Construction Parameters Optimization of CO₂ Composite Fracturing for Horizontal Shale Wells

To ensure the economic feasibility of shale oil and gas exploitation, large-scale hydraulic fracturing is essential for increasing recovery volumes by creating more efficient conductivity channels. However, China's continental shale reservoirs present complex geological conditions, making optimization through traditional hydraulic fracturing challenging. Thus, substituting CO₂ for water in fracturing fluids to enhance shale reservoirs has garnered significant interest. An orthogonal experimental design was implemented to identify the optimal parameters for CO₂ composite fracturing. Analysis of single-factor experiments led to the selection of four key variables: slickwater volume, slickwater displacement, preflush liquid CO₂ volume, and proppant addition volume, resulting in 16 experimental configurations. Using numerical simulation of tight oil shale reservoirs, the effective stimulated reservoir volume for each parameter combination was calculated. Variance analysis revealed that increased slickwater volume significantly enhances fracture initiation and propagation. While variations in slickwater displacement and preflush liquid CO₂ volume influence fracture network morphology and complexity, they have a lesser effect on the stimulated volume compared to slickwater volume. Proppant quantity primarily affects fracture conductivity with minimal impact on stimulated volume. This research underpins the optimization of constructional parameters for CO₂ composite fracturing.