Hydrocarbon Accumulation Characteristics and Resource Potential Evaluation in Deep Carbonate Rock Petroleum System: A Case Study of the Sinian–Cambrian System in the Sichuan Basin, Southwest China

Abstract

Hydrocarbons within a petroleum system exhibit a symbiotic relationship and an orderly distribution pattern. However, previous studies have largely overlooked the hydrocarbons derived from carbonate source rocks and their accumulation processes. In this study, a quantitative model of hydrocarbon generation and expulsion from over-mature source rocks was established using the data-driven hydrocarbon potential method. Subsequently, the accumulation processes and resource potential of these hydrocarbons were systematically evaluated. The results indicate that the source rocks of the Qiongzhusi and Dengying formations contain total organic carbon contents of 1.86% and 2.00%, respectively. The kerogen is predominantly Type I. The hydrocarbon generation and hydrocarbon expulsion thresholds are 0.5% Ro and 0.72% Ro, respectively. The evaluated resources of conventional gas, tight gas, shale gas and residual carbonate gas are 1668.2 × 10¹² m³, 2809.5 × 10¹² m³, 461.1 × 10¹² m³ and 1201.0 × 10¹² m³, respectively. After hydrocarbons are expelled from source rocks, conventional gas is formed through the cracking of the paleo-reservoir and accumulates in the uplift. The formation of tight gas on slopes is characterised by significant reservoir compaction. Residual gas remains trapped in the source rock, where carbonate exhibits a strong capacity to retain hydrocarbons.