Fully coupled analysis of well responses in stress-sensitive reservoirs

A fully coupled geomechanics and single-phase, fluid-flow model is develope d to evaluate the combined effects of stress, fluid flow, and reservoir pro perty changes on well responses in stress-sensitive reservoirs. In particul ar, we pay attention to the interpretation of pressure buildup tests and to changes in the production characteristics of wells. In general, for weak h ydrocarbon reservoirs that exhibit nonlinear, elastic and plastic constitut ive behaviors, and stress-dependent properties such as permeability and por osity, the physical effect contributed from geomechanics may not be ignored in well test analysis. The coupled interaction between geomechanics and re servoir fluid production markedly affects the stress state and reservoir pr operties. Because we are using ai coupled, numerical model, we evaluate the consequences of using; simplified relationships (e.g., permeability as a f unction of pressure). Numerical analyses are performed to quantitatively as sess the impact of reservoir stress sensitivity on practical well test prob lems. The key variables investigated in the study, that are important in ev aluating stress-sensitive reservoirs, include perme- ability, 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 fro m 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.