An Overview of Numerical Reservoir Simulation

Abstract

Numerical reservoir simulation can be defined as the the process of constructing and running a model that mimic the appearance and flow dynamics of an actual reservoir system, including the subsurface porous and permeable reservoir and its other physical components to produce (wellbore) and process the reservoir fluids (surface facilities). The model properties are typically populated from a detailed geological model to capture the heterogeneity of the reservoir system and its effects on the flow. The formulation includes the discretized forms of the flow equations that describe multiphase fluid flow in porous media. These equations are linearized either at the partial differential equation level or at the discretized level to obtain a linear system of equations. The solution is represented at both time and space domains to solve for the time dependent characteristics such as pressures, fluid saturations/compositions and temperatures, which are representative of the performance of a reservoir. Because of the benefits that have been made possible with developments in both theory/formulation/solution-related aspects and computational technologies, numerical reservoir simulation has become a standard tool for decision-making purposes in the petroleum industry. Although these advantages are quite evident, it is still critically important to understand the strengths and weaknesses of the approach similar to any other available approach to forecast the reservoir performance. Objectives and scope of a reservoir simulation study must be carefully determined after considering available resources. This chapter gives an overview of numerical modeling of hydrocarbon reservoirs for those who are not familiar with the subject. Therefore, theoretical foundations are kept such that to describe the general characteristics of a three-phase (black-oil formulation) model in rectangular coordinates, which is the most common type of modeling approach used in most of the reservoir-modeling studies. After summarizing the black-oil formulation and its theoretical foundation, application and practical aspects are presented to highlight the important characteristics of a typical reservoir-simulation study by following the most common guidelines and practical rules followed in the petroleum industry.