Blasingame decline type curves with material balance pseudo-time modified for multi-fractured horizontal wells in shale gas reservoirs

Production decline analysis has been considered as a robust method to obtain the flow parameters, reservoir properties and original gas in place. Although advanced Blasingame production decline analysis methods for vertical wells, fractured wells and horizontal wells in conventional reservoirs are widely used, there is no Blasingame production decline type curves for multi-fractured horizontal wells (MFHW) with considering stimulated reservoir volume (SRV) in shale gas reservoirs yet. Compared with conventional gas reservoirs, multi-flow mechanisms (such as Darcy flow, diffusion and adsorption/desorption) and complex flow behaviors of MFHW exist in shale gas reservoirs, bringing a big challenge for analyzing the rate decline performance of the wells. Thus, in this paper based on the material balance equation in consideration of adsorption/desorption, the material balance pseudo-time of Blasingame decline type curves is modified so as to extend the theory of Blasingame production decline analysis to shale gas reservoirs. Considering the nonlinearity caused by gas desorption and diffusion, and the complex flow of MFHW, a numerical method is applied in this paper to obtain Blasingame type curves. Based on the perpendicular bisection (PEBI) grids, a numerical model considered SRV is developed and the solution is obtained using control volume finite element method and the fully implicit method. Further Blasingame type curve is validated by a simplify model, and Blasingame production decline type curves of the MFHW considering SRV in a shale gas reservoir are plotted through computer programming. Five flow regimes, including early formation linear flow, early radial flow, compound linear flow, the second radial flow and pseudo-steady flow, are recognized. Compared with the modified Blasingame type curves presented in this paper, the ones with traditional pseudo-time have a tendency to underestimate the value of normalized rate, normalized cumulative production, normalized integral derivative cumulative production and the reserve. The effects of relevant parameters including SRV radius, outer region radius, permeability in SRV region and outer region, Langmuir pressure, Langmuir volume and diffusion coefficient on type curves are analyzed as well. This work expands our understanding of a MFHW flow behaviors in shale gas reservoirs, which can be used to estimate with reservoir properties, SRV, and reserves in these types of reservoirs.