When used for the comprehensive evaluation of shale oil sweet spots in the Yingxiongling area,the traditional lithology-electric crossplots face many challenges,including low accuracy and difficulties in selecting optimal sensitive parameters and establishing adaptive evaluation criteria.To address these limitations,we propose a comprehensive evaluation approach that integrates principal component analysis(PCA)-based multi-parameter weighting with the analytic hierarchy process(AHP).This approach facilitates the scientific selection of sensitive parameters and the comprehensive quantitative evaluation of shale oil sweet spots in the Yingxiongling area.Six core parameters are identified through Pearson correlation analysis:porosity,oil saturation,total organic carbon(TOC)content,rock pyrolysis-derived free hydrocarbons content(S1),brittle mineral content,and carbonate content.The weights of these parameters are determined based on the loadings and variance contribution rates of the principal components.Accordingly,a linearly weighted comprehensive evaluation model for sweet spots,along with criteria for classification and comprehensive evaluation,is established.Under the guidance of this novel model,daily oil flow rates of 17.61 m3 and 13.7 m3 were tested from sweet spot intervals in wells C12 and C20,respectively,while a post-fracturing daily oil flow rate of 20.5 m3 was tested in well CP13.For the horizontal section of well CP13,the comprehensive index showed a significant positive correlation with the liquid production contribution rate detected using an oil-phase tracer.These results demonstrate that the proposed model is suitable and can be widely applied in shale oil sweet spot evaluation.
The Gulong Sag in the Songliao Basin is an important region of China where significant breakthroughs have been achieved in the exploration of medium-and high-maturity lacustrine shale oil.However,the major controlling factors and evolution patterns of shale reservoirs in this sag remain poorly understood.This study focuses on shales in the 1st member of the Qingshankou Formation(also referred to as the Qing 1 Member)in the Gulong Sag.By integrating multiple analytical techniques,including Rock-Eval pyrolysis,X-ray diffraction(XRD),scanning electron microscopy(SEM),nitrogen adsorption,high-pressure mercury injection(HPMI),and nuclear magnetic resonance(NMR),we systematically analyze the organic geochemical characteristics of the shales,as well as the reservoir space types and their sizes and distribution patterns.The analytical results show that the shales in the sag contain organic matter dominated by high-quality Type Ⅰ kerogen.These shales were deposited in a semi-deep to deep lacustrine anoxic environment and are currently in oil generation state with moderate to high maturity.Reservoir development in the shales is jointly governed by the sedimentary environment,diagenesis,organic matter type,and thermal evolution.Specifically,intense compaction and cementation in the early stage lead to substantial loss of primary pores.With an increase in thermal maturity,the dissolution of minerals such as feldspars,together with the hydrocarbon generation of organic matter,collectively contribute to secondary pore growth.Consequently,reservoir spaces in the shales progressively evolve into an organic-matter-and clay-hosted composite pore system dominated by nano-scale pores.The reservoir space evolution pattern of shales in the Qing 1 Member established in this study provides an important theoretical basis for shale oil exploration in the Gulong Sag.Furthermore,other relevant patterns and research approaches involved in this study may provide references for the exploration of other shale oil plays.
A systematic review and summary of the developmental history and advances in experimental techniques for carbonate reservoirs reveals that technological progress in experimentation serves as a fundamental driving force behind theoretical and technological innovations in the field.The research results are as follows.(1)The evolution from macro-scale reservoir characterization via visual inspection and magnifying lenses in the 1950s and 1960s to modern digital outcrop acquisition,3D micro-to-nano pore imaging,and multi-scale reservoir heterogeneity characterization and modeling in the 21st century,underscores the pivotal role of theoretical and experimental technological advancements,particularly in carbonate petrology,sedimentology,sequence stratigraphy,and the deployment of sophisticated experimental equipment.(2)"Geochronology,thermometry,barometry,and fluid property tracing"represent the most cutting-edge geochemical testing techniques for carbonate reservoirs in the 21st century.The iterative upgrading from bulk-rock to in-situ micro-area analysis,from solution-based methods to laser ablation,and from point detection to area mapping defines the future trajectory of the field.Furthermore,digital transformation and intelligent development provide the impetus for these technical upgrades,which will yield more comprehensive and reliable data for investigating the genesis of diagenetic fabrics and diagenetic-porosity evolution.(3)The high-temperature and high-pressure(HTHP)visualization apparatus for reservoir formation simulation across tectonic stages in ultra-deep layers is the core equipment for investigating the genetic mechanisms of ultra-deep reservoirs.It can accurately replicate ultra-HTHP geological environments,enabling dynamic forward modeling of water-rock interaction processes across tectonic stages,and integrates in-situ real-time monitoring of fluid properties and rock permeability.This apparatus provides direct experimental evidence for unraveling the formation mechanisms,preservation conditions,and spatial distribution patterns of secondary porosity in ultra-deep carbonate reservoirs.The elucidation of hydrocarbon accumulation mechanisms in ultra-deep carbonate reservoirs via simulation experiments represents a defining future research trend.(4)Reservoir prediction is the ultimate objective of reservoir characterization,evaluation,genesis,and modeling.Given that geophysical techniques are the primary tools for reservoir identification and prediction,it is highly recommended to strengthen the organic integration of experimental carbonate reservoir techniques with geophysical methods.
The fourth member of the Shahejie Formation(Es4)in the Western Sag of the Liaohe Depression,Bohai Bay Basin,hosts multiple types of shale oil.With favorable geological conditions and promising exploration prospects,it represents the primary target for shale oil exploration in the Liaohe oil and gas province.To clarify the enrichment characteristics and exploration potential of shale oil in this province,systematic studies were conducted on the hydrocarbon generation and storage processes and the oil-bearing properties of the Es4 member based on drilling,well logging,seismic surveys,and various analytical test datasets.A shale oil enrichment model was established;sweet spots were identified and evaluated;and exploration practices in this area were systematically analyzed.As indicated by the research results,the total organic carbon content(TOC)ranges from 0.20%to 11.86%,the hydrocarbon generation potential(S1+S2)has a peak value of 100 mg/g and an average value of 40 mg/g,organic matter is dominated by Type Ⅰ‒Ⅱ1,vitrinite reflectance(Ro)ranges from 0.38%to 0.79%,and maximum pyrolysis temperature(Tmax)is mainly at 440～450℃.Overall,the organic matter is characterized by favorable types,high abundance,and is in the medium-to-high maturity stage.The Es4 is mainly composed of clay minerals,quartz,K-feldspar,plagioclase,ammonium feldspar,calcite,dolomite group minerals and pyrite,with well-developed laminae displaying diverse stacking patterns.The main lithofacies include laminated calcareous-dolomitic shale,laminated felsic shale,and laminated mixed shale.Dissolution pores,intercrystalline pores,organic pores,dissolution fractures,and bedding fractures are well developed throughout the member.The overall porosity is relatively low,and the pore system is primarily composed of micro-to nano-scale pores;mesopores(pore diameter of 10～100 nm)are dominant,accompanied by a small proportion of macropores.Oil and gas are mainly stored in bedding fractures,intercrystalline pores,microfractures,organic pores,intergranular pores,and calcite cleavage fractures.Sedimentation provides the essential material basis for shale oil enrichment.Moderate total organic carbon content(TOC of 2%～4%)and medium-to-high thermal maturity are prerequisites for enrichment,resulting in a shale oil enrichment model for this area.Based on a multi-parameter integrated reservoir evaluation method,Type I reservoirs in sublayers c11 and c12 are dominated by calcareous mud shale,while those in sublayers c8‒c10 are dominated by dolomitic(calcareous)mud shale and argillaceous dolomite,with brittleness increasing proportionately with dolomite content.Combined with pre-stack seismic inversion,the planar distribution of sweet spots was predicted.This study systematically summarizes the geological characteristics and enrichment model of shale oil in the Es4 member of the Western Sag and effectively identifies sweet spots,providing a reliable geological basis for shale oil exploration program design in this province.
This study characterized the types,geological features,and differences in gas-bearing properties of reservoir-seepage units,investigated the controlling effects of geological structures,reservoir fractures,and petrophysical properties on gas-bearing potential,and elucidated the differential enrichment mechanisms of natural gas.Using seismic data,imaging logs,core observations,high-pressure mercury injection(HPMI),and production data,we aim to address the challenges of diverse reservoir-seepage unit types and unclear primary controlling factors of natural gas enrichment in the tight sandstones of the Triassic Xujiahe Formation in the western Sichuan Depression,Sichuan Basin.As indicated by the research results,four types of reservoir-seepage units are identified in the study area:fault-fracture,fold-fracture,fault-fold-fracture,and matrix types.The matrix-type units,characterized by underdeveloped tectonic fractures,exhibit inferior petrophysical properties and low gas-bearing potential.In contrast,the fault-fracture,fold-fracture,and fault-fold-fracture types,which are governed by tectonic deformation,feature well-developed fracture networks,enhanced physical properties,and higher gas-bearing potential.Meanwhile,fracture-rich units,medium-and high-angle fractures significantly enhance vertical permeability and expand the effective range of gas charging.Fracture density and the proportion of medium-and high-angle fractures typically decrease with increasing distance from faults,with the 200～600 m range identified as the optimal interval for gas enrichment.Furthermore,the fold width-to-height ratio exerts a clear influence on fracture intensity;areas proximate to fold hinges exhibit higher fracture densities and a greater proportion of medium-and high-angle fractures,providing superior conduits for gas accumulation.Finally,effective pore preservation is critical for gas enrichment in matrix-type units,and those with chlorite rims and superior sorting represent the most favorable sites for accumulation.
