Production performance analysis of multi-fractured horizontal well in shale gas reservoir considering space variable and stress-sensitive fractures

Abstract

Multi-stage fracturing technology makes shale gas production economically viable. In this paper, an innovative model incorporating space variable and stress-sensitive fractures is established for the production of MFHW in shale. Multi-transport mechanisms including Darcy flow, Knudson diffusion, Surface diffusion are considered in the mathematical model. Three space variable conductivity patterns (Linear, Exponential, and Logarithmic variations) are introduced and adopted. Based on the discretization method, a novel method is proposed which can simulate uniform and space varying fractures conveniently. Then the semi-analytical solution is obtained by Stehfest numerical inversion and an iteration method. And good agreements with previous models are observed in the validation. Afterward, the pressure transient type curve is generated and eight flow periods are identified. Subsequently, the influences of several vital parameters are discussed in detail. The results show that space varying fracture enlarges the pressure drop and decreases the productivity of early time. Such an effect is enhanced as the space variable coefficient is increased. And this influence decreases with the increase of initial conductivity. Considering stress-sensitive fractures, a ‘hump’ appears in the pressure derivative curve and the early time productivity decreases. A bigger stress-sensitive coefficient accelerates the appearance of the ‘hump’ and makes the ‘hump’ sharper. The ‘hump’ and productivity decline caused by dynamic conductivity becomes more obvious with the decrease of the minimum conductivity. Complex transport mechanisms enhance inter-porosity flow. The inter-porosity flow would appear earlier with complex transport mechanisms. The model can simulate the gas flow of MFHW more realistically. It can help for better understanding of the production dynamic of MFHW in shale. • A semi-analytical approach is established for the pressure and rate transient of MFHW in shale gas reservoir. • Space variable and stress-sensitive fractures and multi-transport mechanisms of shale gas are considered. • A new solution and an iteration method are utilized to solve the space varying fracture and nonlinear problem. • Effects of some vital parameters on production performance are analyzed.