Bottom-Hole Pressure Optimization in Marine-Continental Transitional Shale Gas Reservoir Considering Stress Sensitivity

Abstract

The bottom-hole pressure (BHP) directly affects the stress state in formation, which in turn affects the productivity of hydraulically fractured horizontal wells. In this study, the porosity and permeability stress sensitivity experiments were conducted on different marine-continental transitional shale samples. The relationships between permeability, porosity and stress were discussed, and three-dimensional (3D) response surfaces based on grid interpolation were established for a more intuitive understanding. The results were then imported into numerical simulations to analyze the impact of permeability sensitivity on gas production at the reservoir scale and to optimize the BHP management strategy. A hysteresis effect in the changes of porosity and permeability has been observed during stress variation. Stress sensitivity of permeability leads to a significant decrease in production in the later stage. Ignoring the shale stress sensitivity would lead to an overestimation of 10-year cumulative gas production by 7.8% for organic-rich dark massive shale (ORDMS) reservoir. By using particle swarm optimization (PSO) algorithm, it is proposed that quickly reducing pressure to critical desorption pressure with subsequently maintaining pressure is critical for long-term stable production and cumulative production maximization.