Micro-nanopore Structure And Effectiveness Evaluation Method Of Lacustrine Mud Shale

With the deepening of exploration and development of conventional oil and gas resources,non-conventional oil and gas resources have gradually become the focus of global oil and gas exploration and development,especially the shale oil resources.A set of organic shale has been developed in Shahejie formation of Jiyang depression,and several wells have made a breakthrough in shale oil exploitation.which indicates that the shale in the study area has a good potential for shale oil exploration and development.However,various rocks,complex micro-nano pore structure,and the heterogeneity of organic and the inorganic component is strong of shale oil reservoirs leads to the unclear classification index of shale oil reservoir efficiency and brings difficulties to the evaluation of shale oil reservoir effectiveness.Taking the lacustrine shale of Shahejie formation in Jiyang depression as the research object,the core observation of coring well,thin slice,XRD.physical properties,SEM.MICP,NMR,nano-CT and well logging data are comprehensively used in this paper and the characteristics of lacustrine shale reservoir and its micro-nano pore structure are deeply understood.It is clear that the characteristic of the micro-nano pore structure is the core index for the division of shale oil reservoir effectiveness.On this basis,the effectiveness evaluation of shale oil reservoirs based on micro-nano pore structure evaluation has been carried out.(1)Based on the data of XRD,thin section analysis and organic geochemistry,the characteristics of lacustrine shale reservoirs in the study area are studied.According to the lithofacies division scheme of "TOC+ structure+lithology",the mudstone facies of lacustrine facies in the study area are divided into six main lithofacies.And the organic-rich laminated mudstone is identified as favorable lithofacies according to the lithofacies characteristics of the oil-producing strata.(2)The results of thin slice analysis and scanning electron microscope show that the reservoir space of lacustrine shale in Jiyang depression is mainly intergranular pore,dissolution pore,microfracture and less organic pore.MICP,NMR and their parameters show that the physical properties of shale oil reservoir are poor,the pore structure is complex,and the heterogeneity is strong.The analysis of micro-nano pore structure of six kinds of lithofacies shows that the micro-nano pore structure of striped marl limestone is the best,and the pore structure of block gray mudstone is the worst.(3)Taking lithofacies as bridge,the relationship between oil bearing property and its micro-nano pore structure of shale oil reservoir is recognized,and TOC evaluation,pore structure evaluation and fracture evaluation are determined as core evaluation indexes of effectiveness of lacustrine shale reservoir.(4)On the basis of analyzing the relationship between lithofacies type and pore structure of shale oil reservoir,the sensitive parameters for evaluating micro-nano pore structure of shale oil reservoir are obtained:the fractal dimension of NMR and the pore component of NMR.And the relationship between sensitive parameters and pore structure parameters of MICP and NMR is discussed.It provides the basis for evaluating the pore structure of shale reservoir on continuous logging section.In addition,fracture is an important index of pore structure at micron and above scale of shale.Based on imaging logging and core analysis,the relationship between fracture development characteristics of lacustrine shale and lithology,physical properties,logging response.fracturing and wavelet transform is analyzed.It is determined that the comprehensive fracturing coefficient and acoustic time difference wavelet coefficient are sensitive parameters for the evaluation of fracture development characteristics.(5)Finally,taking the key well as a reference,the accuracy of the lacustrine shale effective reservoir division result defined by the triple information of "TOC evaluation+pore structure evaluation+fracture evaluation" on the logging profile is verified and applied to the non-test oil well.It provides a new way to evaluate the effectiveness of shale oil reservoir.A series of technical methods are established in this paper to effectively improve the accuracy of the effective reservoir division of the shale oil and have a good application prospect.In addition,the combination of core experimental analysis results and continuous logging information deepens the application of logging curve(especially nuclear magnetic resonance logging)in shale oil reservoir evaluation.