How To Approximate Effects of Geomechanics in Conventional Reservoir Simulation
- A.T. Settari (U. of Calgary) | R.C. Bachman (Taurus Reservoir Solutions Ltd.) | D.A. Walters (Taurus Reservoir Solutions Ltd.)
- Document ID
- Society of Petroleum Engineers
- SPE Annual Technical Conference and Exhibition, 9-12 October, Dallas, Texas
- Publication Date
- Document Type
- Conference Paper
- 2005. Society of Petroleum Engineers
- 4.1.2 Separation and Treating, 5.1.5 Geologic Modeling, 5.5 Reservoir Simulation, 5.1.2 Faults and Fracture Characterisation, 3.2.3 Hydraulic Fracturing Design, Implementation and Optimisation, 2.2.2 Perforating, 1.2.2 Geomechanics
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Geomechanics is often represented in conventional reservoir simulators bypressure dependent treatment of porosity and/or permeability. The paper gives asystematic treatment of the subject and shows different methods forpressure-dependent approximations.
Although there is no single method that would provide the best approximationunder all circumstances, reasonable approximations exist in several situations.For porosity coupling, the primary factor is the type of deformation. Accurateapproximations are given for the cases of uniform depletion with differentdeformation assumptions. For permeability coupling, new methods have beendeveloped and tested against coupled simulations.
The results show clearly that large errors can result from simpleapproaches, in estimating both reservoir pressure decline and wellproductivity/injectivity.
In coupled geomechanical and reservoir modelling, one can correctlyrepresent the dependence of reservoir porosity and permeability on effectivestress or deformation of porous media. However, because of the complexity andcost of coupled modelling, it is often necessary to approximate these effectsin conventional (uncoupled) reservoir simulators. Most commercial models offeroptions for pressure-dependent porosity (or rock compressibility) andpermeability.
In spite of the popularity of the approach, confusion exists about how tobest translate the rock mechanics lab data (measured as a function of effectivestress) to functions of pressure only, and little is known about the errorsresulting from this simplification. This paper gives a systematic discussion ofthe subject and provides methods for the computation of rock compressibilityand pressure depemdent permeability for uncoupled modelling from the truegeomechanical data. Both aspects of the coupling (i.e., coupling via porosityand via permeability) will be treated. The methodology utilizes a combinationof analytical considerations and comparisons of coupled and uncoupledsimulations.
In all reservoirs, the changes in pressure P and temperature Tinduced by recovery operations are accompanied by changes of stress state. Insome problems reservoir undergoes deformation caused by outside forces (e.g.,from another reservoir or aquifer zone). In the first (more common) case theP and T changes are the driving forces causing deformation andstress changes, while in the second the deformations are the driving forcescausing changes in pressure.
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