Abstract:The source rocks of the Lower Cambrian Yurtus Formation have been considered as the main source rocks of marine oil and gas in the Tarim Basin.Currently,the understanding of source rocks of Yurtus Formation is mainly based on the sample analysis in outcrops in the basin margin and drilling core samples in uplift areas of the basin,while the characteristics of source rocks in slope and depression areas are less understood.Understanding the carbon isotope characteristics of kerogen in source rocks of Yurtus formation is of great reference significance for determining the hydrocarbon generation mechanism of source rocks and establishing the correlation between oil and gas sources.In this paper,the organic geochemistry and carbon isotope geochemistry of Ordovician crude oil and natural gas samples from different fault zones in Shunbei area are studied in detail.Based on the quantitative evaluation of the influence of thermal maturity on carbon isotopes of crude oil and natural gas,the initial carbon isotope composition of crude oil and natural gas is reconstructed.The carbon isotopic composition of kerogen from crude oil and natural gas in Shunbei area was recovered by the fractionation between kerogen and oil and gas during hydrocarbon formation.The results show that the carbon isotopes of oil-derived kerogen are mainly in the range of-32.3‰ to-28.8‰,and that of gas-derived kerogen is mainly in the range of-33.1‰ to-29.8‰.The crude oil and natural gas are mainly derived from the mixed source of benthic algae and planktonic algae,and part of crude oils in the Shunbei area are also from the main source of planktonic algae.The light carbon isotope characteristics of kerogen indicate that the oil and gas in Shunbei area mainly come from the source rocks of Yurtus Formation.Based on changes in the assemblage of hydrocarbon forming organisms,the source rocks of Yurtus Formation are divided into oil-generating source rocks with planktonic algae as the main source(δ13C>-30‰),oil-gas generating source rocks with benthic and planktonic algae as the main source(-33.5‰<δ13C<-30‰)and gas-generating source rocks with benthic algae as the main source(δ13 C<-33.5‰).With the increase of thermal maturity of source rocks,the early oil is generated by planktic algae,while the late oil(mainly volatile oil-condensate oil)contributes more,resulting in the early oil isotope is heavier,while the late oil has relatively light carbon isotope characteristics.At the same time,the content of oil source kerogen gradually decreases,while the relative content of gas kerogen(benthic algae)gradually increases,and the total carbon isotope of kerogen in source rocks gradually becomes lighter.Therefore,the different source rock types and hydrocarbon generation processes of kerogens from different sources leads to the complex carbon isotope characteristics of the oil and gas generated from the source rocks of Yurtus Formation(such as the reversal of carbon isotope of the components of the reservoir crude oil group,the reversal of carbon isotope between the chloroform extract of the source rock and kerogen,etc.).The research results can provide a new constraint for the prediction of ultra-deep oil and gas phase state in Tarim Basin.

Abstract:Many recent studies indicate that the relationship between granitic pegmatite and granite is complex and can be summarized simply into four types:"Father-son relationship",i.e.granitic pegmatites are the late products of highly differentiated and evolved granitic magma;"Brotherly relationship",granitic pegmatite and granite are the products of simultaneous or near-simultaneous independent crystallization of magma with similar compositions;"Indirect relationship",formation of rare metal pegmatites through multi-stage partial melting of source granite;"No relationship between granitic pegmatite and granite",relative big time-gap and different source materials for pegmatite and granite are displayed in many pegmatite fields,and anatectic individual pegmatite magma is a reasonable genetic model.Crystal mush reservoir and trans-crustal magmatic system are the important for understanding the relationship between pegmatite and granite.Inheritance(or detrital)minerals for dating and isobaric interference for analysis of hafnium isotopic composition should be pay more attention for the study on the relationship between pegmatite and granite.The establishment and development of techniques and reference materials for isotopic dating need to be enhanced.The study on characteristics and mechanism of non-traditional isotope fractionation during the differentiation and evolution of granitic magma should be strengthened.Petro-geochemical analysis and large-scale mapping of the granite batholith are suggested in order to give more valid evidences for the rare metal pegmatite exploration.

Abstract:Fractured geothermal reservoir reinjection has garnered significant attention for its remarkable effectiveness in enhancing geothermal water supply capacity,raising water levels,and mitigating resource and environmental issues associated with geothermal exploitation.This study focuses on the Yichun Wentang geothermal field,employing time series analysis and hydrogeochemical methods to analyze long-term monitoring data of reinjection volume,extraction volume,water temperature,water level,and water quality during surface water reinjection and extraction processes.The study summarizes the dynamic variations in the geothermal field's temperature field,fluid field,and chemical field,and investigates the sustainability and safety of long-term reinjection in fractured reservoirs.The results indicate that reinjection volume is the primary factor influencing the dynamic changes in the temperature,fluid,and chemical fields.Long-term reinjection raises the geothermal field's water level by 3.952-4.986 m,increases the dynamic amplitude of water level fluctuations by 13.4 times,and reverses the planar distribution direction of water levels.When the reinjection volume remains below the threshold,the production well's water temperature exhibits an inverse correlation with reinjection volume,delayed by 3-12 months;exceeding the threshold leads to a"cliff-like"decline in temperature.Long-term reinjection causes an overall decrease in well temperatures,with a maximum reduction of 6.8-10.0℃,though stabilization occurs after controlling reinjection volume.Reinjection water directly"dilutes"geothermal water,shifting hydrochemical types in the Piper diagram toward surface water characteristics,transitioning from HCO3-Na type to HCO3·SO4-Na·Ca type.Long-term monitoring confirms that the geothermal field remains safe and controllable when reinjection volume is maintained below 9,734 m3/d,increasing resource availability by 414%.Surface water reinjection in fractured reservoirs demonstrates good feasibility and safety,provided the reinjection volume does not exceed the threshold.

Abstract:Influenced by multi-phase thrusting,extensional tectonic movements,and the plastic deformation of mudstone,shale,and gypsum,the deformation of the Biluoco oil shale stratum(BLS)in the Qiangtang basin is extremely complex.Additionally,controversies surrounding paleontological fossil evidence and isotopic geochronology have severely constrained the understanding of the lithological assemblages and their temporal attribution.In response to the intricate structural deformation of BLS,this study conducted detailed structural observations and profile measurements.Based on the thrust-fold system,the stratum was traced and correlated,dividing into three segments with seven types of lithological assemblages from bottom to top.Zircon U-Pb isotopic testing,along with zircon structure and genetic analysis,was performed on the sandstone of the lower segment and the basalt of the middle segment,yielding maximum depositional ages of 166 Ma and 154 Ma,respectively.Integrating regional context,it is concluded that the age of BLS ranges at least from the Middle Jurassic Bathonian to the Late Jurassic Tithonian,with the top possibly extending to the Early Cretaceous Berriasian.The determination of the age for BLS provides new insights for hydrocarbon exploration in the Qiangtang basin,as well as for studies on sedimentary tectonic evolution and oceanic anoxic events.

Abstract:With the continual progressing of shale oil exploration and development in lacustrine facies,the investigation in Qintong sag of Subei basin steps into the stage of whole petroleum system evaluation.The previous oil correlation researches focused on the influence of salinity of lake water during source rock development onto biomarkers,which is hard to satisfy the requirement of oil correlation with the source rocks of"contemporaneous heterotopic facies"for whole petroleum system.This study is on the basis of analysis of controlling of high-resolution sequence stratigraphy driven by paleoclimate on source rock development and distribution,totally 11 shale oil and conventional crude oil samples in Qintong sag have been employed to measure the aryl isoprenoid biomarkers which can reflect sulfuration habitat and be used to correlate the whole petroleum system with source rocks.Meanwhile,the 2,3,6-aryl isoprenoids(2,3,6-AIPs)and 2,3,4-aryl isoprenoids(2,3,4-AIPs)have been applied to build two parameters:C3=Σ(2,3,6-AIPs)/Σ(2,3,4-AIPs)and C4=Σ(2,3,6-AIPs)/Σ(2,3,4-AIPs)+Σ(2,3,6-AIPs),which are utilized to calculate the relative sulfuration intensity and relative paleo-depth of lake water for the source rocks of shale oils and conventional crude oils,respectively.And then,several research results have been obtained as following.(1)The second member of Funing Formation in Qintong sag underwent the low frequency cycle of earlier lake expansion system tract(EEST)→later lake expansion system tract(LEST)→high level system tract(HST),which can be divided into high frequency cycle of 9-fourth level quasi-sequence group(P1-P9),and 32.5-fifth level subsequences,which indicates the total tendency from the(semi-)haline water during the earlier cold and dry paleoclimate evolving into the fresh water during the later warm and humid paleoclimate.(2)The relative higher values of residual total organic carbon(TOC)in the second member of Funing Formation are always corresponding to the maximum lake flooding surface of system tract cycles with warm and humid paleo-climate and fresh water;and the relative lower values of residual TOC being always corresponding to the initial lake flooding surface with cold and dry paleo-climate and(semi-)haline water.This leads to a conclusion that bathyal-deep lake environments with warm,humid paleoclimate and fresh water are more beneficial to organic enrichment.(3)Four types of source rocks in the second member of Funing Formation can be recognized:the first is relatively shallower water column and weaker sulfuration facies;the second being relatively deeper water column and moderate sulfuration facies;the third being deeper water column and intensive sulfuration facies;and the fourth being deeper and fresh water column facies.This research is not only providing a new tool for"contemporaneous heterotopic facies"source rock evolution,but also giving the evidence to establish the distribution sequence of whole petroleum system.

Abstract:Artificial solution mining technology,which converts evaporite minerals in brine aquifers into brine,is crucial for the sustainable development of salt lake resources.However,the dynamic evolution of aquifer hydraulic conductivity induced by mineral dissolution during water injection remains insufficiently understood,hindering accurate process prediction.In this study,a Python-based modeling tool,MF6PQC,coupling MODFLOW6 and PhreeqcRM,was developed to systematically investigate the effects of reactive transport on the hydraulic conductivity of brine aquifers and the overall solution mining process.Simulation results show that aquifer heterogeneity governs the spatiotemporal evolution of hydraulic conductivity.During the early stage of dissolution mining,hydrogeochemical reactions preferentially occur in high permeability zones.The dissolution of highly reactive minerals such as carnallite significantly enhances porosity and hydraulic conductivity,ultimately forming preferential flow paths driven by positive advection-dispersion feedback.Relatively homogeneous aquifers or those with extensive,well-connected high-permeability zones facilitate uniform lixiviant distribution and achieve higher solid-to-liquid conversion efficiency.In contrast,strongly preferential or poorly connected formations interrupted by low permeability barriers limit mineral contact and dissolution,thereby reducing overall solution mining efficiency.This study deepens the understanding of hydraulic conductivity evolution in brine aquifers during water injection and provides a theoretical basis for optimizing salt lake brine resource exploitation.

Abstract:The fold-thrust belt in the northern piedmont of the Tianshan Mountains underwent polyphase tectonic deformation,acquiring its present configuration during the Late Cenozoic contractional regime.Under multiphase superposition,the influence of basement architecture on subsequent compressive deformation remains constrained.This study investigates the Mesozoic structural characteristics and deformation mechanisms in the northern piedmont of the Tianshan Mountains based on seismic,drilling,and field observation data,aiming to reveal the influence and controlling factors of Mesozoic structures on Cenozoic deformation and hydrocarbon migration-accumulation.Strike-slip faults were developed in the Mesozoic in the northern piedmont of Tianshan Mountain,and were covered by the Cretaceous-Cenozoic strata.Under the Late Cenozoic compression environment,the Mesozoic strike-slip fault was reactivated,and the Cenozoic thrust fault and fold superimposed on the Mesozoic fault.The reactivation of Mesozoic structures played an important role in shaping the present structure of the northern piedmont of Tianshan Mountain.According to the deformation sequence,the sedimentary strata in the southern Junggar basin.are divided into three structural layers—shallow,intermediate,and deep.These tiers correspond to upper,middle,and lower hydrocarbon accumulation assemblages,respectively,with the intermediate and deep structural tiers demonstrating particularly significant exploration potential.In this paper it reveals the relationship between deep faults and late compressive structures in the northern piedmont of Tianshan Mountain,explains the influence of multi-stage tectonic evolution on oil and gas exploration,and has reference significance for the study of similar structures in the basins of western China.

Abstract:As an important unconventional energy resource,the efficient development of shale oil is of great significance for ensuring energy security.Shale reservoirs exhibit characteristics of low porosity and permeability,complex pore structures,and diverse mineral compositions,resulting in extremely complex wettability characteristics.Wettability,as a key parameter controlling oil phase occurrence and flow,directly affects shale oil development efficiency.Traditional wettability studies mainly rely on macroscopic contact angle measurements,which struggle to accurately reveal wetting behavior in nanoscale pores and its control mechanisms on oil phase mobility.This study aims to establish a multi-scale wettability characterization method for shale reservoirs and reveal the intrinsic relationships among wettability characteristics,pore structure,and oil phase mobility.Based on Gulong shale samples,macro-and microscopic contact angle measurements were employed to characterize multi-scale wettability features,nuclear magnetic resonance technology was used to independently evaluate oil phase mobility in different-scale pores,and systematic correlation analysis was conducted to explore the control mechanisms of wettability on mobility.The study found that although microscopic contact angles are systematically larger than macroscopic values,the measurement trends from both methods are highly consistent,validating the reliability of cross-scale characterization.Different from previous single-scale understanding,this study reveals that pore structure and mobility require synergistic evaluation:optimal reservoirs may not be those with the highest proportion of large pores,but rather those with balanced pore structure(60%-80%large pore proportion)and high mobility in all pore sizes;additionally,mineral components exhibit differentiated control effects on multi-scale pore system recovery rates,with quartz content showing significant positive correlation with both large and small pore recovery rates,while different clay minerals demonstrate scale-dependent complex influences.Through correlation analysis,qualitative relationships between wettability and mobility,as well as quantitative evaluation models between mineral components and mobility,were established.This research provides new evaluation methods for shale oil reservoir sweet spot identification,emphasizing the need to comprehensively consider the synergistic effects of pore structure,wettability,and mobility.

Abstract:The rift stage(Barremian-Aptian of the Early Cretaceous)of the Santos basin in Brazil is characterized by the development of world-class large-scale lacustrine carbonates deposition.At present,numerous oil and gas discoveries have been made in this field,making it a hot spot for global oil and gas exploration.The development degree of carbonate sediments is the key to the enrichment and accumulation of oil and gas in the basin.Drilling results reveal the development of"two phases and two types"of lacustrine carbonate sediments during the rift stage of the basin:shell limestone of Itapema(ITP)group in early fault-sag depression transition period(Late Barremian-Aptian)and microbial reef limestone of Barra Velha(BV)group in late sag depression period(Mid-Late Aptian).Although both of these"two phases and two types"lacustrine carbonate sediments are biogenic limestone,their genesis mechanisms and lithological combinations differ significantly.In order to clarify the sedimentary differences and main controlling factors of the"two phases and two types"lacustrine carbonate rocks,based on thin section,core,logging,seismic and other data,this paper conducts a systematic petrological and sedimentological study of two types of lacustrine carbonate sediments in the basin,combining micro and macro perspectives.Comprehensive research shows the development of large-scale lacustrine carbonate sediment in the Lower Cretaceous of the Santos basin in Brazil is mainly controlled by paleogeomorphology,paleolake water salinity and paleowater energy changes.Paleogeomorphology controls the distribution and development of sedimentary microfacies of lacustrine carbonate reservoirs,paleowater salinity controls the vertical evolution of lacustrine carbonate sediments types,and paleowater energy and water depth control the microfacies variation of lacustrine carbonate sediments.Finally,it was confirmed that the high-energy freshwater environment in the face of waves is a favorable background for the development of shell limestone reservoir in Itapema Formation,and the shallow medium-high energy semi saline-saline water environment in the face of waves is a favorable background for the development of stromatolitic limestone reservoir in Barra Velha Formation.This points out the directions for finding favorable reservoir development zones and has practical guiding significance for the oil and gas exploration in lacustrine carbonate rocks of Brazil.

Abstract:On 28 May 2025,a large rock-ice avalanche occurred at the Blatten village in Valais,Switzerland.The failure mobilized approximately 8.3 million m³ of material,traveled 3 300 m,and deposited over an area of 2.66 km².The Blatten avalanche caused one fatality,buried the Blatten village and dammed the Lonza River.Integrating remote sensing analysis,seismic signal interpretation and numerical modeling,this study reconstructs the event and identifies its pronounced cascade amplification effects.The failure evolved through three distinct stages:high-altitude collapse,glacier melting and deformation,and transformation into a long-runout avalanche.Progressive debris accumulation and gradual glacier weakening were the key drivers of the large-scale hazard.In addition,low-friction ice and meltwater markedly reduced motion resistance,facilitating the long-runout movement.These findings highlight the need to account for the potential of multiple small-scale failures cascading into catastrophic events in avalanche risk assessments.The Blatten disaster offers important implications for hazard zoning and the planning of major infrastructure projects in high-mountain regions of western China.

Abstract:The bed failure model is the important initiated model for debris flow in channel.However,there is no detail critical condition for bed failure model.In this paper,a series of laboratory experiments were carried out to study the initiation of debris flow by runoff in the channel.The experiments were conducted for the initiation models and critical condition with different particle size,saturated density,internal friction angle,and permeability coefficient.It was found that the slope threshold of debris flow initiation in bed failure model with no cohesion sediment increased with the increasing of sediment saturation density and internal friction.The minimum slope was about 17 degree in the experiments for the bed failure.When the bed slope is greater than the threshold slope,the thickness of the saturated layer of the bed failure decreases with the increase of the bed slope,the minimum sediment saturation thickness may be 0.The critical discharge of debris flow in fluvial transport model is much larger than that in bed failure model.The critical discharge of debris flow in bed failure model is the production of the permeability coefficient of sediment,the depth of saturated water and the width of channel.

Abstract:The formation mechanism of dolomite[CaMg(CO3)2]remains a longstanding enigma in earth sciences.Previous studies have identified certain microorganisms and clay minerals as catalysts in the crystallization of low-temperature protodolomite,a crucial precursor to ordered dolomite.However,the role of cyanobacteria and particularly their potential synergistic effects with clay minerals remain poorly understood.In this study,we investigated bioprecipitation of carbonate minerals using the halotolerant cyanobacterium Synechococcus elongatus FACHB-410 in the presence and absence of montmorillonite.Our results demonstrated that protodolomite occurred as the predominant solid product in the montmorillonite-amended biosystems as confirmed by X-ray diffraction(XRD)and Raman spectroscopy,whereas monohydrocalcite and low-magnesian calcite were the primary products in the montmorillonite-free biosystems.Multiple microscopic techniques,including scanning electron microscopy(SEM),focused ion beam microscopy(FIB-SEM),and transmission electron microscopy(TEM),revealed that protodolomite nucleated as nanocrystals preferentially on montmorillonite surfaces.Density functional theory(DFT)simulations further elucidated that surface electronegativity of montmorillonite played a key role in promoting protodolomite formation by strongly adsorbing Mg2+ions through electrostatic interactions,thereby facilitating their dehydration and significantly lowering the nucleation energy barrier.

Abstract:Due to the modification by ultra-long section and multi-stage complex geological tectonic processes,pre-existing fractures and faults are extremely developed in the southern Sichuan shale,which not only reduce fracturing efficiency but also cause casing deformation and increased economic losses;therefore,for high-risk well segments with extremely developed natural fractures,a multi-stage merged ultra-long stage fracturing mode is implemented to avoid fracturing risks and improve fracturing effectiveness.This study focuses on a well with highly developed fractures in the Weiyuan shale of the Sichuan basin,where pre-existing fractures of various scales are extremely developed throughout the wellbore,indicating significant casing deformation risk during hydraulic fracturing,and after actual casing deformation occurred during hydraulic fracturing,the fracturing plan was adjusted immediately by merging 18 stages into an ultra-long segment of 1 168 m,with 18 fracturing and temporary plugging operations performed on this segment.Based on large-array surface microseismic monitoring,this study characterizes the spatiotemporal propagation characteristics and focal mechanisms of fracture activities,and combined with integrated geological-engineering analysis of microseismic data,3D seismic data,geological surveys,and logging data,clarifies the implementation effect of ultra-long stage hydraulic fracturing,demonstrating that ultra-long stage hydraulic fracturing can reduce the risk of casing deformation in high-risk areas to a certain extent,though highly fractured zones may act as leakage channels for fracturing fluids in ultra-long stages,leading to insufficient stimulation,while adjusting real-time segmentation and fracturing plans for ultra-longsection fracturing based on microseismic responses is beneficial for both reducing casing deformation risks and improving fracturing stimulation effectiveness.

Abstract:Urban solid waste landfill-induced high-steep slope instability often leads to secondary disasters such as extensive building destruction and casualties.To quantitatively evaluate the disaster risk of artificial landfill landslides,this study takes Shenzhen's"12•20"Guangming landslide as a case study,employing the depth-integrated method-based Massflow software to construct a dynamic numerical model that reproduces the entire evolution process of landslide initiation,high-speed movement,and deposition.By coupling with impact pressure calculation methods for landslide masses,the destructive impact effects on surrounding buildings were quantitatively evaluated.An uncertainty analysis framework was introduced,treating geotechnical parameters and sliding surface properties as random variables.A probabilistic analysis model was developed through Latin hypercube sampling,revealing the statistical characteristics of landslide travel distance under multifactorial influences and establishing a correlation model between landslide motion exceedance probability and building impact damage.Building vulnerability was further considered when conducting risk assessments for structures and nearby personnel.The study demonstrates that the depth-integrated method effectively captures the dynamic evolution of landslides,with simulated failure surface morphology,travel distance(1 139 m),and deposition pattern highly consistent with field monitoring data;impact pressure from landslide masses on buildings exhibits a rapid rise to peak values followed by gradual attenuation,with peak pressure decreasing significantly with distance from the landslide source;probabilistic analysis of landslide travel distance based on parameter uncertainty shows the actual deposition zone entirely falls within the 95%confidence interval,and building damage areas align with hazard zoning results.The proposed risk assessment framework integrating depth-integrated modeling and uncertainty analysis provides a novel methodology for quantitative evaluation of engineered landfill landslides,offering significant theoretical and practical implications for solid waste landfill safety management in the context of"zero-waste city"development.

Abstract:As a critical region for the tectonic evolution of the East Asian continental margin,the East China Sea basin has long been debated regarding its basement attributes,subduction processes,and multi-phase tectonic-sedimentary coupling mechanisms.Based on a comprehensive analysis of existing geological and geophysical data,combined with previous evidence and insights,in this paper it systematically summarizes and evaluates key fundamental geological issues of the East China Sea basin,proposing future research directions.The basement controversy centers on two hypotheses:the extension of the South China continental crust versus the accretion of exotic terranes.Abrupt crustal thickness variations and zircon isotopic data provide new evidence for the latter,but the spatiotemporal constraints on crustal evolution and collisional orogenic belts remain unresolved.The Mesozoic subduction process exhibits staged evolution,including low-angle subduction,slab detachment,and magmatic arc migration.The discovery of Early Jurassic island arc magmatic rocks revises the traditional flat-slab subduction model,yet direct evidence for Cretaceous and Cenozoic magmatic arc positions in offshore areas is still lacking,significantly hindering the understanding of Mesozoic basin nature and evolution.The Cenozoic basin architecture in the north is controlled by slab rollback,while the southern region may correlate closely with the South China Sea spreading,though critical evidence linking subduction and South China Sea extension processes is still needed.The Mesozoic paleogeographic framework remains ambiguous,while abrupt Cenozoic provenance shifts and differential tectonic-sedimentary responses are prominent.Current research lacks systematic comparisons of geological evidence among the South China continent,the East China Sea Basin,and the Ryukyu Islands.Future studies should integrate deep geophysical exploration,high-precision geochronology,and numerical modeling to establish a"subduction-magmatism-sedimentation"co-evolution model,providing theoretical support for hydrocarbon exploration and continental margin dynamics research.

Abstract:Multiple sets of lacustrine carbonate rocks are developed in the fourth member of the Shahejie Formation(Es4)in the Leijia area of the western sag of the Liaohe Depression.With favorable geological conditions and promising resource potential,this interval currently serves as the primary target for tight oil exploration in the region.To clarify the characteristics of high-quality reservoirs and define exploration targets,this study integrates cyclostratigraphy,drilling,logging,seismic inversion,and analytical testing data to identify astronomical cycles and analyze reservoir properties,aiming to predict the distribution of high-quality"sweet spot"reservoirs.The main findings are as follows.(1)The Es4 member contains approximately six long eccentricity cycles and nineteen short eccentricity cycles,and the relationship between long eccentricity cycles and oil-bearing intervals in the area is elucidated.(2)High-quality reservoirs in the Leijia area are dominated by dolomite,characterized by fine dolomite crystals(mostly 1-3 μm),well-developed intercrystalline pores and structural fractures,micropores mainly distributed in the 0.3-0.4 μm range,effective throat lengths ranging from 1 to 20 μm,and pore volumes primarily between 0.5-4.0 μm³.Light oil components are mainly hosted within fractures and intercrystalline pores.These tight and brittle dolomites are primarily developed within the Du-3 oil layer.(3)A single-well evaluation was conducted using a multi-parameter fusion method to establish reservoir evaluation criteria.Combined with pre-stack geological inversion data,the study clarified the distribution pattern of high-quality sweet spots within the sequence stratigraphic framework and carried out planar prediction.This research systematically refines the stratigraphy and sedimentary reservoir characteristics of lacustrine carbonates in the Es4 member of the western sag,and effectively identifies sweet spot distribution using pre-stack seismic inversion,providing a robust geological basis for tight oil exploration in the area.

Abstract:Carbonate reservoirs are important carriers of global oil and gas resources.The development characteristics of their internal karst caves and fault systems directly affect the storage and migration capacity of oil and gas.In order to solve the problem of multi-scale fault prediction in deep and ultra-deep carbonate reservoirs,this study takes the Ordovician carbonate rocks in the Tahe oilfield in the Tarim basin as an example and proposes a classification and grading fault prediction technology based on seismic wave field characteristic analysis.The interference mechanism of large-scale fracture-cavity bodies on conventional fault prediction attributes(such as coherence and maximum likelihood)is revealed through three-dimensional forward simulation,and it is found that the"beaded"reflection anomaly at the boundary of the fracture-cavity body will lead to false connectivity of faults and relocation deviation.Based on the differences in the scale and dissolution characteristics of the faults,the fault system in the study area is divided into large-scale broken-dissolution faults(>20 m),medium-scale weak-undissolved faults(10-20 m)and small-scale fractures(<10 m),and targeted prediction methods are developed for each of them:for large-scale faults,a fracture retrieval technology based on gradient structural tensor thinning is proposed to effectively overcome the interference of abnormal boundaries of karst caves;for medium-scale faults,the longitudinal continuity of the faults is significantly improved by combining AFE coherent enhancement attributes with U-Net deep learning algorithm;for small-scale fractures,the Likelihood attribute and structural guidance filtering are used to accurately extract weak reflection signals.Further,a well control multi-attribute fusion model is constructed by fusing multi-scale fault attributes and drilling loss data through deep feed forward neural network(DFNN).The application results show that this technology system has achieved full-scale characterization of the fault system in the complex fracture-cave area of Tahe oilfield.Large-scale strike-slip faults are distributed in a conjugate NNE-NNW direction,medium-scale faults form flower-like structures,and small-scale fractures are densely developed on the active disk(east side)of the fault.This study provides a new technical approach for the prediction of deep carbonate reservoir faults and has important reference value for the exploration and development of similar oil and gas reservoirs.