Restoration of buried organic carbon for catagenesis-affected rocks using Rock-Eval thermal analysis: Assumptions, performance, and uncertainty analysis

Total organic carbon (TOC) content, a classic indicator of rock organic richness, is widely used in geological archives for paleoenvironmental interpretation and petroleum system modeling. However, organic carbon (OC) undergoes significant alteration and loss upon burial, rendering present-day TOC measurements inadequate for reflecting original OC levels. Many approaches have been developed to restore such OC loss based on mass balance principles and Rock-Eval parameters, yet these methods rely on implicit assumptions that introduce uncertainties and have not been tested. Based on a reevaluation of previous restoration methods, this study proposed a mass balance framework with a refined algebraic scheme to reconstruct buried (pre-catagenesis) TOC. A one-at-a-time sensitivity analysis method was introduced to quantify the propagation uncertainties in the model by examining the responses of TOC restoration outputs (TR, f, and σ_TOC) to variations in key inputs (TOC^pd, BI^pd, HI^pd, HI^o, Cc, α, and β). Simulated Rock-Eval data, derived from HI-T_max sigmoid models, was utilized in sensitivity analysis to avoid the influence of source rock heterogeneity and organo-facies variations. Both the simulated and experimental results demonstrate that the proposed model improves the TOC restoration accuracy by accounting for the rock mass changes and OC deductions due to hydrocarbon expulsion. Furthermore, the uncertainties arising from S₁ “carry-over” and mineral matrix effects are resolved through the new equations. This study, from a sensitivity analysis perspective, summarizes the impacts of input parameters in perspectives of kerogen kinetics and thermal maturation, offering a guideline for more robust TOC restoration and evaluation.