Total organic carbon(TOC)content is the most important parameter in determining the quality of source rocks.In a case study of a transitional shale gas reservoir in the Longtan Formation at Well C1 in area Q,the Sichuan Basin,our efforts focus on how to improve TOC calculation for coal-measure shale gas reservoirs.Based on the geological characteristics of the study area and natural gamma ray spectral log data,the △log R method is modified to formulate a dual △log R method based on natural gam-ma ray spectroscopy logging.The reservoir is lithologically divided into two types:coal seam and non-coal seam,according to core TOC data.Th/K and Th/U correlations with TOC contents in coal seams and non-coal seams are analyzed to select the data with the highest correlations for TOC calculation using △log R at coal seams and non-coal seams.The results show improved correla-tions up to 0.78 and 0.85,decreased absolute errors to 0.01％and 0.01％,and decreased relative errors to 14.93％and 12.53％for TOC calculation at coal seams and non-coal seams,Well C1,respectively compared with the traditional method.The dual △log R method based on natural gamma ray spectroscopy logging is also successfully applied to the Y Formation at Well C2 in area S,the Sichuan Basin.The improved method is feasible in the context of high clay content,strong heterogeneity,and black coal seams in the study area;the problem of the low correlation between TOC content and U content could also be solved.This method could be applied to similar prospects and offer technical support to shale gas exploration and production.
total organic carbon contentshale gascoal-measure shaleshale reservoirSichuan Basintransition facies
国家科技期刊平台
NSTL
万方数据
