Evaluation of total organic carbon contents in carbonate source rocks by modified acid treatment method and the geological significance of acid-soluble organic matters

Abstract

Total organic carbon contents are an important parameter in evaluating hydrocarbon source rocks and it shows the hydrocarbon-generating potential of hydrocarbon source rocks. In this study, the total organic carbon of 16 carbonate rocks with different maturity level was determined by a modified acid treatment protocol of the elemental analyzer method. In the modified method, montmorillonite is used to thicken the residue of acid treatment and remaining acid solution. Then, total organic carbon values of “clay-paste” sample were analyzed by the element analysis method. The results of 16 carbonate rocks show that the total organic carbon values with the new method were greater than the conventional total organic carbon test in a majority of the samples. Additionally, the fraction of acid-soluble organic matters was investigated and it shows no clear relationship of the fraction of acid-soluble organic matters with maturity and total organic carbon values in source rocks. Hence, it indicates that the released acid-soluble organic matters are characterized by complex factors that influence their occurrence and compositions.