Investigation of Shale-Gas-Production Behavior: Evaluation of the Effects of Multiple Physics on the Matrix

Summary

Shale gas is a major component of natural-gas supply in the United States. Multistage-fractured horizontal wells significantly improve the production performance of ultralow-permeability shale-gas reservoirs. Researchers have believed that shale-gas-production simulations should take into account the complex-flow behaviors in both fractures and the matrix. However, multiple physics applied on the matrix are generally incomplete in previous studies. In this study, we considered the comprehensive physics that occurred in the matrix including the effective stress, slip flow/pore diffusion, adsorption/desorption, and surface diffusion, as well as the dynamic properties of fractures. We investigated the importance of these features of the physics separately and in an integrated fashion by step-by-step production simulations. Afterward, comprehensive sensitivity analysis was performed with regard to stress dependency of the matrix and fractures. This work shows that natural-fracture spacing is the most prominent factor affecting shale-gas-reservoir performance. The work highlights the importance to gas recovery of mechanical squeezing of the pore volume by the effective stress. Surface diffusion might be essential for gas recovery that depends on surface-diffusivity values. Slip flow and pore diffusion do not significantly contribute to gas recovery even though they increase gas apparent permeability under low pressures.