Numerical Studies on Two-way Coupled Fluid Flow and Geomechanics in Hydrate Deposits
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Coupled flow and geomechanics play an important role in gas hydrate reservoirs because the stiffness of the rock skeleton, porosity and permeability are directly influenced by changes of the fluid (water and gas) and solid (hydrate and water) phase saturations, and the deformation of the reservoir. The fluid and solid phases coexist, yielding a high nonlinearity for flow and mechanics, so the coupled problem for hydrates is exceptionally complicated. In previous study, the stability of hydrate-bearing sediments was assessed by one-way coupled analysis, where the change of fluid properties affects mechanics, but there is no feedback from mechanics to flow. In this paper, we develop and test rigorous two-way coupling between fluid flow and mechanics, where the solutions from mechanics are used to solve the flow problem. We employ the fixed-stress split for a convergent sequential implicit scheme. We have found noticeable differences between one- and two-way couplings for several cases. The nature of the elliptic boundary problem of quasi-static mechanics results in instantaneous compaction or dilation over the domain by loading from reservoir fluid production. This yields the pressure rise-up or drop at early time (low pressure diffusion), which changes the effective stress instantaneously and geological instability may occur. Also, the change of pressure or temperature affects the solid saturation, rock stiffness, porosity, and permeability fields, changing the fluid flow regime. These behaviors cannot be captured by one-way coupling. In conclusion, we developed, verified, and demonstrated the applicability of the tightly coupled sequential approach. It provides a rigorous two-way coupled simulator which is ready to be applied to large scale problems to hydrate-bearing sediments. Copyright 2011, Society of Petroleum Engineers.
author list (cited authors)
Kim, J., Yang, D., Moridis, G. J., & Rutqvist, J.