A Domain Splitting-Based Analytical Approach for Assessing Hydro-Thermo-Geomechanical Responses of Heavy-Oil Reservoirs

Abstract

SummaryFor stress-sensitive heavy-oil reservoirs, geomechanical responses of the reservoir are taken into account because they play an important role in the accurate simulation of all thermal recovery techniques, such as steam-assisted gravity drainage (SAGD) or steamflood. However, full-field numerical simulations of multiphysics processes by any coupling strategies are technically impossible with current computer central processing units (CPUs). Under these conditions, analytical methods can be used as approximate techniques instead of numerical simulators because they are much faster and yet are useful tools for preliminary forecasting and sensitivity studies. In analytical models, inclusion of all flow-variable impacts into geomechanics frameworks make the equations complex and almost impossible to solve. This paper provides a flow-based domain decomposition work flow for performing different analytical coupling schemes in different reservoir compartments.Because the intensity and complexity of reservoir geomechanics vary over reservoir domain, one can divide the reservoir to some subdomains and assess different geomechanical responses separately in each subdomain. The presented analytical proxy suggests decomposition of the entire domain into two parts of “heated zone” and “wetted zone,” for rapid assessment of geomechanics. The heat-flow equation was combined with mass and momentum convective-transport equations to obtain an exact approach that correlates the saturation front of injected hot water to temperature front. The frontal velocities are dynamic interfaces for compartmentalization of the domain. In the heated zone, the total induced stresses were considered because both temperature and pressure increase, and in the wetted (saturated) zone beyond the temperature front, at each instance, the total stress induced is only a function of pressure increase, and, accordingly, stress and strain induced are caused by isotropic unloading. This technique provides a rapid estimate of geomechanical responses (stress and strain profile) in each part of the reservoir (near field and far field).A numerical model was built and implemented in CMG-STARS for a steamflood case to show the robustness and applicability range of the model. The results were analyzed for a synthetic-case single-domain model, and the model sensitivity on some reservoir parameters was checked, while geomechanical responses were not neglected anywhere (near field and far field) in the reservoir. The results of the numerical model were in close agreement with the result of the proposed analytical proxy.