An FR–IR model method for restoring the original organic geochemical parameters of high over-mature source rocks with types I and II kerogen in China

Abstract

Deep natural gas source rocks are generally in a stage of high over-maturity. Based on the TOC and hydrocarbon generation potential (HGP) data, the accuracy of present evaluations of deep oil and gas resource potential are greatly reduced. The original TOC and HGP determine the quanlity of hydrocarbon generation from organic matter (OM), therefore, it is particularly important to restore the original organic geochemical parameters. By determining the HI and Tmax of numerous source rocks ranging in maturity levels from immature to over mature, it was found that the HGP characteristics of marine and continental source rocks with the same OM type were similar, providing a prerequisite for the establishment of forward recovery (FR) and inversion recovery (IR) models. Based on the relationship between the TOC and HI of immature to low-maturity source rocks with types I and II kerogen, the original HI was corrected, and the original TOC thresholds for different OM types of source rocks were determined to optimize the FR–IR model. Through the thermal simulation experiments of many samples, the TOC conversion rates from the immature to over mature stages were obtained, and the FR model was formed. The IR model was established based on geochemical data of the organic source rocks of types I, II1 and II2 with different maturity levels. Finally, by considering the typical marine and continental high over-mature source rocks of the world, the restoration results of the FR and IR models were found to have good correlation (average of 0.96) and coincidence rates (average of 72.2%). It was proven that the established FR–IR model have universal applicability in the restoration of the original TOC and HGP of marine and continental high over-mature source rocks with types I and II kerogen, especially in China.