A New Darcy-Stokes Flow Model for Cavity-Fractured Reservoir

Abstract

AbstractConventional cavity-fractured reservoir has small sizes of cavity and the corresponding flow behavior is presented by the equivalent model for fluid flow in porous media. However, in Tarim Basin, the biggest land oil/gas-baring basin in China, many unconventional fractured reservoirs are found that cavities are the main storage space while both fractures and cavities offer flow paths. Current porous flow model are not applicable due to the large cavities even with the scale of meter. A new flow model is needed to describe the flow behavior in order to successfully develop these cavity-fractured reservoirs.In this paper, fluid flow in Tarim cavity-fractured reservoirs is firstly studied by integrating geology and reservoir engineering. As an example, Tahe Ordovician carbonate reservoir is analyzed in detail. Then, a new Darcy-Stokes model for slightly compressible two-phase flow is built. In our model, flow area is divided into porous flow region and free flow region according to flow characteristics. Porous flow region obeys Darcy's law and is described by the flow in porous media with multiple porosities. On the other hand, free flow region satisfies Navier-Stokes flow and the equation describing slightly compressible two-phase flow is developed. The connection at the interfaces of these two flow regions is derived by the extension of Beavers-Joseph-Saffman boundary condition to two-phase flow.The application of Darcy-Stokes flow model to Tahe reservoir demonstrates that this model gets better prediction on oil production performance than the fractured model with dual porosity.