.The Sichuan Basin and its surrounding areas have the highest geological resources of shale gas,and the commercial development of shale gas has been achieved in the Upper Ordovician Wufeng Formation-Lower Silurian Longmaxi Formation in these areas,with a shale gas production of up to 20×10^(9)m^(3) in 2020.China has seen rapid shale gas exploration and development over the last five years,successively achieving breakthroughs and important findings in many areas and strata.The details are as follows.(1)Large-scale development of middle-shallow shale gas(burial depth:less than 3500 m)has been realized,with the productivity having rapidly increased;(2)breakthroughs have been constantly made in the development of deep shale gas(burial depth:3500-4500 m),and the ultradeep shale gas(burial depth:greater than 4500 m)is under testing;(3)breakthroughs have been made in the development of normal-pressure shale gas,and the assessment of the shale gas in complex tectonic areas is being accelerated;(4)shale gas has been frequently discovered in new areas and new strata,exhibiting a great prospect.Based on the exploration and development practice,three aspects of consensus have been gradually reached on the research progress in the geological theories of shale gas achieved in China.(1)in terms of deep-water fine-grained sediments,organic-rich shales are the base for the formation of shale gas;(2)in terms of high-quality reservoirs,the development of micro-nano organic matter-hosted pores serves as the core of shale gas accumulation;(3)in terms of preservation conditions,weak structural transformation,a moderate degree of thermal evolution,and a high pressure coefficient are the key to shale gas enrichment.As a type of important low-carbon fossil energy,shale gas will play an increasingly important role in achieving the strategic goals of peak carbon dioxide emissions and carbon neutrality.Based on the in-depth study of shale gas geological conditions and current exploration progress,three important directions for shale gas exploration in China in the next five years are put forward.
基金sponsored by the National Basic Research Program of China (Grant No. 2012CB214804,2005CB422107 and G1999043305)the National Natural Science Foundation of China (Grant Nos. 41172125,40972090, and 40672143)+1 种基金the National Key Scientific Project(Grant No. 2011ZX05002-006-007HZ, 2008ZX05005-002-008HZ-1)the Doctoral Fund of Ministry of Education of China (Grant No. 200804250001)
文摘Hydrocarbon preservation conditions have restricted exploration in the Middle and Upper Yangtze,and structural deformation and fluid activity have played an important role in the origin and preservation of oil and gas.In order to study that how the deformation and fluid activity impact the hydrocarbon preservation,we did some field work and collected some calcite vein samples for analysis of deformation periods using acoustic emission and fluid inclusions.Combined with previous studies,the strata distribution,tectonic deformation and fluid characteristics show that there are three structural belts in the study area：East Sichuan,West Hunan and Hubei and the northwestern periphery of the Xuefeng Uplift,and that their tectonic deformation style,fluid inclusion characteristics and hydrocarbon preservation are different.The breakthrough thrusts were well developed in the anticline core,and a lot of hydrocarbon inclusions were found in calcite veins around the thrusts in East Sichuan.The breakthrough thrusts were only in the syncline core in West Hunan and Hubei,and the brine inclusions did not contain hydrocarbon in calcite veins around the thrusts.Many breakthrough thrusts were found in the northwestern periphery of the Xuefeng Uplift,where there were only rare calcite veins.The deformation and hydrocarbon inclusion indicated that when there was no fault breakthrough in East Sichuan,the Paleozoic covered by the Triassic regional cap was good for hydrocarbon preservation.The strata above the Lower Paleozoic were denuded,and lots of brine inclusions and deep infiltration of surface water were found in the West Hunan and Hubei,so only the part of the syncline area with a well developed Silurian regional cap had good preservation conditions.Intense tectonic movements and denudation were widely developed in the northwestern periphery of the Xuefeng Uplift,where there were only paleo-reservoirs,non-hydrocarbon fluid activity and poor preservation conditions.
