The Jurassic Lianggaoshan Formation in eastern Sichuan Basin is a key target for shale oil exploration.It faces challenges in three-pressure prediction due to complex structural and sedimentary interactions,as well as...The Jurassic Lianggaoshan Formation in eastern Sichuan Basin is a key target for shale oil exploration.It faces challenges in three-pressure prediction due to complex structural and sedimentary interactions,as well as strong reservoir anisotropy.These issues often lead to wellbore instability and gas logging anomalies during drilling.This study presents an integrated workflow that combines residual moveout correction using correlation-based dynamic time warping(CDTW),high-resolution seismic waveform indication inversion,and three-pressure prediction of jointing well-seismic data.Applied to the LT1 well block,the workflow effectively corrects anisotropic residual moveout in image gathers,leading to a signal strength increase of over 10%in frequency bands above 30 Hz and enhancing event continuity.High-resolution rock mechanical parameters are obtained through seismic waveform inversion and regional calibration,enabling the prediction of three-dimensional pore pressure,collapse pressure and fracture pressure.The results are consistent with actual drilling gas shows and core data,confirming the method's accuracy and supporting mud weight planning and wellbore stability efforts.This cost-effective and technically robust approach proves highly reliable in complex environments with significant heterogeneity and anisotropy,assisting drilling decisions and risk management in eastern Sichuan and similar challenging geological settings.展开更多
Based on outcrop, drilling, logging, geochemical analysis and seismic data, the karst landform and distribution of Permian volcanic rocks at the end of the sedimentary period of the Maokou Formation in the western Sic...Based on outcrop, drilling, logging, geochemical analysis and seismic data, the karst landform and distribution of Permian volcanic rocks at the end of the sedimentary period of the Maokou Formation in the western Sichuan Basin are examined, and their petroleum geological significance is discussed. Affected by normal faults formed in the early magmatic activities and extension tectonic background in the late sedimentary period of the Maokou Formation, a local karst shallow depression under the background of karst slope came up in the Jianyang area of the western Sichuan Basin, where the residual thickness of the Maokou Formation was thinner. Basic volcanic rocks like pyroclastic rock of eruptive facies, basalt of overflow facies, diabase porphyrite of intrusive facies and sedimentary tuff of volcanic sedimentary facies were formed after karstification. However, under the effects of faulting and karst paleogeomorphology, the volcanic rocks in different areas had different accumulation features. In the Jianyang area, with long eruption time, the volcanic rocks were thick and complex in lithology, and accumulated in the karst depressions. In the Zhongjiang-Santai area located in the karst slope, there’s no fault developed, only thin layers of basalt and sedimentary tuff turned up. The karst landform controls the build-up of thick explosive facies volcanic rocks and also the development of karst reservoirs in the Maokou Formation, and the western Sichuan area has oil and gas exploration potential in volcanic rocks and the Maokou Formation.展开更多
The Sichuan Basin is a major target for shale gas exploration in present China because of its rich gas stored in abundant black shales with multiple bed series.For further guidance or reference,field exploration and d...The Sichuan Basin is a major target for shale gas exploration in present China because of its rich gas stored in abundant black shales with multiple bed series.For further guidance or reference,field exploration and development practices in the shale reservoirs Upper Ordovician WufengeLower Silurian Longmaxi shale reservoirs were studied in terms of development stages and progress,favorable conditions for shale gas accumulation,bottlenecking issues on theories and technologies related to shale gas development,and so on.The following findings were obtained.(1)Shale with rich organic matters originated from the deep shelf has a good quality and great thickness in the continuous beds.The relatively stable wide buffer zones in synclines(anticlines)provides favorable conditions for shale gas accumulation and preservation with well developed micro-fractures and overpressure as necessary factors for a great potential of high shale gas productivity.(2)The bottlenecking technical issues restricting the shale gas industrial development in this study area include the following aspects:understandings of rich-organic matter shale sedimentary facies and modes,shale reservoir diagenetic process and evaluation systems,shale gas generation and accumulation mechanism,geophysical logging identification and prediction of shale gas layers,low resource utilization rate,great uncertainty of shale gas development,no technological breakthrough in the exploration of shale gas reservoirs buried deeper than 3500 m.In conclusion,this study area will be the major target for the shale gas exploration and development in China in a rather long period in the future.展开更多
Recently,a high-yield gas flow of 22.5×10^(4)m^(3)/d was achieved in the wildcat well Yongtan 1,deployed by PetroChina Southwest Oil and Gasfield Company,and an extrusive facies volcaniclastic gas reservoir was f...Recently,a high-yield gas flow of 22.5×10^(4)m^(3)/d was achieved in the wildcat well Yongtan 1,deployed by PetroChina Southwest Oil and Gasfield Company,and an extrusive facies volcaniclastic gas reservoir was first discovered in the Sichuan Basin,which is a major breakthrough in the exploration of volcanic rock gas reservoirs.In order to further evaluate the exploration potential in Permian volcanic rock gas reservoirs in this basin,we systematically reviewed and summarized the exploration process of volcanic rocks in this study area,as well as the characteristics of gas reservoirs of well Yongtan 1,the controlling factors and modes of hydrocarbon accumulation.The following findings were obtained.(1)Over the past five decades of gas exploration of volcanic rocks,the change of exploration thought and progress in seismic prediction contribute to a major discovery in this study area,i.e.,the well location deployment of Yongtan 1 was determined in the Jianyan area,where the volcanic anomalies of the Permian developed outbursts are well developed and the gas reservoir conditions are favorable.This also proves that another new gas exploration area in this basin was found.(2)From the data of Yongtan 1,we found high-quality volcanic porous reservoirs with a thickness of over 100 m developed in the Permian strata,the effusive volcanic rock types dominated by breccia and tuffaceous breccia,reservoir space composed of dissolution pores,interbreccia dissolution pores,and other pores,the porosity of which is 6.68%-13.22%and 10.26%on average,the permeability 0.01-4.43 mD and 2.35 mD on average.(3)This abnormally high pressure gas reservoir was buried 4500-6000 m deep underground with the middle formation pressure being 125.625 MPa and the pressure coefficient being up to 2.22.Methane content in the minor H_(2)S-bearing produced gas flow reached up to 99.03%.(4)Volcanic rocks in the Jianyang-Zhongjiang-Santai area are developed,and they are adjacent to the Cambrian high-quality source rocks in the Deyang-Anyue rifting.The early extensional deep faults play a role in connecting source and storage.There are many sets of caprocks,such as the Upper Permian Longtan Formation and Lower Triassic layered thick paste rocks,providing conditions for forming large-scale tectonic-lithologic composite trap gas reservoirs,and the favorable exploration area reaches up to 6000 km^(2).In conclusion,this major discovery not only proves that Permian volcanic rocks in the Sichuan Basin has large potential for oil and gas exploration,but reaffirms the confidence in changing our exploration thought,speeding up new exploration zones and areas,and discovering more and bigger gas fields.展开更多
The intraplatform shoal dolomite of the Middle Permian Qixia Formation is currently considered the key target of hydrocarbon exploration in the central Sichuan Basin. To systematically investigate the origin of the st...The intraplatform shoal dolomite of the Middle Permian Qixia Formation is currently considered the key target of hydrocarbon exploration in the central Sichuan Basin. To systematically investigate the origin of the stratabound facies-controlled porous dolomites of the Qixia Formation, integrated petrography,logging and seismic analysis were carried out in this work. The results are as following:(1) the dolomite reservoir is universal in the central Sichuan Basin, and its distribution is controlled by intraplatform shoals, with multilayer superposition vertically. Thick massive dolostone may also develop along with the fault.(2) Three replaced dolomites and one dolomite cement were identified: very finely to finely crystalline, anhedral to subhedral dolomite(Rd1);finely to medium crystalline, anhedral to subhedral dolomite(Rd2);coarsely crystalline, subhedral to euhedral dolomite(Rd3) and coarsely crystalline saddle dolomite cement(Sd). Rd2 and Rd3 are partly fabric-retentive, and preserve the original bioclastic ghosts. Sd shows wavy extinction, filled in the breccia veins.(3) The U-Pb dating and homogenization temperatures results indicate that the dolomite and Sd cement are associated with hydrothermal event during the Emeishan large igneous province. The δ^(13)C,^(87)Sr/^(86)Sr, and seawater-like REEY patterns suggest that the dolomitization and Sd precipitation fluids originate from connate seawater heated by elevated heat-flow.(4) The ELIP triggered large scale thermal anomalies in the basin during the Dongwu movement period. The increased temperature and pressure drove the formation water in the intra-platform shoal facies and overcame the binding effect of Mg^(2+) hydrate. Moreover, the deep hydrothermal fluid preferentially penetrated into the porous strata of shoal facies along the faults and fractures, mixed with formation water to some extent, and extensive dolomitization occurred. The facies-controlled dolomite reservoir and the underlying Cambrian source rock form a good source-reservoir assemblage, which can be a key replacement option.展开更多
Previously, stratigraphic evolution and sequence overlapping were represented by “substituting point for surface or multi-point for surface, line for surface or multi-line for surface”, making it difficult to accura...Previously, stratigraphic evolution and sequence overlapping were represented by “substituting point for surface or multi-point for surface, line for surface or multi-line for surface”, making it difficult to accurately reflect the stratigraphic evolution law across a larger area. We investigate the application of the seismic horizontal slice method for medium-short term stratigraphic sequence (four level), divided into reservoir group received, based on a 450 km<sup>2</sup> study area of three-dimensional (3D) seismic fine of the Sa-Pu formations west of the Daqing placanticline using a 50-millisecond horizontal slice. Sa-Pu oil layers can be divided into seven four-level sequences. We believe that a four-level sequence is more accurate in this application than in logging and data logging.展开更多
With the continued expansion of oil and gas exploration,both in the eastern and western regions,the quality of seismic acquisition has become a key factor in oil and gas exploration in complex areas.However,convention...With the continued expansion of oil and gas exploration,both in the eastern and western regions,the quality of seismic acquisition has become a key factor in oil and gas exploration in complex areas.However,conventional seismic acquisition methods cannot efficiently avoid challenging acquisition locations and produce high-quality seismic data.In this regard,based on the curvelet transform,this paper proposes an irregular seismic acquisition method,which utilizes the high-precision characteristics of the curvelet transform and simulated annealing algorithm to establish a method for the evaluation of the coherence of irregular sampling matrices and design of observation systems.The method was verified using forward simulation and actual acquisition data.The results suggest the superior quality of seismic data gathered in complicated areas through this method over those acquired using traditional methods,which can provide technical guidance for the design of observation systems in complex areas.展开更多
Dabie-type porphyry Mo deposits were proposed as a new type of porphyry Mo deposits,and had unique geological characteristics.It is still poorly understood about the magmatic processes that led to the Dabie-type Mo mi...Dabie-type porphyry Mo deposits were proposed as a new type of porphyry Mo deposits,and had unique geological characteristics.It is still poorly understood about the magmatic processes that led to the Dabie-type Mo mineralization.Here,we present zircon U-Pb and Lu-Hf isotopic,whole-rock and biotite elemental,and whole-rock Sr-Nd isotopic analyses on the Lingshan granitic batholith in the Dabie Orogen.It consists of three units(ⅠtoⅢ)that were emplaced before,genetically accompanied with,and after the Mo mineralization.LA-ICP-MS zircon U-Pb dating yielded crystallization ages of 128.2±1.0 Ma(MSWD=1.14)for UnitⅠand ages of 127.8±1.2 Ma(MSWD=0.28)and 126.6±1.8 Ma(MSWD=1.6)for UnitⅡ,indicating that they were emplaced during 130 to 125 Ma.The granites have high SiO_(2)contents(75.84 wt.%to 78.94 wt.%)and low MgO contents(0.07 wt.%to 0.10 wt.%),and are classified as fractionatedⅠ-type granite.UnitsⅠandⅡhave similar Sr-Nd isotopic ratios(ε_(Nd)(t)=-16.2 to-17.2,(^(87)Sr/^(86)Sr)_(i)=0.70540 to 0.70692)and zirconε_(Hf)(t)values(-17.4 to-20.4),indicating they were derived from partial melting of the ancient Yangtze lower crust.Mo mineralized granite from UnitⅡis characterized by the lower oxygen fugacity,fluorine enrichment and high fractionation.Magmas of unitsⅠandⅡhave experienced fractional crystallization,with the assimilation of supracrustal materials that account for the increased TiO_(2),F and Mo contents,and the decreased fO_(2).We proposed that the assimilation in upper-crustal magmatic processes plays key factors for magmatic systems that led to the Dabie-type porphyry Mo deposits.展开更多
Casing deformation is a widespread problem in a certain block of Jiaoshiba Shale Gas Field in Sichuan Basin,China,and it severely limits the development benefits of shale gas in that block.Based on the spatiotemporal ...Casing deformation is a widespread problem in a certain block of Jiaoshiba Shale Gas Field in Sichuan Basin,China,and it severely limits the development benefits of shale gas in that block.Based on the spatiotemporal characteristics of block formation,fracture development,and casing deformation occurrence,this paper employs an integrated geological—engineering research approach to identify the primary mechanisms governing casing deformation within the block and proposes countermeasures to prevent such deformation.The present research indicates the following findings:(1)The block has undergone multiple phases of tectonic superposition,with fracture development serving as the geological factor causing casing deformation.(2)Fracturing activation constitutes the engineering factor causing casing deformation,with 4 mm of formation slip inducing deformation.(3)The fracture activation risk map shows that Class Ⅰ and Class Ⅱ fractures account for 73.36%of the total recorded in the block.Within the most susceptible Class I risk zone,the critical activation pressure increment for fracturing operations ranges from 13.43 MPa to 13.99 MPa.Based on the distribution of casing failure risk zones identified in the fracture activation risk map,this paper proposes relevant technical countermeasures for preventing casing failure from three perspectives:shale gas well location deployment,drilling techniques,and fracturing techniques.These measures provide robust support for safeguarding the integrity of casing systems within the studied block.展开更多
There are abundant hydrothermal events within the Dengying Formation dolomite of the Precambrian system in southwest China.Methods including petrography identification,fluid-inclusion observation,in-situ U-Pb dating,a...There are abundant hydrothermal events within the Dengying Formation dolomite of the Precambrian system in southwest China.Methods including petrography identification,fluid-inclusion observation,in-situ U-Pb dating,and in-situ measurement of rare earth element(REE),etc.are integrated to characterize hydrothermal activity process within the Dengying Formation dolomite.The hydrothermal activity therein can be divided into four stages on the basis of in-situ U-Pb dating results of saddle dolomite cements.The 1st-stage(415.0-400.0 Ma)and 2nd-stage(259.4-248.0 Ma)hydrothermal events are characterized by saddle dolomite filling along the margin of fractures,or filling within dilational breccia and zebra textures.Compared with matrix dolomite and seawater-derived fibrous dolomite,saddle dolomite exhibits obvious negative anomalies of Ce elements.The 3rd-stage(225.6-199.0 Ma)hydrothermal event is represented by galena,sphalerite and other Mississipppi Valley-type(MVT)mineral cements in residual space.The formation of lead-zinc ore is due to the precipitation of metal sulfide caused by the thermo-chemical sulfate reduction(TSR)reaction between hydrothermal fluids and hydrocarbons during the large-scale hydrocarbon charging period.The 4th-stage(130.0-41.0 Ma)hydrothermal event is characterized by quartz and a small amount of fluorite filling the residual pores with dolomites.Quartz and fluorite record the migration of deep high-temperature hydrothermal fluid along early fractures and residual pores.During this period,the hydrothermal fluids result in the heterogeneous structure of bitumen,which is a clear response to high-temperature hydrothermal activity.展开更多
The Canglangpu Formation in the JT1 well area of the Sichuan Basin exhibits strong lateral heterogeneity and complex overpressure mechanisms, leading to ambiguous pore pressure distribution characteristics. Convention...The Canglangpu Formation in the JT1 well area of the Sichuan Basin exhibits strong lateral heterogeneity and complex overpressure mechanisms, leading to ambiguous pore pressure distribution characteristics. Conventional prediction methods, such as the Equivalent Depth Method, are either inapplicable or yield unsatisfactory results (e.g., Fillippone’s method), contributing to frequent drilling incidents like gas kick, overfl ow, and lost circulation, which hinder the safe and effi cient exploration of natural gas. To address these challenges, this paper integrates lithology, physical properties, and overpressure mechanisms of the Canglangpu Formation. From a petrophysical perspective, a pore pressure prediction model independent of lithology and overpressure mechanisms was developed by combining the poroelasticity theory, linear elastic Hooke’s Law, and Biot’s eff ective stress theory, with an analysis of the relationship between carbonate rock strain, external stress, and internal pore pressure. Unlike conventional methods, the model does not rely on the establishment of a normal compaction trend line. Pre-stack seismic inversion was applied to achieve 3D pore pressure prediction for the formation. Results indicate high accuracy, with a relative error of less than 5% compared to measured data, and strong consistency with actual drilling events. The proposed method provides robust technical support for pore pressure prediction in carbonate formations and drilling geological design.展开更多
The northern structural belt of Kuqa Depression is adjacent to the South Tianshan orogenic belt, which are characterized by complex geological conditions. The reservoir quality of the Jurassic Ahe Formation is control...The northern structural belt of Kuqa Depression is adjacent to the South Tianshan orogenic belt, which are characterized by complex geological conditions. The reservoir quality of the Jurassic Ahe Formation is controlled by sedimentation, diagenesis, and tectonics, and show complex pore structure and strong heterogeneity, thereby hindering effective natural gas exploration and development. Core, thin sections, cathodoluminescence (CL), scanning electron microscopy (SEM), conventional well logs and image logs are used to characterize the petrological characteristics and pore systems. Then a comprehensive analysis integrating sedimentation, diagenesis, and tectonics is performed to unravel the reservoir formation mechanism and distribution of reservoir quality. Results show that reservoir properties are generally environmentally selective. Coarse grained sandbodies (gravelly sandstones) formed in high depositional-energy have the best physical properties, while fine sandstone and mudstone with low depositional energy is easily to be tightly compacted, and have poor reservoir quality. Porosity usually decreases with compaction and cementation, and increases due to dissolution. Clay minerals filling pores result in a deterioration of the pore structure. Microfracture formed by fracturing can connect the matrix pores, effectively improving the reservoirs’ permeability. The differential distribution of fractures and in-situ stress plays an important role in modifying reservoir quality. The in-situ stress has obvious control over the matrix physical properties and fracture effectiveness. The matrix physical properties are negatively correlated with the value of horizontal stress difference (Δσ). As the value of Δσ increases, the pore structure becomes more complex, and the macroscopic reservoir quality becomes poor. The smaller the strike divergence between the natural fracture and SHmax, the lower the value of Δσ in the fracture layers is, and the better the fracture effectiveness is. Under the control of ternary factors on the reservoir, sedimentation-diagenesis jointly affect the matrix reservoir quality, while fractures and in-situ stress caused by tectonism affect the permeability and hydrocarbon productivity of the reservoir. Affected by ternary factors, reservoir quality and hydrocarbon productivity show obvious differences within the various structural location. Reservoir quality in tight sandstones can be predicted by integrating sedimentation, diagenesis, and tectonics (fracture and in-situ stress) in a compressional tectonic setting like Kuqa Depression. The research results will provide insights into the efficient exploration of oil and gas in Kuqa Depression as well as similar compressional tectonic settings elsewhere.展开更多
The Cretaceous Koum Basin is a rift-related half-graben in northern Cameroon,which constitutes a portion of the Yola Arm of the Upper Benue Trough.This study presents the first comprehensive dataset combining mineral-...The Cretaceous Koum Basin is a rift-related half-graben in northern Cameroon,which constitutes a portion of the Yola Arm of the Upper Benue Trough.This study presents the first comprehensive dataset combining mineral-ogical,bulk-rock geochemical,and stable C-H-O isotopic data for dark-gray,finegrained mudstones from the basin,providing new insights into its sediment source,paleoenvironment,and geodynamic setting.The mudstones primarily consist of phyllosilicates(~8.6%),feldspars(~30.5%),carbonates(~13.7%),and minor iron oxides(~2.7%),with vermiculite,illite,and kaolinite as the main clay minerals.The presence of analcime,ankerite,and dolomite suggests low-grade metamorphism and/or hydrothermal alteration.Fe_(2)O_(3)/K_(2)O(1.52-6.40)and SiO_(2)/Al_(2)O_(3)(2.97-4.68)ratios classify the mudstones as compositionally immature shales(ICV~1.64)with low-moderate chemical weathering(CIA~56.35;PIA~59.74;R^(3+)/R^(3+)+R^(2+)+M^(+)~0.51).Trace element ratios(Th/Sc~1.70,Zr/Sc~1.33,La/Sc~6.30,La/Th~4.14)indicate an intermediate igneous provenance from a continental crustal source.Paleoenviron-mental proxies suggest deposition in a dynamic basin environment marked by fluctuating redox(C org/P:0.21-178.34)and salinity(Sr/Ba:0.34-3.25;N-values:48-35.92)conditions,ranging from oxic to anoxic and brackish to saline.Major element data(SiO_(2) vs.Al_(2)O_(3)+K_(2)O+Na_(2)O)indicate a semi-arid regime,while Paleoclimatic indicators such as Sr/Cu(1.88-37.47)and C-values(0.12-0.93)suggests alter-nating humid and arid conditions.Notably,stable isotope data,reported here for the first time in the Koum Basin,reveal a predominantly terrestrial,fluvial-deltaic C_(3) plant source for organic carbon(δ^(13)C-25.2‰ to -35.2‰)and complex fluid-rock interactions involving meteoric and magmatic-metamorphic fluids under a warm,equatorial climate(δ^(18)O+3.6‰to +24.9‰,δ^(2)H-104‰ to-50‰).The combined mineralogical,geochemical,and isotopic data point to deposition in a tectonically active continental arc setting,with contributions from ocean island arc and passive margin sources.展开更多
In a very gentle platform-margin paleogeographic environment, platform-margin reef flat facies carbonate reservoir rocks were developed in the Changxing Formation of Yuanba field. Later weak structural evolution and d...In a very gentle platform-margin paleogeographic environment, platform-margin reef flat facies carbonate reservoir rocks were developed in the Changxing Formation of Yuanba field. Later weak structural evolution and diagenetic evolution caused the Changxing Formation to form lithologic traps, with good reservoirs such as dissolved bioclastic dolostone and dissolved pore dolostone. The Changxing Formation gas reservoir is a pseudo-layered porous lithologic gas reservoir under pressure depletion drive, with high H2S and moderate CO2 contents. This paper predictes that the conducting system for the Changxing Formation gas reservoir is possibly composed of the pores and microfractures in the Changxing Formation reservoir, the top erosional surface of the Changxing Formation, as well as the micropores and microfractures in the underlying formations. The Changxing Formation reservoir has experienced 3 hydrocarbon charging stages. This paper suggests that diffusion is the major formation mechanism for this gas reservoir. In the Middle and Late Yanshanian, the Yuanba area entered the major gas charging stage. The gas migrated mainly through diffusion and with the assistance of seepage flow in small faults and microfractures from the source rocks and the other oil-bearing strata to the Changxing Formation carbonate reservoir rocks, forming lithologic gas pools. In the Himalayan Epoch, the lithologic traps were uplifted as a whole without strong modification or overlapping, and were favorable for gas preservation.展开更多
Hydrothermal mineral assemblages and related hydrothermally enhanced fracturing are common in the Precambrian Dengying Formation of Central Sichuan Basin. Petrographic and geochemical analyses of core samples show tha...Hydrothermal mineral assemblages and related hydrothermally enhanced fracturing are common in the Precambrian Dengying Formation of Central Sichuan Basin. Petrographic and geochemical analyses of core samples show that the hydrothermal dolomite reservoirs of Dengying Formation consist of four main types of pores in the reservoir facies. These include: 1) hydrothermal dissolution vug(or pore), 2) intercrystalline pore, 3) residual inter-breccia vug(or pore), and 4) enlarged dissolved-fracture. There are three different fabrics dolomite in hydrothermal dolomite reservoirs, namely, saddle dolomite, fine-medium dolomite and micritic dolomite. Micritic dolomite is the original lithology of host rock. Saddle dolomite with curved or irregular crystal faces was directly crystallized from hydrothermal fluids(average temperature 192°C). Fine-medium dolomites are the products of recrystallization of micritic dolomite, resulting in abnormal geochemical characteristics, such as slight depletion of δ^(18)O, significant enrichment of Mn-Fe and ^(87)Sr/^(86)Sr, and positive Eu anomaly. A model for the distribution of various hydrothermal dolomite reservoir facies is proposed here, which incorporates three fundamental geological controls: 1) extensional tectonics and tectono-hydrothermal events(i.e., the Xingkai Taphrogenesis of Late Sinian-Early Cambrian, and Emei Taphrogenesis of Late Permian), 2) hydrothermal fluid storage in clastic rocks with large thickness(e.g., Nanhua System of Chengjiang Formation and part of Doushantuo Formation), and 3) confining bed for hydrothermal fluids(such as, the shale in Qiongzhusi Formation). The supply of hydrothermal fluid is critical. Large basement-rooted faults and associated grid-like fracture system may function as the channels for upward migration of hydrothermal fluid flow. The intersection of the above-mentioned faults(including the conversion fault), especially transtensional sags above negative flower structures on wrench faults can serve as a key target for future hydrocarbon exploration.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
Hydraulic fracturing is a key technology for the development of unconventional hydrocarbon resources.The proppant placement morphology determines the fracture conductivity,thus affecting the reservoir stimulation effe...Hydraulic fracturing is a key technology for the development of unconventional hydrocarbon resources.The proppant placement morphology determines the fracture conductivity,thus affecting the reservoir stimulation effect.In this paper,the proppant migration and placement within complex fractures was studied by considering the fracture wall roughness through computational fluid mechanics-discrete element method(CFD-DEM)in numerical simulation,which is a key approach to study the proppant migration and placement.The results show that the proppant placement non-uniformity,proppant migration capacity,and proppant volume filled in the far-end and the secondary branched fracture are enhanced within the rough fracture compared with those within smooth fractures.The proppant migration capacity is increased within the fracture at low inclination angles(<60°)and low approach angles(<90°),and the proppant placement area is larger in the inclined fracture than that in the vertical fracture.The rise of injection rate and fracturing fluid viscosity causes more proppants migrate to far-end or secondary fractures,resulting in a non-proppant area within the near-wellbore fracture.An increase by 1.3 times in the injection rate and 3 times in the fracturing fluid viscosity leads to a decrease by 26.6%and 27%,respectively,in the proppant placement area within the near-wellbore fracture.The staged injection with small size proppants followed by large size proppants increases the proppant placement area in the primary fracture by 13%-26%,and that with large size proppants followed by small size proppants increases the proppant placement area by 19%-25%,which is due to that the latter method facilitates filling of the secondary branched fracture.The injection location mainly affects the proppant filling degree within the near-wellbore fractures.Compared with the upper injection,the middle and lower injection is not beneficial to filling of proppants within the near-wellbore fracture.展开更多
Qingshankou shale(Gulong area,China)exhibits strong acoustic anisotropy characteristics,posing significant challenges to its exploration and development.In this study,the five full elastic constants and multipole resp...Qingshankou shale(Gulong area,China)exhibits strong acoustic anisotropy characteristics,posing significant challenges to its exploration and development.In this study,the five full elastic constants and multipole response law of the Qingshankou shale were studied using experimental measurements.Analyses show that the anisotropy parametersϵandγin the study region are greater than 0.4,whereas the anisotropy parameterδis smaller,generally 0.1.Numerical simulations show that the longitudinal and transverse wave velocities of these strong anisotropic rocks vary significantly with inclination angle,and significant differences in group velocity and phase velocity are also present.Acoustic logging measures the group velocity in dipped boreholes;this differs from the phase velocity to some extent.As the dip angle increases,the longitudinal and SH wave velocities increase accordingly,while the qSV-wave velocity initially increases and then decreases,reaching its maximum value at a dip of approximately 40°.These results provide an effective guide for the correction and modeling of acoustic logging time differences in the region.展开更多
Walkaway VSP cannot obtain accurate velocity field,as it asymmetrically reflects ray path and provides uneven coverage to underground target,thereby presenting issues related to imaging quality.In this study,we propos...Walkaway VSP cannot obtain accurate velocity field,as it asymmetrically reflects ray path and provides uneven coverage to underground target,thereby presenting issues related to imaging quality.In this study,we propose combining traveltime tomography and prestack depth migration for VSP of an angle-domain walkaway,in a bid to establish accurate two-dimensional and three-dimensional(3 D)velocity models.First,residual curvature was defined to update velocity,and an accurate velocity field was established.To establish a high-precision velocity model,we deduced the relationship between the residual depth and traveltime of common imaging gathers(CIGs)in walkaway VSP.Solving renewal velocity using the least squares method,a four-parameter tomographic inversion equation was derived comprising formation dip angle,incidence angle,residual depth,and sensitivity matrix.In the angle domain,the reflected wave was divided into up-and down-transmitted waves and their traveltimes were calculated.The systematic cumulative method was employed in prestack depth migration of a complex surface.Through prestack depth migration,the offset-domain CIGs were obtained,and dip angle was established by defining the stack section horizon.Runge–Kutta ray tracing was employed to calculate the ray path from the reflection point to the detection point,to determine the incident angle,and to subsequently calculate the ray path from the reflection point to the irregular surface.The offset-domain residual depths were mapped to the angle domain,and a new tomographic equation was established and solved.Application in the double complex area of the Tarim Basin showed the four-parameter tomographic inversion equation derived in this paper to be both correct and practical and that the migration algorithm was able to adapt to the complex surface.展开更多
INTRODUCTION Distributed acoustic sensing(DAS)is a novel and popular technology for vertical seismic profile(VSP)data acquisition because of its many advantages,including full vertical coverage,high sampling density,l...INTRODUCTION Distributed acoustic sensing(DAS)is a novel and popular technology for vertical seismic profile(VSP)data acquisition because of its many advantages,including full vertical coverage,high sampling density,low cost,and resistance to stressors(high temperature and pressure).The current industrial application of DAS in borehole exploration acquires single-mode fibers.It records strain rates,which are then converted to particle velocities by the modem before being written to the disk.展开更多
基金supported by Science and Technology Cooperation Project of the CNPC-SWPU Innovation Alliance(No.2020CX010202).
文摘The Jurassic Lianggaoshan Formation in eastern Sichuan Basin is a key target for shale oil exploration.It faces challenges in three-pressure prediction due to complex structural and sedimentary interactions,as well as strong reservoir anisotropy.These issues often lead to wellbore instability and gas logging anomalies during drilling.This study presents an integrated workflow that combines residual moveout correction using correlation-based dynamic time warping(CDTW),high-resolution seismic waveform indication inversion,and three-pressure prediction of jointing well-seismic data.Applied to the LT1 well block,the workflow effectively corrects anisotropic residual moveout in image gathers,leading to a signal strength increase of over 10%in frequency bands above 30 Hz and enhancing event continuity.High-resolution rock mechanical parameters are obtained through seismic waveform inversion and regional calibration,enabling the prediction of three-dimensional pore pressure,collapse pressure and fracture pressure.The results are consistent with actual drilling gas shows and core data,confirming the method's accuracy and supporting mud weight planning and wellbore stability efforts.This cost-effective and technically robust approach proves highly reliable in complex environments with significant heterogeneity and anisotropy,assisting drilling decisions and risk management in eastern Sichuan and similar challenging geological settings.
基金Supported by the National Major Science and Technology Project(2016ZX05007004)PetroChina Southwest Oil&Gas Field Branch Company Science and Technology Project(2019ZD01)。
文摘Based on outcrop, drilling, logging, geochemical analysis and seismic data, the karst landform and distribution of Permian volcanic rocks at the end of the sedimentary period of the Maokou Formation in the western Sichuan Basin are examined, and their petroleum geological significance is discussed. Affected by normal faults formed in the early magmatic activities and extension tectonic background in the late sedimentary period of the Maokou Formation, a local karst shallow depression under the background of karst slope came up in the Jianyang area of the western Sichuan Basin, where the residual thickness of the Maokou Formation was thinner. Basic volcanic rocks like pyroclastic rock of eruptive facies, basalt of overflow facies, diabase porphyrite of intrusive facies and sedimentary tuff of volcanic sedimentary facies were formed after karstification. However, under the effects of faulting and karst paleogeomorphology, the volcanic rocks in different areas had different accumulation features. In the Jianyang area, with long eruption time, the volcanic rocks were thick and complex in lithology, and accumulated in the karst depressions. In the Zhongjiang-Santai area located in the karst slope, there’s no fault developed, only thin layers of basalt and sedimentary tuff turned up. The karst landform controls the build-up of thick explosive facies volcanic rocks and also the development of karst reservoirs in the Maokou Formation, and the western Sichuan area has oil and gas exploration potential in volcanic rocks and the Maokou Formation.
基金supported by the National Major Science and Technology Project“A Study on Formation and Enrichment Law,Selection Evaluation Technology and Application of Shale Gas in the Sichuan Basin and Its Periphery”(No.2017ZX05035).
文摘The Sichuan Basin is a major target for shale gas exploration in present China because of its rich gas stored in abundant black shales with multiple bed series.For further guidance or reference,field exploration and development practices in the shale reservoirs Upper Ordovician WufengeLower Silurian Longmaxi shale reservoirs were studied in terms of development stages and progress,favorable conditions for shale gas accumulation,bottlenecking issues on theories and technologies related to shale gas development,and so on.The following findings were obtained.(1)Shale with rich organic matters originated from the deep shelf has a good quality and great thickness in the continuous beds.The relatively stable wide buffer zones in synclines(anticlines)provides favorable conditions for shale gas accumulation and preservation with well developed micro-fractures and overpressure as necessary factors for a great potential of high shale gas productivity.(2)The bottlenecking technical issues restricting the shale gas industrial development in this study area include the following aspects:understandings of rich-organic matter shale sedimentary facies and modes,shale reservoir diagenetic process and evaluation systems,shale gas generation and accumulation mechanism,geophysical logging identification and prediction of shale gas layers,low resource utilization rate,great uncertainty of shale gas development,no technological breakthrough in the exploration of shale gas reservoirs buried deeper than 3500 m.In conclusion,this study area will be the major target for the shale gas exploration and development in China in a rather long period in the future.
基金supported by the Major Science&Technology Special Project of PetroChina Company Limited“Research and Application of Key Technologies for 300×10^(8) m^(3) Gas Productivity in Southwest Oil&Gasfield”(No.:2016E-0604).
文摘Recently,a high-yield gas flow of 22.5×10^(4)m^(3)/d was achieved in the wildcat well Yongtan 1,deployed by PetroChina Southwest Oil and Gasfield Company,and an extrusive facies volcaniclastic gas reservoir was first discovered in the Sichuan Basin,which is a major breakthrough in the exploration of volcanic rock gas reservoirs.In order to further evaluate the exploration potential in Permian volcanic rock gas reservoirs in this basin,we systematically reviewed and summarized the exploration process of volcanic rocks in this study area,as well as the characteristics of gas reservoirs of well Yongtan 1,the controlling factors and modes of hydrocarbon accumulation.The following findings were obtained.(1)Over the past five decades of gas exploration of volcanic rocks,the change of exploration thought and progress in seismic prediction contribute to a major discovery in this study area,i.e.,the well location deployment of Yongtan 1 was determined in the Jianyan area,where the volcanic anomalies of the Permian developed outbursts are well developed and the gas reservoir conditions are favorable.This also proves that another new gas exploration area in this basin was found.(2)From the data of Yongtan 1,we found high-quality volcanic porous reservoirs with a thickness of over 100 m developed in the Permian strata,the effusive volcanic rock types dominated by breccia and tuffaceous breccia,reservoir space composed of dissolution pores,interbreccia dissolution pores,and other pores,the porosity of which is 6.68%-13.22%and 10.26%on average,the permeability 0.01-4.43 mD and 2.35 mD on average.(3)This abnormally high pressure gas reservoir was buried 4500-6000 m deep underground with the middle formation pressure being 125.625 MPa and the pressure coefficient being up to 2.22.Methane content in the minor H_(2)S-bearing produced gas flow reached up to 99.03%.(4)Volcanic rocks in the Jianyang-Zhongjiang-Santai area are developed,and they are adjacent to the Cambrian high-quality source rocks in the Deyang-Anyue rifting.The early extensional deep faults play a role in connecting source and storage.There are many sets of caprocks,such as the Upper Permian Longtan Formation and Lower Triassic layered thick paste rocks,providing conditions for forming large-scale tectonic-lithologic composite trap gas reservoirs,and the favorable exploration area reaches up to 6000 km^(2).In conclusion,this major discovery not only proves that Permian volcanic rocks in the Sichuan Basin has large potential for oil and gas exploration,but reaffirms the confidence in changing our exploration thought,speeding up new exploration zones and areas,and discovering more and bigger gas fields.
基金financially supported by China Petroleum Science and Technology Project (No. 2023ZZ16-01)。
文摘The intraplatform shoal dolomite of the Middle Permian Qixia Formation is currently considered the key target of hydrocarbon exploration in the central Sichuan Basin. To systematically investigate the origin of the stratabound facies-controlled porous dolomites of the Qixia Formation, integrated petrography,logging and seismic analysis were carried out in this work. The results are as following:(1) the dolomite reservoir is universal in the central Sichuan Basin, and its distribution is controlled by intraplatform shoals, with multilayer superposition vertically. Thick massive dolostone may also develop along with the fault.(2) Three replaced dolomites and one dolomite cement were identified: very finely to finely crystalline, anhedral to subhedral dolomite(Rd1);finely to medium crystalline, anhedral to subhedral dolomite(Rd2);coarsely crystalline, subhedral to euhedral dolomite(Rd3) and coarsely crystalline saddle dolomite cement(Sd). Rd2 and Rd3 are partly fabric-retentive, and preserve the original bioclastic ghosts. Sd shows wavy extinction, filled in the breccia veins.(3) The U-Pb dating and homogenization temperatures results indicate that the dolomite and Sd cement are associated with hydrothermal event during the Emeishan large igneous province. The δ^(13)C,^(87)Sr/^(86)Sr, and seawater-like REEY patterns suggest that the dolomitization and Sd precipitation fluids originate from connate seawater heated by elevated heat-flow.(4) The ELIP triggered large scale thermal anomalies in the basin during the Dongwu movement period. The increased temperature and pressure drove the formation water in the intra-platform shoal facies and overcame the binding effect of Mg^(2+) hydrate. Moreover, the deep hydrothermal fluid preferentially penetrated into the porous strata of shoal facies along the faults and fractures, mixed with formation water to some extent, and extensive dolomitization occurred. The facies-controlled dolomite reservoir and the underlying Cambrian source rock form a good source-reservoir assemblage, which can be a key replacement option.
文摘Previously, stratigraphic evolution and sequence overlapping were represented by “substituting point for surface or multi-point for surface, line for surface or multi-line for surface”, making it difficult to accurately reflect the stratigraphic evolution law across a larger area. We investigate the application of the seismic horizontal slice method for medium-short term stratigraphic sequence (four level), divided into reservoir group received, based on a 450 km<sup>2</sup> study area of three-dimensional (3D) seismic fine of the Sa-Pu formations west of the Daqing placanticline using a 50-millisecond horizontal slice. Sa-Pu oil layers can be divided into seven four-level sequences. We believe that a four-level sequence is more accurate in this application than in logging and data logging.
基金innovation consortium project of China Petroleum and Southwest Petroleum University(No.2020CX010201)Sichuan Science and Technology Program(No.2024NSFSC0081)。
文摘With the continued expansion of oil and gas exploration,both in the eastern and western regions,the quality of seismic acquisition has become a key factor in oil and gas exploration in complex areas.However,conventional seismic acquisition methods cannot efficiently avoid challenging acquisition locations and produce high-quality seismic data.In this regard,based on the curvelet transform,this paper proposes an irregular seismic acquisition method,which utilizes the high-precision characteristics of the curvelet transform and simulated annealing algorithm to establish a method for the evaluation of the coherence of irregular sampling matrices and design of observation systems.The method was verified using forward simulation and actual acquisition data.The results suggest the superior quality of seismic data gathered in complicated areas through this method over those acquired using traditional methods,which can provide technical guidance for the design of observation systems in complex areas.
基金supported by the National Science and Technology Major Project(No.2024ZD1001005)the National Natural Science Foundation of China(No.42172103)+2 种基金the Natural Science Foundation of Hubei Province(Nos.2023AFD206,2024AFD401,2025AFD439,2025AFD452)the Research Fund Program of Hubei Key Laboratory of Resources and Eco-Environment Geology(Nos.HBREGKFJJ-202302,HBREGKFJJ-202402)the State Key Laboratory of Geological Processes and Mineral Resources(No.GPMR202424)。
文摘Dabie-type porphyry Mo deposits were proposed as a new type of porphyry Mo deposits,and had unique geological characteristics.It is still poorly understood about the magmatic processes that led to the Dabie-type Mo mineralization.Here,we present zircon U-Pb and Lu-Hf isotopic,whole-rock and biotite elemental,and whole-rock Sr-Nd isotopic analyses on the Lingshan granitic batholith in the Dabie Orogen.It consists of three units(ⅠtoⅢ)that were emplaced before,genetically accompanied with,and after the Mo mineralization.LA-ICP-MS zircon U-Pb dating yielded crystallization ages of 128.2±1.0 Ma(MSWD=1.14)for UnitⅠand ages of 127.8±1.2 Ma(MSWD=0.28)and 126.6±1.8 Ma(MSWD=1.6)for UnitⅡ,indicating that they were emplaced during 130 to 125 Ma.The granites have high SiO_(2)contents(75.84 wt.%to 78.94 wt.%)and low MgO contents(0.07 wt.%to 0.10 wt.%),and are classified as fractionatedⅠ-type granite.UnitsⅠandⅡhave similar Sr-Nd isotopic ratios(ε_(Nd)(t)=-16.2 to-17.2,(^(87)Sr/^(86)Sr)_(i)=0.70540 to 0.70692)and zirconε_(Hf)(t)values(-17.4 to-20.4),indicating they were derived from partial melting of the ancient Yangtze lower crust.Mo mineralized granite from UnitⅡis characterized by the lower oxygen fugacity,fluorine enrichment and high fractionation.Magmas of unitsⅠandⅡhave experienced fractional crystallization,with the assimilation of supracrustal materials that account for the increased TiO_(2),F and Mo contents,and the decreased fO_(2).We proposed that the assimilation in upper-crustal magmatic processes plays key factors for magmatic systems that led to the Dabie-type porphyry Mo deposits.
文摘Casing deformation is a widespread problem in a certain block of Jiaoshiba Shale Gas Field in Sichuan Basin,China,and it severely limits the development benefits of shale gas in that block.Based on the spatiotemporal characteristics of block formation,fracture development,and casing deformation occurrence,this paper employs an integrated geological—engineering research approach to identify the primary mechanisms governing casing deformation within the block and proposes countermeasures to prevent such deformation.The present research indicates the following findings:(1)The block has undergone multiple phases of tectonic superposition,with fracture development serving as the geological factor causing casing deformation.(2)Fracturing activation constitutes the engineering factor causing casing deformation,with 4 mm of formation slip inducing deformation.(3)The fracture activation risk map shows that Class Ⅰ and Class Ⅱ fractures account for 73.36%of the total recorded in the block.Within the most susceptible Class I risk zone,the critical activation pressure increment for fracturing operations ranges from 13.43 MPa to 13.99 MPa.Based on the distribution of casing failure risk zones identified in the fracture activation risk map,this paper proposes relevant technical countermeasures for preventing casing failure from three perspectives:shale gas well location deployment,drilling techniques,and fracturing techniques.These measures provide robust support for safeguarding the integrity of casing systems within the studied block.
文摘There are abundant hydrothermal events within the Dengying Formation dolomite of the Precambrian system in southwest China.Methods including petrography identification,fluid-inclusion observation,in-situ U-Pb dating,and in-situ measurement of rare earth element(REE),etc.are integrated to characterize hydrothermal activity process within the Dengying Formation dolomite.The hydrothermal activity therein can be divided into four stages on the basis of in-situ U-Pb dating results of saddle dolomite cements.The 1st-stage(415.0-400.0 Ma)and 2nd-stage(259.4-248.0 Ma)hydrothermal events are characterized by saddle dolomite filling along the margin of fractures,or filling within dilational breccia and zebra textures.Compared with matrix dolomite and seawater-derived fibrous dolomite,saddle dolomite exhibits obvious negative anomalies of Ce elements.The 3rd-stage(225.6-199.0 Ma)hydrothermal event is represented by galena,sphalerite and other Mississipppi Valley-type(MVT)mineral cements in residual space.The formation of lead-zinc ore is due to the precipitation of metal sulfide caused by the thermo-chemical sulfate reduction(TSR)reaction between hydrothermal fluids and hydrocarbons during the large-scale hydrocarbon charging period.The 4th-stage(130.0-41.0 Ma)hydrothermal event is characterized by quartz and a small amount of fluorite filling the residual pores with dolomites.Quartz and fluorite record the migration of deep high-temperature hydrothermal fluid along early fractures and residual pores.During this period,the hydrothermal fluids result in the heterogeneous structure of bitumen,which is a clear response to high-temperature hydrothermal activity.
基金supported by innovation consortium project of China Petroleum and Southwest Petroleum University (No.2020CX010201)Sichuan Science and Technology Program (No. 2024NSFSC0081)。
文摘The Canglangpu Formation in the JT1 well area of the Sichuan Basin exhibits strong lateral heterogeneity and complex overpressure mechanisms, leading to ambiguous pore pressure distribution characteristics. Conventional prediction methods, such as the Equivalent Depth Method, are either inapplicable or yield unsatisfactory results (e.g., Fillippone’s method), contributing to frequent drilling incidents like gas kick, overfl ow, and lost circulation, which hinder the safe and effi cient exploration of natural gas. To address these challenges, this paper integrates lithology, physical properties, and overpressure mechanisms of the Canglangpu Formation. From a petrophysical perspective, a pore pressure prediction model independent of lithology and overpressure mechanisms was developed by combining the poroelasticity theory, linear elastic Hooke’s Law, and Biot’s eff ective stress theory, with an analysis of the relationship between carbonate rock strain, external stress, and internal pore pressure. Unlike conventional methods, the model does not rely on the establishment of a normal compaction trend line. Pre-stack seismic inversion was applied to achieve 3D pore pressure prediction for the formation. Results indicate high accuracy, with a relative error of less than 5% compared to measured data, and strong consistency with actual drilling events. The proposed method provides robust technical support for pore pressure prediction in carbonate formations and drilling geological design.
基金supported by Science Foundation of China University of Petroleum,Beijing(No.2462023QNXZ010,No.2462023XKBH012,No.2462024XKBH009)China Postdoctoral Science Foundation(No.2024M753612,No.GZC20233101).
文摘The northern structural belt of Kuqa Depression is adjacent to the South Tianshan orogenic belt, which are characterized by complex geological conditions. The reservoir quality of the Jurassic Ahe Formation is controlled by sedimentation, diagenesis, and tectonics, and show complex pore structure and strong heterogeneity, thereby hindering effective natural gas exploration and development. Core, thin sections, cathodoluminescence (CL), scanning electron microscopy (SEM), conventional well logs and image logs are used to characterize the petrological characteristics and pore systems. Then a comprehensive analysis integrating sedimentation, diagenesis, and tectonics is performed to unravel the reservoir formation mechanism and distribution of reservoir quality. Results show that reservoir properties are generally environmentally selective. Coarse grained sandbodies (gravelly sandstones) formed in high depositional-energy have the best physical properties, while fine sandstone and mudstone with low depositional energy is easily to be tightly compacted, and have poor reservoir quality. Porosity usually decreases with compaction and cementation, and increases due to dissolution. Clay minerals filling pores result in a deterioration of the pore structure. Microfracture formed by fracturing can connect the matrix pores, effectively improving the reservoirs’ permeability. The differential distribution of fractures and in-situ stress plays an important role in modifying reservoir quality. The in-situ stress has obvious control over the matrix physical properties and fracture effectiveness. The matrix physical properties are negatively correlated with the value of horizontal stress difference (Δσ). As the value of Δσ increases, the pore structure becomes more complex, and the macroscopic reservoir quality becomes poor. The smaller the strike divergence between the natural fracture and SHmax, the lower the value of Δσ in the fracture layers is, and the better the fracture effectiveness is. Under the control of ternary factors on the reservoir, sedimentation-diagenesis jointly affect the matrix reservoir quality, while fractures and in-situ stress caused by tectonism affect the permeability and hydrocarbon productivity of the reservoir. Affected by ternary factors, reservoir quality and hydrocarbon productivity show obvious differences within the various structural location. Reservoir quality in tight sandstones can be predicted by integrating sedimentation, diagenesis, and tectonics (fracture and in-situ stress) in a compressional tectonic setting like Kuqa Depression. The research results will provide insights into the efficient exploration of oil and gas in Kuqa Depression as well as similar compressional tectonic settings elsewhere.
文摘The Cretaceous Koum Basin is a rift-related half-graben in northern Cameroon,which constitutes a portion of the Yola Arm of the Upper Benue Trough.This study presents the first comprehensive dataset combining mineral-ogical,bulk-rock geochemical,and stable C-H-O isotopic data for dark-gray,finegrained mudstones from the basin,providing new insights into its sediment source,paleoenvironment,and geodynamic setting.The mudstones primarily consist of phyllosilicates(~8.6%),feldspars(~30.5%),carbonates(~13.7%),and minor iron oxides(~2.7%),with vermiculite,illite,and kaolinite as the main clay minerals.The presence of analcime,ankerite,and dolomite suggests low-grade metamorphism and/or hydrothermal alteration.Fe_(2)O_(3)/K_(2)O(1.52-6.40)and SiO_(2)/Al_(2)O_(3)(2.97-4.68)ratios classify the mudstones as compositionally immature shales(ICV~1.64)with low-moderate chemical weathering(CIA~56.35;PIA~59.74;R^(3+)/R^(3+)+R^(2+)+M^(+)~0.51).Trace element ratios(Th/Sc~1.70,Zr/Sc~1.33,La/Sc~6.30,La/Th~4.14)indicate an intermediate igneous provenance from a continental crustal source.Paleoenviron-mental proxies suggest deposition in a dynamic basin environment marked by fluctuating redox(C org/P:0.21-178.34)and salinity(Sr/Ba:0.34-3.25;N-values:48-35.92)conditions,ranging from oxic to anoxic and brackish to saline.Major element data(SiO_(2) vs.Al_(2)O_(3)+K_(2)O+Na_(2)O)indicate a semi-arid regime,while Paleoclimatic indicators such as Sr/Cu(1.88-37.47)and C-values(0.12-0.93)suggests alter-nating humid and arid conditions.Notably,stable isotope data,reported here for the first time in the Koum Basin,reveal a predominantly terrestrial,fluvial-deltaic C_(3) plant source for organic carbon(δ^(13)C-25.2‰ to -35.2‰)and complex fluid-rock interactions involving meteoric and magmatic-metamorphic fluids under a warm,equatorial climate(δ^(18)O+3.6‰to +24.9‰,δ^(2)H-104‰ to-50‰).The combined mineralogical,geochemical,and isotopic data point to deposition in a tectonically active continental arc setting,with contributions from ocean island arc and passive margin sources.
基金supported by the National Major Fundamental Research and Development project(No. 2005CB422100)the project of Southern Exploration Division Company,SINOPEC
文摘In a very gentle platform-margin paleogeographic environment, platform-margin reef flat facies carbonate reservoir rocks were developed in the Changxing Formation of Yuanba field. Later weak structural evolution and diagenetic evolution caused the Changxing Formation to form lithologic traps, with good reservoirs such as dissolved bioclastic dolostone and dissolved pore dolostone. The Changxing Formation gas reservoir is a pseudo-layered porous lithologic gas reservoir under pressure depletion drive, with high H2S and moderate CO2 contents. This paper predictes that the conducting system for the Changxing Formation gas reservoir is possibly composed of the pores and microfractures in the Changxing Formation reservoir, the top erosional surface of the Changxing Formation, as well as the micropores and microfractures in the underlying formations. The Changxing Formation reservoir has experienced 3 hydrocarbon charging stages. This paper suggests that diffusion is the major formation mechanism for this gas reservoir. In the Middle and Late Yanshanian, the Yuanba area entered the major gas charging stage. The gas migrated mainly through diffusion and with the assistance of seepage flow in small faults and microfractures from the source rocks and the other oil-bearing strata to the Changxing Formation carbonate reservoir rocks, forming lithologic gas pools. In the Himalayan Epoch, the lithologic traps were uplifted as a whole without strong modification or overlapping, and were favorable for gas preservation.
基金funded by the National Science and Technology Major Project(grant No.2016ZX05052)the National Natural Science Foundation of China(grant No.41072102)
文摘Hydrothermal mineral assemblages and related hydrothermally enhanced fracturing are common in the Precambrian Dengying Formation of Central Sichuan Basin. Petrographic and geochemical analyses of core samples show that the hydrothermal dolomite reservoirs of Dengying Formation consist of four main types of pores in the reservoir facies. These include: 1) hydrothermal dissolution vug(or pore), 2) intercrystalline pore, 3) residual inter-breccia vug(or pore), and 4) enlarged dissolved-fracture. There are three different fabrics dolomite in hydrothermal dolomite reservoirs, namely, saddle dolomite, fine-medium dolomite and micritic dolomite. Micritic dolomite is the original lithology of host rock. Saddle dolomite with curved or irregular crystal faces was directly crystallized from hydrothermal fluids(average temperature 192°C). Fine-medium dolomites are the products of recrystallization of micritic dolomite, resulting in abnormal geochemical characteristics, such as slight depletion of δ^(18)O, significant enrichment of Mn-Fe and ^(87)Sr/^(86)Sr, and positive Eu anomaly. A model for the distribution of various hydrothermal dolomite reservoir facies is proposed here, which incorporates three fundamental geological controls: 1) extensional tectonics and tectono-hydrothermal events(i.e., the Xingkai Taphrogenesis of Late Sinian-Early Cambrian, and Emei Taphrogenesis of Late Permian), 2) hydrothermal fluid storage in clastic rocks with large thickness(e.g., Nanhua System of Chengjiang Formation and part of Doushantuo Formation), and 3) confining bed for hydrothermal fluids(such as, the shale in Qiongzhusi Formation). The supply of hydrothermal fluid is critical. Large basement-rooted faults and associated grid-like fracture system may function as the channels for upward migration of hydrothermal fluid flow. The intersection of the above-mentioned faults(including the conversion fault), especially transtensional sags above negative flower structures on wrench faults can serve as a key target for future hydrocarbon exploration.
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financial support of the National Natural Science Foundation of China(Grant No.52074332)express their gratitude to project ZR2020YQ36 supported by Shandong Provincial Science Fund for Excellent Young Scholars。
文摘Hydraulic fracturing is a key technology for the development of unconventional hydrocarbon resources.The proppant placement morphology determines the fracture conductivity,thus affecting the reservoir stimulation effect.In this paper,the proppant migration and placement within complex fractures was studied by considering the fracture wall roughness through computational fluid mechanics-discrete element method(CFD-DEM)in numerical simulation,which is a key approach to study the proppant migration and placement.The results show that the proppant placement non-uniformity,proppant migration capacity,and proppant volume filled in the far-end and the secondary branched fracture are enhanced within the rough fracture compared with those within smooth fractures.The proppant migration capacity is increased within the fracture at low inclination angles(<60°)and low approach angles(<90°),and the proppant placement area is larger in the inclined fracture than that in the vertical fracture.The rise of injection rate and fracturing fluid viscosity causes more proppants migrate to far-end or secondary fractures,resulting in a non-proppant area within the near-wellbore fracture.An increase by 1.3 times in the injection rate and 3 times in the fracturing fluid viscosity leads to a decrease by 26.6%and 27%,respectively,in the proppant placement area within the near-wellbore fracture.The staged injection with small size proppants followed by large size proppants increases the proppant placement area in the primary fracture by 13%-26%,and that with large size proppants followed by small size proppants increases the proppant placement area by 19%-25%,which is due to that the latter method facilitates filling of the secondary branched fracture.The injection location mainly affects the proppant filling degree within the near-wellbore fractures.Compared with the upper injection,the middle and lower injection is not beneficial to filling of proppants within the near-wellbore fracture.
基金supported by Major Science and Technology Special Project of China National Petroleum Corporation"Research on Large scale Storage and Production Increase and Exploration and Development Technology of Continental Shale Oil"(2023ZZ15)。
文摘Qingshankou shale(Gulong area,China)exhibits strong acoustic anisotropy characteristics,posing significant challenges to its exploration and development.In this study,the five full elastic constants and multipole response law of the Qingshankou shale were studied using experimental measurements.Analyses show that the anisotropy parametersϵandγin the study region are greater than 0.4,whereas the anisotropy parameterδis smaller,generally 0.1.Numerical simulations show that the longitudinal and transverse wave velocities of these strong anisotropic rocks vary significantly with inclination angle,and significant differences in group velocity and phase velocity are also present.Acoustic logging measures the group velocity in dipped boreholes;this differs from the phase velocity to some extent.As the dip angle increases,the longitudinal and SH wave velocities increase accordingly,while the qSV-wave velocity initially increases and then decreases,reaching its maximum value at a dip of approximately 40°.These results provide an effective guide for the correction and modeling of acoustic logging time differences in the region.
基金supported by the national project "Geophysical Complex Technologies for Reservoirs and Unconventional Gas Reservoirs"(No.2017 ZX05018-004-003)
文摘Walkaway VSP cannot obtain accurate velocity field,as it asymmetrically reflects ray path and provides uneven coverage to underground target,thereby presenting issues related to imaging quality.In this study,we propose combining traveltime tomography and prestack depth migration for VSP of an angle-domain walkaway,in a bid to establish accurate two-dimensional and three-dimensional(3 D)velocity models.First,residual curvature was defined to update velocity,and an accurate velocity field was established.To establish a high-precision velocity model,we deduced the relationship between the residual depth and traveltime of common imaging gathers(CIGs)in walkaway VSP.Solving renewal velocity using the least squares method,a four-parameter tomographic inversion equation was derived comprising formation dip angle,incidence angle,residual depth,and sensitivity matrix.In the angle domain,the reflected wave was divided into up-and down-transmitted waves and their traveltimes were calculated.The systematic cumulative method was employed in prestack depth migration of a complex surface.Through prestack depth migration,the offset-domain CIGs were obtained,and dip angle was established by defining the stack section horizon.Runge–Kutta ray tracing was employed to calculate the ray path from the reflection point to the detection point,to determine the incident angle,and to subsequently calculate the ray path from the reflection point to the irregular surface.The offset-domain residual depths were mapped to the angle domain,and a new tomographic equation was established and solved.Application in the double complex area of the Tarim Basin showed the four-parameter tomographic inversion equation derived in this paper to be both correct and practical and that the migration algorithm was able to adapt to the complex surface.
文摘INTRODUCTION Distributed acoustic sensing(DAS)is a novel and popular technology for vertical seismic profile(VSP)data acquisition because of its many advantages,including full vertical coverage,high sampling density,low cost,and resistance to stressors(high temperature and pressure).The current industrial application of DAS in borehole exploration acquires single-mode fibers.It records strain rates,which are then converted to particle velocities by the modem before being written to the disk.
