Performance Evaluation and Pressure Control Strategies for Shale Oil Gas Huff-And-Puff

Optimization of gas huff-and-puff strategies in Subei shale reservoirs is constrained by an insufficient understanding of production characteristics and control mechanisms. Systematic gas huff-and-puff experiments were performed on shale cores from Members 2 and 4 of the Funing Formation. The investigation quantified the impacts of fracture types, production pressure, soaking time, and distinct pressure drawdown strategies. Experimental results indicate that the oil recovery factor is controlled by the degree of fracture development and reservoir stress sensitivity primarily. While initial production capacity is enhanced by fractures significantly, gas channeling pathways are formed easily, leading to a reduction in oil exchange ratio simultaneously. The mobilization of deep matrix oil is favored by low production pressure and extended soaking duration. This combination ensures sufficient gas diffusion and optimizes the oil-gas exchange rate in micropores effectively. In the integrated matrix-fracture system, the CO2 stepwise pressure drawdown and fixed pressure platform strategies outperform the one-step pressure drawdown strategy significantly. The CO2 multicycle fixed pressure platform strategy achieves the maximum cumulative recovery factor of 43.9% compared to only 28.6% for N2 stepwise pressure drawdown. Furthermore, produced oil composition is lightened and residual oil sweeping efficiency is optimized by the fixed pressure platform strategy via the moderation of effective stress. Consequently, a differentiated development strategy is proposed to inhibit gas channeling in fracture networks while ensuring sufficient diffusion in matrix pores, identifying the CO2 multicycle fixed pressure platform as the optimal technical route for efficient shale oil development.