Study on the restitution coefficient of original total organic carbon for high mature marine source rocks

Abstract

On the basis of the results of hydropyrolysis simulations for about 90 different types of immature to mature source rocks selected from about 5 000 marine source rocks in China, along with the natural thermal evolution profiles, the following conclusions were obtained. (1) Total organic carbon (TOC) content of excellent marine source rocks does not change obviously when Ro<0.8% or Ro>1.3%, and the residual TOC content is decreasing gradually with the maturity increase at 0.8%<Ro<1.3%. (2) At the high-post mature stage (Ro>1.3%), the decreased maximums of residual TOC content for the kerogen of sapropel (I), II₁, and II are usually 40%, 32% and 24%, respectively, and their TOC restitution coefficient is, respectively, 1.68, 1.48 and 1.32. (3) Both the TOC decreasing amplitude and the restitution coefficient decrease gradually with the decrease of TOC content for the source rocks with low organic matter abundance (usually 0.3%res. of solid bitumen and shale with high organic matter abundance (TOC>30%) also require no restitution at the high mature stage. Such kind of TOC restitution is further supported by the coincidence of the decrease of residual TOC with the decreasing of S₁+S₂ and the increasing of hydrocarbon quantity during the experimental simulation of hydrocarbon generation and expulsion for marine source rocks (0.3%<TOC<30%) in natural thermal evolution profiles.