Abstract
Fracture-cave carbonate reservoirs occur widely in source rocks and are prospects for exploitation worldwide. However, the presence of massive caves and multiscale fracture systems results in extremely complex fluid flow patterns. Therefore, in this paper, a discrete network model for fracture-cave reservoirs was established to study fluid flow characteristics and pressure distributions in complex flow regimes. In this study, the cave system was treated as a free-flow region, and the fluid flow in fracture systems followed the Navier-Stokes and Darcy equations, respectively. After discrete modeling, the Galerkin finite element method was used for numerical calculation of the single-phase free flow; the method maintains a high-precision result with low grid orientations during the simulation. In addition, because only one linear equation requires solving at each step, the solution is obtained quickly. Moreover, based on the proposed discrete media network model of fracture-cave reservoirs and the finite element numerical calculation method, a corresponding simulator was also developed. The finite element numerical simulation method based on the characteristic-based split (CBS) algorithm has proven to be applicable to complex flow problems in fracture-cave reservoirs.
Highlights
Fracture-cave reservoirs play a vital role in the petroleum industry, as these reservoirs contain large volumes of oil and are widely distributed in areas such as Saudi Arabia, Iran, Iraq, Mexico, Oman, and Syria [1]
The finite element method (FEM) has been widely used in the field of solid mechanics and is widely used in the petroleum research, providing an important approach to numerical simulation of problems involving discrete fractured networks [2, 3]
The theory of the characteristic-based split (CBS) algorithm is based on the split- and characteristic-Galerkin procedures, which are extended in the FEM
Summary
Fracture-cave reservoirs play a vital role in the petroleum industry, as these reservoirs contain large volumes of oil and are widely distributed in areas such as Saudi Arabia, Iran, Iraq, Mexico, Oman, and Syria [1]. The FEM has been widely used in the field of solid mechanics and is widely used in the petroleum research, providing an important approach to numerical simulation of problems involving discrete fractured networks [2, 3]. The simulation results showed that the model can predict the transient pressure response in complex naturally fractured reservoirs; in addition, it can be used to match pressure data and diagnose characteristic properties of naturally fractured reservoirs. Because of the lack of a systematic theory and appropriate modeling techniques, research on theories and techniques of numerical simulation using discrete medium models to model giant fracture-cave reservoirs is still in an exploratory stage, with existing studies concentrating mostly on fractured media. We applied the FEM to the study of fracture-cave reservoirs based on a CBS discrete medium model
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