A drainage and gas recovery optimization method for maximizing natural energy utilization efficiency in shale gas wells

During the natural-energy production stage of shale gas wells without external energy supply, the utilization efficiency of formation energy directly determines a single well’s cumulative gas production and free-flowing life. Using the maximization of natural-energy utilization efficiency as the criterion, this paper establishes an integrated reservoir–wellbore–process energy model to determine the intervention timing and production allocation of the velocity string and foam drainage processes, and to predict the cumulative gas production and free-flowing life after optimization. The model couples three parts: on the reservoir side, based on Tan fractal theory, it accounts for matrix stress sensitivity, Knudsen diffusion, Klinkenberg slippage, and Langmuir adsorption–desorption; on the fracture side, it defines a non-uniform conductivity distribution function along the horizontal section, which agrees with field PLT measurements; on the wellbore side, it establishes a variable-mass-flow pressure-drop equation accounting for density variation. Application to Well W1 in the Sichuan Basin shows that the optimized scheme improves natural-energy utilization efficiency by reducing wellbore energy loss, thereby prolonging the effective production period and increasing cumulative gas production during the natural-energy production stage.