Pressure transient analysis of a multi-horizontal-well pad by a semi-analytical model: Methodology and case study

Drilling more infill multi-fractured horizontal wells (MFHWs) is one of the most direct oil and gas production methods in unconventional reservoirs with high recovery. MFHWs in the multi-horizontal-well pad can be easily interfered by the adjacent wells during well testing. Unfortunately, most of the existing well testing models for MFHWs are limited to a single well. A semi-analytical well testing model for transient pressure analysis in a multi-horizontal-well pad is presented in this work.In the proposed model, the entire formation is divided into three domains, namely matrix, natural fracture, and hydraulic fracture, to describe unconventional reservoirs comprehensively. With Laplace transform and Stehfest numerical inversion techniques, the reservoir models with matrix and natural fracture systems are solved analytically. The solutions of the hydraulic fracture model for multiple MFHWs are obtained by the finite difference method. The pressure superposition method and production rate relationship are used to characterize the impact from the adjacent wells. The general solutions of the multi-well reservoir model and hydraulic fracture model are then coupled to obtain the tested well's bottom-hole pressure. The results of the proposed model are in good agreement with the commercial numerical software. The multi-horizontal-well pad's integrated flow regimes can be divided into a bilinear flow, linear formation flow, the pseudo radial flow of hydraulic fracture, multi-MFHW effect, cross-flow between matrix and natural fracture, and formation pseudo radial flow. The pseudo radial flow of hydraulic fracture, the multi-MFHW effect, cross flow, and formation pseudo radial flow have unique characteristics in the multi-horizontal-well pad, and these flow regimes are highly affected by the adjacent MFHWs properties and well-spacing. With the change of well-spacing, the multi-MFHW effect is characterized by the linear flow inside the multi-horizontal-well pad or the multi-well pad's biradial flow. The comparison of pseudo-steady-state (PSS) flow and transient flow indicates that different cross-flow conditions from the matrix to natural fracture will only affect the derivative curve's cross-flow behavior. The case study shows that the proposed model can obtain a more accurate interpretation result of the tested well under the adjacent well's effect.