Practice of Digital Wellbore Inversion of Coal Seam Structure and Evaluation Method of Organic Matter Abundance
Coalbed methane is one of the typical types of self-generated and self-stored gas reservoirs.Methane gas is mainly generated by the thermal evolution of organic carbon in coal seams and adsorbed in large quantities on the surface of pores.The content of organic components is crucial for the gas generation and storage capacity of coal seams.However,the reservoir structure of coalbed methane is complex,with interbedded development of organic coal-rock component structures and inorganic leat.The strong heterogeneity within the layers and the difficulty in visuali-zing the longitudinal coal seam structure in a single well greatly hinder the evaluation of organic matter abundance and efficient development of coalbed methane in single wells.Full-diameter CT scanning is an important experimen-tal technique for large-scale core analysis in recent years.The grayscale values obtained by this technique are close-ly related to the composition of coal and rock.The higher the grayscale value,the higher the ash content,density,and mineral content of coal and rock,and vice versa.Taking the Daning-Jixian Block as the research object,this study combines full-diameter CT scanning technology with wellbore interpretation technology to explore the relation-ship between rock grayscale and logging data such as gamma,density,and sonic transit time.A mathematical model for digital well logging inversion of coal seam structure is established,and combined with the relationship between grayscale and organic components,a method for evaluating organic matter abundance in single wells using full-di-ameter CT scanning is proposed.The comparison between the inverted cross-section of Well A1 in the study area and the real grayscale cross-section obtained by full-diameter CT scanning shows a high degree of similarity,and the distribution pattern of inverted grayscale values is consistent with that of real CT grayscale values,indicating that the inversion model can effectively reflect the heterogeneity structure changes within the coal seam.The digital well-bore inversion and organic matter abundance evaluation method can provide strong technical support for fracturing section selection and production capacity prediction of coalbed methane wells in the study area.
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