Management of Stress Sensitive Reservoirs Using Two Coupled Stress-Reservoir Simulation Tools: ECL2VIS and ATH2VIS

Abstract

Abstract The stress state in and around a reservoir can change dramatically due to changes in pore pressure, temperature and water saturation caused by either depletion or water injection. Both depletion and water injection may cause deformation of the rock and alteration of the rock fabric, which in turn gives rise to phenomena such as compaction and subsidence, induced fracturing, opening of natural fractures and fault slip. These mechanical and chemical phenomena continuously affect the reservoir properties, the flow pattern in the reservoir and ultimately the recovery factor. In addition, changes of stress within the reservoir and in the overburden require special consideration in the design of wells to prevent sand production and casing collapse and for later infill drilling. To capture the link between flow and concomitant depletion and/or injection pressures and in situ stresses at field scale, it is essential to perform coupled reservoir-geomechanical simulations. This paper introduces the ECL2VIS and ATH2VIS tools, which provide a two-way link between the reservoir simulators ECLIPSETM1 and ATHOSTM2 and the geomechanical stress simulator VISAGETM3. The basic versions of these coupled simulators take the pore pressure and temperature increments calculated by the flow simulator and use them in the geomechanical simulator, which calculates corresponding changes in stresses that are used to update the permeability in the flow simulator. The latest versions of ECL2VIS and ATH2VIS address the issues of compaction drive. These versions will also allow for the modification of the mechanical properties of reservoir rocks due to corresponding changes of water saturation. The compaction-drive algorithm, with or without water weakening effects, forces the pore volume calculated by the flow simulator to be similar if not equal to the pore volume obtained from strain calculations.