An Efficient Localized Nonlinear Solver for Simulating Natural Depletion of Unconventional Reservoirs with Complex Fracture Networks

Abstract

Summary Simulating unconventional reservoirs efficiently and accurately poses a big challenge. Transient flow can last for a long period and sharp solution gradients appear because of the severe permeability contrast between fracture and matrix. Although high-resolution well and fracture models are required to achieve sufficient accuracy, they are computationally too demanding for field models with many hydraulic-fracture stages. This paper aims to develop a nonlinear solution method, which is applicable to discrete fracture models (DFMs) for unconventional reservoirs. The localization algorithm takes advantage of solution locality on timestep and Newton iteration levels. We study the new method through multiple natural-depletion cases containing discrete fractures and compositional models. It is found that a large extent of solution locality displays over iterations as well as timesteps. The developed nonlinear solver exhibits outstanding simulation efficiency compared with a standard solver. A significant speedup is achieved by focusing computations to the locales that undergo considerable solution changes. Moreover, nonlinear convergence performance is maintained, with no degradation of the solution results.