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The History of Simulation The use of computer simulation in petroleum engineering started in the area of reservoir fluid flow where it was called reservoir simulation. Although today, simulation is finding acceptance in other related areas, reservoir simulation is still the dominant area of application, and therefore will be the focus of this review. In order to appreciate the advances made in reservoir simulation, and to see the current trend in its development, one needs to look back at its history. Although the first attempts at simulation date back to the 1950s, the first useful numerical models for solving reservoir flow problems were developed in the 1960s. Athat time, the mainframe computers barely reached the power of today's PCs and the first commercial simulators were able to solve only relatively simple problems of two-dimensional flow, first single-phase and then multi-phase, using what is now called the IMPES method. The lecture of Donald Peaceman, one of the pioneers of simulation is an illuminating reminiscence of these early days(1) The 1970s saw tremendous activity both in the development of numerical techniques and in the applications of simulation models. By the end of the decade, the major techniques which are still used today were firmly established, and the acceptance of-simulation by practising engineers was growing. At the same time several books on simulation appeared(2–5). However, the application of simulation models to real problems was still a rather specialized activity, requiring experience in their use and in the interpretation of the results, because the models were not too reliable. With the 1980s came the explosion in computer hardware as well as in software and computer literacy. The vectorrocessing machines provided computing power for solving larger and/or more complex problems. Compositional, steam flooding, in situ combustion, and micellar-polymer flooding simulators were developed, and simulation studies with many thousands of computational cells became possible. Also, simulation ceased to be the domain of major oil companies or specialized consulting firms and became accessible to smaller companies or even individuals. Today's phase of this process is marked by the migration ofoftware to PCs and its extensive packaging with emphasis an graphical user interfaces. This development is recorded in the growing volume of literature(6–11). Current State of Simulation Tools Reservoir simulation has now matured to the point that most models are regarded as tools which can be used by a wide range of users, and very cost-effectively. Some of the current developments which have contributed to this transition are described below. Model Formulations From the multiplicity of different formulations of both the physics and numerics, emerged the generalized black oil/miscible/compositional model as the most practical and widely-used. The black oil model with a miscible option (sometimes called a four-component model) is now the "workhorse" of reservoir simulation. Fully compositional models can now be used as a rule in black-oil mode, facilitating studies of tertiary processes after primary or waterflood. Efficient methods have been developed for characterizing the compositional PVT and their implementation in simulators. |
