Based on the technological demands for significantly enhancing oil recovery and long-term CO_(2)sequestration in the lacustrine oil reservoirs of China,this study systematically reviews the progress and practices of C...Based on the technological demands for significantly enhancing oil recovery and long-term CO_(2)sequestration in the lacustrine oil reservoirs of China,this study systematically reviews the progress and practices of CO_(2)flooding and storage technologies in recent years.It addresses the key technological needs and challenges faced in scaling up the application of CO_(2)flooding and storage to mature,developed oil fields,and analyzes future development directions.During the pilot test phase(2006-2019),continuous development and application practices led to the establishment of the first-generation CO_(2)flooding and storage technology system for lacustrine reservoirs.In the industrialization phase(since 2020),significant advances and insights have been achieved in terms of confined phase behavior,storage mechanisms,reservoir engineering,sweep control,engineering process and storage monitoring,enabling the maturation of the second-generation CO_(2)flooding and storage theories and technologies to effectively support the demonstration projects of Carbon Capture,Utilization and Storage(CCUS).To overcome key technical issues such as low miscibility,difficulty in gas channeling control,high process requirements,limited application scenarios,and coordination challenges in CO_(2)flooding and storage,and to support the large-scale application of CCUS,it is necessary to strengthen research on key technologies for establishing the third-generation CO_(2)flooding and storage technological system incorporating miscibility enhancement and transformation,comprehensive regulation for sweep enhancement,whole-process engineering techniques and equipment,long-term storage monitoring safety,and synergistic optimization of flooding and storage.展开更多
In 2012,China's first national shale gas demonstrations areas were set up in the Sichuan Basin.After 10 years'construction and practice,the giant marine shale gas area of 10×10^(12) m^(3) level is built u...In 2012,China's first national shale gas demonstrations areas were set up in the Sichuan Basin.After 10 years'construction and practice,the giant marine shale gas area of 10×10^(12) m^(3) level is built up in the Sichuan Basin,and shale gas steps into a new stage of large-scale benefit exploration and development.In order to systematically summarize the achievements in shale gas exploration and development and provide guidance and reference for the exploration and development of deep shale gas and shale oil&gas in other areas,this paper systematically summarizes the main characteristics,development models and key identification and evaluation technologies for quality reservoirs of Wufeng Formation-Longmaxi Formation shale gas by analyzing the electric property,lithofacies,reservoir parameters and microscopic porosity of key wells in the basin.And the following research results are obtained.First,biogenetic siliceous shale,calcareous shale and mixed shale are main lithofacies types in quality shale gas reservoirs,and they are formed in the environment of semi-deep and deep water continental shelf.Their lateral distribution is controlled by the paleogeomorphology and their vertical development is influenced by provenance,redox condition and paleo productivity.They are 25-90 m thick.Second,in the quality shale gas reservoirs develop organic pores,inorganic pore and microfractures(including lamina/bedding fractures),among which,organic pore is one of the main reservoir spaces and microfracture is not only indispensable reservoir space,but also production pathway.The reservoir space of shale gas is overall micro-nano pore,and macropores play an important role in shale gas enrichment.Third,three development models of quality reservoir are established,including sedimentary type,diagenesis type and reworking type.The sedimentary type is the foundation.Multiple quality reservoirs are developed in the high U/Th interval of graptolite belt at the bottom of Longmaxi Formation,and their thickness is mainly controlled by paleogeomorphology and especially greater in the depression area.The diagenesis type is divided into three forms,i.e.,syngenetic-early diagenetic rigid support,middle-late diagenetic mineral-organic matter transformation,and overpressure relief compaction.The reworking type is dominated by quality reservoirs with microfractures.Fourth,the core technologies for identifying and evaluating quality shale gas reservoir include large-size core and rock slice observation,high-accuracy rock mineral identification,experimental gas content test and simulation,SEM microscopic characterization,3D microscopic pore reconstruction,comprehensive geophysical interpretation and prediction and big data analysis.In conclusion,nearly 10 years'research and practice achievements in demonstration area construction can deepen the understanding on domestic quality shale gas reservoirs,promote the effective development of the theories and technologies related to shale gas reservoirs,improve the prediction accuracy of shale gas sweet spot zones/intervals,and expand the shale gas exploration and development achievements of demonstration areas.展开更多
In recent years,much attention has been paid to the development environment,biogenetic compositions and hydrocarbon generation characteristics of ancient source rocks in the deep strata of the Sichuan Basin because oi...In recent years,much attention has been paid to the development environment,biogenetic compositions and hydrocarbon generation characteristics of ancient source rocks in the deep strata of the Sichuan Basin because oil and gas exploration extends continuously to the deep and ultra-deep strata and a giant gas field with the explored reserves of more than 1×10^(12)m^(3)was discovered in the Middle and Upper ProterozoiceLower Paleozoic strata in the stable inherited paleo-uplift of the central Sichuan Basin.Based on the previous geological research results,outcrop section of the Datangpo Fm,Nanhua System,at the southeastern margin of the Sichuan Basin was observed and the samples taken from the source rocks were tested and analyzed in terms of their organic geochemistry and organic petrology.It is shown that high-quality black shale source rocks of the Datangpo Fm are developed in the tensional background at the southeastern margin of the Sichuan Basin between two glacial ages,i.e.,Gucheng and Nantuo ages in the Nanhua Period.Their thickness is 16e180 m and mineral compositions are mainly clay minerals and clastic quartz.Besides,shale in the Datangpo Fm is of high-quality sapropel type source rock with high abundance at an overmature stage,and it is characterized by low pristane/phytane ratios(0.32-0.83),low gammacerane abundance,high-abundance tricyclic terpane and higher-content C_(27)and C_(29)gonane,indicating that biogenetic compositions are mainly algae and microbes in a strong reducing environment with low salinity.It is concluded that the Datangpo Fm source rocks may be developed in the rift of Nanhua System in central Sichuan Basin.Paleo-uplifts and paleo-slopes before the Caledonian are the favorable locations for the accumulation of dispersed liquid hydrocarbons and paleo-reservoirs derived from the Datangpo Fm source rocks.In addition,scale accumulation zones of dispersed organic matter cracking gas and paleo-reservoirs originated from the Datangpo Fm source rocks may be discovered in the stable area inside the Sichuan Basin.展开更多
A high-yield gasflow is produced from the dolomite reservoirs of the Ordovician Penglaiba Fm in Well Luosi 2 in the Southwest Depression of the Tarim Basin,recording as the most important major oil and gas discovery i...A high-yield gasflow is produced from the dolomite reservoirs of the Ordovician Penglaiba Fm in Well Luosi 2 in the Southwest Depression of the Tarim Basin,recording as the most important major oil and gas discovery in the Maigaiti slope in recent 20 years.In this paper,the success and failure of wells drilled into the Ordovician during the exploration in the Maigaiti slope and its periphery were analyzed to clarify the future exploration targets in this area.Then,the distribution characteristics of Ordovician limestone weathered crust and internal dolomite reservoirs were investigated,the relationship between structural traps(e.g.formation and evolution)and hydrocarbon accumulation was analyzed,and the main factors controlling the Ordovician hydrocarbon accumulation in this area were defined.Finally,the relationship between hydrocarbon distribution and Neoproterozoic rift system was discussed.Accordingly,somefindings were obtained.First,the Ordovician dolomite reservoirs are more developed than limestone reservoirs.Limestone weathered crust reservoirs of Middle Ordovician Yingshan Fm(upper member)are mainly distributed in fault zones,and their reservoir space is mainly composed of high-angle unfilled fractures.Internal dolomite reservoirs of Lower Ordovician Yingshan Fm(lower member)and Penglaiba Fm are laterally and stably distributed and their reservoir space is mainly composed of small dissolved pores which present“strings of beads”reflection characteristics on seismic profiles.Second,the Ordovician hydrocarbon is mainly discovered in the fault zones and the lithologic traps consisting of Ordovician karst dolomite reservoirs at periclines are the main exploration targets in subsequent operations.Third,the distribution of Cambrian source rocks is the key factor restricting the success rate of Ordovician oil and gas exploration.Under the control of Neoproterozoic rift system in the SW Tarim depression,the middle section of this depression is favorable for oil and gas exploration,and it includes multiple hydrocarbon source-reservoir-caprock assemblages,such as Ordovician-Upper Cambrian dolomites and Carboniferous mudstones,and Lower Cambrian dolomite and Middle Cambrian gypsum salt rocks.展开更多
In recent years,fueled by significant advancements in oil exploration technologies within the Ordos Basin,an increasing number of low-permeability or ultra-low-permeability reservoirs have been identified.Elucidating ...In recent years,fueled by significant advancements in oil exploration technologies within the Ordos Basin,an increasing number of low-permeability or ultra-low-permeability reservoirs have been identified.Elucidating their reservoir characteristics and formation mechanisms has become a critical priority for sustainable hydrocarbon development.The study focused on the Chang 6 Member of the Upper Triassic Yanchang Formation in the Heshui area of the Ordos Basin,systematically investigating its petrological features,porosity and permeability characteristics,diagenesis,and diagenetic evolution sequence.By integrating core observation,thin-section identification,and physical property measurements,a comprehensive quantitative evaluation of reservoir pore evolution was performed.These analytical outcomes were subsequently applied to simulate hydrocarbon migration and accumulation.These research results will provide a scientific basis for in-depth quantitative study of the pore evolution in ultra-low-permeability oil reservoirs and accurately constructing basin models.As indicated,the reservoir lithology in the study area predominantly comprises siltstone interbedded with mudstone or argillaceous siltstone,characterized by low porosity and permeability.Through diagenetic characteristics-based reconstruction constrained by the existing porosity data,pore evolution during diagenesis was quantitatively modeled.The simulated pore evolution aligns with actual geological observations,validating the reliability of the methodology.Furthermore,the quantified pore evolution results were applied to simulate hydrocarbon migration using PetroMod software,showing that hydrocarbon charging in the basin began at the end of the Late Jurassic(J3),peaking in hydrocarbon generation,expulsion,and accumulation by the end of the Early Cretaceous(K1)and maintaining high accumulation rates until the late Cretaceous,though significantly decreasing at the present stage.The simulation results were verified by comparison with actual drilling data,which confirms their reliability and applicability to other analogous oilfields.展开更多
To enhance the comprehension of flow characteristics and enrich the well-test theory of slanted wells,this study established a well-test model for a slanted well in a heterogeneous multi-zonal reservoir.The model cons...To enhance the comprehension of flow characteristics and enrich the well-test theory of slanted wells,this study established a well-test model for a slanted well in a heterogeneous multi-zonal reservoir.The model considered closed boundaries at both the top and bottom,as well as an external boundary with infinite,closed,or constant pressure on the horizontal plane.We took the bi-zonal composite model as an example to carry out concrete analysis.Various contemporary mathematical techniques,including Laplace integral transformation,separation of variables,and eigenfunction methods,were employed to solve the model.The pressure solution in real space was obtained through Duhamel's principle and Stehfest numerical inversion,then analytical curves created,and flow stages were defined for a slanted well in a bi-zonal composite reservoir.In addition,we performed a sensitivity analysis on some parameters affecting the curves.For a tri-zonal composite model,we also plotted the well-test curves and categorized them.Finally,we validated the model through the interpretation of an example well.The results show that the fluid flow of a slanted well in a bi-zonal composite reservoir can be divided into seven main stages,including wellbore storage effect(WSE)stage,skin effect(SE)stage,linear flow(LF)stage,radial flow(RF)stage of the 1st zone,transitional flow(TF)stage from the 1st to the 2nd zone,RF stage of the 2nd zone,and the external boundary response stage.The position of the pressure curve at the SE stage and LF stage decreases as the length and inclination angle increase.Correspondingly,the pressure curve at the RF stage of the 2nd zone and external boundary response stage decreases with increasing mobility ratio.Furthermore,as the radius of the 1st zone increases,the pressure curve at the RF stage of the 1st zone and the TF stage shifts towards the right.The established model and plotted curves provide a theoretical basis for further studies on the flow behavior of slanted wells in composite reservoirs.展开更多
The formation of Mesozoic natural gas in the Pengyang area of southwestern Ordos Basin is discussed,from the perspective of microbial community characteristics,in order to clarify the relationship between the origin o...The formation of Mesozoic natural gas in the Pengyang area of southwestern Ordos Basin is discussed,from the perspective of microbial community characteristics,in order to clarify the relationship between the origin of natural gas and its associated indigenous microbial community.The types and diversity of indigenous microbial communities associated with the oil reservoir were studied by means of collecting reservoir formation water samples from exploration wells.The indigenous microbial communities in the Chang 8 member of the Yanchang Formation were primarily distributed within Proteobacteria and Firmicutes,including the specific species and genera of Methylobacter,Pseudomonas,Haibacter,Toxobacillus,Acinetobacter and Adura actinomyces.The results of diversity analysis shows that the number of common genes was 5448,while the number of unique genes and information was less.This reflects the fact that the strata in the study area are relatively closed and not invaded by external water sources,which leads to the development of biological community diversity.In conjunction with the analysis of geochemical characteristics of oil and gas reservoirs in this area,this indicates that the study area possesses the necessary geological conditions for microbial degradation.It is the first time that the species and diversity of the indigenous microbial community in the Ordos Basin have been analyzed,showing that microbial degradation is the main cause of natural gas formation here,changes the characteristics of crude oil in this area and provides first-hand information on the impact of indigenous microorganisms on the reservoir.展开更多
Silicalites are extensively developed in the Liujiang Formation(Fm.)of the Frasnian in the Dianqiangui Basin and are often associated with carbonaceous shales.This stratigraphic combination represents a special sequen...Silicalites are extensively developed in the Liujiang Formation(Fm.)of the Frasnian in the Dianqiangui Basin and are often associated with carbonaceous shales.This stratigraphic combination represents a special sequence stratigraphy formed in special deep-water environments,which not only gives the shales unusual spatio-temporal distribution features,but also induces the shales in the Liujiang Fm.to frequently be rich in organic matter(OM).This study summarises the special deep-water sedimentary succession of the Liujiang Fm.,which is mainly distributed around synsedimentary faults,as well as establishing the sequence stratigraphic frameworks of the Liujiang Fm.in the west-east and southwest-northeast directions.Under the sequence stratigraphic frameworks,the spatio-temporal distribution features of the organic-rich shales of the Liujiang Fm.and the regional variations of the Liujiang Fm.were investigated.In addition,the rock components and OM occurrence states of the organic-rich shales were also observed and described in detail under the microscope.The results show that the organic-rich shales were formed temporally primarily during the third-order sea-level falling stage,developed spatially mainly on the east and west sides of the study area,as well as that the OM accumulation is closely related to tentaculitoids and seems to be influenced by a'biological pump'.展开更多
Connate water strongly restricts shale gas enrichment and production,and most artificially injected water is confined in shale pore networks owing to low water recovery during hydraulic fracturing,which leads to a mor...Connate water strongly restricts shale gas enrichment and production,and most artificially injected water is confined in shale pore networks owing to low water recovery during hydraulic fracturing,which leads to a more complex pore water distribution.However,previous studies have focused on the water vapor sorption of gas shales rather than liquid pore water.This study clarifies the occurrence and distribution of pore water and the controlling factors by conducting thermogravimetry(TGA)under liquid water saturation and water vapor sorption experiments on four gas shales from the Wufeng Formation in South China.Nuclear magnetic resonance(NMR)T_(2)and T_(1)-T_(2)technologies were used to monitor the dynamic changes and states of moisture,and the microscopic pore structures during water vapor sorption were detected using low-temperature nitrogen adsorption-desorption.The results indicate that TGA is adequate for determining the adsorbed,bound,and movable water contents.These four gas shales are characterized by high adsorbed and movable water contents,and some bound water.The adsorbed water primarily occurs in tiny pores(<100 nm),controlled by organic matter,followed by clay mine rals.The movable water,typically associated with quartz,primarily exists in pores of>100 nm,particularly macropores of>1000 nm.The bound water predominantly correlates with pores ranging from 10 to 2000 nm in clay minerals.The water vapor sorption process of the gas shale is well clarified.Water molecules primarily adsorb on the clay mineral's hydrophilic surface,followed by oxygen functional groups in the organic matter.Therefore,clay mine rals control water vapor sorption at low relative humidity(RH<0.75),whereas organic matter primarily affects vapor sorption at high RH.The TGA of liquid wate r-saturated gas shales can clarify the water distributions in full-scale pore networks,whereas the water vapor sorption method primarily discloses the moisture in small nanopores(<100 nm)but ignores most bound and movable water.This paper provides insight into liquid water distribution and occurre nce states within shale pore netwo rks,contributing to a better understanding of gas-wate r-rock interaction systems in-situ and hydraulic fracturing shale gas formations.展开更多
Hydrothermal Dolomite(HTD)is present in the Upper Sinian(Upper Proterozoic)Dengying Formation,east Sichuan Basin,China.The strata are comprised by primary dolomite.The HTD has various textures,including zebra dolomite...Hydrothermal Dolomite(HTD)is present in the Upper Sinian(Upper Proterozoic)Dengying Formation,east Sichuan Basin,China.The strata are comprised by primary dolomite.The HTD has various textures,including zebra dolomite,subhorizontal sheet-like cavities filled by saddle dolomite and breccias cemented by saddle dolomites as well occur as a fill of veins and fractures.Also co-occur MVT type lead-zinc ores in the study area.Theδ13C andδ18O isotopes of HTD in the Upper Sinian Dengying Formation are lighter than those of the host rocks,while STSr/86Sr is higher.The apparent difference in carbon,oxygen and strontium isotopes,especially the large difference in S7Sr/S6Sr isotopes ratio indicate crystallization from hot basinal and/or hydrothermal fluids.Saddle dolomite was precipitated at temperatures of 270-320℃.The diagenetic parasequences of mineral assemblage deposited in the Dengying Formation are:(1)dolomite host rock→sphalerite-galena-barite-fluorite;(2)dolomite host rock→saddle dolomite→quartz;(3)dolomite host rock→saddle dolomite→bitumen;(4)dolomite host rock→saddle dolomite→barite.The mean chemical composition of the host dolomite matrix and HTD didn't change much during hydrothermal process.The fluids forming the HTDs in the Dengying Formation were mixtures of freshwater from the unconformity at the top of Sinian,fluids from diagenetic compaction and hydrocarbon generation&expulsion from the Lower Cambrian Niutitang Formation mudstones or the Doushantuo Formation silty mudstones,and hydrothermal fluids from the basement.The hydrocarbon reservoirs associated with the HTD were mostly controlled by the basement faults and fractures and karsting processes at the unconformity separating Sinian and Cambrian strata.The hydrocarbon storage spaces of HTD included dissolved cavities and intercrystalline pores.Dissolution cavities are extensive at the top of Dengying Formation,up to about 46m below the unconformity between Sinian and Cambrian and were generated mainly during karstification.Hydrothermal alteration enhanced the reservoir property of the Dengying Formation dolomites with 3%-5%increase in porosity.No agreement has been reached why zebra dolomite occurs only in the Upper Sinian strata,which would indicate that HTD mineralization occurred during two different periods,each of them related to major extensional tectonic event.The early one related to the Xingkai taphrogenesis(Z2-C1)and the later one to the Emei taphrogenesis(D2-T2).But,all the data from saddle dolomite suggest that the predominant crystallization occurred during the latter event.展开更多
Based on a large number of newly added deep well data in recent years,the subsidence of the Ordos Basin in the Mid-Late Triassic is systematically studied,and it is proposed that the Ordos Basin experienced two import...Based on a large number of newly added deep well data in recent years,the subsidence of the Ordos Basin in the Mid-Late Triassic is systematically studied,and it is proposed that the Ordos Basin experienced two important subsidence events during this depositional period.Through contrastive analysis of the two stages of tectonic subsidence,including stratigraphic characteristics,lithology combination,location of catchment area and sedimentary evolution,it is proposed that both of them are responses to the Indosinian Qinling tectonic activity on the edge of the craton basin.The early subsidence occurred in the Chang 10 Member was featured by high amplitude,large debris supply and fast deposition rate,with coarse debris filling and rapid subsidence accompanied by rapid accumulation,resulting in strata thickness increasing from northeast to southwest in wedge-shape.The subsidence center was located in Huanxian–Zhenyuan–Qingyang–Zhengning areas of southwestern basin with the strata thickness of 800–1300 m.The subsidence center deviating from the depocenter developed multiple catchment areas,until then,unified lake basin has not been formed yet.Under the combined action of subsidence and Carnian heavy rainfall event during the deposition period of Chang 7 Member,a large deep-water depression was formed with slow deposition rate,and the subsidence center coincided with the depocenter basically in the Mahuangshan–Huachi–Huangling areas.The deep-water sediments were 120–320 m thick in the subsidence center,characterized by fine grain.There are differences in the mechanism between the two stages of subsidence.The early one was the response to the northward subduction of the MianLüe Ocean and intense depression under compression in Qinling during Mid-Triassic.The later subsidence is controlled by the weak extensional tectonic environment of the post-collision stage during Late Triassic.展开更多
In this study,a new adaptive morphological filter is developed based on the mathematical morphology algorithm and characteristics of the subtle differences in the waveform morphology in seismic data.The algorithm impr...In this study,a new adaptive morphological filter is developed based on the mathematical morphology algorithm and characteristics of the subtle differences in the waveform morphology in seismic data.The algorithm improves the traditional morphological dilation and corrosion operations.In this study,we propose a multiscale adaptive operator based on the principle of morphological structural“probes”and present the corresponding mathematical proof.Simulation experiments and actual seismic data processing results show that compared with traditional morphological filters,the constructed OCCO-based multistructure adaptive morphological filter can suppress noise to the greatest extent.Moreover,it can effectively improve the SNR of the images,and offers great application prospects.展开更多
The sedimentary, paleogeomorphological and reservoir characteristics of the Jurassic Yan’an Formation in the southwestern Ordos Basin, northwestern China, were studied by means of casting thin sections, scanning elec...The sedimentary, paleogeomorphological and reservoir characteristics of the Jurassic Yan’an Formation in the southwestern Ordos Basin, northwestern China, were studied by means of casting thin sections, scanning electron microscopy, inclusion analysis and identification of low-amplitude structures. A model for reservoir formation is established, and the controlling effects of sedimentary facies, paleotopography, low-amplitude structures and formation water on oil reservoirs are revealed. There are significant differences in the sedimentary characteristics, structural morphology and paleowater characteristics between the reservoirs above the Yan 10 Member and those in the Yan 9 to Yan 7 Members. The Yan 10 Member contains fluvial sediments, whereas the Yan 9 to Yan 7 members contain delta-plain anastomosing-river deposits. The distribution of high-permeability reservoir is controlled by pre-Jurassic paleogeomorphology and sedimentary facies. Some of these facies exhibit high porosity and high permeability in a lowpermeability background. The main hydrocarbon accumulation period was the late Early Cretaceous, filling was continuous, and the charging strength altered from weak to strong and then from strong to weak. The Yan 10 reservoir is mainly controlled by the paleogeomorphology: hydrocarbons migrated upward at a high speed through the unconformity surface, and accumulated in the favorable traps formed by paleogeomorphic structural units, such as gentle slopes or channel island. Furthermore, groundwater alternation in these areas was relatively stagnant, providing good reservoir preservation conditions. The reservoirs in the Yan 9 and higher members are controlled by the sedimentary facies, lowamplitude structure and paleowater characteristics. Hydrocarbons migrated through the three-dimensional delivery system, influenced by favorable sedimentary facies and high-salinity groundwater, then accumulated in the favorable low-amplitude structural traps that formed during the hydrocarbon production period.展开更多
Crude oil has been discovered in the Paleogene and Neogene units of the Weixinan Sag in the Beibu Gulf Basin.To determine the source and accumulation mode of this crude oil,12 crude oil samples and 27 source rock samp...Crude oil has been discovered in the Paleogene and Neogene units of the Weixinan Sag in the Beibu Gulf Basin.To determine the source and accumulation mode of this crude oil,12 crude oil samples and 27 source rock samples were collected and an extensive organic geochemical analysis was conducted on them.Based on the geological conditions and the analytical results,the types,origins and accumulation patterns of crude oil in the study area were elucidated.Except for a shallowly-buried and biodegraded crude oil deposit in Neogene rocks,the crude oil samples in the study area were normal.All of the crude oils were derived from lacustrine source rocks.According to biomarker compositions,the crude oils could be divided into two families,A and B,distinctions that were reinforced by differences in carbon isotope composition and spatial distribution.Oil-source correlation analysis based on biomarkers revealed that Family A oils were derived from the mature oil shale at the bottom of the second member of the Liushagang Formation,while the Family B oils formed in the mature shale of the Liushagang Formation.The Family A oils,generated by oil shale,mainly migrated laterally along sand bodies and were then redistributed in adjacent reservoirs above and below the oil shale layer,as well as in shallow layers at high structural positions,occupying a wide distribution range.The Family B oils were generated by other shale units before migrating vertically along faults to form reservoirs nearby,resulting in a narrow distribution range.展开更多
The Fengcheng Formation is a crucial source rock and the primary reservoir for oil accumulation in the Mahu Sag.Crude oils are distributed throughout the Fengcheng Formation,ranging from the edge to the interior of th...The Fengcheng Formation is a crucial source rock and the primary reservoir for oil accumulation in the Mahu Sag.Crude oils are distributed throughout the Fengcheng Formation,ranging from the edge to the interior of the sag in the southern Mahu Sag.These crude oils originate from in-situ source rocks in shallowly buried areas and the inner deep sag.During migration,the crude oil from the inner deep sag affects the source rocks close to carrier beds,leading to changes in the organic geochemical characteristics of the source rocks.These changes might alter source rock evaluations and oil-source correlation.Based on data such as total organic carbon(TOC),Rock-Eval pyrolysis of source rocks,and gas chromatography-mass spectrometry(GC-MS)of the saturated fraction,and considering the geological characteristics of the study area,we define the identification characteristics of source rock affected by migrated hydrocarbons and establish the various patterns of influence that migrated hydrocarbons have on the source rock of the Fengcheng Formation in the southern Mahu Sag.The source rocks of the Fengcheng Formation are mostly fair to good,containing mainly Type II organic matter and being thermally mature enough to generate oil.Source rocks affected by migrated hydrocarbons exhibit relatively high hydrocarbon contents(S1/TOC>110 mg HC/g TOC,Extract/TOC>30%,HC:hydrocarbon),relatively low Rock-Eval Tmax values,and relatively high tricyclic terpane contents with a descending and mountain-shaped distribution.Furthermore,biomarker composition parameters indicate a higher thermal maturity than in-situ source rocks.Through a comparison of the extract biomarker fingerprints of adjacent reservoirs and mudstones in different boreholes,three types of influence patterns of migrated hydrocarbons are identified:the edge-influence of thin sandstone-thick mudstone,the mixed-influence of sandstone-mudstone interbedded,and the full-influence of thick sandstone-thin mudstone.This finding reminds us that the influence of migrated hydrocarbons must be considered when evaluating source rocks and conducting oil-source correlation.展开更多
The discovery of unconventional hydrocarbon resources since the late 20th century changed geologists’understanding of hydrocarbon migration and accumulations and provides a solution to energy shortage.In 2016,unconve...The discovery of unconventional hydrocarbon resources since the late 20th century changed geologists’understanding of hydrocarbon migration and accumulations and provides a solution to energy shortage.In 2016,unconventional oil production in the USA accounted for 41%of the total oil production;and unconventional natural gas production in China accounted for 35%of total gas production,showing strong growth momentum of unconventional hydrocarbons explorations.Unconventional hydrocarbons generally coexist with conventional petroleum resources;they sometimes distribute in a separate system,not coexisting with a conventional system.Identification and prediction of unconventional resources and their potentials are prominent challenges for geologists.This study analyzed the results of 12,237 drilling wells in six representative petroliferous basins in China and studied the correlations and differences between conventional and unconventional hydrocarbons by comparing their geological features.Migration and accumulation of conventional hydrocarbon are caused dominantly by buoyance.Wepropose a concept of buoyance-driven hydrocarbon accumulation depth to describe the deepest hydrocarbon accumulation depth driven dominantly by buoyance;beyond this depth the buoyance becomes unimportant for hydrocarbon accumulation.We found that the buoyance-driven hydrocarbon accumulation depth in petroliferous basins controls the different oil/gas reservoirs distribution and resource potentials.Hydrocarbon migration and accumulations above this depth is dominated by buoyancy,forming conventional reservoirs in traps with high porosity and permeability,while hydrocarbon migration and accumulation below this depth is dominated by non-buoyancy forces(mainly refers to capillary force,hydrocarbon volumeexpansion force,etc.),forming unconventional reservoirs in tight layers.The buoyance-driven hydrocarbon accumulation depths in six basins in China range from 1200mto 4200 m,which become shallowerwith increasing geothermal gradient,decreasing particle size of sandstone reservoir layers,or an uplift in the whole petroliferous basin.The predicted unconventional resource potential belowthe buoyance-driven hydrocarbon accumulation depth in six basins in China is more than 15.71×10^(9) t oil equivalent,among them 4.71×10^(9) t reserves have been proved.Worldwide,94%of 52,926 oil and gas reservoirs in 1186 basins are conventional reservoirs and only 6%of them are unconventional reservoirs.These 94%conventional reservoirs show promising exploration prospects in the deep area below buoyance-driven hydrocarbon accumulation depth.展开更多
The Upper Paleogene lacustrine fine-grained sandstones in the hinterlands of the northern Qaidam Basin mainly contain two sweet spot intervals.Fracture/fault,microfacies,petrology,pore features,diagenesis,etc.,were in...The Upper Paleogene lacustrine fine-grained sandstones in the hinterlands of the northern Qaidam Basin mainly contain two sweet spot intervals.Fracture/fault,microfacies,petrology,pore features,diagenesis,etc.,were innovatively combined to confirm the controlling factors on the reservoir quality of shallow delta-lacustrine fine-grained sandstones.The diagenesis of the original lake/surface/meteoric freshwater and acidic fluids related to the faults and unconformity occurred in an open geochemical system.Comprehensive analysis shows that the Upper Paleogene fine-grained sandstones were primarily formed in the early diagenetic B substage to the middle diagenetic A substage.Reservoir quality was controlled by fault systems,microfacies,burial-thermal history,diagenesis,hydrocarbon charging events(HCE),and abnormally high pressure.Shallow and deep double fault systems are the pathways for fluid flow and hydrocarbon migration.Sandstones developed in the high energy settings such as overwater(ODC)and underwater distributary channels(UDC)provide the material foundation for reservoirs.Moderate burial depth(3000-4000 m),moderate geothermal field(2.7-3.2℃/100 m),and late HCE(later than E3)represent the important factors to protect and improve pore volume.Meteoric freshwater with high concentrations of CO_(2)and organic acids from thermal decarboxylation are the main fluids leading to the dissolution and reformation of feldspar,rock fragments,calcite and anhydrite cements.Abnormally high pressure caused by the undercompaction in a large set of argillaceous rocks is the key to form high-quality reservoirs.Abnormal pressure zones reduced and inhibited the damage of compaction and quartz overgrowth to reservoir pores,allowing them to be better preserved.A reservoir quality evaluation model with bidirectional migration pathways,rich in clay minerals,poor in cements,superimposed dissolution and abnormally high pressure was proposed for the ODC/UDC finegrained sandstones.This model will facilitate the future development of fine-grained sandstone reservoirs both in the Upper Paleogene of the Qaidam Basin and elsewhere.展开更多
Cenozoic fine-grained sedimentary rocks in the southwestern Qaidam Basin,as typical salinized lacustrine sediments,are significantly different from those in other freshwater lakes under the impact of the high salinity...Cenozoic fine-grained sedimentary rocks in the southwestern Qaidam Basin,as typical salinized lacustrine sediments,are significantly different from those in other freshwater lakes under the impact of the high salinity in the lake.Many fine-grained sedimentary rock samples were selected from the lower member of Neogene(N_(1))in the Gaskule Oilfield,Qaidam Basin,northwest China,with the aim to analyze and test their petrology,pore structure,and organic geochemical characteristics and determine its genesis and geological significance.Based on previous results,a new genesis of mixed sedimentary rocks is proposed.The Cenozoic lacustrine fine-grained sedimentary rocks in SW Qaidam Basin belong to mixed sedimentary rocks,which can be divided into three types,including carbonate and terrigenous clastic-bearing mudstone,carbonate-bearing to terrigenous clastic mixed sedimentary rocks,and carbonate-terrigenous clastic mixed sedimentary rocks.The geneses of mixing are quite different from that of mixed marine rocks.According to the sedimentary characteristics of the salinized lakes,three new geneses of mixed deposits are proposed:syn-sedimentary mixing,varve interbedded mixing,and biogenic mixing.The reservoir spaces of the Cenozoic lacustrine fine-grained sedimentary rocks in SW Qaidam Basin include residual intergranular pores,intercrystalline pores,microfractures,and minor dissolved pores.The reservoirs have super-low porosity and ultra-low permeability,with a porosity of 1.82%-21.04%,averaging 7.71%,and permeability of(0.0028-254.86)×10^(−3)μm^(2),averaging 2.82×10^(−3)μm^(2).The test results of total organic carbon(TOC)content show that the highest content of organic carbon reached 1.41%,and those of vitrinite reflectance show that Ro ranges from 0.525%-0.824%,with an average of 0.806%.The organic geochemical characteristics show that the fine-grained mixed sedimentary rocks of SW Qaidam Basin have the potential for self-generation and self-storage.As an unconventional reservoir,it has potential industrial value.This is the first study of fine-grained sedimentary rocks in the Qaidam Basin,which offers certain theoretical and practical values.展开更多
To clarify the formation and distribution of feldspar dissolution pores and predict the distribution of high-quality reservoir in gravity flow sandstone of the 7^(th) member of Triassic Yanchang Formation(Chang 7 Memb...To clarify the formation and distribution of feldspar dissolution pores and predict the distribution of high-quality reservoir in gravity flow sandstone of the 7^(th) member of Triassic Yanchang Formation(Chang 7 Member)in the Ordos Basin,thin sections,scanning electron microscopy,energy spectrum analysis,X-ray diffraction whole rock analysis,and dissolution experiments are employed in this study to investigate the characteristics and control factors of feldspar dissolution pores.The results show that:(1)Three types of diagenetic processes are observed in the feldspar of Chang 7 sandstone in the study area:secondary overgrowth of feldspar,replacement by clay and calcite,and dissolution of detrital feldspar.(2)The feldspar dissolution of Chang 7 tight sandstone is caused by organic acid,and is further affected by the type of feldspar,the degree of early feldspar alteration,and the buffering effect of mica debris on organic acid.(3)Feldspars have varying degrees of dissolution.Potassium feldspar is more susceptible to dissolution than plagioclase.Among potassium feldspar,orthoclase is more soluble than microcline,and unaltered feldspar is more soluble than early kaolinized or sericitized feldspar.(4)The dissolution experiment demonstrated that the presence of mica can hinder the dissolution of feldspar.Mica of the same mass has a significantly stronger capacity to consume organic acids than feldspar.(5)Dissolution pores in feldspar of Chang 7 Member are more abundant in areas with low mica content,and they improve the reservoir physical properties,while in areas with high mica content,the number of feldspar dissolution pores decreases significantly.展开更多
Based on the geological and geochemical analysis of potential source rocks in different formations and the classification of crude oil types,combined with the hydrocarbon generation thermal simulation experiments,the ...Based on the geological and geochemical analysis of potential source rocks in different formations and the classification of crude oil types,combined with the hydrocarbon generation thermal simulation experiments,the source,genesis,and distribution of different types of oils in the Mahu large oil province of the Junggar Basin are investigated.Four sets of potential source rocks are developed in the Mahu Sag.Specifically,the source rocks of the Permian Fengcheng Formation have the highest hydrocarbon generation potential and contain mainly TypesⅡandⅠorganic matters,with a high oil generation capacity.In contrast,the source rocks in other formations exhibit lower hydrocarbon generation potential and contain mainly TypeⅢorganic matter,with dominant gas generation.Oils in the Mahu Sag can be classified as three types:A,B and C,which display ascending,mountainous and descending C_(20)-C_(21)-C_(23)tricyclic terpenes abundance patterns in sequence,and gradually increasing relative content of tricyclic terpenes and sterane isomerization parameters,indicating an increasing oil maturity.Different types of oils are distributed spatially in an obviously orderly manner:Type A oil is close to the edge of the sag,Type C oil is concentrated in the center of the sag,and Type B oil lies in the slope area between Type A and Type C.The results of oil-source correlation and thermal simulation experiments show that the three types of oils come from the source rocks of the Fengcheng Formation at different thermal evolution stages.This new understanding of the differential genesis of oils in the Mahu Sag reasonably explains the source,distribution,and genetic mechanism of the three types of oils.The study results are of important guidance for the comprehensive and three-dimensional oil exploration,the identification of oil distribution in the total petroleum system,and the prediction of favorable exploration areas in the Mahu Sag.展开更多
基金Supported by the China National Key R&D Program(2023YFF0614100)National Science and Technology Major Project of China(2024ZD14066)+1 种基金Major Project of PetroChina Company Limited(2021ZZ01)Key R&D Project of Xinjiang Uygur Autonomous Region of China(2024B03001).
文摘Based on the technological demands for significantly enhancing oil recovery and long-term CO_(2)sequestration in the lacustrine oil reservoirs of China,this study systematically reviews the progress and practices of CO_(2)flooding and storage technologies in recent years.It addresses the key technological needs and challenges faced in scaling up the application of CO_(2)flooding and storage to mature,developed oil fields,and analyzes future development directions.During the pilot test phase(2006-2019),continuous development and application practices led to the establishment of the first-generation CO_(2)flooding and storage technology system for lacustrine reservoirs.In the industrialization phase(since 2020),significant advances and insights have been achieved in terms of confined phase behavior,storage mechanisms,reservoir engineering,sweep control,engineering process and storage monitoring,enabling the maturation of the second-generation CO_(2)flooding and storage theories and technologies to effectively support the demonstration projects of Carbon Capture,Utilization and Storage(CCUS).To overcome key technical issues such as low miscibility,difficulty in gas channeling control,high process requirements,limited application scenarios,and coordination challenges in CO_(2)flooding and storage,and to support the large-scale application of CCUS,it is necessary to strengthen research on key technologies for establishing the third-generation CO_(2)flooding and storage technological system incorporating miscibility enhancement and transformation,comprehensive regulation for sweep enhancement,whole-process engineering techniques and equipment,long-term storage monitoring safety,and synergistic optimization of flooding and storage.
文摘In 2012,China's first national shale gas demonstrations areas were set up in the Sichuan Basin.After 10 years'construction and practice,the giant marine shale gas area of 10×10^(12) m^(3) level is built up in the Sichuan Basin,and shale gas steps into a new stage of large-scale benefit exploration and development.In order to systematically summarize the achievements in shale gas exploration and development and provide guidance and reference for the exploration and development of deep shale gas and shale oil&gas in other areas,this paper systematically summarizes the main characteristics,development models and key identification and evaluation technologies for quality reservoirs of Wufeng Formation-Longmaxi Formation shale gas by analyzing the electric property,lithofacies,reservoir parameters and microscopic porosity of key wells in the basin.And the following research results are obtained.First,biogenetic siliceous shale,calcareous shale and mixed shale are main lithofacies types in quality shale gas reservoirs,and they are formed in the environment of semi-deep and deep water continental shelf.Their lateral distribution is controlled by the paleogeomorphology and their vertical development is influenced by provenance,redox condition and paleo productivity.They are 25-90 m thick.Second,in the quality shale gas reservoirs develop organic pores,inorganic pore and microfractures(including lamina/bedding fractures),among which,organic pore is one of the main reservoir spaces and microfracture is not only indispensable reservoir space,but also production pathway.The reservoir space of shale gas is overall micro-nano pore,and macropores play an important role in shale gas enrichment.Third,three development models of quality reservoir are established,including sedimentary type,diagenesis type and reworking type.The sedimentary type is the foundation.Multiple quality reservoirs are developed in the high U/Th interval of graptolite belt at the bottom of Longmaxi Formation,and their thickness is mainly controlled by paleogeomorphology and especially greater in the depression area.The diagenesis type is divided into three forms,i.e.,syngenetic-early diagenetic rigid support,middle-late diagenetic mineral-organic matter transformation,and overpressure relief compaction.The reworking type is dominated by quality reservoirs with microfractures.Fourth,the core technologies for identifying and evaluating quality shale gas reservoir include large-size core and rock slice observation,high-accuracy rock mineral identification,experimental gas content test and simulation,SEM microscopic characterization,3D microscopic pore reconstruction,comprehensive geophysical interpretation and prediction and big data analysis.In conclusion,nearly 10 years'research and practice achievements in demonstration area construction can deepen the understanding on domestic quality shale gas reservoirs,promote the effective development of the theories and technologies related to shale gas reservoirs,improve the prediction accuracy of shale gas sweet spot zones/intervals,and expand the shale gas exploration and development achievements of demonstration areas.
文摘In recent years,much attention has been paid to the development environment,biogenetic compositions and hydrocarbon generation characteristics of ancient source rocks in the deep strata of the Sichuan Basin because oil and gas exploration extends continuously to the deep and ultra-deep strata and a giant gas field with the explored reserves of more than 1×10^(12)m^(3)was discovered in the Middle and Upper ProterozoiceLower Paleozoic strata in the stable inherited paleo-uplift of the central Sichuan Basin.Based on the previous geological research results,outcrop section of the Datangpo Fm,Nanhua System,at the southeastern margin of the Sichuan Basin was observed and the samples taken from the source rocks were tested and analyzed in terms of their organic geochemistry and organic petrology.It is shown that high-quality black shale source rocks of the Datangpo Fm are developed in the tensional background at the southeastern margin of the Sichuan Basin between two glacial ages,i.e.,Gucheng and Nantuo ages in the Nanhua Period.Their thickness is 16e180 m and mineral compositions are mainly clay minerals and clastic quartz.Besides,shale in the Datangpo Fm is of high-quality sapropel type source rock with high abundance at an overmature stage,and it is characterized by low pristane/phytane ratios(0.32-0.83),low gammacerane abundance,high-abundance tricyclic terpane and higher-content C_(27)and C_(29)gonane,indicating that biogenetic compositions are mainly algae and microbes in a strong reducing environment with low salinity.It is concluded that the Datangpo Fm source rocks may be developed in the rift of Nanhua System in central Sichuan Basin.Paleo-uplifts and paleo-slopes before the Caledonian are the favorable locations for the accumulation of dispersed liquid hydrocarbons and paleo-reservoirs derived from the Datangpo Fm source rocks.In addition,scale accumulation zones of dispersed organic matter cracking gas and paleo-reservoirs originated from the Datangpo Fm source rocks may be discovered in the stable area inside the Sichuan Basin.
文摘A high-yield gasflow is produced from the dolomite reservoirs of the Ordovician Penglaiba Fm in Well Luosi 2 in the Southwest Depression of the Tarim Basin,recording as the most important major oil and gas discovery in the Maigaiti slope in recent 20 years.In this paper,the success and failure of wells drilled into the Ordovician during the exploration in the Maigaiti slope and its periphery were analyzed to clarify the future exploration targets in this area.Then,the distribution characteristics of Ordovician limestone weathered crust and internal dolomite reservoirs were investigated,the relationship between structural traps(e.g.formation and evolution)and hydrocarbon accumulation was analyzed,and the main factors controlling the Ordovician hydrocarbon accumulation in this area were defined.Finally,the relationship between hydrocarbon distribution and Neoproterozoic rift system was discussed.Accordingly,somefindings were obtained.First,the Ordovician dolomite reservoirs are more developed than limestone reservoirs.Limestone weathered crust reservoirs of Middle Ordovician Yingshan Fm(upper member)are mainly distributed in fault zones,and their reservoir space is mainly composed of high-angle unfilled fractures.Internal dolomite reservoirs of Lower Ordovician Yingshan Fm(lower member)and Penglaiba Fm are laterally and stably distributed and their reservoir space is mainly composed of small dissolved pores which present“strings of beads”reflection characteristics on seismic profiles.Second,the Ordovician hydrocarbon is mainly discovered in the fault zones and the lithologic traps consisting of Ordovician karst dolomite reservoirs at periclines are the main exploration targets in subsequent operations.Third,the distribution of Cambrian source rocks is the key factor restricting the success rate of Ordovician oil and gas exploration.Under the control of Neoproterozoic rift system in the SW Tarim depression,the middle section of this depression is favorable for oil and gas exploration,and it includes multiple hydrocarbon source-reservoir-caprock assemblages,such as Ordovician-Upper Cambrian dolomites and Carboniferous mudstones,and Lower Cambrian dolomite and Middle Cambrian gypsum salt rocks.
基金funded by National Science and Technology Major Projects(Grant No.2016ZX05050,2017ZX05001002-008)China National Petroleum Corporation Major Projects(No.2021DJ2203)Key Laboratory of Petroleum Resources Exploration and Evaluation,Gansu Province(No.KLPREEGS-2024-22)。
文摘In recent years,fueled by significant advancements in oil exploration technologies within the Ordos Basin,an increasing number of low-permeability or ultra-low-permeability reservoirs have been identified.Elucidating their reservoir characteristics and formation mechanisms has become a critical priority for sustainable hydrocarbon development.The study focused on the Chang 6 Member of the Upper Triassic Yanchang Formation in the Heshui area of the Ordos Basin,systematically investigating its petrological features,porosity and permeability characteristics,diagenesis,and diagenetic evolution sequence.By integrating core observation,thin-section identification,and physical property measurements,a comprehensive quantitative evaluation of reservoir pore evolution was performed.These analytical outcomes were subsequently applied to simulate hydrocarbon migration and accumulation.These research results will provide a scientific basis for in-depth quantitative study of the pore evolution in ultra-low-permeability oil reservoirs and accurately constructing basin models.As indicated,the reservoir lithology in the study area predominantly comprises siltstone interbedded with mudstone or argillaceous siltstone,characterized by low porosity and permeability.Through diagenetic characteristics-based reconstruction constrained by the existing porosity data,pore evolution during diagenesis was quantitatively modeled.The simulated pore evolution aligns with actual geological observations,validating the reliability of the methodology.Furthermore,the quantified pore evolution results were applied to simulate hydrocarbon migration using PetroMod software,showing that hydrocarbon charging in the basin began at the end of the Late Jurassic(J3),peaking in hydrocarbon generation,expulsion,and accumulation by the end of the Early Cretaceous(K1)and maintaining high accumulation rates until the late Cretaceous,though significantly decreasing at the present stage.The simulation results were verified by comparison with actual drilling data,which confirms their reliability and applicability to other analogous oilfields.
文摘To enhance the comprehension of flow characteristics and enrich the well-test theory of slanted wells,this study established a well-test model for a slanted well in a heterogeneous multi-zonal reservoir.The model considered closed boundaries at both the top and bottom,as well as an external boundary with infinite,closed,or constant pressure on the horizontal plane.We took the bi-zonal composite model as an example to carry out concrete analysis.Various contemporary mathematical techniques,including Laplace integral transformation,separation of variables,and eigenfunction methods,were employed to solve the model.The pressure solution in real space was obtained through Duhamel's principle and Stehfest numerical inversion,then analytical curves created,and flow stages were defined for a slanted well in a bi-zonal composite reservoir.In addition,we performed a sensitivity analysis on some parameters affecting the curves.For a tri-zonal composite model,we also plotted the well-test curves and categorized them.Finally,we validated the model through the interpretation of an example well.The results show that the fluid flow of a slanted well in a bi-zonal composite reservoir can be divided into seven main stages,including wellbore storage effect(WSE)stage,skin effect(SE)stage,linear flow(LF)stage,radial flow(RF)stage of the 1st zone,transitional flow(TF)stage from the 1st to the 2nd zone,RF stage of the 2nd zone,and the external boundary response stage.The position of the pressure curve at the SE stage and LF stage decreases as the length and inclination angle increase.Correspondingly,the pressure curve at the RF stage of the 2nd zone and external boundary response stage decreases with increasing mobility ratio.Furthermore,as the radius of the 1st zone increases,the pressure curve at the RF stage of the 1st zone and the TF stage shifts towards the right.The established model and plotted curves provide a theoretical basis for further studies on the flow behavior of slanted wells in composite reservoirs.
基金financially supported by National Science and Technology Major Projects(Grant Nos.2016ZX05050,2017ZX05001002-008)CNPC Major Projects(Grant No.2021DJ2203)The Open Fund by the State Key Laboratory of Continental Dynamics,Northwest University and the Key Laboratory for Digital Land and Resources of Jiangxi Province(Grant No.DLLJ202017)。
文摘The formation of Mesozoic natural gas in the Pengyang area of southwestern Ordos Basin is discussed,from the perspective of microbial community characteristics,in order to clarify the relationship between the origin of natural gas and its associated indigenous microbial community.The types and diversity of indigenous microbial communities associated with the oil reservoir were studied by means of collecting reservoir formation water samples from exploration wells.The indigenous microbial communities in the Chang 8 member of the Yanchang Formation were primarily distributed within Proteobacteria and Firmicutes,including the specific species and genera of Methylobacter,Pseudomonas,Haibacter,Toxobacillus,Acinetobacter and Adura actinomyces.The results of diversity analysis shows that the number of common genes was 5448,while the number of unique genes and information was less.This reflects the fact that the strata in the study area are relatively closed and not invaded by external water sources,which leads to the development of biological community diversity.In conjunction with the analysis of geochemical characteristics of oil and gas reservoirs in this area,this indicates that the study area possesses the necessary geological conditions for microbial degradation.It is the first time that the species and diversity of the indigenous microbial community in the Ordos Basin have been analyzed,showing that microbial degradation is the main cause of natural gas formation here,changes the characteristics of crude oil in this area and provides first-hand information on the impact of indigenous microorganisms on the reservoir.
基金financially supported by the Key R&D Program of Guangxi Zhuang Autonomous Region(2021AB30011)。
文摘Silicalites are extensively developed in the Liujiang Formation(Fm.)of the Frasnian in the Dianqiangui Basin and are often associated with carbonaceous shales.This stratigraphic combination represents a special sequence stratigraphy formed in special deep-water environments,which not only gives the shales unusual spatio-temporal distribution features,but also induces the shales in the Liujiang Fm.to frequently be rich in organic matter(OM).This study summarises the special deep-water sedimentary succession of the Liujiang Fm.,which is mainly distributed around synsedimentary faults,as well as establishing the sequence stratigraphic frameworks of the Liujiang Fm.in the west-east and southwest-northeast directions.Under the sequence stratigraphic frameworks,the spatio-temporal distribution features of the organic-rich shales of the Liujiang Fm.and the regional variations of the Liujiang Fm.were investigated.In addition,the rock components and OM occurrence states of the organic-rich shales were also observed and described in detail under the microscope.The results show that the organic-rich shales were formed temporally primarily during the third-order sea-level falling stage,developed spatially mainly on the east and west sides of the study area,as well as that the OM accumulation is closely related to tentaculitoids and seems to be influenced by a'biological pump'.
基金This study was financially supported by the National Natural Science Foundation of China(42302160)the PhD Scientific Research and Innovation Foundation of the Education Department of Hainan Province Joint Project of Sanya Yazhou Bay Science and Technology City(HSPHDSRF-2024-07-001)Educational Reform of Hainan Higher Education Institutions(Hnjg2024-276)。
文摘Connate water strongly restricts shale gas enrichment and production,and most artificially injected water is confined in shale pore networks owing to low water recovery during hydraulic fracturing,which leads to a more complex pore water distribution.However,previous studies have focused on the water vapor sorption of gas shales rather than liquid pore water.This study clarifies the occurrence and distribution of pore water and the controlling factors by conducting thermogravimetry(TGA)under liquid water saturation and water vapor sorption experiments on four gas shales from the Wufeng Formation in South China.Nuclear magnetic resonance(NMR)T_(2)and T_(1)-T_(2)technologies were used to monitor the dynamic changes and states of moisture,and the microscopic pore structures during water vapor sorption were detected using low-temperature nitrogen adsorption-desorption.The results indicate that TGA is adequate for determining the adsorbed,bound,and movable water contents.These four gas shales are characterized by high adsorbed and movable water contents,and some bound water.The adsorbed water primarily occurs in tiny pores(<100 nm),controlled by organic matter,followed by clay mine rals.The movable water,typically associated with quartz,primarily exists in pores of>100 nm,particularly macropores of>1000 nm.The bound water predominantly correlates with pores ranging from 10 to 2000 nm in clay minerals.The water vapor sorption process of the gas shale is well clarified.Water molecules primarily adsorb on the clay mineral's hydrophilic surface,followed by oxygen functional groups in the organic matter.Therefore,clay mine rals control water vapor sorption at low relative humidity(RH<0.75),whereas organic matter primarily affects vapor sorption at high RH.The TGA of liquid wate r-saturated gas shales can clarify the water distributions in full-scale pore networks,whereas the water vapor sorption method primarily discloses the moisture in small nanopores(<100 nm)but ignores most bound and movable water.This paper provides insight into liquid water distribution and occurre nce states within shale pore netwo rks,contributing to a better understanding of gas-wate r-rock interaction systems in-situ and hydraulic fracturing shale gas formations.
基金funded by National Basic Research Program of China(Grant No.2012CB214805)
文摘Hydrothermal Dolomite(HTD)is present in the Upper Sinian(Upper Proterozoic)Dengying Formation,east Sichuan Basin,China.The strata are comprised by primary dolomite.The HTD has various textures,including zebra dolomite,subhorizontal sheet-like cavities filled by saddle dolomite and breccias cemented by saddle dolomites as well occur as a fill of veins and fractures.Also co-occur MVT type lead-zinc ores in the study area.Theδ13C andδ18O isotopes of HTD in the Upper Sinian Dengying Formation are lighter than those of the host rocks,while STSr/86Sr is higher.The apparent difference in carbon,oxygen and strontium isotopes,especially the large difference in S7Sr/S6Sr isotopes ratio indicate crystallization from hot basinal and/or hydrothermal fluids.Saddle dolomite was precipitated at temperatures of 270-320℃.The diagenetic parasequences of mineral assemblage deposited in the Dengying Formation are:(1)dolomite host rock→sphalerite-galena-barite-fluorite;(2)dolomite host rock→saddle dolomite→quartz;(3)dolomite host rock→saddle dolomite→bitumen;(4)dolomite host rock→saddle dolomite→barite.The mean chemical composition of the host dolomite matrix and HTD didn't change much during hydrothermal process.The fluids forming the HTDs in the Dengying Formation were mixtures of freshwater from the unconformity at the top of Sinian,fluids from diagenetic compaction and hydrocarbon generation&expulsion from the Lower Cambrian Niutitang Formation mudstones or the Doushantuo Formation silty mudstones,and hydrothermal fluids from the basement.The hydrocarbon reservoirs associated with the HTD were mostly controlled by the basement faults and fractures and karsting processes at the unconformity separating Sinian and Cambrian strata.The hydrocarbon storage spaces of HTD included dissolved cavities and intercrystalline pores.Dissolution cavities are extensive at the top of Dengying Formation,up to about 46m below the unconformity between Sinian and Cambrian and were generated mainly during karstification.Hydrothermal alteration enhanced the reservoir property of the Dengying Formation dolomites with 3%-5%increase in porosity.No agreement has been reached why zebra dolomite occurs only in the Upper Sinian strata,which would indicate that HTD mineralization occurred during two different periods,each of them related to major extensional tectonic event.The early one related to the Xingkai taphrogenesis(Z2-C1)and the later one to the Emei taphrogenesis(D2-T2).But,all the data from saddle dolomite suggest that the predominant crystallization occurred during the latter event.
基金Supported by the National Science and Technology Major Project(2017ZX05001)CNPC Science and Technology Project(2021DJ22).
文摘Based on a large number of newly added deep well data in recent years,the subsidence of the Ordos Basin in the Mid-Late Triassic is systematically studied,and it is proposed that the Ordos Basin experienced two important subsidence events during this depositional period.Through contrastive analysis of the two stages of tectonic subsidence,including stratigraphic characteristics,lithology combination,location of catchment area and sedimentary evolution,it is proposed that both of them are responses to the Indosinian Qinling tectonic activity on the edge of the craton basin.The early subsidence occurred in the Chang 10 Member was featured by high amplitude,large debris supply and fast deposition rate,with coarse debris filling and rapid subsidence accompanied by rapid accumulation,resulting in strata thickness increasing from northeast to southwest in wedge-shape.The subsidence center was located in Huanxian–Zhenyuan–Qingyang–Zhengning areas of southwestern basin with the strata thickness of 800–1300 m.The subsidence center deviating from the depocenter developed multiple catchment areas,until then,unified lake basin has not been formed yet.Under the combined action of subsidence and Carnian heavy rainfall event during the deposition period of Chang 7 Member,a large deep-water depression was formed with slow deposition rate,and the subsidence center coincided with the depocenter basically in the Mahuangshan–Huachi–Huangling areas.The deep-water sediments were 120–320 m thick in the subsidence center,characterized by fine grain.There are differences in the mechanism between the two stages of subsidence.The early one was the response to the northward subduction of the MianLüe Ocean and intense depression under compression in Qinling during Mid-Triassic.The later subsidence is controlled by the weak extensional tectonic environment of the post-collision stage during Late Triassic.
基金This work was supported National Key R&D Program of China(2017YFC0601505).
文摘In this study,a new adaptive morphological filter is developed based on the mathematical morphology algorithm and characteristics of the subtle differences in the waveform morphology in seismic data.The algorithm improves the traditional morphological dilation and corrosion operations.In this study,we propose a multiscale adaptive operator based on the principle of morphological structural“probes”and present the corresponding mathematical proof.Simulation experiments and actual seismic data processing results show that compared with traditional morphological filters,the constructed OCCO-based multistructure adaptive morphological filter can suppress noise to the greatest extent.Moreover,it can effectively improve the SNR of the images,and offers great application prospects.
基金National Science and Technology Major Projects(Grant No.2016ZX05050,2017ZX05001002-008)CNPC Major Projects(Grant No.2016E-0501).
文摘The sedimentary, paleogeomorphological and reservoir characteristics of the Jurassic Yan’an Formation in the southwestern Ordos Basin, northwestern China, were studied by means of casting thin sections, scanning electron microscopy, inclusion analysis and identification of low-amplitude structures. A model for reservoir formation is established, and the controlling effects of sedimentary facies, paleotopography, low-amplitude structures and formation water on oil reservoirs are revealed. There are significant differences in the sedimentary characteristics, structural morphology and paleowater characteristics between the reservoirs above the Yan 10 Member and those in the Yan 9 to Yan 7 Members. The Yan 10 Member contains fluvial sediments, whereas the Yan 9 to Yan 7 members contain delta-plain anastomosing-river deposits. The distribution of high-permeability reservoir is controlled by pre-Jurassic paleogeomorphology and sedimentary facies. Some of these facies exhibit high porosity and high permeability in a lowpermeability background. The main hydrocarbon accumulation period was the late Early Cretaceous, filling was continuous, and the charging strength altered from weak to strong and then from strong to weak. The Yan 10 reservoir is mainly controlled by the paleogeomorphology: hydrocarbons migrated upward at a high speed through the unconformity surface, and accumulated in the favorable traps formed by paleogeomorphic structural units, such as gentle slopes or channel island. Furthermore, groundwater alternation in these areas was relatively stagnant, providing good reservoir preservation conditions. The reservoirs in the Yan 9 and higher members are controlled by the sedimentary facies, lowamplitude structure and paleowater characteristics. Hydrocarbons migrated through the three-dimensional delivery system, influenced by favorable sedimentary facies and high-salinity groundwater, then accumulated in the favorable low-amplitude structural traps that formed during the hydrocarbon production period.
文摘Crude oil has been discovered in the Paleogene and Neogene units of the Weixinan Sag in the Beibu Gulf Basin.To determine the source and accumulation mode of this crude oil,12 crude oil samples and 27 source rock samples were collected and an extensive organic geochemical analysis was conducted on them.Based on the geological conditions and the analytical results,the types,origins and accumulation patterns of crude oil in the study area were elucidated.Except for a shallowly-buried and biodegraded crude oil deposit in Neogene rocks,the crude oil samples in the study area were normal.All of the crude oils were derived from lacustrine source rocks.According to biomarker compositions,the crude oils could be divided into two families,A and B,distinctions that were reinforced by differences in carbon isotope composition and spatial distribution.Oil-source correlation analysis based on biomarkers revealed that Family A oils were derived from the mature oil shale at the bottom of the second member of the Liushagang Formation,while the Family B oils formed in the mature shale of the Liushagang Formation.The Family A oils,generated by oil shale,mainly migrated laterally along sand bodies and were then redistributed in adjacent reservoirs above and below the oil shale layer,as well as in shallow layers at high structural positions,occupying a wide distribution range.The Family B oils were generated by other shale units before migrating vertically along faults to form reservoirs nearby,resulting in a narrow distribution range.
文摘The Fengcheng Formation is a crucial source rock and the primary reservoir for oil accumulation in the Mahu Sag.Crude oils are distributed throughout the Fengcheng Formation,ranging from the edge to the interior of the sag in the southern Mahu Sag.These crude oils originate from in-situ source rocks in shallowly buried areas and the inner deep sag.During migration,the crude oil from the inner deep sag affects the source rocks close to carrier beds,leading to changes in the organic geochemical characteristics of the source rocks.These changes might alter source rock evaluations and oil-source correlation.Based on data such as total organic carbon(TOC),Rock-Eval pyrolysis of source rocks,and gas chromatography-mass spectrometry(GC-MS)of the saturated fraction,and considering the geological characteristics of the study area,we define the identification characteristics of source rock affected by migrated hydrocarbons and establish the various patterns of influence that migrated hydrocarbons have on the source rock of the Fengcheng Formation in the southern Mahu Sag.The source rocks of the Fengcheng Formation are mostly fair to good,containing mainly Type II organic matter and being thermally mature enough to generate oil.Source rocks affected by migrated hydrocarbons exhibit relatively high hydrocarbon contents(S1/TOC>110 mg HC/g TOC,Extract/TOC>30%,HC:hydrocarbon),relatively low Rock-Eval Tmax values,and relatively high tricyclic terpane contents with a descending and mountain-shaped distribution.Furthermore,biomarker composition parameters indicate a higher thermal maturity than in-situ source rocks.Through a comparison of the extract biomarker fingerprints of adjacent reservoirs and mudstones in different boreholes,three types of influence patterns of migrated hydrocarbons are identified:the edge-influence of thin sandstone-thick mudstone,the mixed-influence of sandstone-mudstone interbedded,and the full-influence of thick sandstone-thin mudstone.This finding reminds us that the influence of migrated hydrocarbons must be considered when evaluating source rocks and conducting oil-source correlation.
基金by the National Natural Science Foundation of China(No.U19B6003-02)the National Basic Research Program(973)of China(No.2011CB201100).
文摘The discovery of unconventional hydrocarbon resources since the late 20th century changed geologists’understanding of hydrocarbon migration and accumulations and provides a solution to energy shortage.In 2016,unconventional oil production in the USA accounted for 41%of the total oil production;and unconventional natural gas production in China accounted for 35%of total gas production,showing strong growth momentum of unconventional hydrocarbons explorations.Unconventional hydrocarbons generally coexist with conventional petroleum resources;they sometimes distribute in a separate system,not coexisting with a conventional system.Identification and prediction of unconventional resources and their potentials are prominent challenges for geologists.This study analyzed the results of 12,237 drilling wells in six representative petroliferous basins in China and studied the correlations and differences between conventional and unconventional hydrocarbons by comparing their geological features.Migration and accumulation of conventional hydrocarbon are caused dominantly by buoyance.Wepropose a concept of buoyance-driven hydrocarbon accumulation depth to describe the deepest hydrocarbon accumulation depth driven dominantly by buoyance;beyond this depth the buoyance becomes unimportant for hydrocarbon accumulation.We found that the buoyance-driven hydrocarbon accumulation depth in petroliferous basins controls the different oil/gas reservoirs distribution and resource potentials.Hydrocarbon migration and accumulations above this depth is dominated by buoyancy,forming conventional reservoirs in traps with high porosity and permeability,while hydrocarbon migration and accumulation below this depth is dominated by non-buoyancy forces(mainly refers to capillary force,hydrocarbon volumeexpansion force,etc.),forming unconventional reservoirs in tight layers.The buoyance-driven hydrocarbon accumulation depths in six basins in China range from 1200mto 4200 m,which become shallowerwith increasing geothermal gradient,decreasing particle size of sandstone reservoir layers,or an uplift in the whole petroliferous basin.The predicted unconventional resource potential belowthe buoyance-driven hydrocarbon accumulation depth in six basins in China is more than 15.71×10^(9) t oil equivalent,among them 4.71×10^(9) t reserves have been proved.Worldwide,94%of 52,926 oil and gas reservoirs in 1186 basins are conventional reservoirs and only 6%of them are unconventional reservoirs.These 94%conventional reservoirs show promising exploration prospects in the deep area below buoyance-driven hydrocarbon accumulation depth.
基金supported by the National Major Science and Technology Projects of China(No.2016ZX05033-001002)the National Natural Science Foundation of China(No.41272155)the China Scholarship Council。
文摘The Upper Paleogene lacustrine fine-grained sandstones in the hinterlands of the northern Qaidam Basin mainly contain two sweet spot intervals.Fracture/fault,microfacies,petrology,pore features,diagenesis,etc.,were innovatively combined to confirm the controlling factors on the reservoir quality of shallow delta-lacustrine fine-grained sandstones.The diagenesis of the original lake/surface/meteoric freshwater and acidic fluids related to the faults and unconformity occurred in an open geochemical system.Comprehensive analysis shows that the Upper Paleogene fine-grained sandstones were primarily formed in the early diagenetic B substage to the middle diagenetic A substage.Reservoir quality was controlled by fault systems,microfacies,burial-thermal history,diagenesis,hydrocarbon charging events(HCE),and abnormally high pressure.Shallow and deep double fault systems are the pathways for fluid flow and hydrocarbon migration.Sandstones developed in the high energy settings such as overwater(ODC)and underwater distributary channels(UDC)provide the material foundation for reservoirs.Moderate burial depth(3000-4000 m),moderate geothermal field(2.7-3.2℃/100 m),and late HCE(later than E3)represent the important factors to protect and improve pore volume.Meteoric freshwater with high concentrations of CO_(2)and organic acids from thermal decarboxylation are the main fluids leading to the dissolution and reformation of feldspar,rock fragments,calcite and anhydrite cements.Abnormally high pressure caused by the undercompaction in a large set of argillaceous rocks is the key to form high-quality reservoirs.Abnormal pressure zones reduced and inhibited the damage of compaction and quartz overgrowth to reservoir pores,allowing them to be better preserved.A reservoir quality evaluation model with bidirectional migration pathways,rich in clay minerals,poor in cements,superimposed dissolution and abnormally high pressure was proposed for the ODC/UDC finegrained sandstones.This model will facilitate the future development of fine-grained sandstone reservoirs both in the Upper Paleogene of the Qaidam Basin and elsewhere.
基金This work is supported by the Science and Technology Project(Grant No.2019k02)of CNPC Qinghai Oilfield Company.
文摘Cenozoic fine-grained sedimentary rocks in the southwestern Qaidam Basin,as typical salinized lacustrine sediments,are significantly different from those in other freshwater lakes under the impact of the high salinity in the lake.Many fine-grained sedimentary rock samples were selected from the lower member of Neogene(N_(1))in the Gaskule Oilfield,Qaidam Basin,northwest China,with the aim to analyze and test their petrology,pore structure,and organic geochemical characteristics and determine its genesis and geological significance.Based on previous results,a new genesis of mixed sedimentary rocks is proposed.The Cenozoic lacustrine fine-grained sedimentary rocks in SW Qaidam Basin belong to mixed sedimentary rocks,which can be divided into three types,including carbonate and terrigenous clastic-bearing mudstone,carbonate-bearing to terrigenous clastic mixed sedimentary rocks,and carbonate-terrigenous clastic mixed sedimentary rocks.The geneses of mixing are quite different from that of mixed marine rocks.According to the sedimentary characteristics of the salinized lakes,three new geneses of mixed deposits are proposed:syn-sedimentary mixing,varve interbedded mixing,and biogenic mixing.The reservoir spaces of the Cenozoic lacustrine fine-grained sedimentary rocks in SW Qaidam Basin include residual intergranular pores,intercrystalline pores,microfractures,and minor dissolved pores.The reservoirs have super-low porosity and ultra-low permeability,with a porosity of 1.82%-21.04%,averaging 7.71%,and permeability of(0.0028-254.86)×10^(−3)μm^(2),averaging 2.82×10^(−3)μm^(2).The test results of total organic carbon(TOC)content show that the highest content of organic carbon reached 1.41%,and those of vitrinite reflectance show that Ro ranges from 0.525%-0.824%,with an average of 0.806%.The organic geochemical characteristics show that the fine-grained mixed sedimentary rocks of SW Qaidam Basin have the potential for self-generation and self-storage.As an unconventional reservoir,it has potential industrial value.This is the first study of fine-grained sedimentary rocks in the Qaidam Basin,which offers certain theoretical and practical values.
基金Supported by the National Natural Science Foundation of China(42202176)CNPC-Southwest University of Petroleum Innovation Consortium Cooperation Project(2020CX050103).
文摘To clarify the formation and distribution of feldspar dissolution pores and predict the distribution of high-quality reservoir in gravity flow sandstone of the 7^(th) member of Triassic Yanchang Formation(Chang 7 Member)in the Ordos Basin,thin sections,scanning electron microscopy,energy spectrum analysis,X-ray diffraction whole rock analysis,and dissolution experiments are employed in this study to investigate the characteristics and control factors of feldspar dissolution pores.The results show that:(1)Three types of diagenetic processes are observed in the feldspar of Chang 7 sandstone in the study area:secondary overgrowth of feldspar,replacement by clay and calcite,and dissolution of detrital feldspar.(2)The feldspar dissolution of Chang 7 tight sandstone is caused by organic acid,and is further affected by the type of feldspar,the degree of early feldspar alteration,and the buffering effect of mica debris on organic acid.(3)Feldspars have varying degrees of dissolution.Potassium feldspar is more susceptible to dissolution than plagioclase.Among potassium feldspar,orthoclase is more soluble than microcline,and unaltered feldspar is more soluble than early kaolinized or sericitized feldspar.(4)The dissolution experiment demonstrated that the presence of mica can hinder the dissolution of feldspar.Mica of the same mass has a significantly stronger capacity to consume organic acids than feldspar.(5)Dissolution pores in feldspar of Chang 7 Member are more abundant in areas with low mica content,and they improve the reservoir physical properties,while in areas with high mica content,the number of feldspar dissolution pores decreases significantly.
文摘Based on the geological and geochemical analysis of potential source rocks in different formations and the classification of crude oil types,combined with the hydrocarbon generation thermal simulation experiments,the source,genesis,and distribution of different types of oils in the Mahu large oil province of the Junggar Basin are investigated.Four sets of potential source rocks are developed in the Mahu Sag.Specifically,the source rocks of the Permian Fengcheng Formation have the highest hydrocarbon generation potential and contain mainly TypesⅡandⅠorganic matters,with a high oil generation capacity.In contrast,the source rocks in other formations exhibit lower hydrocarbon generation potential and contain mainly TypeⅢorganic matter,with dominant gas generation.Oils in the Mahu Sag can be classified as three types:A,B and C,which display ascending,mountainous and descending C_(20)-C_(21)-C_(23)tricyclic terpenes abundance patterns in sequence,and gradually increasing relative content of tricyclic terpenes and sterane isomerization parameters,indicating an increasing oil maturity.Different types of oils are distributed spatially in an obviously orderly manner:Type A oil is close to the edge of the sag,Type C oil is concentrated in the center of the sag,and Type B oil lies in the slope area between Type A and Type C.The results of oil-source correlation and thermal simulation experiments show that the three types of oils come from the source rocks of the Fengcheng Formation at different thermal evolution stages.This new understanding of the differential genesis of oils in the Mahu Sag reasonably explains the source,distribution,and genetic mechanism of the three types of oils.The study results are of important guidance for the comprehensive and three-dimensional oil exploration,the identification of oil distribution in the total petroleum system,and the prediction of favorable exploration areas in the Mahu Sag.
