Due to limited data on the geochemical properties of natural gas,estimations are needed for the effective gas source rock in evaluating gas potential.However,the pronounced heterogeneity of mudstones in lacustrine suc...Due to limited data on the geochemical properties of natural gas,estimations are needed for the effective gas source rock in evaluating gas potential.However,the pronounced heterogeneity of mudstones in lacustrine successions complicates the prediction of the presence and geochemical characteristics of gas source rocks.In this paper,the Liaohe Subbasin of Northeast China is used as an example to construct a practical methodology for locating effective gas source rocks in typical lacustrine basins.Three types of gas source rocks,microbial,oil-type,and coal-type,were distinguished according to the different genetic types of their natural gas.A practical three-dimensional geological model was developed,refined,and applied to determine the spatial distribution of the mudstones in the Western Depression of the Liaohe Subbasin and to describe the geochemical characteristics(the abundance,type,and maturation levels of the organic matter).Application of the model in the subbasin indicates that the sedimentary facies have led to heterogeneity in the mudstones,particularly with respect to organic matter types.The effective gas source rock model constructed for the Western Depression shows that the upper sequence(SQ2)of the Fourth member(Mbr 4)of the Eocene Shahejie Formation(Fm)and the lower and middle sequences(SQ3 and SQ4)of the Third member(Mbr 3)form the principal gas-generating interval.The total volume of effective gas source rocks is estimated to be 586 km^(3).The effective microbial,oil-type,and coal-type gas source rocks are primarily found in the shallow western slope,the central sags,and the eastern slope of the Western Depression,respectively.This study provides a practical approach for more accurately identifying the occurrence and geochemical characteristics of effective natural gas source rocks,enabling a precise quantitative estimation of natural gas reserves.展开更多
The saline lacustrine hybrid sedimentary rocks are complex in lithology and unknown for their sedimentary mechanisms.The hybrid sedimentary rocks samples from the Neogene upper Ganchaigou Formation to lower Youshashan...The saline lacustrine hybrid sedimentary rocks are complex in lithology and unknown for their sedimentary mechanisms.The hybrid sedimentary rocks samples from the Neogene upper Ganchaigou Formation to lower Youshashan Formation(N_(1)-N_(2)^(1))in the Fengxi area Qaidam Basin,were investigated through core-log and petrology-geochemistry cross-analysis by using the core,casting thin section,scanning electron microscope,X-ray diffraction,logging,and carbon/oxygen isotopic data.The hybrid sedimentary rocks in the Fengxi area,including terrigenous clastic rock and lacustrine carbonate rock,were deposited in a shallow lake environment far from the source,or occasionally in a semi-deep lake environment,with 5 lithofacies types and 6 microfacies types recognized.Stable carbon and oxygen isotopic compositions reveal that the formation of sedimentary cycles is controlled by a climate-driven compensation-undercompensation cyclic mechanism.A sedimentary cycle model of hybrid sedimentary rocks in an arid and saline setting is proposed.According to this model,in the compensation period,the lake level rises sharply,and microfacies such as mud flat,sand-mud flat and beach are developed,with physical subsidence as the dominant sedimentary mechanism;in the undercompensation period,the lake level falls slowly,and microfacies such as lime-mud flat,lime-dolomite flat and algal mound/mat are developed,with chemical-biological process as the dominant sedimentary mechanism.In the saline lacustrine sedimentary system,lacustrine carbonate rock is mainly formed along with regression,the facies change is not interpreted by the accommodation believed traditionally,but controlled by the temporary fluctuation of lake water chemistry caused by climate change.The research results update the interpreted high-resolution sequence model and genesis of hybrid sedimentary rocks in the saline lacustrine basin and provide a valuable guidance for exploring unconventional hydrocarbons of saline lacustrine facies.展开更多
Based on the studies of the Songliao Basin characterized by Cretaceous down-warping, of the Jurassic compressional flexural Junggar basin and of the Bohai Bay Basin characterized by Paleogene rifting, the multiple-gra...Based on the studies of the Songliao Basin characterized by Cretaceous down-warping, of the Jurassic compressional flexural Junggar basin and of the Bohai Bay Basin characterized by Paleogene rifting, the multiple-grades slope break has developed in lacustrine basins of different origins. Their genetic types can be divided into tectonic slope break, depositional slope break and erodent slope break. The dominant agent of the slope break is tectogenesis, and the scale of slope breaks relates with the size of tectogenesis. The results of the study show that control of mutual grades slope breaks on atectonic traps mainly represent: 1) Atectonic traps develop close to mutual grades slope breaks, with beads-shaped distribution along the slope breaks. 2) In the longitudinal direction, the development of atectonic traps is characterized by the inheritance. 3) Different slope breaks and their different geographical positions can lead to different development types of atectonic traps. 4) A slope break can form different kinds of atectonic traps because of its great lateral variation. 5) The existence of mutual-grade slope breaks leads to different responses of erosion and deposition at different geographical positions in the basin. The oil source bed, reservoir and cap rock combination of atectonic traps is fine. 6) The oil-bearing condition of atectonic traps controlled by slope breaks is very favorable.展开更多
Diagenetic traps in conglomerate in nearshore subaqueous fans in the steep slope zones of rift basins have been important exploration targets for subtle reservoirs in eastern China. However, the mechanism of how those...Diagenetic traps in conglomerate in nearshore subaqueous fans in the steep slope zones of rift basins have been important exploration targets for subtle reservoirs in eastern China. However, the mechanism of how those traps were formed is not clear, which inhibits further exploration for this type of reservoir. In order to solve the problem, we take as an example nearshore subaqueous fans in the upper part of the fourth member of the Shahejie Formation （Es4s） on the north slope of the Minfeng Subsag in the Dongying Sag. Combining different research methods, such as core observation, thin section examination, scanning electron microscope （SEM） observation, fluid-inclusion analysis, carbon and oxygen isotope analysis of carbonate cements, and analysis of core properties, we studied the genetic mechanisms of diagenetic traps on the basis of diagenetic environment evolution and diagenetic evolution sequence in different sub/micro-facies. Conglomerate in Es4s in the north Minfeng Subsag experienced several periods of transition between alkaline and acidic environments as ＂alkaline-acidic-alkaline-acidic-weak alkaline＂. As a result, dissolution and cementation are also very complex, and the sequence is ＂early pyrite cementation / siderite cementation / gypsum cementation / calcite and dolomite cementation- feldspar dissolution / quartz overgrowth quartz dissolution / ferroan calcite cementation / ankerite cementation / lime-mud matrix recrystallization / feldspar overgrowth carbonate dissolution / feldspar dissolution / quartz overgrowth / pyrite cementation＂. The difference in sedimentary characteristics between different sub/micro-facies of nearshore subaqueous fans controls diagenetic characteristics. Inner fan conglomerates mainly experienced compaction and lime-mud matrix recrystallization, with weak dissolution, which led to a reduction in the porosity and permeability crucial to reservoir formation. Lime-mud matrix recrystallization results in a rapid decrease in porosity and permeability in inner fan conglomerates in middle-to-deep layers. Because acid dissolution reworks reservoirs and hydrocarbon filling inhibits cementation, reservoirs far from mudstone layers in middle fan braided channels develop a great number of primary pores and secondary pores, and are good enough to be effective reservoirs of hydrocarbon. With the increase of burial depth, both the decrease of porosity and permeability of inner fan conglomerates and the increase of the physical property difference between inner fans and middle fans enhance the quality of seals in middle-to-deep layers. As a result, inner fan conglomerates can be sealing layers in middle-to-deep buried layers. Reservoirs adjacent to mudstones in middle fan braided channels and reservoirs in middle fan interdistributaries experienced extensive cementation, and tight cemented crusts formed at both the top and bottom of conglomerates, which can then act as cap rocks. In conclusion, diagenetic traps in conglomerates of nearshore subaqueous fans could be developed with inner fan conglomerates as lateral or vertical sealing layers, tight carbonate crusts near mudstone layers in middle fan braided channels as well as lacustrine mudstones as cap rocks, and conglomerates far from mudstone layers in middle fan braided channels as reservoirs. Lime-mud matrix recrystallization of inner fan conglomerates and carbonate cementation of conglomerates adjacent to mudstone layers in middle fan braided channels took place from 32 Ma B.R to 24.6 Ma B.P., thus the formation of diagenetic traps was from 32 Ma B.R to 24.6 Ma B.R and diagenetic traps have a better hydrocarbon sealing ability from 24 Ma B.P.. The sealing ability of inner fans gradually increases with the increase of burial depth and diagenetic traps buried more than 3,200 m have better seals.展开更多
Pore structure plays an important role in the gas storage and flow capacity of shale gas reservoirs. Fieldemission environmental scanning electron microscopy（FE-SEM） in combination with low-pressure carbon dioxide g...Pore structure plays an important role in the gas storage and flow capacity of shale gas reservoirs. Fieldemission environmental scanning electron microscopy（FE-SEM） in combination with low-pressure carbon dioxide gas adsorption（CO2GA）,nitrogen gas adsorption（N2GA）,and high-pressure mercury intrusion（HPMI） were used to study the nanostructure pore morphology and pore-size distributions（PSDs） of lacustrine shale from the Upper Triassic Yanchang Formation,Ordos Basin. Results show that the pores in the shale reservoirs are generally nanoscale and can be classified into four types： organic,interparticle,intraparticle,and microfracture. The interparticle pores between clay particles and organic-matter pores develop most often,l with pore sizes that vary from several to more than 100 nm. Mercury porosimetry analysis shows total porosities ranging between 1.93 and 7.68%,with a mean value of 5.27%. The BET surface areas as determined by N2 adsorption in the nine samples range from 10 to 20 m2/g and the CO2 equivalent surface areas（2 nm）vary from 18 to 71 m2/g. Together,the HPMI,N2 GA,and CO2 GA curves indicate that the pore volumes are mainly due to pores 100 nm in size. In contrast,however,most of the specific surface areas are provided by the micropores. The total organic carbon（TOC） and clay minerals are the primary controls of the structures of nanoscale pores（especially micropores and mesopores）. Micropores are predominantly determined by the content of the TOC,and mesopores are possibly related to the content of clay minerals,particularly the illite-montmorillonite mixed-layer content.展开更多
Three types of turbidites are identified in the studied area, including proximal turbidite along the northern steep slope （alluvial fans, fan delta, and subaqueous fans via short-distance transportation）, distal tur...Three types of turbidites are identified in the studied area, including proximal turbidite along the northern steep slope （alluvial fans, fan delta, and subaqueous fans via short-distance transportation）, distal turbidites along the southern gentle slope （stacked sliding of delta and fan delta front）, and fluxoturbidite in the central depression. Detailed studies of several case histories and the relationship between sedimentary facies and faults suggest a significant role of tectonic setting and faults in the development of turbidite, which created source areas, effected slope topography, controlled the climate and paleo-environment, and formed enough slope angle and slope break for sedimentary instabilities and massive block movement to form turbidite. According to statistics, 0.86%, with an average value of 40.3%, of the trap volumes in the 69 identified Tertiary lacustrine turbidites in the Jiyang Superdepression in the Bohai Bay Basin are filled with oil. The porosity and permeability of turbidite sands vary widely. The productive reservoirs are generally those from the braided channels of both distal and proximal turbidite, and from the main channel of proximal turbidite, with a low carbonate content and the porosity and permeability higher than 12% and 1 mD respectively. Most of the lithologic oil pools in the Jiyang Superdepression are enveloped by the effective source rocks, and the percentage of the trap volume generally increases with the hydrocarbon expulsion intensity of source rocks. This is in contrast with structural-lithologic traps （i.e. proximal turbidite along the steep slope and distal turbidite along the gentle slope）, in which, graben-boundary faults play an important role in oil migration, as the turbidites are not in direct contact with effective hydrocarbon source rocks.展开更多
The genesis of the fine crystalline dolomites that exhibit good to excellent reservoir properties in the upper fourth member of the Eocene Shahejie Formation（Es4s）around the Sikou Sag, Bohai Bay Basin, is uncertain....The genesis of the fine crystalline dolomites that exhibit good to excellent reservoir properties in the upper fourth member of the Eocene Shahejie Formation（Es4s）around the Sikou Sag, Bohai Bay Basin, is uncertain. This paper investigates the formation mechanisms of this fine crystalline dolomite using XRD, SEM, thin section analysis and geochemical data. The stratigraphy of the Sikou lacustrine carbonate is dominated by the repetition of metre-scale, high-frequency deposition cycles, and the amount of dolomite within a cycle increases upward from the cycle bottom. These dolomite crystals are 2–30 μm in length, subhedral to anhedral in shape and typically replace both grains and matrix. They also occur as rim cement and have thin lamellae within ooid cortices. Textural relations indicate that the dolomite predates equant sparry calcite cement and coarse calcite cement. The Sr concentrations of dolomites range from 900 to 1200 ppm. Dolomite δ18O values（-11.3 to-8.2 ‰ PDB） are depleted relative to calcite mudstone（-8.3 to-5.4 ‰ PDB） that precipitated from lake water, while δ13C values（0.06–1.74 ‰ PDB） are within the normal range of calcite mudstone values（-2.13 to 1.99 ‰ PDB）. High87Sr/86Sr values（0.710210–0.710844） indicate that amounts of Ca2＋ and Mg2＋have been derived from the chemical weathering of Palaeozoic carbonate bedrocks. The high strontium concentration indicates that hypersaline conditions were maintainedduring the formation of the dolomites and that the dolomites were formed by the replacement of precursor calcite or by direct precipitation.展开更多
Comparative analyses of petroleum generation potential,reservoir volume,frackability,and oil mobility were conducted on 102 shale cores from the Dongpu Depression.Results show the shale has high organic matter content...Comparative analyses of petroleum generation potential,reservoir volume,frackability,and oil mobility were conducted on 102 shale cores from the Dongpu Depression.Results show the shale has high organic matter contents composed of oil-prone type I and type II kerogens within the oil window.Various types of pores and fractures exist in the shale,with a porosity of up to 14.9%.The shale has high brittle mineral contents,extensive fractures,and high potential for oil mobility due to high seepage capacity and overpressure.Although the petroleum generation potential of the shale at Well PS18-8 is relatively greater than that at Well PS18-1,oil content of the latter is greater due to the greater TOC.The porosity and fracture density observed in Well PS18-1 are greater and more conducive to shale oil enrichment.Although the shales in Wells PS18-1 and PS18-8 have similar brittle mineral contents,the former is more favorable for anthropogenic fracturing due to a higher preexisting fracture density.Besides,the shale at Well PS18-1 has a higher seepage capacity and overpressure and therefore a higher oil mobility.The fracture density and overpressure play key roles in shale oil enrichment.展开更多
A new type of shale oil in alkaline lacustrine sediments has been discovered in the Late Paleozoic Fengcheng Formation,Mahu Sag,Junggar Basin,China.The fine-grained sedimentary rocks deposited in this alkaline lacustr...A new type of shale oil in alkaline lacustrine sediments has been discovered in the Late Paleozoic Fengcheng Formation,Mahu Sag,Junggar Basin,China.The fine-grained sedimentary rocks deposited in this alkaline lacustrine environment can be divided into four types and eight sub-types:mudstone(with no alkali minerals),including massive dolomitic mudstone,and massive and laminated calcareous mudstone;dolomite,including massive argillaceous dolomite(with alkali minerals),and massive and laminated argillaceous dolomite(with no alkali minerals);evaporites;and pyroclastic rocks.The massive argillaceous dolomite(with alkali minerals)and pyroclastic rocks have the highest shale oil potential,with average oil saturation index(OSI)values of 344.67 and 124.65 mg HC/g TOC,respectively.Shale oil exploration in the representative well MY1 indicates that the Fengcheng Formation is thick and contains abundant natural fractures,brittle minerals,and mobile oil.The entire Fengcheng Formation is oilbearing and contains three concentrated stratigraphic intervals of shale oil(i.e.,sweet spots).Well MY1 indicates that,compared with source rocks developed in marine and sulfate-type saline basins,the fine-grained sedimentary rocks deposited in alkaline lacustrine environments can also have high shale oil potential.The co-existence and regular distribution of conventional and unconventional reservoirs in the Fengcheng Formation indicate that it is an ideal exploration target for multiple resource types.展开更多
Hydrocarbon-producing lacustrine basins are widely developed in the world, and China has a large number of lacustrine basins that have developed since the early Permian. The organic-rich shale-dominated heterogeneous ...Hydrocarbon-producing lacustrine basins are widely developed in the world, and China has a large number of lacustrine basins that have developed since the early Permian. The organic-rich shale-dominated heterogeneous source rock intervals in Chinese lacustrine basins generally contain frequent thin interbeds of stratigraphically associated sandstone, siltstone, marl, dolomite, and limestone. The concept of ‘‘Hybrid Plays＇ ＇ as put forth in this article recognizes this pattern of alternating organicrich shale and organic-lean interbeds and existence of mixed unconventional and conventional plays. Hybrid Plays in lacustrine source rock intervals present a unique closed petroleum system hosting continuous hydrocarbons.The interbedded organic-lean siliciclastic and/or carbonateplays are efficiently charged with hydrocarbons via short migration pathways from the adjacent organic-rich shale that is often also a self-sourced play. We assert ‘‘Hybrid Plays＇ ＇ provide the most realistic exploration model for targeting multiple-stacked and genetically related very tight shale, tight and conventional plays together in the entire source rock interval rather than individual plays only. The Hybrid Play model has been proven and works for a wide variety of lacustrine rift, sag and foreland basins in China.展开更多
Taking the mixed pre-salt carbonate rocks in the upper member of Eocene Xiaganchaigou Formation(E_(3)^(2))of Yingxi area in the Qaidam Basin as an example,the lithofacies and controlling mechanisms of reservoir format...Taking the mixed pre-salt carbonate rocks in the upper member of Eocene Xiaganchaigou Formation(E_(3)^(2))of Yingxi area in the Qaidam Basin as an example,the lithofacies and controlling mechanisms of reservoir formation are analyzed based on a large dataset of cores,thin sections and geochemical analysis.The reservoirs in E_(3)^(2)pre-salt layers have five types of lithofacies,of them,mixed granular calcareous dolostone,massive calcareous dolostone,plaque calcareous dolostone,and laminated dolomtic limestone are of sedimentary origin,and breccia calcareous dolostone is of tectonic origin.The four types of sedimentary lithofacies are divided into two types of saline sedimentary sequence lithofacies combinations,low-energy type in the sag area and low to high-energy type in the slope and paleo-uplift zone in the depression.Affected by high-frequency supply of continental clastic material,the two types of salty sedimentary sequences are mostly incomplete subtypes of lithofacies.Lithofacies have strong impacts on pre-salt reservoirs in E_(3)^(2):(1)Lithofacies type and sedimentary sequence controlled the formation and distribution of dolomite intercrystalline pores and dissolved pores during the pene-sedimentary period.(2)The structure of laminated dolomitic limestone controlled the formation of large-scale laminated fractures and high permeability channels during the diagenetic period.(3)Granular,massive,plaque calcareous dolostones have low mud content and strong brittleness,in the late tectonic reactivation period,the distribution of the three types of lithofacies,together with their distance from the top large slip faults and secondary faults,controlled the formation and distribution of high-efficiency fracture-cave brecciaed calcareous dolostone reservoirs.The above research led to the composite lithofacies-tectonic formation model of pre-salt reservoir in E_(3)^(2)of Yingxi area.The tempo-spatial distribution of tectonic breccia calcareous dolostone reservoirs,laminated dolomitic limestone shale oil reservoirs and granular,massive calcareous dolostone dissolved-intercrystalline pore tight reservoirs in various structural belts of the studied area have been figured out.These findings gave new insights into tight-shale oil accumulation theory in mixed carbonate successions from saline lacustrine basins,aiding in high efficient exploration and development of petroleum in the studied area.展开更多
The conventional lithofacies and facies model of subaerial and marine pyroclastic rocks cannot reflect the characteristics of subaqueous volcanic edifice in lacustrine basins.In order to solve this problem,the lithofa...The conventional lithofacies and facies model of subaerial and marine pyroclastic rocks cannot reflect the characteristics of subaqueous volcanic edifice in lacustrine basins.In order to solve this problem,the lithofacies of subaqueous eruptive pyroclastic rocks is discussed and the facies model is established by taking the tuff cone of Cretaceous Huoshiling Formation in the Chaganhua area of the Changling fault depression,Songliao Basin as the research object.The results indicate that the subaqueous eruptive pyroclastic rocks in the Songliao Basin can be divided into two facies and four subfacies.The two facies are the subaqueous explosive facies and the volcanic sedimentary facies that is formed during the eruption interval.The subaqueous explosive facies can be further divided into three subfacies:gas-supported hot pyroclastic flow subfacies,water-laid density current subfacies and subaqueous fallout subfacies.The volcanic sedimentary facies consists of pyroclastic sedimentary rocks containing terrigenous clast subfacies.A typical facies model of the tuff cone that is formed by subaqueous eruptions in the Songliao Basin was established.The tuff cone is generally composed of multiple subaqueous eruption depositional units and can be divided into two facies associations:near-source facies association and far-source facies association.The complete vertical succession of one depositional unit of the near-source facies association is composed of pyroclastic sedimentary rocks containing terrigenous clast subfacies,gas-supported hot pyroclastic flow subfacies,water-laid density current subfacies and subaqueous fallout subfacies from bottom to top.The depositional unit of the far-source facies association is dominated by the subaqueous fallout subfacies and contains several thin interlayered deposits of the water-laid density current subfacies.The gas-supported hot pyroclastic flow subfacies and the pyroclastic sedimentary rocks containing terrigenous clast subfacies are favorable subaqueous eruptive facies for reservoirs in continental lacustrine basins.展开更多
Compared with marine facies shale strata,lacustrine shale strata are more complicated in geological conditions,and thus more difficult to explore and develop.To realize economic exploration and development of lacustri...Compared with marine facies shale strata,lacustrine shale strata are more complicated in geological conditions,and thus more difficult to explore and develop.To realize economic exploration and development of lacustrine shale oil,the geological regularities of accumulation and high yield of retained movable petroleum in shale should be understood first.In this work,taking the shale strata of Kong 2 Member and Sha 3 Member in the Paleogene of Huanghua depression in the Bohai Bay Basin as examples,based on the previous joint analysis results of over ten thousand core samples and the latest oil testing,production test and geochemical data of more than 30 horizontal wells,accumulation conditions and models of retained movable petroleum in lacustrine shale were studied comprehensively.The study shows that at moderate organic matter abundance(with TOC from 2%to 4%),shale strata have the best match between oil content and brittleness,and thus are rich in oil and good in fracability.Moderate ancient lake basin size and moderate sediment supply intensity are the internal factors leading to best coupling of organic matter abundance and brittle mineral content in the shale formation.Moderate thermal evolution maturity of Ro of 0.7%–1.0%(at burial depth of 3200 to 4300 m)is the interval where oil generation from thermal evolution and oil adsorption by kerogen in shale layers match best,and retained movable petroleum is high in proportion.Moderate diagenetic evolution stage(3200 to 4300 m in the middle diagenetic stage A)is conducive to the formation of a large number of dissolved pores and organic matter pores,which provide storage space for shale oil enrichment.Moderate development degree of natural fractures(without damaging the shale oil roof and floor sealing conditions)is conducive to the storage,seepage and preservation of shale oil.The research results have overthrown the general understanding that high organic matter abundance,high maturity,and high development degree of natural fractures are conducive to shale oil enrichment,and have guided the comprehensive evaluation of shale oil and gas sweet spots and well deployment in the second member of the Kongdian Formation in the Cangdong sag and the Shahejie Formation in the Qikou sag.Industrial development of the shale oil in Kong 2 Member of the Cangdong sag has made major breakthrough,and important signs of shale oil have been found in Sha 3 Member of the Qikou sag,demonstrating huge exploration potential of lacustrine shale oil.展开更多
High-yielding oil wells were recently found in the first member of Paleogene Shahejie Formation,the Binhai area of Qikou Sag,providing an example of medium-and deep-buried high-quality reservoirs in the central part o...High-yielding oil wells were recently found in the first member of Paleogene Shahejie Formation,the Binhai area of Qikou Sag,providing an example of medium-and deep-buried high-quality reservoirs in the central part of a faulted lacustrine basin.By using data of cores,cast thin sections,scanning electron microscope and physical property tests,the sedimentary facies,physical properties and main control factors of the high-quality reservoirs were analyzed.The reservoirs are identified as deposits of slump-type sub-lacustrine fans,which are marked by muddy fragments,slump deformation structure and Bouma sequences in sandstones.They present mostly medium porosity and low permeability,and slightly medium porosity and high permeability.They have primary intergranular pores,intergranular and intragranular dissolution pores in feldspar and detritus grains,and structural microcracks as storage space.The main factors controlling the high quality reservoirs are as follows:(1)Favorable sedimentary microfacies of main and proximal distributary gravity flow channels.The microfacies with coarse sediment were dominated by transportation and deposition of sandy debris flow,and the effect of deposition on reservoir properties decreases with the increase of depth.(2)Medium texture maturity.It is shown by medium-sorted sandstones that were formed by beach bar sediment collapsing and redepositing,and was good for the formation of the primary intergranular pores.(3)High content of intermediate-acid volcanic rock detritus.The reservoir sandstone has high content of detritus of various components,especially intermediate-acid volcanic rock detritus,which is good for the formation of dissolution pores.(4)Organic acid corrosion.It was attributed to hydrocarbon maturity during mesodiagenetic A substage.(5)Early-forming and long lasting overpressure.A large-scale overpressure compartment was caused by under-compaction and hydrocarbon generation pressurization related to thick deep-lacustrine mudstone,and is responsible for the preservation of abundant primary pores.(6)Regional transtensional tectonic action.It resulted in the structural microcracks.展开更多
Re-Os radiometric dating of crude oil can be used to constrain the timing of hydrocarbon generation,migration or charge.This approach has been successfully applied to marine petroleum systems;however,this study report...Re-Os radiometric dating of crude oil can be used to constrain the timing of hydrocarbon generation,migration or charge.This approach has been successfully applied to marine petroleum systems;however,this study reports on its application to lacustrine-sourced natural crude oils.Oil s amples from multiple wells producing from the Cretaceous Nantun Formation in the Wuerxun-Beier depression of the Hailar Basin in NE China were analysed.Subsets of the Re-Os data are compatible with a Cretaceous hydrocarbon generation event(131.1±8.4 Ma)occurring within 10 Myr of deposition of the Nantun Formation source rocks.In addition,two younger age trends of 54±12 Ma and 1.28±0.69 Ma can be regressed from the Re-Os data,which may reflect the timing of subsequent hydrocarbon generation events.The Re-Os geochronometer,when combined with complementary age dating techniques,can provide direct temporal constraints on the evolution of petroleum system in a terrestrial basin.展开更多
Through the long development processes of reservoir sedimentation and diagenesis, acidic and alkaline fluids play key roles in controlling deep reservoir development. However, the ways in which deep fluids control and...Through the long development processes of reservoir sedimentation and diagenesis, acidic and alkaline fluids play key roles in controlling deep reservoir development. However, the ways in which deep fluids control and transform the reservoir under complex fault conditions remain unclear. In this study, a 2D model was established based on a typical sub-salt to intra-salt vertical profile in the Qaidam Basin, China. Based on measured data, multiphase flow reaction and solute transport simulation technology were used to analyze fluids flow and migration in the intra-salt and sub-salt reservoirs, determine the mineral dissolution, precipitation, and transformation in the reservoir caused by the deep fluids, and calculate the changes in reservoir porosity. Results show that deep fluid migrates preferentially along dominant channels and triggers a series of fluid–rock chemical reactions. In the first stage, a large amount of anhydrite precipitated in the fault as a result of upward migration of deep saline fluid, resulting in the formation of anhydrite veins and blockage at the base of the fault. In the second stage, organic acids caused minerals dissolution and a vertical channel was opened in previously blocked area, which promoted continuous upward migration of organic acids and the formation of secondary pores. This study clarifies the transformative effects of deep alkaline and acidic fluids on the reservoir. Moreover, the important fluid transport role of faults and their effect on reservoir development were determined.展开更多
Based on comprehensive analysis of seismic,logging,core,thin section data,and stable isotopic compositions of carbon and oxygen,the sedimentary filling characteristics of the Lower Cretaceous Barra Velha Formation seq...Based on comprehensive analysis of seismic,logging,core,thin section data,and stable isotopic compositions of carbon and oxygen,the sedimentary filling characteristics of the Lower Cretaceous Barra Velha Formation sequence in H oil field,Santos Basin,are studied,and the high-frequency sequence stratigraphic framework is established,and the spatial distribution of reef-shoal bodies are predicted and the controlling factors are discussed.During the depositional period of the Barra Velha Formation,the study area is a slope-isolated platform-slope sedimentary pattern from southwest to northeast and the change of climate background from rift to depression periods has resulted in the variation of sedimentary characteristics from the lower third-order sequence SQ1(BVE 300 Member)of low-energy deep water to the upper third-order sequence SQ2(BVE 200 and 100 members)of high-energy shallow water in the Barra Velha Formation.The activities of extensional faults and strike-slip faults in rift period and the sedimentary differentiation from platform margin to intra-platform in depression period made the sedimentary paleogeomorphology in these two periods show features of“three ridges and two depressions”.The reef-shoal bodies mainly developed in the SQ2-LHST period,with vertical development positions restricted by the periodic oscillation of the lake level,and developed on the top of each high-frequency sequence stratigraphic unit in SQ2-LHST in the platform.The strike-slip fault activity controlled the distribution of the reef-shoal bodies on the plane by changing the sedimentary paleogeomorphology.The positive flower-shaped strike-slip faults made the formation of local highlands at the margins of and inside the shallow water platforms and which became high-energy sedimentary zones,creating conditions for the development of reef-shoal bodies.展开更多
Pure shales in the first member of Qingshankou Formation(simplified as Qing 1 Member)in the southern Songliao Basin,i.e.,the semi-deep and deep lacustrine shales,are characterized by a high content of clay minerals an...Pure shales in the first member of Qingshankou Formation(simplified as Qing 1 Member)in the southern Songliao Basin,i.e.,the semi-deep and deep lacustrine shales,are characterized by a high content of clay minerals and poor hydrocarbon mobility,making the development of shale oil difficult.According to the drilling and testing results,the shale of Qing 1 Member can be classified into 3 lithofacies,i.e.,bedded argillaceous shale,laminated diamictite shale,and interbedded felsic shale.The TOC and brittle minerals control the enrichment of shale oil,of them,TOC controls the total oil content,in other words,the total oil content increases with the increase of TOC;while the laminae made up of brittle minerals contain a large number of bigger intergranular pores which are favorable enrichment space for movable shale oil.In consideration of the origins of the 3 lithofacies,two shale oil enrichment models are classified,i.e.,the deep lacustrine high-TOC bedded argillaceous shale(Model-I)and the semi-deep lacustrine moderate-high-TOC laminated diamictite shale(Model-II).In the Model-I,the shale is characterized by high hydrocarbon generation ability,high total oil content,abundant horizontal bedding fractures,and vertical and high angle fractures locally;the complex fracture network formed by horizontal bedding fractures and vertical fractures improve the storage capacity and permeability of the shale reservoir,increase the enrichment space for movable oil.In the Model-II,the shale is characterized by good hydrocarbon generation ability and fairly high total oil content,and as the brittle laminae contain large intergranular pores,the shale has a higher movable oil content.Based on the two models,shale oil sweet-spot areas of 2880 km2 in the southern Songliao Basin are favorable for further exploration.Aimed at the difficulties in reservoir fracturing of the lacustrine shale with a high content of clay minerals,the composite fracturing technology with supercritical carbon dioxide was used in the shale oil reservoir for the first time,realizing large-scale volume fracturing in shale with a high content of clay minerals and strong heterogeneity,marking a breakthrough of oil exploration in continental shale with a high content of clay minerals in China.展开更多
Alkaline-lacustrine deposition and its evolution model in Permian Fengcheng Formation at the Mahu sag, Junggar Basin were investigated through core and thin-section observation, geochemical and elemental analysis, log...Alkaline-lacustrine deposition and its evolution model in Permian Fengcheng Formation at the Mahu sag, Junggar Basin were investigated through core and thin-section observation, geochemical and elemental analysis, logging response and lithofacies identification. Six lithofacies are developed in the Fengcheng Formation. The Feng 2 Member(P1 f2) is dominated by lithofacies with alkaline minerals, while the upper part of the Feng 1 Member(P1 f1) and the lower part of the Feng 3 Member(P1 f3) are primarily organic-rich mudstones that are interbedded with dolomite and dolomitic rock. Paleoenvironment evolution of Fengcheng Formation can be divided into 5 stages, which was controlled by volcanic activity and paleoclimate. The first stage(the early phase of P1 f1) was characterized by intensive volcanic activity and arid climate, developing pyroclastics and sedimentary volcaniclastic rocks. The secondary stage(the later phase of P1 f1) had weak volcanic activity and humid climate that contributed to the development of organic-rich mudstone, forming primary source rock in the Fengcheng Formation. The increasing arid climate at the third stage(the early phase of P1 f2) resulted in shrinking of lake basin and increasing of salinity, giving rise to dolomite and dolomitic rocks. The continuous aird climate, low lake level and high salinity at the fourth stage(the later phase of P1 f2) generated special alkaline minerals, e.g., trona, indicating the formation of alkaline-lacustrine. The humid climate made lake level rise and desalted lake water, therefore, the fifth stage(P1 f3) dominated by the deposition of terrigenous clastic rocks and dolomitic rocks.展开更多
文摘Due to limited data on the geochemical properties of natural gas,estimations are needed for the effective gas source rock in evaluating gas potential.However,the pronounced heterogeneity of mudstones in lacustrine successions complicates the prediction of the presence and geochemical characteristics of gas source rocks.In this paper,the Liaohe Subbasin of Northeast China is used as an example to construct a practical methodology for locating effective gas source rocks in typical lacustrine basins.Three types of gas source rocks,microbial,oil-type,and coal-type,were distinguished according to the different genetic types of their natural gas.A practical three-dimensional geological model was developed,refined,and applied to determine the spatial distribution of the mudstones in the Western Depression of the Liaohe Subbasin and to describe the geochemical characteristics(the abundance,type,and maturation levels of the organic matter).Application of the model in the subbasin indicates that the sedimentary facies have led to heterogeneity in the mudstones,particularly with respect to organic matter types.The effective gas source rock model constructed for the Western Depression shows that the upper sequence(SQ2)of the Fourth member(Mbr 4)of the Eocene Shahejie Formation(Fm)and the lower and middle sequences(SQ3 and SQ4)of the Third member(Mbr 3)form the principal gas-generating interval.The total volume of effective gas source rocks is estimated to be 586 km^(3).The effective microbial,oil-type,and coal-type gas source rocks are primarily found in the shallow western slope,the central sags,and the eastern slope of the Western Depression,respectively.This study provides a practical approach for more accurately identifying the occurrence and geochemical characteristics of effective natural gas source rocks,enabling a precise quantitative estimation of natural gas reserves.
基金Supported by CNPC Prospective and Basic Science and Technology Major Project(2023ZZ02)Petro China Science and Technology Major Project(2021DJ0402.2021DJ0202)。
文摘The saline lacustrine hybrid sedimentary rocks are complex in lithology and unknown for their sedimentary mechanisms.The hybrid sedimentary rocks samples from the Neogene upper Ganchaigou Formation to lower Youshashan Formation(N_(1)-N_(2)^(1))in the Fengxi area Qaidam Basin,were investigated through core-log and petrology-geochemistry cross-analysis by using the core,casting thin section,scanning electron microscope,X-ray diffraction,logging,and carbon/oxygen isotopic data.The hybrid sedimentary rocks in the Fengxi area,including terrigenous clastic rock and lacustrine carbonate rock,were deposited in a shallow lake environment far from the source,or occasionally in a semi-deep lake environment,with 5 lithofacies types and 6 microfacies types recognized.Stable carbon and oxygen isotopic compositions reveal that the formation of sedimentary cycles is controlled by a climate-driven compensation-undercompensation cyclic mechanism.A sedimentary cycle model of hybrid sedimentary rocks in an arid and saline setting is proposed.According to this model,in the compensation period,the lake level rises sharply,and microfacies such as mud flat,sand-mud flat and beach are developed,with physical subsidence as the dominant sedimentary mechanism;in the undercompensation period,the lake level falls slowly,and microfacies such as lime-mud flat,lime-dolomite flat and algal mound/mat are developed,with chemical-biological process as the dominant sedimentary mechanism.In the saline lacustrine sedimentary system,lacustrine carbonate rock is mainly formed along with regression,the facies change is not interpreted by the accommodation believed traditionally,but controlled by the temporary fluctuation of lake water chemistry caused by climate change.The research results update the interpreted high-resolution sequence model and genesis of hybrid sedimentary rocks in the saline lacustrine basin and provide a valuable guidance for exploring unconventional hydrocarbons of saline lacustrine facies.
文摘Based on the studies of the Songliao Basin characterized by Cretaceous down-warping, of the Jurassic compressional flexural Junggar basin and of the Bohai Bay Basin characterized by Paleogene rifting, the multiple-grades slope break has developed in lacustrine basins of different origins. Their genetic types can be divided into tectonic slope break, depositional slope break and erodent slope break. The dominant agent of the slope break is tectogenesis, and the scale of slope breaks relates with the size of tectogenesis. The results of the study show that control of mutual grades slope breaks on atectonic traps mainly represent: 1) Atectonic traps develop close to mutual grades slope breaks, with beads-shaped distribution along the slope breaks. 2) In the longitudinal direction, the development of atectonic traps is characterized by the inheritance. 3) Different slope breaks and their different geographical positions can lead to different development types of atectonic traps. 4) A slope break can form different kinds of atectonic traps because of its great lateral variation. 5) The existence of mutual-grade slope breaks leads to different responses of erosion and deposition at different geographical positions in the basin. The oil source bed, reservoir and cap rock combination of atectonic traps is fine. 6) The oil-bearing condition of atectonic traps controlled by slope breaks is very favorable.
基金co-funded by the National Natural Science Foundation of China (41102058)the National Science and Technology Special Grant (2011ZX05006-003)the Fundamental Research Funds for the Central Universities (12CX04001A)
文摘Diagenetic traps in conglomerate in nearshore subaqueous fans in the steep slope zones of rift basins have been important exploration targets for subtle reservoirs in eastern China. However, the mechanism of how those traps were formed is not clear, which inhibits further exploration for this type of reservoir. In order to solve the problem, we take as an example nearshore subaqueous fans in the upper part of the fourth member of the Shahejie Formation （Es4s） on the north slope of the Minfeng Subsag in the Dongying Sag. Combining different research methods, such as core observation, thin section examination, scanning electron microscope （SEM） observation, fluid-inclusion analysis, carbon and oxygen isotope analysis of carbonate cements, and analysis of core properties, we studied the genetic mechanisms of diagenetic traps on the basis of diagenetic environment evolution and diagenetic evolution sequence in different sub/micro-facies. Conglomerate in Es4s in the north Minfeng Subsag experienced several periods of transition between alkaline and acidic environments as ＂alkaline-acidic-alkaline-acidic-weak alkaline＂. As a result, dissolution and cementation are also very complex, and the sequence is ＂early pyrite cementation / siderite cementation / gypsum cementation / calcite and dolomite cementation- feldspar dissolution / quartz overgrowth quartz dissolution / ferroan calcite cementation / ankerite cementation / lime-mud matrix recrystallization / feldspar overgrowth carbonate dissolution / feldspar dissolution / quartz overgrowth / pyrite cementation＂. The difference in sedimentary characteristics between different sub/micro-facies of nearshore subaqueous fans controls diagenetic characteristics. Inner fan conglomerates mainly experienced compaction and lime-mud matrix recrystallization, with weak dissolution, which led to a reduction in the porosity and permeability crucial to reservoir formation. Lime-mud matrix recrystallization results in a rapid decrease in porosity and permeability in inner fan conglomerates in middle-to-deep layers. Because acid dissolution reworks reservoirs and hydrocarbon filling inhibits cementation, reservoirs far from mudstone layers in middle fan braided channels develop a great number of primary pores and secondary pores, and are good enough to be effective reservoirs of hydrocarbon. With the increase of burial depth, both the decrease of porosity and permeability of inner fan conglomerates and the increase of the physical property difference between inner fans and middle fans enhance the quality of seals in middle-to-deep layers. As a result, inner fan conglomerates can be sealing layers in middle-to-deep buried layers. Reservoirs adjacent to mudstones in middle fan braided channels and reservoirs in middle fan interdistributaries experienced extensive cementation, and tight cemented crusts formed at both the top and bottom of conglomerates, which can then act as cap rocks. In conclusion, diagenetic traps in conglomerates of nearshore subaqueous fans could be developed with inner fan conglomerates as lateral or vertical sealing layers, tight carbonate crusts near mudstone layers in middle fan braided channels as well as lacustrine mudstones as cap rocks, and conglomerates far from mudstone layers in middle fan braided channels as reservoirs. Lime-mud matrix recrystallization of inner fan conglomerates and carbonate cementation of conglomerates adjacent to mudstone layers in middle fan braided channels took place from 32 Ma B.R to 24.6 Ma B.P., thus the formation of diagenetic traps was from 32 Ma B.R to 24.6 Ma B.R and diagenetic traps have a better hydrocarbon sealing ability from 24 Ma B.P.. The sealing ability of inner fans gradually increases with the increase of burial depth and diagenetic traps buried more than 3,200 m have better seals.
文摘Pore structure plays an important role in the gas storage and flow capacity of shale gas reservoirs. Fieldemission environmental scanning electron microscopy（FE-SEM） in combination with low-pressure carbon dioxide gas adsorption（CO2GA）,nitrogen gas adsorption（N2GA）,and high-pressure mercury intrusion（HPMI） were used to study the nanostructure pore morphology and pore-size distributions（PSDs） of lacustrine shale from the Upper Triassic Yanchang Formation,Ordos Basin. Results show that the pores in the shale reservoirs are generally nanoscale and can be classified into four types： organic,interparticle,intraparticle,and microfracture. The interparticle pores between clay particles and organic-matter pores develop most often,l with pore sizes that vary from several to more than 100 nm. Mercury porosimetry analysis shows total porosities ranging between 1.93 and 7.68%,with a mean value of 5.27%. The BET surface areas as determined by N2 adsorption in the nine samples range from 10 to 20 m2/g and the CO2 equivalent surface areas（2 nm）vary from 18 to 71 m2/g. Together,the HPMI,N2 GA,and CO2 GA curves indicate that the pore volumes are mainly due to pores 100 nm in size. In contrast,however,most of the specific surface areas are provided by the micropores. The total organic carbon（TOC） and clay minerals are the primary controls of the structures of nanoscale pores（especially micropores and mesopores）. Micropores are predominantly determined by the content of the TOC,and mesopores are possibly related to the content of clay minerals,particularly the illite-montmorillonite mixed-layer content.
文摘Three types of turbidites are identified in the studied area, including proximal turbidite along the northern steep slope （alluvial fans, fan delta, and subaqueous fans via short-distance transportation）, distal turbidites along the southern gentle slope （stacked sliding of delta and fan delta front）, and fluxoturbidite in the central depression. Detailed studies of several case histories and the relationship between sedimentary facies and faults suggest a significant role of tectonic setting and faults in the development of turbidite, which created source areas, effected slope topography, controlled the climate and paleo-environment, and formed enough slope angle and slope break for sedimentary instabilities and massive block movement to form turbidite. According to statistics, 0.86%, with an average value of 40.3%, of the trap volumes in the 69 identified Tertiary lacustrine turbidites in the Jiyang Superdepression in the Bohai Bay Basin are filled with oil. The porosity and permeability of turbidite sands vary widely. The productive reservoirs are generally those from the braided channels of both distal and proximal turbidite, and from the main channel of proximal turbidite, with a low carbonate content and the porosity and permeability higher than 12% and 1 mD respectively. Most of the lithologic oil pools in the Jiyang Superdepression are enveloped by the effective source rocks, and the percentage of the trap volume generally increases with the hydrocarbon expulsion intensity of source rocks. This is in contrast with structural-lithologic traps （i.e. proximal turbidite along the steep slope and distal turbidite along the gentle slope）, in which, graben-boundary faults play an important role in oil migration, as the turbidites are not in direct contact with effective hydrocarbon source rocks.
基金supported by the National Basic Research Program of China (Grant No. 2014CB239002)Natural Science Foundation of Shandong Province, China (Grant No. ZR2014DQ016)
文摘The genesis of the fine crystalline dolomites that exhibit good to excellent reservoir properties in the upper fourth member of the Eocene Shahejie Formation（Es4s）around the Sikou Sag, Bohai Bay Basin, is uncertain. This paper investigates the formation mechanisms of this fine crystalline dolomite using XRD, SEM, thin section analysis and geochemical data. The stratigraphy of the Sikou lacustrine carbonate is dominated by the repetition of metre-scale, high-frequency deposition cycles, and the amount of dolomite within a cycle increases upward from the cycle bottom. These dolomite crystals are 2–30 μm in length, subhedral to anhedral in shape and typically replace both grains and matrix. They also occur as rim cement and have thin lamellae within ooid cortices. Textural relations indicate that the dolomite predates equant sparry calcite cement and coarse calcite cement. The Sr concentrations of dolomites range from 900 to 1200 ppm. Dolomite δ18O values（-11.3 to-8.2 ‰ PDB） are depleted relative to calcite mudstone（-8.3 to-5.4 ‰ PDB） that precipitated from lake water, while δ13C values（0.06–1.74 ‰ PDB） are within the normal range of calcite mudstone values（-2.13 to 1.99 ‰ PDB）. High87Sr/86Sr values（0.710210–0.710844） indicate that amounts of Ca2＋ and Mg2＋have been derived from the chemical weathering of Palaeozoic carbonate bedrocks. The high strontium concentration indicates that hypersaline conditions were maintainedduring the formation of the dolomites and that the dolomites were formed by the replacement of precursor calcite or by direct precipitation.
基金This study was fnancially supported by the China Postdoctoral Science Foundation(2019M660054)Science Foundation of China University of Petroleum(Beijing)(2462019BJRC005)+3 种基金Strategic Cooperation Technology Projects of CNPC and CUPB(ZLZX2020-01-05)Natural Science Foundation of China(41872148,41872128)NSFC Basic Research Program on Deep Petroleum Resource Accumulation and Key Engineering Technologies(U19B6003-02)the Science Projects of the Sinopec Zhongyuan Oilfeld Company(P15022).
文摘Comparative analyses of petroleum generation potential,reservoir volume,frackability,and oil mobility were conducted on 102 shale cores from the Dongpu Depression.Results show the shale has high organic matter contents composed of oil-prone type I and type II kerogens within the oil window.Various types of pores and fractures exist in the shale,with a porosity of up to 14.9%.The shale has high brittle mineral contents,extensive fractures,and high potential for oil mobility due to high seepage capacity and overpressure.Although the petroleum generation potential of the shale at Well PS18-8 is relatively greater than that at Well PS18-1,oil content of the latter is greater due to the greater TOC.The porosity and fracture density observed in Well PS18-1 are greater and more conducive to shale oil enrichment.Although the shales in Wells PS18-1 and PS18-8 have similar brittle mineral contents,the former is more favorable for anthropogenic fracturing due to a higher preexisting fracture density.Besides,the shale at Well PS18-1 has a higher seepage capacity and overpressure and therefore a higher oil mobility.The fracture density and overpressure play key roles in shale oil enrichment.
基金funded by PetroChina Science and Technology Major Project(Grant No.2019E-2602)。
文摘A new type of shale oil in alkaline lacustrine sediments has been discovered in the Late Paleozoic Fengcheng Formation,Mahu Sag,Junggar Basin,China.The fine-grained sedimentary rocks deposited in this alkaline lacustrine environment can be divided into four types and eight sub-types:mudstone(with no alkali minerals),including massive dolomitic mudstone,and massive and laminated calcareous mudstone;dolomite,including massive argillaceous dolomite(with alkali minerals),and massive and laminated argillaceous dolomite(with no alkali minerals);evaporites;and pyroclastic rocks.The massive argillaceous dolomite(with alkali minerals)and pyroclastic rocks have the highest shale oil potential,with average oil saturation index(OSI)values of 344.67 and 124.65 mg HC/g TOC,respectively.Shale oil exploration in the representative well MY1 indicates that the Fengcheng Formation is thick and contains abundant natural fractures,brittle minerals,and mobile oil.The entire Fengcheng Formation is oilbearing and contains three concentrated stratigraphic intervals of shale oil(i.e.,sweet spots).Well MY1 indicates that,compared with source rocks developed in marine and sulfate-type saline basins,the fine-grained sedimentary rocks deposited in alkaline lacustrine environments can also have high shale oil potential.The co-existence and regular distribution of conventional and unconventional reservoirs in the Fengcheng Formation indicate that it is an ideal exploration target for multiple resource types.
基金National Natural Science Foundation of China (Grant Numbers 40872077 and 41272122)China National Key Technology Research and Development Program (Grant Number 2001BA605A09-1)+1 种基金Sinopec’s Petroleum Exploration and Production Research Institute (Grant No. G5800-15-ZS-WX038)EGI’s China Shale Gas and Shale Oil Plays Consortia (100980) sponsored by 20 multi-national oil companies
文摘Hydrocarbon-producing lacustrine basins are widely developed in the world, and China has a large number of lacustrine basins that have developed since the early Permian. The organic-rich shale-dominated heterogeneous source rock intervals in Chinese lacustrine basins generally contain frequent thin interbeds of stratigraphically associated sandstone, siltstone, marl, dolomite, and limestone. The concept of ‘‘Hybrid Plays＇ ＇ as put forth in this article recognizes this pattern of alternating organicrich shale and organic-lean interbeds and existence of mixed unconventional and conventional plays. Hybrid Plays in lacustrine source rock intervals present a unique closed petroleum system hosting continuous hydrocarbons.The interbedded organic-lean siliciclastic and/or carbonateplays are efficiently charged with hydrocarbons via short migration pathways from the adjacent organic-rich shale that is often also a self-sourced play. We assert ‘‘Hybrid Plays＇ ＇ provide the most realistic exploration model for targeting multiple-stacked and genetically related very tight shale, tight and conventional plays together in the entire source rock interval rather than individual plays only. The Hybrid Play model has been proven and works for a wide variety of lacustrine rift, sag and foreland basins in China.
基金Supported by the China National Science and Technology Major Project(2017ZX05001-002,2016ZX05046-006)Petro China Science and Technology Major Project(2019B-0309)。
文摘Taking the mixed pre-salt carbonate rocks in the upper member of Eocene Xiaganchaigou Formation(E_(3)^(2))of Yingxi area in the Qaidam Basin as an example,the lithofacies and controlling mechanisms of reservoir formation are analyzed based on a large dataset of cores,thin sections and geochemical analysis.The reservoirs in E_(3)^(2)pre-salt layers have five types of lithofacies,of them,mixed granular calcareous dolostone,massive calcareous dolostone,plaque calcareous dolostone,and laminated dolomtic limestone are of sedimentary origin,and breccia calcareous dolostone is of tectonic origin.The four types of sedimentary lithofacies are divided into two types of saline sedimentary sequence lithofacies combinations,low-energy type in the sag area and low to high-energy type in the slope and paleo-uplift zone in the depression.Affected by high-frequency supply of continental clastic material,the two types of salty sedimentary sequences are mostly incomplete subtypes of lithofacies.Lithofacies have strong impacts on pre-salt reservoirs in E_(3)^(2):(1)Lithofacies type and sedimentary sequence controlled the formation and distribution of dolomite intercrystalline pores and dissolved pores during the pene-sedimentary period.(2)The structure of laminated dolomitic limestone controlled the formation of large-scale laminated fractures and high permeability channels during the diagenetic period.(3)Granular,massive,plaque calcareous dolostones have low mud content and strong brittleness,in the late tectonic reactivation period,the distribution of the three types of lithofacies,together with their distance from the top large slip faults and secondary faults,controlled the formation and distribution of high-efficiency fracture-cave brecciaed calcareous dolostone reservoirs.The above research led to the composite lithofacies-tectonic formation model of pre-salt reservoir in E_(3)^(2)of Yingxi area.The tempo-spatial distribution of tectonic breccia calcareous dolostone reservoirs,laminated dolomitic limestone shale oil reservoirs and granular,massive calcareous dolostone dissolved-intercrystalline pore tight reservoirs in various structural belts of the studied area have been figured out.These findings gave new insights into tight-shale oil accumulation theory in mixed carbonate successions from saline lacustrine basins,aiding in high efficient exploration and development of petroleum in the studied area.
基金Supported by the National Natural Science Foundation of China (41790453,41972313)。
文摘The conventional lithofacies and facies model of subaerial and marine pyroclastic rocks cannot reflect the characteristics of subaqueous volcanic edifice in lacustrine basins.In order to solve this problem,the lithofacies of subaqueous eruptive pyroclastic rocks is discussed and the facies model is established by taking the tuff cone of Cretaceous Huoshiling Formation in the Chaganhua area of the Changling fault depression,Songliao Basin as the research object.The results indicate that the subaqueous eruptive pyroclastic rocks in the Songliao Basin can be divided into two facies and four subfacies.The two facies are the subaqueous explosive facies and the volcanic sedimentary facies that is formed during the eruption interval.The subaqueous explosive facies can be further divided into three subfacies:gas-supported hot pyroclastic flow subfacies,water-laid density current subfacies and subaqueous fallout subfacies.The volcanic sedimentary facies consists of pyroclastic sedimentary rocks containing terrigenous clast subfacies.A typical facies model of the tuff cone that is formed by subaqueous eruptions in the Songliao Basin was established.The tuff cone is generally composed of multiple subaqueous eruption depositional units and can be divided into two facies associations:near-source facies association and far-source facies association.The complete vertical succession of one depositional unit of the near-source facies association is composed of pyroclastic sedimentary rocks containing terrigenous clast subfacies,gas-supported hot pyroclastic flow subfacies,water-laid density current subfacies and subaqueous fallout subfacies from bottom to top.The depositional unit of the far-source facies association is dominated by the subaqueous fallout subfacies and contains several thin interlayered deposits of the water-laid density current subfacies.The gas-supported hot pyroclastic flow subfacies and the pyroclastic sedimentary rocks containing terrigenous clast subfacies are favorable subaqueous eruptive facies for reservoirs in continental lacustrine basins.
基金Supported by the PetroChina Science and Technology Major Project(2019E-2601,2018E-11)
文摘Compared with marine facies shale strata,lacustrine shale strata are more complicated in geological conditions,and thus more difficult to explore and develop.To realize economic exploration and development of lacustrine shale oil,the geological regularities of accumulation and high yield of retained movable petroleum in shale should be understood first.In this work,taking the shale strata of Kong 2 Member and Sha 3 Member in the Paleogene of Huanghua depression in the Bohai Bay Basin as examples,based on the previous joint analysis results of over ten thousand core samples and the latest oil testing,production test and geochemical data of more than 30 horizontal wells,accumulation conditions and models of retained movable petroleum in lacustrine shale were studied comprehensively.The study shows that at moderate organic matter abundance(with TOC from 2%to 4%),shale strata have the best match between oil content and brittleness,and thus are rich in oil and good in fracability.Moderate ancient lake basin size and moderate sediment supply intensity are the internal factors leading to best coupling of organic matter abundance and brittle mineral content in the shale formation.Moderate thermal evolution maturity of Ro of 0.7%–1.0%(at burial depth of 3200 to 4300 m)is the interval where oil generation from thermal evolution and oil adsorption by kerogen in shale layers match best,and retained movable petroleum is high in proportion.Moderate diagenetic evolution stage(3200 to 4300 m in the middle diagenetic stage A)is conducive to the formation of a large number of dissolved pores and organic matter pores,which provide storage space for shale oil enrichment.Moderate development degree of natural fractures(without damaging the shale oil roof and floor sealing conditions)is conducive to the storage,seepage and preservation of shale oil.The research results have overthrown the general understanding that high organic matter abundance,high maturity,and high development degree of natural fractures are conducive to shale oil enrichment,and have guided the comprehensive evaluation of shale oil and gas sweet spots and well deployment in the second member of the Kongdian Formation in the Cangdong sag and the Shahejie Formation in the Qikou sag.Industrial development of the shale oil in Kong 2 Member of the Cangdong sag has made major breakthrough,and important signs of shale oil have been found in Sha 3 Member of the Qikou sag,demonstrating huge exploration potential of lacustrine shale oil.
基金Supported by the CNPC Science and Technology Major Project(2018E-11)
文摘High-yielding oil wells were recently found in the first member of Paleogene Shahejie Formation,the Binhai area of Qikou Sag,providing an example of medium-and deep-buried high-quality reservoirs in the central part of a faulted lacustrine basin.By using data of cores,cast thin sections,scanning electron microscope and physical property tests,the sedimentary facies,physical properties and main control factors of the high-quality reservoirs were analyzed.The reservoirs are identified as deposits of slump-type sub-lacustrine fans,which are marked by muddy fragments,slump deformation structure and Bouma sequences in sandstones.They present mostly medium porosity and low permeability,and slightly medium porosity and high permeability.They have primary intergranular pores,intergranular and intragranular dissolution pores in feldspar and detritus grains,and structural microcracks as storage space.The main factors controlling the high quality reservoirs are as follows:(1)Favorable sedimentary microfacies of main and proximal distributary gravity flow channels.The microfacies with coarse sediment were dominated by transportation and deposition of sandy debris flow,and the effect of deposition on reservoir properties decreases with the increase of depth.(2)Medium texture maturity.It is shown by medium-sorted sandstones that were formed by beach bar sediment collapsing and redepositing,and was good for the formation of the primary intergranular pores.(3)High content of intermediate-acid volcanic rock detritus.The reservoir sandstone has high content of detritus of various components,especially intermediate-acid volcanic rock detritus,which is good for the formation of dissolution pores.(4)Organic acid corrosion.It was attributed to hydrocarbon maturity during mesodiagenetic A substage.(5)Early-forming and long lasting overpressure.A large-scale overpressure compartment was caused by under-compaction and hydrocarbon generation pressurization related to thick deep-lacustrine mudstone,and is responsible for the preservation of abundant primary pores.(6)Regional transtensional tectonic action.It resulted in the structural microcracks.
基金funded by Daqing Oilfield Co.,Ltd.project entitled"Geochronology and oil-source rock correlations in complex reservoirs(No.DQYT-1201002-2018-JS-150)"PetroChina Co.,Ltd.project(No.2016E-0202)。
文摘Re-Os radiometric dating of crude oil can be used to constrain the timing of hydrocarbon generation,migration or charge.This approach has been successfully applied to marine petroleum systems;however,this study reports on its application to lacustrine-sourced natural crude oils.Oil s amples from multiple wells producing from the Cretaceous Nantun Formation in the Wuerxun-Beier depression of the Hailar Basin in NE China were analysed.Subsets of the Re-Os data are compatible with a Cretaceous hydrocarbon generation event(131.1±8.4 Ma)occurring within 10 Myr of deposition of the Nantun Formation source rocks.In addition,two younger age trends of 54±12 Ma and 1.28±0.69 Ma can be regressed from the Re-Os data,which may reflect the timing of subsequent hydrocarbon generation events.The Re-Os geochronometer,when combined with complementary age dating techniques,can provide direct temporal constraints on the evolution of petroleum system in a terrestrial basin.
基金supported by the Natural Science Foundation of China(No.41902045,41702249)the Strategic Priority Research Program of the Chinese Academy of Sciences,Grant No.XDA14010401.
文摘Through the long development processes of reservoir sedimentation and diagenesis, acidic and alkaline fluids play key roles in controlling deep reservoir development. However, the ways in which deep fluids control and transform the reservoir under complex fault conditions remain unclear. In this study, a 2D model was established based on a typical sub-salt to intra-salt vertical profile in the Qaidam Basin, China. Based on measured data, multiphase flow reaction and solute transport simulation technology were used to analyze fluids flow and migration in the intra-salt and sub-salt reservoirs, determine the mineral dissolution, precipitation, and transformation in the reservoir caused by the deep fluids, and calculate the changes in reservoir porosity. Results show that deep fluid migrates preferentially along dominant channels and triggers a series of fluid–rock chemical reactions. In the first stage, a large amount of anhydrite precipitated in the fault as a result of upward migration of deep saline fluid, resulting in the formation of anhydrite veins and blockage at the base of the fault. In the second stage, organic acids caused minerals dissolution and a vertical channel was opened in previously blocked area, which promoted continuous upward migration of organic acids and the formation of secondary pores. This study clarifies the transformative effects of deep alkaline and acidic fluids on the reservoir. Moreover, the important fluid transport role of faults and their effect on reservoir development were determined.
基金Supported by the National Science and Technology Major Project of China(2016ZX05033-002-008).
文摘Based on comprehensive analysis of seismic,logging,core,thin section data,and stable isotopic compositions of carbon and oxygen,the sedimentary filling characteristics of the Lower Cretaceous Barra Velha Formation sequence in H oil field,Santos Basin,are studied,and the high-frequency sequence stratigraphic framework is established,and the spatial distribution of reef-shoal bodies are predicted and the controlling factors are discussed.During the depositional period of the Barra Velha Formation,the study area is a slope-isolated platform-slope sedimentary pattern from southwest to northeast and the change of climate background from rift to depression periods has resulted in the variation of sedimentary characteristics from the lower third-order sequence SQ1(BVE 300 Member)of low-energy deep water to the upper third-order sequence SQ2(BVE 200 and 100 members)of high-energy shallow water in the Barra Velha Formation.The activities of extensional faults and strike-slip faults in rift period and the sedimentary differentiation from platform margin to intra-platform in depression period made the sedimentary paleogeomorphology in these two periods show features of“three ridges and two depressions”.The reef-shoal bodies mainly developed in the SQ2-LHST period,with vertical development positions restricted by the periodic oscillation of the lake level,and developed on the top of each high-frequency sequence stratigraphic unit in SQ2-LHST in the platform.The strike-slip fault activity controlled the distribution of the reef-shoal bodies on the plane by changing the sedimentary paleogeomorphology.The positive flower-shaped strike-slip faults made the formation of local highlands at the margins of and inside the shallow water platforms and which became high-energy sedimentary zones,creating conditions for the development of reef-shoal bodies.
基金Supported by the China Geological Survey Project(DD20190115)
文摘Pure shales in the first member of Qingshankou Formation(simplified as Qing 1 Member)in the southern Songliao Basin,i.e.,the semi-deep and deep lacustrine shales,are characterized by a high content of clay minerals and poor hydrocarbon mobility,making the development of shale oil difficult.According to the drilling and testing results,the shale of Qing 1 Member can be classified into 3 lithofacies,i.e.,bedded argillaceous shale,laminated diamictite shale,and interbedded felsic shale.The TOC and brittle minerals control the enrichment of shale oil,of them,TOC controls the total oil content,in other words,the total oil content increases with the increase of TOC;while the laminae made up of brittle minerals contain a large number of bigger intergranular pores which are favorable enrichment space for movable shale oil.In consideration of the origins of the 3 lithofacies,two shale oil enrichment models are classified,i.e.,the deep lacustrine high-TOC bedded argillaceous shale(Model-I)and the semi-deep lacustrine moderate-high-TOC laminated diamictite shale(Model-II).In the Model-I,the shale is characterized by high hydrocarbon generation ability,high total oil content,abundant horizontal bedding fractures,and vertical and high angle fractures locally;the complex fracture network formed by horizontal bedding fractures and vertical fractures improve the storage capacity and permeability of the shale reservoir,increase the enrichment space for movable oil.In the Model-II,the shale is characterized by good hydrocarbon generation ability and fairly high total oil content,and as the brittle laminae contain large intergranular pores,the shale has a higher movable oil content.Based on the two models,shale oil sweet-spot areas of 2880 km2 in the southern Songliao Basin are favorable for further exploration.Aimed at the difficulties in reservoir fracturing of the lacustrine shale with a high content of clay minerals,the composite fracturing technology with supercritical carbon dioxide was used in the shale oil reservoir for the first time,realizing large-scale volume fracturing in shale with a high content of clay minerals and strong heterogeneity,marking a breakthrough of oil exploration in continental shale with a high content of clay minerals in China.
基金Supported by the China National Science and Technology Major Project(2017ZX05001)the PetroChina Science and Technology Major Project(2016B-0302)
文摘Alkaline-lacustrine deposition and its evolution model in Permian Fengcheng Formation at the Mahu sag, Junggar Basin were investigated through core and thin-section observation, geochemical and elemental analysis, logging response and lithofacies identification. Six lithofacies are developed in the Fengcheng Formation. The Feng 2 Member(P1 f2) is dominated by lithofacies with alkaline minerals, while the upper part of the Feng 1 Member(P1 f1) and the lower part of the Feng 3 Member(P1 f3) are primarily organic-rich mudstones that are interbedded with dolomite and dolomitic rock. Paleoenvironment evolution of Fengcheng Formation can be divided into 5 stages, which was controlled by volcanic activity and paleoclimate. The first stage(the early phase of P1 f1) was characterized by intensive volcanic activity and arid climate, developing pyroclastics and sedimentary volcaniclastic rocks. The secondary stage(the later phase of P1 f1) had weak volcanic activity and humid climate that contributed to the development of organic-rich mudstone, forming primary source rock in the Fengcheng Formation. The increasing arid climate at the third stage(the early phase of P1 f2) resulted in shrinking of lake basin and increasing of salinity, giving rise to dolomite and dolomitic rocks. The continuous aird climate, low lake level and high salinity at the fourth stage(the later phase of P1 f2) generated special alkaline minerals, e.g., trona, indicating the formation of alkaline-lacustrine. The humid climate made lake level rise and desalted lake water, therefore, the fifth stage(P1 f3) dominated by the deposition of terrigenous clastic rocks and dolomitic rocks.
