Comparison of Source Rock Kerogen Kinetics Using a Data-Driven Model and Based on Rock-Eval Pyrolysis Data

Abstract

Rock-Eval/TOC analysis and data interpretation provide a quick, easy and cost effective way for source rock evaluation. However, there are misconceptions in source rock kinetics evaluation, which have led some practitioners to believe that if kerogen type is the same, hydrocarbon generation kinetics of different source rocks will be similar. Kerogen type classification is designed mainly for evaluation of ultimate generation potential. Organic matters with similar potential may behave differently under thermal stress due to fundamental differences in their molecular structure. This study compares source rock hydrocarbon generation kinetics of 22 source rock units from sedimentary basins across the world. The comparison is based on a data-driven model and uses Rock-Eval datasets. Comparisons are conducted on source rocks that contain the same types (I, II or III) of kerogen based on their hydrogen indices but are from different settings: (1) marine vs non-marine; (2) saline vs fresh water bodies; (3) different geological times and (4) different environments of the same basin. The study reveals that generation kinetics vary greatly even for the same types of kerogen. The kinetics of type I kerogen from the Ordovician Red River marine source rock in Williston Basin are characterized by a delayed onset of hydrocarbon generation at Tmax 450°C and a narrow generation window of 15°C Tmax. In contrast, the non-marine type I kerogen from the Cenozoic source rocks in Eastern China shows an early start of oil generation at Tmax 430°C. Non-marine type II source rocks from China display higher generation potential with a narrow temperature window of decomposition as compared with typical North American marine source rocks. Depending on their maceral assemblage, the onset temperature of hydrocarbon generation of type III kerogen can vary greatly. For example, the Tertiary Aklak Sequence containing type III kerogen from the Beaufort-Mackenzie Basin has an onset hydrocarbon generation temperature at Tmax of 410°C, which is contrary to many other Type III kerogens that generate at higher temperatures than Type I and II kerogens. This is likely due to the presence of diterpenoid resinite in these deltaic sediments. This paper discusses the statistical model, presents the results and demonstrates the innovative approach of studying oil generation kinetics using conventional Rock-Eval data without involving specially designed and costly laboratory pyrolysis experiments.

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015