| Popis: |
Nature is inherently multiphase and multicomponent. Water being ubiquitous in nature, any oil and gas formation is necessarily multiphase. In general, conditions pertaining to fluid, commonly designated as “black oil,” show the presence of water, oil, and gas. For simplicity, previous chapters have dealt with single-phase fluid. This chapter presents the basics of modeling a black-oil reservoir. In this context, we present the necessary engineering concepts for multiphase flow in porous media, followed by the derivation of the flow equation for any component in the system in a 1-D rectangular reservoir. Then, using CVFD terminology, we present the component general flow equations in a multiphase, multidimensional system, which apply to interior and boundary reservoir blocks. From these component flow equations, the basic flow models of two-phase oil/water, oil/gas, and gas/water and three-phase oil/water/gas are derived. The accumulation terms in flow equations are expressed in terms of changes in the reservoir block unknowns over a time step. We present the equations for phase production and injection rates from single-block and multiblock wells operating with different conditions. The treatment of boundary conditions as fictitious wells is presented and discussed in detail. Methods of linearization of nonlinear terms in multiphase flow are discussed. We introduce two of the basic methods for solving the linearized multiphase flow equations, the implicit pressure–explicit saturation (IMPES) and simultaneous solution (SS) methods. Because this chapter forms an introduction to the simulation of multiphase flow, we present the two solution methods (IMPES and SS) as they apply to the two-phase oil/water flow model only. The extensions of these methods to other flow models are straightforward, whereas the application of additional solution methods, such as the sequential (SEQ) and the fully implicit methods, is discussed elsewhere. More recently, Mustafiz et al., 2008a , Mustafiz et al., 2008b developed a new solution technique that solves nonlinear equations without linearization. Recently, the possibility of generating multiple solutions in the form of cloud points, which can then be used to draw the boundary of probable solutions, has been discussed in the literature. Such analysis is likely to unlock future directions of knowledge-based simulation. |
