Effect of stress anisotropy on well productivity in unconventional gas reservoirs

Relative magnitude of in-situ stresses and their direction can control production performance of non-fractured and hydraulically fractured horizontal wells in unconventional gas reservoirs. The in-situ stresses influence wellbore instability, hydraulic fractures propagation, reservoir permeability anisotropy, and direction of gas flow in the reservoir. This paper presents the evaluation of the factors associated with horizontal stress anisotropy that control production performance in tight gas, shale gas, and coal bed methane reservoirs with normal faulting stress regime. Rock mechanical modeling and reservoir simulation are carried out based on the typical data from a West Australian unconventional gas reservoir, in order to understand the effect of stress anisotropy on permeability anisotropy and well productivity for difference cases of non-fractured and hydraulically fractured horizontal wells. The study results highlight the significance of well completion system, horizontal well orientation, and direction of in-situ horizontal stresses in controlling well productivity. In non-fractured or hydraulically fractured wells, production performance may noticeably be different when horizontal wellbore orientation is parallel or perpendicular to the maximum horizontal stress direction. Understandings of these factors are vital in designing the well completion and stimulation strategy that ensures maximum well productivity.