In-situ characterization of nonlinear flow behavior of fluid in ultra-low permeability oil reservoirs

Abstract

Correlating velocity-gradient relation is crucial for understanding flow behavior of fluid in low-permeability oil reservoirs. Instead of experimental approaches, this paper utilized downhole pressure data analysis for in-situ characterization of nonlinear flow behavior at low velocity. We introduced a dynamic permeability concept, which connects flow equation and nonlinear flow behavior. We then employed pseudo-linear function, piecewise function and continuous function to characterize the nonlinear flow behavior. The transient pressure type curves response ascended in the late-time flow period with consideration of nonlinear flow effect, suggesting that nonlinear flow equations can affect the characteristic of the type curves. The coefficients of approximation function are considered to be model parameters and are determined by downhole pressure analysis. Through our workflow, we can obtain a velocity-gradient relation, describing the nonlinear flow behavior of in-situ fluid. The practicality and efficiency of our new method are illustrated by comprehensive case studies. The in-situ flow behavior in reservoir scale can be characterized by normalizing multiple velocity-gradient curves derived from individual well analysis. Compared with core-flooding experiments, the proposed method is more convenient and economic to characterize flow behaviors in low-permeability oil reservoirs.