A Domain Splitting-Based Analytical Model for Rapid Assessment of Hydro-thermo-geomechanical Responses of Large Scale Heavy Oil Reservoirs: A Steamflood Application

Abstract

Abstract For stress-sensitive heavy oil reservoirs, geomechanical responses of the reservoir are taken into account as they play an important role in the accurate simulation of all thermal recovery techniques, such as SAGD, or steamflood. However full- field numerical simulations of multi-physics processes by any coupling strategies are technically impossible with current computer CPUs. Under these conditions, analytical methods can be used as approximate techniques instead of numerical simulators, as they are much faster and yet are useful tools for preliminary forecasting and sensitivity studies. In analytical models, inclusions of all flow variables impacts into geomechanics frameworks make the equations so complex and almost impossible to solve. This paper provides a flow-based domain decomposition workflow for performing different analytical coupling schemes in different reservoir compartments. Since the intensity and complexity of reservoir geomechanics vary over reservoir domain, one can divide the reservoir to some sub-domains and assess different geomechanical responses separately in each sub-domain. The presented analytical proxy, suggest decomposition of the whole domain in 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 due to 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 due to 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 steam-flood case to show the robustness and applicability range of the model. The results were analyzed for synthetic case single-domain model and the model sensitivity on some reservoir parameters were checked, and at the same time geomechanical responses were not neglected anywhere (near-filed and far field) in the reservoir.