A decoupled model for compositional non-isothermal multiphase flow in porous media and multiphysics approaches for two-phase flow
Jochen Fritz · OPUS Publication Server of the University of Stuttgart (University of Stuttgart) · 2010
The demands of computational resources of a simulator and the necessary efforts in defining boundary and initial conditions increase with the physical complexity of a model. Thus, a trade-off between physical accuracy and computational demands of a model are made. In many practical applications of porous media flow simulators, the most complex processes are confined to a small part of the model domain. In such a case, either high complexities are neglected in favor of a slim model or all processes are captured with a complex model which is superfluous in large parts of the domain. As a compromise between both options, an interface coupling method is introduced. It couples simple and complex models and adapts the resulting multiscale model to the actually occurring physical processes. As a basis for this, a decoupled formulation for non-isothermal compositional multiphase flow is introduced. It provides the advantage that the size of the linear system of equations does not grow with the number of phases or components involved. This work reviews the common concepts for the description of multiphase flow in porous media and provides a consistent derivation of the conservation equations of non-isothermal compositional flow and transport processes. Based on these equations, decoupled formulations for isothermal and non-isothermal compositional flow are derived using the concept of local conservation of total fluid volume. The implementation of the derived formulations into a finite volume method with an implicit pressure explicit concentration time discretization is presented. The resulting simulation tool is tested and verified with results from different experimental and computational investigations and its range of applicability is considered. Based on the decoupled formulations derived before, an isothermal and a non-isothermal multiphysics concepts for the transition of complexity within a porous media domain is presented. Furthermore, a simple and robust subdomain control scheme is developed which assures optimal adaption of the model complexity to the occurring processes at any time. Both models are implemented and tested towards their accordance with the globally complex decoupled models. It is shown that computational demands of a simulator can be lowered by incorporation of the multiphysics schemes. Finally, further ideas for the extension of the multiphysics towards more complex systems and possible interfaces with multiscale methods are considered.