Estimation of Total Organic Carbon in shales through color manifestations

Abstract

Recently shale gas resources have emerged as a viable energy source and have become an attractive target because they represent a huge resource. Total organic carbon (TOC) content of shales is one of the key reservoir parameters and for source rock assessment its measurement is the first priority. Here the authors have collected different types of banded inhomogeneous shale samples and have tried to estimate their TOC content by identification of color (intensity) of lithobands (namely coal, dark shale, gray shale and silt) in shales by naked eye by assigning numeric values to the bands based on their color intensity. Total Color Assessment (TCA) of the samples was calculated by dividing summation of the product of the band thickness and their respective color value with total length of the sample. The relationship between TCA and TOC shows significantly high coefficient of determination and hence can be used as a significant first order field tool for estimation of TOC. For TCA <5, the estimated TOC values (calculated from TCA) are very close to the actual TOC values.