Shudi Fan

This study aims to optimize gas production in shale reservoirs by investigating the impact of hydraulic fracturing and two-phase gas-water flow within fracture-induced zones. A multi-domain, multi-phase fractal model was developed, incorporating fractal dimensions to represent the microstructure of shale reservoirs, which consist primarily of kerogen, inorganic matrix, and fractures. Key parameters, including fracture-induced zone width, maximum water relative permeability, and hydraulic fracture aperture, were analyzed for their effects on gas output and microstructure evolution. Results indicate that moderate hydraulic fracturing improves gas production, while excessive water reflux outside the optimal range diminishes output. Additionally, increased water relative permeability and hydraulic fracture aperture promote fracture and pore development, while lowering the entry pressure of the non-wetting phase facilitates matrix pore growth.

As one of the most significant clean energy sources, the migration characteristics and extraction processes of coalbed methane (CBM) have been extensively studied. The structural distribution and evolutionary characteristics of reservoir fractures, as the main conduit for gas migration, significantly affect the permeability and gas production. However, few models have been able to quantitatively and accurately explore reservoir micro-macro interactions under coupled thermal-fluid-solid effects. This work develops a new highly coupled model based on the widely-adopted power-law function to quantify reservoir thermal conduction effect, gas pressure evolution, reservoir deformation, in-situ stress, adsorption-desorption effect and reservoir microstructure evolution. Three parameters are adopted to quantitatively characterize the reservoir structure: (1) fracture power index (to characterize the fracture density), (2) fracture length ratio r_f (to characterize the fracture size) and (3) the maximum fracture length l. The results demonstrate that the fractal network is a special kind of network in the power-law length distribution. And the proposed power-law seepage model is able to accurately characterize the evolution of reservoir microstructure and the impact of microevolution on extraction under multi-field coupling effects, compared to the traditional power-law model. The proposed model can provide a good theoretical and practical support for the study of CBM migration and extraction.