Driving forces and their relative contributions to hydrocarbon expulsion from deep source rocks: A case of the Cambrian source rocks in the Tarim Basin

Abstract

To thoroughly understand the dynamic mechanism of hydrocarbon expulsion from deep source rocks, in this study, five types of hydrocarbon expulsion dynamics (thermal expansion, hydrocarbon diffusion, compaction, product volume expansion, and capillary pressure difference (CPD)) are studied. A model is proposed herein to evaluate the relative contribution of different dynamics for hydrocarbon expulsion using the principle of mass balance, and the model has been applied to the Cambrian source rocks in the Tarim Basin. The evaluation results show that during hydrocarbon expulsion from the source rocks, the relative contribution of CPD is the largest (>50%), followed by compaction (10%–40%), product volume expansion (5%–30%), and thermal expansion (2%–20%). The relative contribution of diffusion to hydrocarbon expulsion is minimal (<10%). These results demonstrate that CPD plays an important role in the hydrocarbon expulsion process of deep source rocks. The hydrocarbon expulsion process of source rocks can be categorized into three stages based on the contribution of different dynamics to the process: the first stage is dominated by compaction and diffusion to expel hydrocarbons, the second stage is dominated by product volume expansion and CPD, and the third stage is dominated by product volume expansion and CPD. This research offers new insights into hydrocarbon exploration in tight oil and gas reservoirs.