Numerical Evaluation of a Life-Cycle Strategy for Shale Oil Recovery Enhancement with SC-CO2

Abstract

Supercritical CO2 (SC-CO2) has been widely used in shale oil to enhance oil recovery (EOR). However, current work often discusses the utilization of SC-CO2 in one specific way, such as pre-fracturing, huff-n-puff and flooding. In this work, we propose a life-cycle utilization of SC-CO2 in shale oil wells in Changqing oilfield in China, including CO2 pre-injection from neighboring vertical wells, hydraulic fracturing of horizontal wells, CO2 pre-fracturing after a period of production and the last inter-stage CO2 flooding. After history matching, two practical wells are chosen to demonstrate the effectiveness of the proposed CO2 utilization strategy. Stress changes, dynamic fracture propagation, and fluid composition variations are all considered and simulated in a coupled numerical model. As demonstrated, the performance of the proposed strategy is influenced by multiple operational parameters, such as timing, injected volume, and injection rate. Optimization results show that pre-injection into vertical wells raises the bottom-hole pressure in horizontal wells by 2.5 MPa and improves the Estimated Ultimate Recovery (EUR, defined as 20-year cumulative oil production) by 45%. Subsequent refracturing of the horizontal well further increases EUR by another 33%. Final inter-stage flooding helps restore pore pressure within the stimulated reservoir volume (SRV) by 3–5 MPa, contributing an additional 10% increment of EUR. This study provides a life-cycle utilization strategy for SC-CO2 in shale oil recovery enhancement, and an integrated numerical model is built to quantify the effectiveness of CO2-EOR at different periods. The findings provide important guidance for future field tests to maximize the potential of SC-CO2 in shale oil EOR through systematic utilization.