Restoring the original hydrocarbon-generating potential of deep source rocks: A critical review and a novel method using the Songliao Basin, China, as a case study

Abstract

Deep source rocks are typically in a high-to-overmature stage, characterized by lower than original values of total organic carbon. Thus, resource evaluation is significantly influenced by the accuracy of the measured data and the restoration methods of original (pre-thermal maturation) values. Therefore, reliable data for assessing petroleum and natural gas resources generated during the burial process are urgently needed. This study first critically reviews commonly used methods for restoring the original TOC (TOC_o) and hydrocarbon-generating potential (HGP). The principles, advantages, and disadvantages of each method are discussed, and a novel workflow for evaluating the resource is proposed. The workflow involves four steps: (1) selecting a fit for-the-purpose method for original TOC and HGP restoration; (2) establishing original restoration coefficients by weighted TOC and HGP restoration formulas; (3) assessing the remaining resource potential through hydrocarbon generation and expulsion; and (4) validating the assessment results. Using the Permian source rocks in the Songliao Basin as an example, this workflow restores the total remaining resource amount (65.3 × 10⁹ t). Predicted results indicate that high-value areas with remaining resource potential are near the Heyupao Sag (57.7 × 10⁸ t), Chaoyanggou Terrace (73.5 × 10⁸ t), and Binxian-Wangfu Sag (39.0 × 10⁸ t). The advantages of this workflow include: (1) overcoming the limitations of the original TOC and HGP restoration method by selecting the most suitable restoration model; (2) directly identifying the original TOC spatial distribution using recovery coefficient, which overcomes the heterogeneity in the spatial distribution of organic matter types; and (3) accurately verifying the remaining resource potential presence based on tectonic and thermal evolution. The proposed workflow significantly improves the credibility of resource evaluations and is likely applicable to other deep and ultradeep buried source rocks worldwide.