Through core observation,thin section identification,X-ray diffraction analysis,scanning electron microscopy,and low-temperature nitrogen adsorption and isothermal adsorption experiments,the lithology and pore charact...Through core observation,thin section identification,X-ray diffraction analysis,scanning electron microscopy,and low-temperature nitrogen adsorption and isothermal adsorption experiments,the lithology and pore characteristics of the Upper Carboniferous bauxite series in eastern Ordos Basin were analyzed to reveal the formation and evolution process of the bauxite reservoirs.A petrological nomenclature and classification scheme for bauxitic rocks based on three units(aluminum hydroxides,iron minerals and clay minerals)is proposed.It is found that bauxitic mudstone is in the form of dense massive and clastic structures,while the(clayey)bauxite is of dense massive,pisolite,oolite,porous soil and clastic structures.Both bauxitic mudstone and bauxite reservoirs develop dissolution pores,intercrystalline pores,and microfractures as the dominant gas storage space,with the porosity less than 10% and mesopores in dominance.The bauxite series in the North China Craton can be divided into five sections,i.e.,ferrilite(Shanxi-style iron ore,section A),bauxitic mudstone(section B),bauxite(section C),bauxite mudstone(debris-containing,section D)and dark mudstone-coal section(section E).The burrow/funnel filling,lenticular,layered/massive bauxite deposits occur separately in the karst platforms,gentle slopes and low-lying areas.The karst platforms and gentle slopes are conducive to surface water leaching,with strong karstification,well-developed pores,large reservoir thickness and good physical properties,but poor strata continuity.The low-lying areas have poor physical properties but relatively continuous and stable reservoirs.The gas enrichment in bauxites is jointly controlled by source rock,reservoir rock and fractures.This recognition provides geological basis for the exploration and development of natural gas in the Upper Carboniferous in the study area and similar bauxite systems.展开更多
The well-developed coal electricity generation and coal chemical industries have led to huge carbon dioxide(CO_(2))emissions in the northeastern Ordos Basin.The geological storage of CO_(2) in saline aquifers is an ef...The well-developed coal electricity generation and coal chemical industries have led to huge carbon dioxide(CO_(2))emissions in the northeastern Ordos Basin.The geological storage of CO_(2) in saline aquifers is an effective backup way to achieve carbon neutrality.In this case,the potential of saline aquifers for CO_(2) storage serves as a critical basis for subsequent geological storage project.This study calculated the technical control capacities of CO_(2) of the saline aquifers in the fifth member of the Shiqianfeng Formation(the Qian-5 member)based on the statistical analysis of the logging and the drilling and core data from more than 200 wells in the northeastern Ordos Basin,as well as the sedimentary facies,formation lithology,and saline aquifer development patterns of the Qian-5 member.The results show that(1)the reservoirs of saline aquifers in the Qian-5 member,which comprise distributary channel sand bodies of deltaic plains,feature low porosities and permeabilities;(2)The study area hosts three NNE-directed saline aquifer zones,where saline aquifers generally have a single-layer thickness of 3‒8 m and a cumulative thickness of 8‒24 m;(3)The saline aquifers of the Qian-5 member have a total technical control capacity of CO_(2) of 119.25×10^(6) t.With the largest scale and the highest technical control capacity(accounting for 61%of the total technical control capacity),the Jinjie-Yulin saline aquifer zone is an important prospect area for the geological storage of CO_(2) in the saline aquifers of the Qian-5 member in the study area.展开更多
In this paper, the Chang 2 reservoir in Zichang Area of Ordos Basin, the second largest sedimentary basin in China, is classified and evaluated by using logging and core data, thin section identification and electron ...In this paper, the Chang 2 reservoir in Zichang Area of Ordos Basin, the second largest sedimentary basin in China, is classified and evaluated by using logging and core data, thin section identification and electron microscopy. The main sedimentary microfacies of Chang 2<sub>1</sub><sup>3</sup> is braided river delta sedimentary system in geological history, and there are three main sedimentary microfacies types: swamp microfacies, distributary channel microfacies and natural embankment microfacies on land. The heterogeneity in the study area is as follows: Chang 2<sub>1</sub><sup>2</sup> formation has the strongest heterogeneity, followed by Chang 2<sub>1</sub><sup>1</sup> formation with strong heterogeneity, and finally Chang 2<sub>1</sub><sup>3</sup> formation with medium heterogeneity. The reservoirs of Chang 2 member in the study area are dominated by III<sub>a</sub>, II<sub>b</sub> and III<sub>b</sub>, and the reservoirs are mainly composed of ultra-low porosity and low permeability reservoirs and low porosity and low permeability reservoirs.展开更多
Using high-precision zircon U-Pb ID-TIMS geochronology,tuffs from the Chang 9 shale and the Chang 7 shale were dated.The tuff in the Chang 9 shale is 241.47±0.17 Ma,which falls between the top tuff age of 241.06&...Using high-precision zircon U-Pb ID-TIMS geochronology,tuffs from the Chang 9 shale and the Chang 7 shale were dated.The tuff in the Chang 9 shale is 241.47±0.17 Ma,which falls between the top tuff age of 241.06±0.12 Ma and the bottom tuff age of 241.558±0.093 Ma in the Chang 7 shale.These reveal that the Chang 9 and Chang 7 shales are contemporaneous,belonging to the Ladinian stage of the Middle Triassic.This insight expands the region of the main source rock of Chang 7 to the northeast and will inform the search for the deep Chang 9 shale petroleum system,increasing the scope for exploring the Chang 7 shale system in northern Shaanxi.The research results clarify the relationship between the two sets of shale in the Yanchang Formation and redefine the distribution range of the Chang 7 shale in the Ordos Basin.At the same time,it shows that there is a cross-layer problem in the stratigraphic division of the Yanchang Formation in different regions,the high-precision U-Pb dating technology providing a reference for the fine stratigraphic correlation of other continental basins in the world.展开更多
To quantify the pore characteristics of various macerals in Chang 7 lacustrine shales,macerals were effectively identified according to their optical and morphological characteristics,and the nanoscale pore structure ...To quantify the pore characteristics of various macerals in Chang 7 lacustrine shales,macerals were effectively identified according to their optical and morphological characteristics,and the nanoscale pore structure of macerals was observed by scanning electron microscope.Meanwhile,the reflectances of different positions in the same pieces of vitrinite or solid bitumen with heterogeneous pores development were measured.The results showed that the average contents of sapropelinite,liptinite,vitrinite,inertinite and solid bitumen are 42.7%,8.7%,13.6%,13.8% and 21.2%,respectively,which suggests that the source of the organic matter of the Chang 7 shales is a mixed source input.The organic pores of Chang 7 shales are enriched,and the pore shapes are mostly round or elliptical.The pore size of organic pores has a wide distribution,mainly concentrate in the range of 100-400 nm,and the average plane porosity of organic pores is 10.13%.The size order of the organic pores in various macerals is:solid bitumen<bituminite<alginite<vitrinite<fusinite<liptinite.The abundance order of organic matter pores of each maceral is as follows:alginite>fusinite>bituminite>solid bitumen>vitrinite>liptinite.OM pores are mainly contributed by bituminite,solid bitumen and fusinite.The plane porosity of bituminite increases with maturity.In the process of thermal evolution,the plane porosity of fusinite is distributed in the two ranges of 20%-28% and 1%-7%.The former is mainly the primary pores of the fusinite itself,and the latter is the secondary pores formed in the thermal evolution.As for the organic pores of other macerals,no obvious thermal evolution law was found.Meanwhile,the surface imperfections of vitrinite or solid bitumen is enhanced by the enrichment of organic pores(an increase in pore size or pore number),which may result in the underestimation of their reflectances.展开更多
Reconstructing paleoenvironments has long been considered a vital component for understanding the development and evolution of carbonate reservoirs.The Middle Ordovician Period is considered the archetypical greenhous...Reconstructing paleoenvironments has long been considered a vital component for understanding the development and evolution of carbonate reservoirs.The Middle Ordovician Period is considered the archetypical greenhouse interval,and also a critical period in biological evolution.The Middle Darriwilian isotope carbon excursion has been observed in many areas of the world and may be related to the biological explosions caused by decreases in the temperature.The thick carbonate rocks in the fifth member of the Middle Ordovician Majiagou Formation in the Dingbei area of the Ordos Basin were chosen as an example,based on the concentration of major,trace and rare earth elements as well as C,O and Sr isotopic analyses,the paleoenvironment was reconstructed.And its impact on natural gas exploration was analyzed.The results show that the seawater paleotemperature was 29℃,suboxicanoxic paleoredox conditions were observed,and the seawater paleosalinity was high.A large number of plankton in the biological explosion caused a rapid increase in the total organic carbon in carbonate rocks,which provided natural gas as supplemental source rocks.Affected by early meteoric water,the dissolution of gypsum laid the foundation for high-quality reservoirs,and the residual gypsum also further preserved natural gas.This study provides new data for the paleoenvironment and a theoretical basis for further natural gas exploration.展开更多
The Yellow River is usually assumed to record tectonic activities and climatic changes;however,a systematic study was lack in the sedimentology,stratigraphy,geomorphology and geochronology for the entire Yellow River ...The Yellow River is usually assumed to record tectonic activities and climatic changes;however,a systematic study was lack in the sedimentology,stratigraphy,geomorphology and geochronology for the entire Yellow River though various geologic scholars have conducted numerous works in individual basins.This review focused on well-preserved fluvial terrace sequences that formed along this river on northeastern(NE)Tibetan Plateau and Ordos Block over the past 2.6 Ma.After comparing numerous initial incision ages at different segments along the Yellow River,we found out that the youngest initial incision may occur at ca.150 ka at the Longyang Gorge.The Yellow River may transit from multiple separated endorheic drainages to an entire external drainage after 150 ka,which may cause differentiations in the apparent incision rates before and after 150 ka;thus apparent net incision rates were calculated respectively for the Yellow River before 150 ka and the drainage network post 150 ka.Apparent net incision rates prior to 0.15 Ma were calculated as 0.15,0.29,0.10,0.12 and 0.03 mm/a respectively in Tongde-Xunhua,Lanzhou-Linxia basins,Heishan,Jinshan and Fenwei-Sanmen Gorges in this review,which mainly reflected Kunhuang-Gonghe Tectonic Event,generated by the Indo-Asian collision and diminishing as the NE Tibetan Plateau eastward extruding at ca.1.8-0.15 Ma.Apparent net incision rates post 0.15 Ma were calculated respectively for NE Tibetan Plateau and Ordos Block,considering their different base level.On NE Tibetan Plateau,four fluvial degradational phases were identified between ca.105~70,53~40,25~16 and 12~6 ka associated with terrace levels respectively,at average elevations of 96,40,20 and 10.5 meters above the current river level(m arl)within a range of 5~96 m arl;and four broad periods in the last 150 ka on Ordos Block:possibly marine oxygen isotope stage(MIS)5,ca.118 to 72 ka,most of MIS 3,ca.44~28 ka,transition from LGM to last deglacial ca.20 to 16 ka,and 4~3 ka at average elevations of 67.5,26,19 and 11.5 m arl.These degradational phases post 0.15 Ma were associated with multiple processes including enhanced fluvial discharge with an increase in monsoonal precipitation and/or melt water in deglaciation.展开更多
To explore the genesis of the laminated calcite veins developed in the black shale of Chang 73 submember of the Ordos Basin,the petrology,microstructure and geochemistry of calcite veins are studied using thin section...To explore the genesis of the laminated calcite veins developed in the black shale of Chang 73 submember of the Ordos Basin,the petrology,microstructure and geochemistry of calcite veins are studied using thin sections,fluid inclusions,trace elements and isotopic geochemistry.The source,the time of formation,the mechanism of formation,and the dynamic background of the veins are discussed.The veins are mostly made up of calcite,mixed with lenticular or spindle-shape solid wall rock inclusions.Three structures are identified in the calcite minerals:fibrous,rhombic cleavage,and wedge-like structure.Trace elements and isotopes of carbon and oxygen confirm that the calcite veins were formed from a high density hydrothermal fluid.It is assumed that calcite veins formed prior to wall rock consolidation during the formation of the Qinling Orogenic Belt in the Middle and Late Triassic.The results show that the sedimentary sources of Chang 73 submember were influenced by hydrothermal materials besides terrigenous detritus.The fibrous calcite is different from the fibrous calcite reported in the morphology and mechanism of formation.In this way,the research complements and improves the morphology and the mechanism of formation of fibrous calcite.展开更多
The reservoirs in the seventh member of the Triassic Yanchang Formation (Chang 7 Member) in the Qingcheng Oilfield of the Ordos Basin are characterized by thin sandbody, tight rocks, high heterogeneity, low formation ...The reservoirs in the seventh member of the Triassic Yanchang Formation (Chang 7 Member) in the Qingcheng Oilfield of the Ordos Basin are characterized by thin sandbody, tight rocks, high heterogeneity, low formation pressure coefficient, and complex geomorphology. Through the efforts in the stages of exploration, appraisal, pilot testing and development, a series of key technologies have been formed, including “sweet spot” optimization, differentiated three-dimensional well deployment, fast drilling and completion of large-cluster horizontal well, intensively-staged volume fracturing in long horizontal well, and optimization of rational production system. Furthermore, a production organization mode represented by factory-like operations on loess platform has been implemented. Application of these technologies has enabled to significantly improve the single-well production of the Qingcheng Oilfield, reduce the investment cost, and realize a large-scale and beneficial development at a full cost below $55 per barrel. In 2022, the annual production of Chang 7 shale oil in the Ordos Basin reached 221×10^(4) t, accounting for 70% of the annual shale oil production of China. The practice of development technologies in the Qingcheng Oilfield provides valuable references for efficient development of continental shale oil.展开更多
This paper depicts the distribution of the Wushenqi paleo-uplift in the Ordos Basin by using the latest drilling and seismic data, and analyzes the tectonic evolution of the paleo-uplift with the support of Bischke cu...This paper depicts the distribution of the Wushenqi paleo-uplift in the Ordos Basin by using the latest drilling and seismic data, and analyzes the tectonic evolution of the paleo-uplift with the support of Bischke curve and balanced section. The compressional Wushenqi paleo-uplift which developed in the Early Caledonian orogeny(Huaiyuan orogeny) is approximately a ellipse extending in S-N direction. Its long axis is about 194 km and short axis is about 55-94 km in nearly W-E direction. The denudation thickness and area of the Cambrian in the core are 170-196 m and 11 298 km^(2), respectively. It was mainly formed during the Huaiyuan orogeny according to the chronostratigraphic framework. It was in the embryonic stage in the Middle-Late Cambrian, denuded after developed obviously at the end of Late Cambrian. The paleo-uplift of the 3rd member of the Ordovician Majiagou Formation was reactivated and reduced in area. In the sedimentary period of the Ma 4 Member-pre-Carboniferous, the paleo-uplift experienced non-uniform uplift and denudation. It entered the stable period of burial and preservation in the Carboniferous and later period. The Wushenqi paleo-uplift was formed on the weak area of the basement and tectonic belts, into an compressional structure with irregular morphology, under the control of the non-coaxial compression in the south and north and the stress transmitted by the uplift in the basin. The Wushenqi paleo-uplift has a controlling effect on the sedimentary reservoirs and hydrocarbon accumulation.展开更多
The Ordos Basin is the largest continental multi-energy mineral basin in China,which is rich in coal,oil and gas,and uranium resources.The exploitation of mineral resources is closely related to reservoir water.The ch...The Ordos Basin is the largest continental multi-energy mineral basin in China,which is rich in coal,oil and gas,and uranium resources.The exploitation of mineral resources is closely related to reservoir water.The chemical properties of reservoir water are very important for reservoir evaluation and are significant indicators of the sealing of reservoir oil and gas resources.Therefore,the caprock of the Chang 6 reservoir in the Yanchang Formation was evaluated.The authors tested and analyzed the chemical characteristics of water samples selected from 30 wells in the Chang 6 reservoir of Ansai Oilfield in the Ordos Basin.The results show that the Chang 6 reservoir water in Ansai Oilfield is dominated by calcium-chloride water type with a sodium chloride coefficient of generally less than 0.5.The chloride magnesium coefficients are between 33.7 and 925.5,most of which are greater than 200.The desulfurization coefficients range from 0.21 to 13.4,with an average of 2.227.The carbonate balance coefficients are mainly concentrated below 0.01,with an average of 0.008.The calcium and magnesium coefficients are between 0.08 and 0.003,with an average of 0.01.Combined with the characteristics of the four-corner layout of the reservoir water,the above results show that the graphics are basically consistent.The study indicates that the Chang 6 reservoir in Ansai Oilfield in the Ordos Basin is a favorable block for oil and gas storage with good sealing properties,great preservation conditions of oil and gas,and high pore connectivity.展开更多
Through core observation,thin section identification,and logging and testing data analysis,the types and characteristics of event deposits in the ninth member of Yanchang Formation of Triassic(Chang 9 Member)in southw...Through core observation,thin section identification,and logging and testing data analysis,the types and characteristics of event deposits in the ninth member of Yanchang Formation of Triassic(Chang 9 Member)in southwestern Ordos Basin,China,are examined.There are 4 types and 9 subtypes of event deposits,i.e.earthquake,gravity flow,volcanic and anoxic deposits,in the Chang 9 Member in the study area.Based on the analysis of the characteristics and distribution of such events deposits,it is proposed that the event deposits are generally symbiotic or associated,with intrinsic genetic relations and distribution laws.Five kinds of sedimentary microfacies with relatively developed event deposits are identified,and the genetic model of event deposits is discussed.Seismites are mainly developed in the lake transgression stage when the basin expands episodically,and commonly affected by liquefaction flow,gravity action and brittle shear deformation.Gravity flow,mainly distributed in the high water level period,sandwiched in the fine-grained sediments of prodelta or semi-deep lake,or creates banded or lobate slump turbidite fan.It is relatively developed above the seismites strata.The volcanic event deposits are only seen in the lower part of the Chang 9 Member,showing abrupt contact at the top and bottom,which reflects the volcanic activity at the same time.Anoxic deposits are mostly formed in the late stage of lake transgression to the highstand stage.Very thick organic-rich shales are developed in the highstand stage of Chang 9 Member,and the event deposits in the depositional period of these shales are conducive to potential reservoirs.展开更多
The geological characteristics and enrichment laws of the shale oil in the third submember of the seventh member of Triassic Yanchang Formation(Chang 7_(3)) in the Ordos Basin were analyzed by using the information of...The geological characteristics and enrichment laws of the shale oil in the third submember of the seventh member of Triassic Yanchang Formation(Chang 7_(3)) in the Ordos Basin were analyzed by using the information of core observations, experiments and logging, and then the exploration potential and orientation of the Chang 7_(3) shale oil were discussed. The research findings are obtained in three aspects. First, two types of shale oil, i.e. migratory-retained and retained, are recognized in Chang 7_(3). The former is slightly better than the latter in quality. The migratory-retained shale oil reservoir is featured with the frequent interbedding and overlapping of silty-sandy laminae caused by sandy debris flow and low-density turbidity current and semi-deep-deep lacustrine organic-rich shale laminae. The retained shale oil reservoir is composed of black shale with frequent occurrence of bedding and micro-laminae. Second, high-quality source rocks provide a large quantity of hydrocarbon-rich high-quality fluids with high potential energy. The source-reservoir pressure difference provides power for oil accumulation in thin interbeds of organic-poor sandstones with good seepage conditions and in felsic lamina, tuffaceous lamina and bedding fractures in shales. Hydrocarbon generation-induced fractures, bedding fractures and microfractures provide high-speed pathways for oil micro-migration. Frequent sandstone interlayers and felsic laminae provide a good space for large-scale hydrocarbon accumulation, and also effectively improve the hydrocarbon movability. Third, sand-rich areas around the depression are the main targets for exploring migratory-retained shale oil. Mature deep depression areas are the main targets for exploring retained oil with medium to high maturity. Theoretical research and field application of in-situ conversion in low-mature deep depression areas are the main technical orientations for exploring retained shale oil with low to medium maturity.展开更多
The major enrichment type of shale oil in the Chang 7_(3) shale of Upper Triassic Yanchang Formation in the Ordos Basin is unknown.This paper analyzes the organic matter transformation ratio,hydrocarbon expulsion effi...The major enrichment type of shale oil in the Chang 7_(3) shale of Upper Triassic Yanchang Formation in the Ordos Basin is unknown.This paper analyzes the organic matter transformation ratio,hydrocarbon expulsion efficiency and roof/floor sealing conditions of the Chang 7_(3) shale,and evaluates the major enrichment type of shale oil in this interval.The average organic matter transformation ratio of the Chang 7_(3) shale is about 45%;in other words,more than 50%of the organic matters have not transformed to hydrocarbons,and the lower the maturity,the greater the proportion of untransformed organic matters.The cumulative hydrocarbon expulsion efficiency of the transformed hydrocarbon is 27.5% on average,and the total proportion of untransformed organic matters plus retained hydrocarbons is greater than 70%.The relative hydrocarbon expulsion efficiency of the Chang 7_(3) shale is 60%on average,that is,about 40% of hydrocarbons retain in the shale.The Chang 7_(3) shale corresponds to Chang 7_(1+2) and Chang 8 sandstones as the roof and floor,respectively,and is further overlaid by Chang 6 shale,where extensive low porosity and low permeability–tight oil reservoirs have formed in the parts with relatively good porosity and permeability.Moreover,the Chang 7_(3) shale is tested to be in a negative pressure system(the pressure coefficient of 0.80–0.85).Therefore,the roof/floor sealing conditions of the Chang 7_(3) shale are poor.The retained hydrocarbons appear mostly in absorbed status,with low mobility.It is concluded that the medium–high mature shale oil is not the major enrichment type of shale oil in the Chang 7_(3) shale,but there may be enrichment opportunity for shale oil with good mobility in the areas where the sealing conditions are good without faults and fractures and oil reservoirs are formed off Chang 7_(1+2),Chang 6 and Chang 8.Furthermore,low–medium mature shale oil is believed to have great potential and is the major enrichment type of shale oil in the Chang 7_(3) shale.It is recommended to prepare relevant in-situ conversion technologies by pilot test and figure out the resource availability and distribution.展开更多
The oil and gas potential of the Yan'an Formation in the Ordos Basin has yet to be fully tapped. In this study, the pore structure, mobile fluid saturation, and water flooding micro-mechanism of the Yan'an For...The oil and gas potential of the Yan'an Formation in the Ordos Basin has yet to be fully tapped. In this study, the pore structure, mobile fluid saturation, and water flooding micro-mechanism of the Yan'an Formation sandstone are systematically studied through the application of a series of rock physics and fluid experiments. The results show that there is a good positive correlation between porosity and permeability, and the reservoirs are divided into types Ⅰ, Ⅱ, and Ⅲ. Mercury injection tests show that the average pore throat radius of the oil-bearing reservoir ranges from 1 to 7 μm. The displacement pressure of the Yan'an Formation is also relatively low, and it decreases from 0.1 MPa to 0.01 MPa as the rock porosity increases from 11% to 18%. NMR tests show that small (diameter <0.5 μm) and medium pores (diameter ranging from 0.5 to 2.5 μm) are predominant in the reservoir. Different types of reservoirs have different characteristics of relative permeability curve. In addition, when the average oil recovery rate is less than 1 ml/min, the oil displacement efficiency increases faster. However, when the average oil recovery rate is between 1–3.5 ml/min, the oil displacement efficiency is maintained at around 27%–30%. Physical properties of the reservoir, pore-throat structure, experimental pressure difference, and pore volume injected — all have significant effects on oil displacement efficiency. For Type Ⅰ and Type Ⅱ reservoirs, the increase of the pore volume injected has a significant effect on oil displacement efficiency. However, for Type Ⅲ reservoirs, the change of pore volume injected has insignificant effect on oil displacement efficiency. This study provides a reference for the formulation of estimated ultimate recovery (EUR) measures for similar sandstone reservoirs.展开更多
Shale samples from the Ordovician Wulalike Formation at the western margin of the Ordos Basin are studied to define the types, microstructures and connectivity of pores as well as the relationships between the pore st...Shale samples from the Ordovician Wulalike Formation at the western margin of the Ordos Basin are studied to define the types, microstructures and connectivity of pores as well as the relationships between the pore structures and gas content of the samples by using experimental techniques such as high-resolution field emission scanning electron microscopy (FESEM), mercury injection capillary pressure (MICP), low-temperature nitrogen adsorption (LTNA), CO_(2) adsorption, and focused ion beam scanning electron microscopy (FIB-SEM). The results show that the shale has 10 different lithofacies, typical mixed sedimentary characteristics, and poorly developed pores. The reservoir space mainly consists of intercrystalline pores, dissolution pores, intergranular pores, and micro-fissures, with organic pores occasionally visible. The pore size is mostly within 0.4–250 nm range but dominated by micropores and mesopores less than 20 nm, with pore numbers peaking at pore sizes of 0.5 nm, 0.6 nm, 0.82 nm, 3 nm, and 10 nm, respectively. The pores are poorly connected and macropores are rarely seen, which may explain the low porosity and low permeability of the samples. Samples with high content of organic matter and felsic minerals are potential reservoirs for oil and gas with their favorable physical properties and high connectivity. The pores less than 5 nm contribute significantly to the specific surface area and serve as important storage space for adsorbed gas.展开更多
The Upper Paleozoic(Carboniferous to Permian) succession in the east margin of the Ordos Basin in the North China Craton has a potential to contain significant hydrocarbon resources, though attention have been mainly ...The Upper Paleozoic(Carboniferous to Permian) succession in the east margin of the Ordos Basin in the North China Craton has a potential to contain significant hydrocarbon resources, though attention have been mainly attracted for its successful development of coalbed methane(CBM). To improve the previous resource estimates and evaluate the hydrocarbon play possibilities, this study incorporated new discoveries of hydrocarbon units and their stratigraphic relation with source rocks, hydrocarbon migration and trapping configurations. Continuous hydrocarbon accumulation units were identified within the Upper Paleozoic, including the Taiyuan, Shanxi and Xiashihezi formations with great tight gas potential, and the Taiyuan and Shanxi formations also containing shale gas and CBM. Different strata combinations are identified with coal deposition and favour for continuous gas accumulations, including the tidal flat, deltaic and fluvial systems distributed in most of the study areas. Methane was not only generated from the thick coal seams in the Taiyuan and Shanxi formations, but also from shale and dark mudstones. The coal, shale and tight sandstones are proved of remarkable gas content and hydrocarbon indications, and the gas saturation of tight sandstones decreases upward. The stacked deposit combinations vary isochronally in different areas, while the coal seams were developed stably showing good gas sources. Two key stages control the hydrocarbon enrichment, the continuous subsidence from coal forming to Late Triassic and the anomalous paleo-geothermal event happened in Early Cretaceous, as indicated by the fluid inclusions evidence. Extensive areas show good hydrocarbon development potential presently, and more works should be focused on the evaluation and selection of good reservoir combinations.展开更多
We apply ambient noise tomography to significant seismic data resources in a region including the northeastern Tibetan plateau,the Ordos block and the Sichuan basin.The seismic data come from about 160 stations of the...We apply ambient noise tomography to significant seismic data resources in a region including the northeastern Tibetan plateau,the Ordos block and the Sichuan basin.The seismic data come from about 160 stations of the provincial broadband digital seismograph networks of China.Ambient noise cross-correlations are performed on the data recorded between 2007 and 2009 and high quality inter-station Rayleigh phase velocity dispersion curves are obtained between periods of 6 s to 35 s.Resulting Rayleigh wave phase velocity maps possess a lateral resolution between 100 km and 200 km.The phase velocities at short periods (<20 s) are lower in the Sichuan basin,the northwest segment of the Ordos block and the Weihe graben,and outline sedimentary deposits.At intermediate and long periods (>25 s),strong high velocity anomalies are observed within the Ordos block and the Sichuan basin and low phase velocities are imaged in the northeastern Tibetan plateau,reflecting the variation of crustal thickness from the Tibetan plateau to the neighboring regions in the east.Crustal and uppermost mantle shear wave velocities vary strongly between the Tibetan plateau,the Sichuan basin and the Ordos block.The Ordos block and the Sichuan basin are dominated by high shear wave velocities in the crust and uppermost mantle.There is a triangle-shaped low velocity zone located in the northeastern Tibetan plateau,whose width narrows towards the eastern margin of the plateau.No low velocity zone is apparent beneath the Qinling orogen,suggesting that mass may not be able to flow eastward through the boundary between the Ordos block and the Sichuan basin in the crust and uppermost mantle.展开更多
Sandy debris flow is a new genetic type of sand bodies,which has gained much attention in recent years and its corresponding theory is proved to be a significant improvement and even partial denial to the 'Bouma S...Sandy debris flow is a new genetic type of sand bodies,which has gained much attention in recent years and its corresponding theory is proved to be a significant improvement and even partial denial to the 'Bouma Sequence' and 'turbidite fan' deep-water sedimentary theories to some point. Oil exploration researchers are highly concerned with sandy debris flows for its key role in controlling oil and gas accumulation processes.In this article,by applying sandy debris flows theory and combining a lot work o...展开更多
A systematic analysis of southwestern Ordos Basin's sedimentary characteristics,internal architectural element association styles and depositional model was illustrated through core statistics,well logging data an...A systematic analysis of southwestern Ordos Basin's sedimentary characteristics,internal architectural element association styles and depositional model was illustrated through core statistics,well logging data and outcrop observations in Chang 8 oil-bearing group.This analysis indicates that shallow water delta sediments dominated by a fluvial system is the primary sedimentary system of the Chang 8 oil-bearing group of the Yanchang Formation in southwestern Ordos Basin.Four microfacies with fine grain sizes are identified: distributary channels,sheet sandstone,mouth bar and interdistributary fines.According to the sandbody's spatial distribution and internal architecture,two types of sandbody architectural element associations are identified: amalgamated distributary channels and thin-layer lobate sandstone.In this sedimentary system,net-like distributary channels at the delta with a narrow ribbon shape compose the skeleton of the sandbody that extends further into the delta front and shades into contiguous lobate distribution sheet sandstone in the distal delta front.The mouth bar is largely absent in this system.By analyzing the palaeogeomorphology,the palaeostructure background,sedimentary characteristics,sedimentary facies types and spatial distribution of sedimentary facies during the Chang 8 period,a distinctive depositional model of the Chang 8 shallow water fluvial-dominated delta was established,which primarily consists of straight multi-phase amalgamated distributary channels in the delta plain,net-like distributary channels frequently diverting and converging in the proximal delta front,sheet sandstones with dispersing contiguous lobate shapes in the distal delta front,and prodelta or shallow lake mudstones.展开更多
基金Supported by the PetroChina Science and Technology Innovation Fund Project(2021DQ02-1003)Basic Research Project for Central Universities(2022JCCXDC02).
文摘Through core observation,thin section identification,X-ray diffraction analysis,scanning electron microscopy,and low-temperature nitrogen adsorption and isothermal adsorption experiments,the lithology and pore characteristics of the Upper Carboniferous bauxite series in eastern Ordos Basin were analyzed to reveal the formation and evolution process of the bauxite reservoirs.A petrological nomenclature and classification scheme for bauxitic rocks based on three units(aluminum hydroxides,iron minerals and clay minerals)is proposed.It is found that bauxitic mudstone is in the form of dense massive and clastic structures,while the(clayey)bauxite is of dense massive,pisolite,oolite,porous soil and clastic structures.Both bauxitic mudstone and bauxite reservoirs develop dissolution pores,intercrystalline pores,and microfractures as the dominant gas storage space,with the porosity less than 10% and mesopores in dominance.The bauxite series in the North China Craton can be divided into five sections,i.e.,ferrilite(Shanxi-style iron ore,section A),bauxitic mudstone(section B),bauxite(section C),bauxite mudstone(debris-containing,section D)and dark mudstone-coal section(section E).The burrow/funnel filling,lenticular,layered/massive bauxite deposits occur separately in the karst platforms,gentle slopes and low-lying areas.The karst platforms and gentle slopes are conducive to surface water leaching,with strong karstification,well-developed pores,large reservoir thickness and good physical properties,but poor strata continuity.The low-lying areas have poor physical properties but relatively continuous and stable reservoirs.The gas enrichment in bauxites is jointly controlled by source rock,reservoir rock and fractures.This recognition provides geological basis for the exploration and development of natural gas in the Upper Carboniferous in the study area and similar bauxite systems.
基金funded by the Top 10 key scientific and technological projects of CHN Energy in 2021 entitled Research and Demonstration of Technology for Carbon Dioxide Capture and Energy Recycling Utilization(GJNYKJ[2021]No.128,No.:GJNY-21-51)the Carbon Neutrality College(Yulin)Northwest University project entitled Design and research of large-scale CCUS cluster construction in Yulin area,Shaanxi Province(YL2022-38-01).
文摘The well-developed coal electricity generation and coal chemical industries have led to huge carbon dioxide(CO_(2))emissions in the northeastern Ordos Basin.The geological storage of CO_(2) in saline aquifers is an effective backup way to achieve carbon neutrality.In this case,the potential of saline aquifers for CO_(2) storage serves as a critical basis for subsequent geological storage project.This study calculated the technical control capacities of CO_(2) of the saline aquifers in the fifth member of the Shiqianfeng Formation(the Qian-5 member)based on the statistical analysis of the logging and the drilling and core data from more than 200 wells in the northeastern Ordos Basin,as well as the sedimentary facies,formation lithology,and saline aquifer development patterns of the Qian-5 member.The results show that(1)the reservoirs of saline aquifers in the Qian-5 member,which comprise distributary channel sand bodies of deltaic plains,feature low porosities and permeabilities;(2)The study area hosts three NNE-directed saline aquifer zones,where saline aquifers generally have a single-layer thickness of 3‒8 m and a cumulative thickness of 8‒24 m;(3)The saline aquifers of the Qian-5 member have a total technical control capacity of CO_(2) of 119.25×10^(6) t.With the largest scale and the highest technical control capacity(accounting for 61%of the total technical control capacity),the Jinjie-Yulin saline aquifer zone is an important prospect area for the geological storage of CO_(2) in the saline aquifers of the Qian-5 member in the study area.
文摘In this paper, the Chang 2 reservoir in Zichang Area of Ordos Basin, the second largest sedimentary basin in China, is classified and evaluated by using logging and core data, thin section identification and electron microscopy. The main sedimentary microfacies of Chang 2<sub>1</sub><sup>3</sup> is braided river delta sedimentary system in geological history, and there are three main sedimentary microfacies types: swamp microfacies, distributary channel microfacies and natural embankment microfacies on land. The heterogeneity in the study area is as follows: Chang 2<sub>1</sub><sup>2</sup> formation has the strongest heterogeneity, followed by Chang 2<sub>1</sub><sup>1</sup> formation with strong heterogeneity, and finally Chang 2<sub>1</sub><sup>3</sup> formation with medium heterogeneity. The reservoirs of Chang 2 member in the study area are dominated by III<sub>a</sub>, II<sub>b</sub> and III<sub>b</sub>, and the reservoirs are mainly composed of ultra-low porosity and low permeability reservoirs and low porosity and low permeability reservoirs.
基金supported by the Research Program of the Research Institute of Petroleum Exploration and Development of the Changqing Oilfield(Grant No.J2019168)。
文摘Using high-precision zircon U-Pb ID-TIMS geochronology,tuffs from the Chang 9 shale and the Chang 7 shale were dated.The tuff in the Chang 9 shale is 241.47±0.17 Ma,which falls between the top tuff age of 241.06±0.12 Ma and the bottom tuff age of 241.558±0.093 Ma in the Chang 7 shale.These reveal that the Chang 9 and Chang 7 shales are contemporaneous,belonging to the Ladinian stage of the Middle Triassic.This insight expands the region of the main source rock of Chang 7 to the northeast and will inform the search for the deep Chang 9 shale petroleum system,increasing the scope for exploring the Chang 7 shale system in northern Shaanxi.The research results clarify the relationship between the two sets of shale in the Yanchang Formation and redefine the distribution range of the Chang 7 shale in the Ordos Basin.At the same time,it shows that there is a cross-layer problem in the stratigraphic division of the Yanchang Formation in different regions,the high-precision U-Pb dating technology providing a reference for the fine stratigraphic correlation of other continental basins in the world.
基金This project was funded by the National Natural Science Foundation of China(41972161)the 2021 American Association of Petroleum Geologists Foundation Grants-in-Aid Program and Science and Technology Cooperation Project of the CNPC-SWPU Innovation Alliance(2020CX050103).
文摘To quantify the pore characteristics of various macerals in Chang 7 lacustrine shales,macerals were effectively identified according to their optical and morphological characteristics,and the nanoscale pore structure of macerals was observed by scanning electron microscope.Meanwhile,the reflectances of different positions in the same pieces of vitrinite or solid bitumen with heterogeneous pores development were measured.The results showed that the average contents of sapropelinite,liptinite,vitrinite,inertinite and solid bitumen are 42.7%,8.7%,13.6%,13.8% and 21.2%,respectively,which suggests that the source of the organic matter of the Chang 7 shales is a mixed source input.The organic pores of Chang 7 shales are enriched,and the pore shapes are mostly round or elliptical.The pore size of organic pores has a wide distribution,mainly concentrate in the range of 100-400 nm,and the average plane porosity of organic pores is 10.13%.The size order of the organic pores in various macerals is:solid bitumen<bituminite<alginite<vitrinite<fusinite<liptinite.The abundance order of organic matter pores of each maceral is as follows:alginite>fusinite>bituminite>solid bitumen>vitrinite>liptinite.OM pores are mainly contributed by bituminite,solid bitumen and fusinite.The plane porosity of bituminite increases with maturity.In the process of thermal evolution,the plane porosity of fusinite is distributed in the two ranges of 20%-28% and 1%-7%.The former is mainly the primary pores of the fusinite itself,and the latter is the secondary pores formed in the thermal evolution.As for the organic pores of other macerals,no obvious thermal evolution law was found.Meanwhile,the surface imperfections of vitrinite or solid bitumen is enhanced by the enrichment of organic pores(an increase in pore size or pore number),which may result in the underestimation of their reflectances.
基金This study was financially supported by the National Natural Science Foundation of China(U19B6003)Frontier Project of Chinese Academy of Sciences(XDA14010201)National Key Natural Science Foundation of China(91755211).
文摘Reconstructing paleoenvironments has long been considered a vital component for understanding the development and evolution of carbonate reservoirs.The Middle Ordovician Period is considered the archetypical greenhouse interval,and also a critical period in biological evolution.The Middle Darriwilian isotope carbon excursion has been observed in many areas of the world and may be related to the biological explosions caused by decreases in the temperature.The thick carbonate rocks in the fifth member of the Middle Ordovician Majiagou Formation in the Dingbei area of the Ordos Basin were chosen as an example,based on the concentration of major,trace and rare earth elements as well as C,O and Sr isotopic analyses,the paleoenvironment was reconstructed.And its impact on natural gas exploration was analyzed.The results show that the seawater paleotemperature was 29℃,suboxicanoxic paleoredox conditions were observed,and the seawater paleosalinity was high.A large number of plankton in the biological explosion caused a rapid increase in the total organic carbon in carbonate rocks,which provided natural gas as supplemental source rocks.Affected by early meteoric water,the dissolution of gypsum laid the foundation for high-quality reservoirs,and the residual gypsum also further preserved natural gas.This study provides new data for the paleoenvironment and a theoretical basis for further natural gas exploration.
基金supported by the National Natural Science Foundation of China(Grant No.41472155),Grant No.ZR2022QD083,LYHZW202248 and NSFC 417644073Cultivating Young Talents in the Universities of Shandong Province(LUJIAOKEHAN2021-51,granted to L.Yu)。
文摘The Yellow River is usually assumed to record tectonic activities and climatic changes;however,a systematic study was lack in the sedimentology,stratigraphy,geomorphology and geochronology for the entire Yellow River though various geologic scholars have conducted numerous works in individual basins.This review focused on well-preserved fluvial terrace sequences that formed along this river on northeastern(NE)Tibetan Plateau and Ordos Block over the past 2.6 Ma.After comparing numerous initial incision ages at different segments along the Yellow River,we found out that the youngest initial incision may occur at ca.150 ka at the Longyang Gorge.The Yellow River may transit from multiple separated endorheic drainages to an entire external drainage after 150 ka,which may cause differentiations in the apparent incision rates before and after 150 ka;thus apparent net incision rates were calculated respectively for the Yellow River before 150 ka and the drainage network post 150 ka.Apparent net incision rates prior to 0.15 Ma were calculated as 0.15,0.29,0.10,0.12 and 0.03 mm/a respectively in Tongde-Xunhua,Lanzhou-Linxia basins,Heishan,Jinshan and Fenwei-Sanmen Gorges in this review,which mainly reflected Kunhuang-Gonghe Tectonic Event,generated by the Indo-Asian collision and diminishing as the NE Tibetan Plateau eastward extruding at ca.1.8-0.15 Ma.Apparent net incision rates post 0.15 Ma were calculated respectively for NE Tibetan Plateau and Ordos Block,considering their different base level.On NE Tibetan Plateau,four fluvial degradational phases were identified between ca.105~70,53~40,25~16 and 12~6 ka associated with terrace levels respectively,at average elevations of 96,40,20 and 10.5 meters above the current river level(m arl)within a range of 5~96 m arl;and four broad periods in the last 150 ka on Ordos Block:possibly marine oxygen isotope stage(MIS)5,ca.118 to 72 ka,most of MIS 3,ca.44~28 ka,transition from LGM to last deglacial ca.20 to 16 ka,and 4~3 ka at average elevations of 67.5,26,19 and 11.5 m arl.These degradational phases post 0.15 Ma were associated with multiple processes including enhanced fluvial discharge with an increase in monsoonal precipitation and/or melt water in deglaciation.
文摘To explore the genesis of the laminated calcite veins developed in the black shale of Chang 73 submember of the Ordos Basin,the petrology,microstructure and geochemistry of calcite veins are studied using thin sections,fluid inclusions,trace elements and isotopic geochemistry.The source,the time of formation,the mechanism of formation,and the dynamic background of the veins are discussed.The veins are mostly made up of calcite,mixed with lenticular or spindle-shape solid wall rock inclusions.Three structures are identified in the calcite minerals:fibrous,rhombic cleavage,and wedge-like structure.Trace elements and isotopes of carbon and oxygen confirm that the calcite veins were formed from a high density hydrothermal fluid.It is assumed that calcite veins formed prior to wall rock consolidation during the formation of the Qinling Orogenic Belt in the Middle and Late Triassic.The results show that the sedimentary sources of Chang 73 submember were influenced by hydrothermal materials besides terrigenous detritus.The fibrous calcite is different from the fibrous calcite reported in the morphology and mechanism of formation.In this way,the research complements and improves the morphology and the mechanism of formation of fibrous calcite.
基金Supported by the PetroChina Science and Technology Major Project(2021DJ1806,2023ZZ15).
文摘The reservoirs in the seventh member of the Triassic Yanchang Formation (Chang 7 Member) in the Qingcheng Oilfield of the Ordos Basin are characterized by thin sandbody, tight rocks, high heterogeneity, low formation pressure coefficient, and complex geomorphology. Through the efforts in the stages of exploration, appraisal, pilot testing and development, a series of key technologies have been formed, including “sweet spot” optimization, differentiated three-dimensional well deployment, fast drilling and completion of large-cluster horizontal well, intensively-staged volume fracturing in long horizontal well, and optimization of rational production system. Furthermore, a production organization mode represented by factory-like operations on loess platform has been implemented. Application of these technologies has enabled to significantly improve the single-well production of the Qingcheng Oilfield, reduce the investment cost, and realize a large-scale and beneficial development at a full cost below $55 per barrel. In 2022, the annual production of Chang 7 shale oil in the Ordos Basin reached 221×10^(4) t, accounting for 70% of the annual shale oil production of China. The practice of development technologies in the Qingcheng Oilfield provides valuable references for efficient development of continental shale oil.
基金Supported by the Major Science and Technology Project of PetroChina Changqing Oilfield Company (ZDZX2021-01)。
文摘This paper depicts the distribution of the Wushenqi paleo-uplift in the Ordos Basin by using the latest drilling and seismic data, and analyzes the tectonic evolution of the paleo-uplift with the support of Bischke curve and balanced section. The compressional Wushenqi paleo-uplift which developed in the Early Caledonian orogeny(Huaiyuan orogeny) is approximately a ellipse extending in S-N direction. Its long axis is about 194 km and short axis is about 55-94 km in nearly W-E direction. The denudation thickness and area of the Cambrian in the core are 170-196 m and 11 298 km^(2), respectively. It was mainly formed during the Huaiyuan orogeny according to the chronostratigraphic framework. It was in the embryonic stage in the Middle-Late Cambrian, denuded after developed obviously at the end of Late Cambrian. The paleo-uplift of the 3rd member of the Ordovician Majiagou Formation was reactivated and reduced in area. In the sedimentary period of the Ma 4 Member-pre-Carboniferous, the paleo-uplift experienced non-uniform uplift and denudation. It entered the stable period of burial and preservation in the Carboniferous and later period. The Wushenqi paleo-uplift was formed on the weak area of the basement and tectonic belts, into an compressional structure with irregular morphology, under the control of the non-coaxial compression in the south and north and the stress transmitted by the uplift in the basin. The Wushenqi paleo-uplift has a controlling effect on the sedimentary reservoirs and hydrocarbon accumulation.
基金supported by the Jiangsu Natural Science Foundation project(SBK2021045820)the Chongqing Natural Science Foundation general Project(cstc2021jcyj-msxmX0624)+1 种基金the Graduate Innovation Program of China University of Mining and Technology(2022WLKXJ002)the Postgraduate Research&Practice Innovation Program of Jiangsu Province(KYCX22_2600).
文摘The Ordos Basin is the largest continental multi-energy mineral basin in China,which is rich in coal,oil and gas,and uranium resources.The exploitation of mineral resources is closely related to reservoir water.The chemical properties of reservoir water are very important for reservoir evaluation and are significant indicators of the sealing of reservoir oil and gas resources.Therefore,the caprock of the Chang 6 reservoir in the Yanchang Formation was evaluated.The authors tested and analyzed the chemical characteristics of water samples selected from 30 wells in the Chang 6 reservoir of Ansai Oilfield in the Ordos Basin.The results show that the Chang 6 reservoir water in Ansai Oilfield is dominated by calcium-chloride water type with a sodium chloride coefficient of generally less than 0.5.The chloride magnesium coefficients are between 33.7 and 925.5,most of which are greater than 200.The desulfurization coefficients range from 0.21 to 13.4,with an average of 2.227.The carbonate balance coefficients are mainly concentrated below 0.01,with an average of 0.008.The calcium and magnesium coefficients are between 0.08 and 0.003,with an average of 0.01.Combined with the characteristics of the four-corner layout of the reservoir water,the above results show that the graphics are basically consistent.The study indicates that the Chang 6 reservoir in Ansai Oilfield in the Ordos Basin is a favorable block for oil and gas storage with good sealing properties,great preservation conditions of oil and gas,and high pore connectivity.
基金Supported by the PetroChina Scientific Research and Technological Development Project(2021DJ0402).
文摘Through core observation,thin section identification,and logging and testing data analysis,the types and characteristics of event deposits in the ninth member of Yanchang Formation of Triassic(Chang 9 Member)in southwestern Ordos Basin,China,are examined.There are 4 types and 9 subtypes of event deposits,i.e.earthquake,gravity flow,volcanic and anoxic deposits,in the Chang 9 Member in the study area.Based on the analysis of the characteristics and distribution of such events deposits,it is proposed that the event deposits are generally symbiotic or associated,with intrinsic genetic relations and distribution laws.Five kinds of sedimentary microfacies with relatively developed event deposits are identified,and the genetic model of event deposits is discussed.Seismites are mainly developed in the lake transgression stage when the basin expands episodically,and commonly affected by liquefaction flow,gravity action and brittle shear deformation.Gravity flow,mainly distributed in the high water level period,sandwiched in the fine-grained sediments of prodelta or semi-deep lake,or creates banded or lobate slump turbidite fan.It is relatively developed above the seismites strata.The volcanic event deposits are only seen in the lower part of the Chang 9 Member,showing abrupt contact at the top and bottom,which reflects the volcanic activity at the same time.Anoxic deposits are mostly formed in the late stage of lake transgression to the highstand stage.Very thick organic-rich shales are developed in the highstand stage of Chang 9 Member,and the event deposits in the depositional period of these shales are conducive to potential reservoirs.
基金Supported by the CNPC Science and Technology Project (2021DJ1806)the National Key Basic Research and Development Program (973 Program),China (2014CB239003)。
文摘The geological characteristics and enrichment laws of the shale oil in the third submember of the seventh member of Triassic Yanchang Formation(Chang 7_(3)) in the Ordos Basin were analyzed by using the information of core observations, experiments and logging, and then the exploration potential and orientation of the Chang 7_(3) shale oil were discussed. The research findings are obtained in three aspects. First, two types of shale oil, i.e. migratory-retained and retained, are recognized in Chang 7_(3). The former is slightly better than the latter in quality. The migratory-retained shale oil reservoir is featured with the frequent interbedding and overlapping of silty-sandy laminae caused by sandy debris flow and low-density turbidity current and semi-deep-deep lacustrine organic-rich shale laminae. The retained shale oil reservoir is composed of black shale with frequent occurrence of bedding and micro-laminae. Second, high-quality source rocks provide a large quantity of hydrocarbon-rich high-quality fluids with high potential energy. The source-reservoir pressure difference provides power for oil accumulation in thin interbeds of organic-poor sandstones with good seepage conditions and in felsic lamina, tuffaceous lamina and bedding fractures in shales. Hydrocarbon generation-induced fractures, bedding fractures and microfractures provide high-speed pathways for oil micro-migration. Frequent sandstone interlayers and felsic laminae provide a good space for large-scale hydrocarbon accumulation, and also effectively improve the hydrocarbon movability. Third, sand-rich areas around the depression are the main targets for exploring migratory-retained shale oil. Mature deep depression areas are the main targets for exploring retained oil with medium to high maturity. Theoretical research and field application of in-situ conversion in low-mature deep depression areas are the main technical orientations for exploring retained shale oil with low to medium maturity.
基金Supported by the National Natural Science Foundation of China(U22B6004).
文摘The major enrichment type of shale oil in the Chang 7_(3) shale of Upper Triassic Yanchang Formation in the Ordos Basin is unknown.This paper analyzes the organic matter transformation ratio,hydrocarbon expulsion efficiency and roof/floor sealing conditions of the Chang 7_(3) shale,and evaluates the major enrichment type of shale oil in this interval.The average organic matter transformation ratio of the Chang 7_(3) shale is about 45%;in other words,more than 50%of the organic matters have not transformed to hydrocarbons,and the lower the maturity,the greater the proportion of untransformed organic matters.The cumulative hydrocarbon expulsion efficiency of the transformed hydrocarbon is 27.5% on average,and the total proportion of untransformed organic matters plus retained hydrocarbons is greater than 70%.The relative hydrocarbon expulsion efficiency of the Chang 7_(3) shale is 60%on average,that is,about 40% of hydrocarbons retain in the shale.The Chang 7_(3) shale corresponds to Chang 7_(1+2) and Chang 8 sandstones as the roof and floor,respectively,and is further overlaid by Chang 6 shale,where extensive low porosity and low permeability–tight oil reservoirs have formed in the parts with relatively good porosity and permeability.Moreover,the Chang 7_(3) shale is tested to be in a negative pressure system(the pressure coefficient of 0.80–0.85).Therefore,the roof/floor sealing conditions of the Chang 7_(3) shale are poor.The retained hydrocarbons appear mostly in absorbed status,with low mobility.It is concluded that the medium–high mature shale oil is not the major enrichment type of shale oil in the Chang 7_(3) shale,but there may be enrichment opportunity for shale oil with good mobility in the areas where the sealing conditions are good without faults and fractures and oil reservoirs are formed off Chang 7_(1+2),Chang 6 and Chang 8.Furthermore,low–medium mature shale oil is believed to have great potential and is the major enrichment type of shale oil in the Chang 7_(3) shale.It is recommended to prepare relevant in-situ conversion technologies by pilot test and figure out the resource availability and distribution.
基金supported by the Guiding Science and Technology Planning Project of Daqing(Grant No.zd-2021-36)Postdoctoral Scientific Research Developmental Fund of Heilongjiang Province,China(Grant No.LBH-Z21084)Natural Science Foundation of Heilongjiang Province(Grant No.LH 2022E019).
文摘The oil and gas potential of the Yan'an Formation in the Ordos Basin has yet to be fully tapped. In this study, the pore structure, mobile fluid saturation, and water flooding micro-mechanism of the Yan'an Formation sandstone are systematically studied through the application of a series of rock physics and fluid experiments. The results show that there is a good positive correlation between porosity and permeability, and the reservoirs are divided into types Ⅰ, Ⅱ, and Ⅲ. Mercury injection tests show that the average pore throat radius of the oil-bearing reservoir ranges from 1 to 7 μm. The displacement pressure of the Yan'an Formation is also relatively low, and it decreases from 0.1 MPa to 0.01 MPa as the rock porosity increases from 11% to 18%. NMR tests show that small (diameter <0.5 μm) and medium pores (diameter ranging from 0.5 to 2.5 μm) are predominant in the reservoir. Different types of reservoirs have different characteristics of relative permeability curve. In addition, when the average oil recovery rate is less than 1 ml/min, the oil displacement efficiency increases faster. However, when the average oil recovery rate is between 1–3.5 ml/min, the oil displacement efficiency is maintained at around 27%–30%. Physical properties of the reservoir, pore-throat structure, experimental pressure difference, and pore volume injected — all have significant effects on oil displacement efficiency. For Type Ⅰ and Type Ⅱ reservoirs, the increase of the pore volume injected has a significant effect on oil displacement efficiency. However, for Type Ⅲ reservoirs, the change of pore volume injected has insignificant effect on oil displacement efficiency. This study provides a reference for the formulation of estimated ultimate recovery (EUR) measures for similar sandstone reservoirs.
基金funded by a National Science and Technology Major Project(No.2016ZX05007)Chinese Academy of Sciences(CAS)Strategic Leading Science&Technology Program(No.XDA14010000)CNPC's"Fourteenth Five-Year Plan"forward-looking basic strategic major scientific and technological project(No.2021DJ3102).
文摘Shale samples from the Ordovician Wulalike Formation at the western margin of the Ordos Basin are studied to define the types, microstructures and connectivity of pores as well as the relationships between the pore structures and gas content of the samples by using experimental techniques such as high-resolution field emission scanning electron microscopy (FESEM), mercury injection capillary pressure (MICP), low-temperature nitrogen adsorption (LTNA), CO_(2) adsorption, and focused ion beam scanning electron microscopy (FIB-SEM). The results show that the shale has 10 different lithofacies, typical mixed sedimentary characteristics, and poorly developed pores. The reservoir space mainly consists of intercrystalline pores, dissolution pores, intergranular pores, and micro-fissures, with organic pores occasionally visible. The pore size is mostly within 0.4–250 nm range but dominated by micropores and mesopores less than 20 nm, with pore numbers peaking at pore sizes of 0.5 nm, 0.6 nm, 0.82 nm, 3 nm, and 10 nm, respectively. The pores are poorly connected and macropores are rarely seen, which may explain the low porosity and low permeability of the samples. Samples with high content of organic matter and felsic minerals are potential reservoirs for oil and gas with their favorable physical properties and high connectivity. The pores less than 5 nm contribute significantly to the specific surface area and serve as important storage space for adsorbed gas.
基金supported by the Natural Science Foundation of China(grant No.41702171)the Beijing Municipal Excellent Talents Foundation(grant No.2017000020124G107)+1 种基金2017 Open Project Fund of State Key Laboratory of Coal Resources and Safe Mining(grant No.SKLCRSM17KFA12)the Joint Research Fund for Overseas Chinese Scholars and Scholars in HongKong and Macao(grant No.41728005)
文摘The Upper Paleozoic(Carboniferous to Permian) succession in the east margin of the Ordos Basin in the North China Craton has a potential to contain significant hydrocarbon resources, though attention have been mainly attracted for its successful development of coalbed methane(CBM). To improve the previous resource estimates and evaluate the hydrocarbon play possibilities, this study incorporated new discoveries of hydrocarbon units and their stratigraphic relation with source rocks, hydrocarbon migration and trapping configurations. Continuous hydrocarbon accumulation units were identified within the Upper Paleozoic, including the Taiyuan, Shanxi and Xiashihezi formations with great tight gas potential, and the Taiyuan and Shanxi formations also containing shale gas and CBM. Different strata combinations are identified with coal deposition and favour for continuous gas accumulations, including the tidal flat, deltaic and fluvial systems distributed in most of the study areas. Methane was not only generated from the thick coal seams in the Taiyuan and Shanxi formations, but also from shale and dark mudstones. The coal, shale and tight sandstones are proved of remarkable gas content and hydrocarbon indications, and the gas saturation of tight sandstones decreases upward. The stacked deposit combinations vary isochronally in different areas, while the coal seams were developed stably showing good gas sources. Two key stages control the hydrocarbon enrichment, the continuous subsidence from coal forming to Late Triassic and the anomalous paleo-geothermal event happened in Early Cretaceous, as indicated by the fluid inclusions evidence. Extensive areas show good hydrocarbon development potential presently, and more works should be focused on the evaluation and selection of good reservoir combinations.
基金supported by Chinese Academy of Sciences grant kzcx2-yw-142 and Y009021002National Natural Science Foundation of China under grant No. 40974034+1 种基金NSF-EAR award 0944022NSF-OISE 0730154 at the University of Colorado at Boulder
文摘We apply ambient noise tomography to significant seismic data resources in a region including the northeastern Tibetan plateau,the Ordos block and the Sichuan basin.The seismic data come from about 160 stations of the provincial broadband digital seismograph networks of China.Ambient noise cross-correlations are performed on the data recorded between 2007 and 2009 and high quality inter-station Rayleigh phase velocity dispersion curves are obtained between periods of 6 s to 35 s.Resulting Rayleigh wave phase velocity maps possess a lateral resolution between 100 km and 200 km.The phase velocities at short periods (<20 s) are lower in the Sichuan basin,the northwest segment of the Ordos block and the Weihe graben,and outline sedimentary deposits.At intermediate and long periods (>25 s),strong high velocity anomalies are observed within the Ordos block and the Sichuan basin and low phase velocities are imaged in the northeastern Tibetan plateau,reflecting the variation of crustal thickness from the Tibetan plateau to the neighboring regions in the east.Crustal and uppermost mantle shear wave velocities vary strongly between the Tibetan plateau,the Sichuan basin and the Ordos block.The Ordos block and the Sichuan basin are dominated by high shear wave velocities in the crust and uppermost mantle.There is a triangle-shaped low velocity zone located in the northeastern Tibetan plateau,whose width narrows towards the eastern margin of the plateau.No low velocity zone is apparent beneath the Qinling orogen,suggesting that mass may not be able to flow eastward through the boundary between the Ordos block and the Sichuan basin in the crust and uppermost mantle.
文摘Sandy debris flow is a new genetic type of sand bodies,which has gained much attention in recent years and its corresponding theory is proved to be a significant improvement and even partial denial to the 'Bouma Sequence' and 'turbidite fan' deep-water sedimentary theories to some point. Oil exploration researchers are highly concerned with sandy debris flows for its key role in controlling oil and gas accumulation processes.In this article,by applying sandy debris flows theory and combining a lot work o...
基金Project(SQ2013CB021013)supported by the National Key Basic Research Program of ChinaProject(41002045)supported by the National Natural Science Foundation of China
文摘A systematic analysis of southwestern Ordos Basin's sedimentary characteristics,internal architectural element association styles and depositional model was illustrated through core statistics,well logging data and outcrop observations in Chang 8 oil-bearing group.This analysis indicates that shallow water delta sediments dominated by a fluvial system is the primary sedimentary system of the Chang 8 oil-bearing group of the Yanchang Formation in southwestern Ordos Basin.Four microfacies with fine grain sizes are identified: distributary channels,sheet sandstone,mouth bar and interdistributary fines.According to the sandbody's spatial distribution and internal architecture,two types of sandbody architectural element associations are identified: amalgamated distributary channels and thin-layer lobate sandstone.In this sedimentary system,net-like distributary channels at the delta with a narrow ribbon shape compose the skeleton of the sandbody that extends further into the delta front and shades into contiguous lobate distribution sheet sandstone in the distal delta front.The mouth bar is largely absent in this system.By analyzing the palaeogeomorphology,the palaeostructure background,sedimentary characteristics,sedimentary facies types and spatial distribution of sedimentary facies during the Chang 8 period,a distinctive depositional model of the Chang 8 shallow water fluvial-dominated delta was established,which primarily consists of straight multi-phase amalgamated distributary channels in the delta plain,net-like distributary channels frequently diverting and converging in the proximal delta front,sheet sandstones with dispersing contiguous lobate shapes in the distal delta front,and prodelta or shallow lake mudstones.
