Modeling and numerical simulations of Carbonate karst reservoirs is a challenging problem because of the presence of vugs and caves which are connected through fracture networks at multiple scales. In this paper, we propose a unified approach to this problem by using the Stokes-Brinkman equations which combine both Stokes and Darcy flows. These equations are capable of representing porous media (porous rock) as well as free-flow regions (fractures, vugs, and caves) in a single system of equations. The Stokes-Brinkman equations also generalize the traditional Darcy-Stokes coupling without sacrificing the modeling rigor. Thus, it allows us to use a single set of equations to represent multiphysics phenomena on multiple scales. The local Stokes-Brinkman equations are used to perform accurate scale-up. We present numerical results for permeable rock matrix populated with elliptical vugs and we consider upscaling to two different coarse-scale grids-5Â5 and 10Â10. Both constant and variable background permeability matrices are considered and the effect the vugs have on the overall permeability is evaluated. The Stokes-Brinkman equations are also used to study several vug/cave configurations which are typical of Tahe oilfield in China.

We present a novel approach for flow simulations through naturally-fractured vuggy carbonate reservoirs. This approach generalizes upscaling methods which have been successfully used to perform reservoir simulations on geological (fine) scales. Typically, vugular porous media is described using both Stokes and Darcy's equations at the fine-scale. We propose the use of simplified model based on StokesBrinkman equations. Stokes and Darcy equations can be obtained from these equations by appropriate choice of parameters. Moreover, in the presence of damaged zones between vugular regions and Darcy regions, Stokes-Brinkman equations allow a seamless transition.The upscaling of fine-scale equations is addressed within homogenization theory. Appropriate local problems are solved to compute the effective permeabilities, which are further used for the simulations on the field scale. We present numerical results for homogeneous and heterogeneous background permeability fields. Our results show that the coarse-scale permeability field is greatly affected when the background permeability is heterogeneous. This is due to the fact that the high flow channels connecting some of the vugs significantly alter the upscaled permeability. We compare the coarse-scale pressure obtained from upscaled equations with the averaged fine-scale pressure. The results are in agreement which indicates that the upscaled models are accurate for practical purposes.

fax 01-972-952-9435. AbstractModeling and numerical simulations of Carbonate Karst reservoirs is a challenging problem due to the presence of vugs and caves which are connected via fracture networks at multiple scales. In this paper we propose a unified approach to this problem by using the Stokes-Brinkman equations which combine both Stokes and Darcy flows. These equations are capable of representing porous media (porous rock) as well as free flow regions (fractures, vugs, caves) in a single system of equations. The Stokes-Brinkman equations also generalize the traditional Darcy-Stokes coupling without sacrificing the modeling rigor. Thus, it allows us to use a single set of equations to represent multiphysics phenomena on multiple scales. The local Stokes-Brinkman equations are used to perform accurate scale-up. We present numerical results for permeable rock matrix populated with elliptical vugs. Both constant and variable background permeability matrices are considered and the effect the vugs have on the overall permeability is evaluated. Fracture networks connecting isolated vugs are also studied. It is shown that the Stokes-Brinkman equations provide a natural way of modeling realistic reservoir conditions, such as partially filled fractures.

We present a novel approach for flow simulations through naturally-fractured vuggy carbonate reservoirs. This approach generalizes upscaling methods which have been successfully used to perform reservoir simulations on geological (fine) scales. Typically, vugular porous media is described using both Stokes and Darcy's equations at the fine-scale. We propose the use of simplified model based on StokesBrinkman equations. Stokes and Darcy equations can be obtained from these equations by appropriate choice of parameters. Moreover, in the presence of damaged zones between vugular regions and Darcy regions, Stokes-Brinkman equations allow a seamless transition.The upscaling of fine-scale equations is addressed within homogenization theory. Appropriate local problems are solved to compute the effective permeabilities, which are further used for the simulations on the field scale. We present numerical results for homogeneous and heterogeneous background permeability fields. Our results show that the coarse-scale permeability field is greatly affected when the background permeability is heterogeneous. This is due to the fact that the high flow channels connecting some of the vugs significantly alter the upscaled permeability. We compare the coarse-scale pressure obtained from upscaled equations with the averaged fine-scale pressure. The results are in agreement which indicates that the upscaled models are accurate for practical purposes.