Flow Mechanism and Transient Pressure Analysis of Multi-Stage Fractured Horizontal Well

Shale gas reservoirs are typical unconventional natural gas resources characterized by low porosity and low permeability of the formation. To enhance production and provide an economically justified production rate, the multi-stage fractured horizontal well (MFHW) technology has been widely used in shale gas reservoirs. More attention has been paid recently to studying the mechanism of multi-scale flow in shale. However, the mechanism of gas seepage in shale in a multi-stage fractured horizontal well has not been systematically discussed. In the previously published conventional studies, the authors have not presented a comprehensive analysis of the adsorption, desorption, and diffusion mechanisms participating in gas seepage, particularly within a linear flow model. In this paper, the linear superposition method is applied to describe the non-Darcy flow behavior in nano/micro-scale pores and the Darcy flow behavior in macropores and natural/induced fractures in a shale matrix. Based on the flow mode, the shale reservoir and the area around the multi-stage fractured horizontal well are divided into three zones: the outer region flow, the inner region flow, and the flow in the hydraulic fractures. Based on the trilinear flow model, the authors consider the differences in properties between the initial shale reservoir and the induced fracture network of the stimulated reservoir volume (SRV). In this model, the dimensionless variables, Duhamel principle, and numerical Stehfest algorithm are combined to analyze the dynamic bottomhole pressure, adsorption-desorption behavior, multi-scale flow mechanism, and complex SRV geometry in the MFHW area. Based on the established model, the effect of the key factors and their influence on the dimensionless pressure and pressure derivate curves are considered..