合川-潼南地区茅口组一段泥灰岩总有机碳含量测井评价方法OA

To address the complex lithology,limited core data,difficulty in accurately evaluating total organic carbon(TOC)content,and unclear understanding of the distribution law of high-quality hydrocarbon source rocks in marlstone of the First Member of Maokou formation(Mao1 member)in the Hechuan-Tongnan Area,Sichuan Basin,logging,core and geochemical test data from the study area.Select the logging information sensitive to source rock such as resistivity,sonic and natural gamma ray,verify the applicability of two conventional logging evaluation methods:the modified Δlog R method and the natural gamma method.A lithology indicator curve is constructed to divide lithologic units,and the lithology-weighted ΔlogR-GR method is adopted to establish the TOC prediction model.The vertical and areal distribution characteristics of regional source rocks are also analyzed.The results show that:①TOC content in the Mao1 member marlstone ranges from 0.04%to 3.32%,with an average of 0.78%;the average vitrinite reflectance is 2.45%,indicating a marine source rock with moderate organic richness and high thermal maturity.②The average absolute errors of TOC calculated by the modified Δlog R method and the natural gamma method are 0.26%and 0.21%,respectively,demonstrating complementary accuracy between the two methods.③The lithology-weighted Δlog R—GR method effectively reduces interference caused by lithology and special minerals such as talc,reducing the average absolute error of TOC calculation to 0.14%,significantly improving prediction accuracy.④The effective thickness of source rocks in the Mao1 member ranges from 29.0 to 51.0 m,averaging 42.9 m.Vertically,source rock quality in the Mao1a submember is superior to that in the lower submembers.Horizontally,the thickest source rocks occur in the southeastern part of the region,gradually thinning from southeast to northwest,with a good correspondence between source rock thickness and single-well gas testing productivity.It is concluded that the lithology-weighted Δlog R—GR method is suitable for quantitative TOC evaluation in complex lithology marlstone in the study area.The achievement provides reliable technical support for favorable zone selection,well placement and comprehensive reservoir evaluation in the Mao1 member.