A transient analysis method for a multi-horizontal-well pad with well interference and gas–water flow in shale

Complex fracture networks generated by fracturing treatments and the gas–water flow have intensified the well interference in shale gas reservoirs. In this paper, a high-precision numerical model is developed to capture the effects of well interference and gas–water flow on pressure transient behaviors of multi-horizontal-well pads. The unstructured Voronoi grid approach is employed to discretize the physical model. The model's accuracy is verified through published analytical solutions. The findings reveal that a multi-horizontal-well pad in shale gas reservoirs can exhibit up to ten distinct flow regimes. An increase in residual water saturation reduces the water flow ability and leads to an earlier commencement of the gas–water flow regime. Once the formation water becomes flowable, higher water saturation delays the initiation of all flow regimes. The well interference regime exhibits characteristics of the linear flow due to the increased well spacing. As fracture propagation leads to the well communication, the effect of fracture half-length on pressure transient behaviors becomes negligible. The case study from the Fuling shale gas reservoir demonstrates that the proposed model achieves a satisfactory fit to the actual pressure data and the pressure transient behaviors manifest a typical boundary-dominated flow regime.