Review of Coupling Techniques in Field Examples
Review of Coupling Techniques in Field Examples
Studies to test the geo-mechanical behavior of porous rocks through various coupling techniques reveal diverse results. Fontaine, Onaisi and Samier (2006) carried out geo-mechanical simulation to test parameters that affect the flow of reservoirs, by making a link between in-situ stress and flow. The research method compared five techniques for reservoir simulations to two fields and two validation cases. A review of the research approach found that the method used by Fontaine, Onaisi and Samier (2006), to be validated and credible. This is because the study provided literary support for its research problem, identified as the challenge of the management of reservoir stresses by linking geo-mechanics and fluid flow.
Fontaine, Onaisi and Samier (2006) simulation approach is effective since it fills in the problems identified in literature for coupling and non-coupling reservoir simulations for flow and stress. The approach is efficient since it increased accuracy and feasibility of simulations for complex and large-scale reservoir systems, which previous studies had found difficult to prove. Fontaine, Onaisi and Samier (2006) used the one-way coupling method to identify the effects of stress on permeability. Fostering accuracy and feasibility increase was by the use of porosity and permeability multipliers in the simulator that defined the curves and pressure of oil phases. Fontaine, Onaisi and Samier (2006) simulation also incorporated a coupling method to simultaneously identified and solved flow unknowns- pressure, displacement, and saturation. The effectiveness of this approach emanates when Fontaine, Onaisi and Samier (2006) tested compaction and subsidence on the North Sea Chalk field. This simulation test provided more credible and accurate results since compaction is responsible for non-linear porosity changes.
The application of Fontaine, Onaisi and Samier (2006) simulation on field examples created a technique superior to the methods developed by Dean et al. (2006) and Gutierrez & Lewis (1998). While Fontaine, Onaisi and Samier’s (2006) simulation tested on field examples, Dean et al. (2006) and Gutierrez & Lewis’s (1998) approach untested, but rather used 3-D simulations of rocks to test iterations. Dean et al. (2006) and Gutierrez & Lewis’s (1998) may have factored in geo-mechanics problems that induce subsidence and compaction in their simulations, but did not test their accuracy and feasibility.
Testing on field examples as Fontaine, Onaisi and Samier’s (2006) did, would have enabled them to adjust their simulation to match compaction and subsidence seen real reservoirs. This is a considerable gap in Dean et al. (2006) and Gutierrez & Lewis’s (1998) researches since the effects of geo-mechanics like non-unique stress paths and stress arching create discrepancies between laboratory results and field results. By carrying out a field test as done by Fontaine, Onaisi and Samier’s (2006), would have revealed the level of reaction of the simulator to real life reservoir factors like rock compressibility constant, nonlinear behavior of compressibility, nonlinear behavior of compressibility with porosity multipliers and flow direction in all dimensions.
The use of 3D simulations and iterations creates significant errors in results, since this method does not factor in the effects of regions with no hydrocarbon or no flow. Simulations not tested on field examples do not fully describe stress dynamics contributed by non-equilibrium stress like no hydrocarbon or no flow. Fontaine, Onaisi and Samier’s (2006) field examples overcome this problem as they factor in all linear and non-linear geo-mechanical properties. Dean et al. (2006) and Gutierrez & Lewis’s (1998) techniques should have simulated compaction with elastic compressibility constant to approximate pseudo-coupling and realize exceptionally accuracy of their method.
Dean et al. (2006) and Gutierrez & Lewis’s (1998) simulations did not consider the effects of radical faults on reservoir stress. Gutierrez & Lewis’s (1998) looked at stresses like in-situ stress, rock deformation, fluid pressure and permeability, while Dean et al. (2006) looked at subsidence and compaction caused by reservoir volume and pressure from non-pay regions. Carrying out a case study using these simulations would produce results with substantial deviations from reality. This is because the simulations would not account for stresses from reactivated faults as Dean et al. (2006) and Gutierrez & Lewis’s (1998) simulations make the assumption that all serious faults are closed. These simulations should have based their geo-mechanical method on the one-way or explicit coupling method used by Fontaine, Onaisi and Samier’s (2006), which predicts fault displacement and stress evolution.
Apart from comparing simulation results with field examples, Dean et al. (2006) and Gutierrez & Lewis’s (1998) should have tested their simulation to validated cases as Fontaine, Onaisi and Samier’s (2006) did. Comparing simulation results with published cases that have solved similar problems makes it possible for a researcher to tell the level of deviation of their results. Fontaine, Onaisi and Samier’s (2006), tested their simulation results to a validated case the analyzed depletion in a single and homogeneous sugar-box reservoir with and without non-pay regions. It is evident that an integrated coupling method offers a more accurate and feasible simulation for large and complex reservoir systems. Since real reservoirs undergo varies stress and flow factors, a geo-mechanical simulation should be tested on field examples, and its results compared to validated cases to reduce the margin of error as in Fontaine, Onaisi and Samier’s (2006) study.
References
Dean, R.H., Gai, X., Minkoff, S.E. and Stone, C.M. (2006). A Comparison of Techniques for Coupling Porous Flow and Geomechanics. Society of Petroleum Engineers Journal, 11(1), 32-140.
Fontaine, G., Onaisi, A. and Samier, P. (2006). Comparisons of Uncoupled and Various Coupling Techniques for Practical Field Examples. Society of Petroleum Engineers Journal, 11(1), 89-102.
Gutierrez, M. and Lewis, U. (1998). The Role of Geomechanics in Reservoir Simulation. SPE/ISRM 47392 Eurock’98, 2. Trondheim, Norway, July 8-10, 439-448.
