Management of Stress Sensitive Reservoirs Using Two Coupled Stress-Reservoir Simulation Tools : ECL2VIS and ATH2VIS
- Atef Onaisi (Total Fina Elf) | Pierre Samier (Total Fina Elf) | Nick Koutsabeloulis (V.I.P.S. Ltd.) | Pascal Longuemare (IFP Institut Français du Petrole)
- Document ID
- Society of Petroleum Engineers
- Abu Dhabi International Petroleum Exhibition and Conference, 13-16 October, Abu Dhabi, United Arab Emirates
- Publication Date
- Document Type
- Conference Paper
- 2002. Society of Petroleum Engineers
- 4.1.5 Processing Equipment, 4.3.4 Scale, 5.3.2 Multiphase Flow, 1.7 Pressure Management, 1.10 Drilling Equipment, 5.5 Reservoir Simulation, 5.1.2 Faults and Fracture Characterisation, 5.1.1 Exploration, Development, Structural Geology, 5.5.8 History Matching, 1.2.2 Geomechanics, 5.7.2 Recovery Factors, 2.4.3 Sand/Solids Control, 4.1.2 Separation and Treating, 3 Production and Well Operations, 1.6 Drilling Operations, 5.8.6 Naturally Fractured Reservoir, 3.2.5 Produced Sand / Solids Management and Control, 5.2.1 Phase Behavior and PVT Measurements, 5.3.4 Integration of geomechanics in models, 6.5.2 Water use, produced water discharge and disposal, 3.2.3 Hydraulic Fracturing Design, Implementation and Optimisation, 5.8.7 Carbonate Reservoir, 5.1.5 Geologic Modeling
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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 reservoirgeomechanical 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.
The importance of Geomechanics in problems such as wellbore stability, hydraulic fracturing and subsidence is well known. In recent years, there has been growing awareness of the importance of the link between fluid flow and geomechanics in the management of stress sensitive reservoirs1-8. Standard reservoir simulation of compaction drive accounts for nonlinear porosity changes as reported from uniaxial strain tests on cores. In many cases, laboratoryderived compressibility must be adjusted to match the contribution of compaction to total hydrocarbon recovery. Geomechanical effects such as stress arching and non-unique stress path are among the causes of discrepancy between laboratory-derived and field compressibility factors. If compressibility varies linearly with the mean reservoir pressure, then predictive reservoir modeling can be achieved without coupling between stress and flow. However, geomechanical effects are rarely linear for a number of reasons. These include load variations due to modification of pressure, temperature and saturation, change of the mechanism of production, progressive activation of faults and fractures that affect mechanisms such as stress arching and a non-linear stress path. Unlike standard compaction drive simulation, there is no simple linear method to account for the effects of stress on permeability especially for fractured systems, where the changes of permeability might be directional, localized and strongly non-linear.
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