Fully Coupled Analysis of Well Responses in Stress-Sensitive Reservoirs

Abstract

Summary A fully coupled geomechanics and single-phase, fluid-flow model is developed to evaluate the combined effects of stress, fluid flow, and reservoir property changes on well responses in stresssensitive reservoirs. In particular, we pay attention to the interpretation of pressure buildup tests and to changes in the production characteristics of wells. In general, for weak hydrocarbon reservoirs that exhibit nonlinear, elastic and plastic constitutive behaviors, and stress-dependent properties such as permeability and porosity, the physical effect contributed from geomechanics may not be ignored in well test analysis. The coupled interaction between geomechanics and reservoir fluid production markedly affects the stress state and reservoir properties. Because we are using a coupled, numerical model, we evaluate the consequences of using simplified relationships (e.g., permeability as a function of pressure). Numerical analyses are performed to quantitatively assess the impact of reservoir stress sensitivity on practical well test problems. The key variables investigated in the study, that are important in evaluating stress-sensitive reservoirs, include permeability, porosity, and constitutive behaviors of reservoir rock including hysteresis and loading conditions. The development of high-stress regions around wellbores and its consequences on well performance are considered. The numerical results from the study indicate that for analyzing highly stress-sensitive reservoirs, a fully coupled geomechanics and fluid-flow modeling approach is necessary and the developed model employed in this study provides such a tool.