Use of Computer Graphics in Large-Scale Reservoir Simulation

This article, written by Technology Editor Dennis Denney, contains highlights of paper IPTC 10281, "Muse: A Multimodal Reservoir Simulation Environment," by J.A. Pita, SPE, N.M. Al-Zamel, and A.H. Dogru, SPE, Saudi Aramco, prepared for the 2005 International Petroleum Technology Conference, Doha, Qatar, 21-23 November. A new environment integrating a voice-advisory system with multimodal visualization was built for Saudi Aramco's in-house reservoir simulator. Engineers can simultaneously visualize oil saturation, hear changes in reservoir pressure, and feel rock permeability interactively as they move a 3D mouse throughout the reservoir. Engineers also can provide operational and surveillance rules so that the computer automatically checks conditions on any variables. The system can take a number of actions, such as using sound synthesis to speak directly to the engineer, when these conditions occur. The system runs on a Microsoft Windows-XP-based personal computer (PC) with dual processors. Introduction New-generation reservoir simulators, capable of handling millions of cells, imply that geological detail can be handled without intensive scaling up, which can lead to direct seismic integration with reservoir simulation. Unfortunately, the ability to analyze information has not fully kept pace with these advances. Recently, devices that function as a "3D mouse" with haptic (i.e., touch) capabilities have appeared. These devices have the ability to navigate and probe inside Earth models. Saudi Aramco's Multimodal Simulation Environment (Muse) is an environment that integrates a voice-advisory system with multimodal visualization. This environment provides stereo-capable 3D visualization, force feedback by use of haptic devices, and data sonification. Multimodal Data Analysis In contrast with conventional environments that provide only 3D visualization as the means for data interpretation and analysis, this system uses two additional "channels" for sensorial interaction: touch (haptics) and sound (sonification). Reservoir-simulation results that are loaded into the system can be attached to one or more of these three channels. The number of data volumes (i.e., simulation variables) that can be loaded is limited only by the amount of addressable system memory, but only three volumes can be attached to channels. The other volumes resident in the system can be toggled at any time into the channels. All loaded volumes, either attached to channels or not, can be monitored by the system by use of rules prescribed by the engineer. For example, the engineer can visualize 3D pressure distribution, feel permeability changes with the haptic device, and hear oil or gas saturation through the system speakers. The values of these properties are assigned to a range of 0 to 255, similar to a typical color map. Also, simulation results such as 3D distribution of the mole fraction of hydrogen sulfide (H2S) or acoustic impedance from a petroelastic model can be tracked as events, even if they are not directly attached to any channels. Visualization Channel So-called "rainbow" color maps are typical (e.g., blue for low values, red for high). The color map panel is fully editable, and engineers can choose the upper and lower limits to concentrate on specific value ranges, if so desired. Figs. 1 through 3 show typical 3D displays of different simulation-output variables (pressure, gas saturation, and H2S mole fraction, respectively). Fig. 1 also shows the channel selection menu. A separate opacity map enables parts of the volume to be made translucent to reveal only specific ranges of the data. The data shown correspond to a nine-component compositional simulation of 500,000 cells for a gas/condensate reservoir.

Petroleum engineers can mathematically model the behaviour of a petroleum reservoir, allowing them to determine the optimum way to exploit a reservoir. A numerical reservoir model consists of a series of different equations with each representing a different aspect of the physical nature of the reservoir and its fluids. We begin the chapter by considering the key equations and conditions that must be incorporated into any model to simulate the processes within a reservoir. A fully functional reservoir simulation model is very complex to set up and to solve. The equations that describe the characteristics and properties of the reservoir and its fluids, as well as how the fluids flow through the formation, must be accurately defined, and, often, re-written in ways that are amenable in numerical solution. In this chapter we examine some of the key aspects of numerical modelling by setting up a much simpler numerical model that will predict the flow of heat through a sandstone formation. We see how a simple equation can be used to predict temperature profiles within the sandstone at any time. This chapter also discusses some of the features of commercially available reservoir-simulation packages.

Saudi Technology Centers Knowledge is power and technology is a game-changer. Those are the key maxims that Saudi Aramco says it is using to shape its strategy as it aims to become the world’s leading integrated energy and chemicals company by 2020. “At Saudi Aramco, we are pushing forward from a traditional role as buyers and consumers of technology to our new global technology and R&D strategy. We envision becoming an enabler and creator of new technologies,” Khaled Al-Buraik, vice president of petroleum engineering and development at Saudi Aramco, said during the Offshore Technology Conference (OTC) in May in Houston. “There is new urgency as well as new optimism about where we are going. In the past we have been focused primarily on crude oil and gas; now we are progressing to become fully integrated in gas production, including unconventionals, refining, and chemicals.” To help meet the goal, the company is boosting its global network of R&D centers. In addition to its local center in Dhahran, the Advanced Research Center in the Exploration and Petroleum Engineering Center, Saudi Aramco plans to open three new centers in the US. “We are emphasizing high-impact technologies that typically involve long-range strategies. We are pursuing R&D to bring about breakthrough achievements—not simple or merely incremental enhancements,” Al-Buraik said. “We believe that achieving our research and technology goals requires expansion and interaction with the best talent worldwide.” The objective of these centers is to leverage international scientific expertise, gain better access to technology, and strengthen collaboration with industry and academia. A new center in Houston will be the company’s largest center outside Saudi Arabia. A second North American center will be located in Cambridge, Massachusetts, focusing on computational modeling and nanotechnology research. The third center will be located in Detroit, and will be designed to extend the energy giant’s global research and development network. The Houston and Cambridge centers will be operational by the third quarter of this year, and all three will be operated by Aramco Services Company, a subsidiary of Saudi Aramco. The company also has research centers in Thuwal, Saudi Arabia; Delft, Netherlands; Paris; and Beijing; and a technology center in Aberdeen.

This paper provides an overview of an advanced visualization system for visualizing giga-cell simulation models to assist Reservoir Engineers in managing and developing Saudi Arabia’s giant fields. The challenges in the hydrocarbon industry require the use of the latest technology to maximize recovery in a cost-effective manner. Over the last few years, reservoir simulation activities have undergone major transformation toward the use of giga-cell simulation models [1]. This transformation stems from the use of advanced data acquisition solutions and advanced modeling packages to capture and model physically large fields. Fine scale-grid blocks capture detailed description of geologic heterogeneity that is necessary to model the complexity of fluid flow in the subsurface. Giga-cell simulation models are currently generated using Saudi Aramco’s GigaPOWERS parallel reservoir simulator [2]. The size of reservoir simulation models continues to grow to exceed the billion-cell barrier. The design of a high performance computational platform for simulation of giant reservoir models has been discussed in other literature [3]. In this paper, we focus on the simulation post-processing visualization system developed, which consists of advanced technologies for handling and visualizing massive amounts of data. Implemented techniques include: Remote visualization utilizing graphics processing clusters, parallel data loading, level of detail graphics rendering and hierarchal multi-resolution data structure. In addition, a number of advanced visualization features that have been implemented are highlighted in this paper, such as the ability to display fluid patterns in the field by utilizing streamlines and vector fields, advanced volume visualization techniques based on streamlines and wells filtering to help engineers better understand the fluid flow in subsurface reservoirs. Furthermore, the performance considerations, challenges and impact on reservoir simulation studies are also discussed.

In order to better meet user needs, user-oriented interactive design introduces computer graphics technology to generate, process, and transmit graphical information more effectively, thereby enhancing the practicality, simplicity, convenience, and enjoyment of interactive media. This paper aims to discuss the application of computer graphics in interactive media design. In order to analyze and compare the use of different computer graphics (CG) technologies in different scenarios, this paper classifies the interactive media into three categories according to the different focuses of the purposes, namely distributed interaction media, commercial interaction media and informational interaction media, and discusses the application of computer graphics in interactive media design with specific examples. This paper analyzes and compares the use of different CG technologies in interactive media according to their different purposes, namely distributed interaction media, commercial interaction media and informational interaction media. The paper concludes with a summary of the current applications of computer graphics in interactive media design, and an outlook on the future use of CG technology in interactive media design.

On Job Training (OJT) for new fresh graduate reservoir engineers has been implemented at Saudi Aramco. The workshop is offered following completion of the company run on-boarding program offered by Upstream Professional Development Center (UPDC). The objective of this new training is to accelerate the young engineers' knowledge and experience and reduce the professional gap existing in the oil industry. This is being achieved by going in detail through one of the mature reservoirs with a long production history. The young engineers are chartered with the main objective of the reservoir engineers which is the SWEEP. They are trained to conduct detailed analyses of wells and reservoir production/injection performance with the primary focus of determining the current sweep efficiency. Participants are tasked to develop solutions to improve the recovery and the sweep areally and vertically to ensure that the maximum percentage of the reserve is produced. The number of the participants in each workshop is 12 with different level of experience varying from few months to three years. The participants come from different Up-stream organizations; Reservoir Management, Reservoir Simulation, Reservoir Description, Well testing, Facilities and Computer engineers; Geologist and Geophysicists. The workshop starts with explaining the ROLE OF RESERVOIR MANAGEMENT. It segments the process into three main areas. The first is to understand the static nature of the reservoir mainly the matrix information. The second is the dynamic part which is the fluid movements and its properties. And the third part is the integrations between the two natures which is used to further understand the complexity of the reservoir and the inter connection between the wells. The participants practice during their training the ability of extracting the data related to the field and analyzing it thoroughly. Then the data is put-together and integrated to explain the fluid dynamic movements. The trainees as well, develop their reservoir thinking skills by identifying the challenges and formulating future action plans to improve the sweep and maximize the oil recovery. OJT accelerate learning of young engineers from a variety of universities around the world. This training provided a solid foundation for participants as it help them to deal with real-life examples and help them to sharpen their analyzing and thinking abilities to prepare them for the new reservoir engineering era.

One of Saudi Aramco's strategic objectives is to prepare the work force to meet evolving technical challenges in Petroleum Engineering (PE). To address this important objective, the Petroleum Engineering Technologist Development Program (TDP) was established to provide the opportunity for young engineers to become recognized experts in critical technical disciplines. The TDP provides organizational support for the participants to progress in professional and managerial careers to ultimately fulfill Saudi Aramco's business needs. The program is overseen by management and technical advisory committees. New candidates are selected based on competency, years of experience, outstanding performance and strong personal skills. In addition, they must have demonstrated technical ability, resourcefulness, and dedication to address emerging technical and operational challenges. The technical advisory committee will assist in selecting an area of specialty based on Company requirements, candidates' interests and expertise. Also, they will nominate a mentor (subject matter expert) to guide and manage development of technical and soft skills. Each participant has a competency development road map based on a plan to develop required technical and soft skills. The participants must complete all required tasks and develop expertise in his area of specialty. In addition, the candidates are trained during rotational development assignments and, in many cases, they enroll in an advanced degree program. They need to meet specific TDP graduation requirements including publication in technical journals and active participation in international technical meetings and forums. In addition, to graduate from the TDP, a candidate is must demonstrate to the technical review committee that he has achieved technical expertise in his chosen specialty. Saudi Aramco designed the TDP to ensure young engineers have the opportunity to become technical experts in critical specialties. The program has successfully met its goals as evidenced by the number of successful graduates.

Fractured wells are frequently encountered in petroleum engineering. They can be hydraulically fractured wells to improve oil production or wells intersecting natural fractures. Due to the presence of the fractures, the flow behavior and the pressure distribution in the vicinity of the fractured well are complex and the numerical modelling for this kind of wells is complicated. In this paper, we will discuss the numerical methods for the fractured well modelling by reservoir simulators. Introduction The study of fractured wells has received more attention in well test analysis for a long time. Some analytical or semi-analytical formulas have been developed for several simple cases, such as a fully penetrating hydraulically fractured vertical well, a longitudinal fractured horizontal well or a transverse fractured horizontal well. But these formulas cannot be used for the flow simulation for a field study or for the study of the complex wells and fractures. To handle these cases, a reservoir simulator can be used. During this decade, several numerical simulation studies for fractured wells have been published. In all these studies, fine gridblocks are used around the wells and the fractures. The requirement of grid refinement and the impacts of the grid discretization on the well performance is particularly discussed by Hegre. Although using grid refinement gives accurate simulation results, it is expensive and prohibitive for a full field simulation. In well test analysis, an equivalent wellbore radius rw, eq is introduced for the infinite conductivity fracture. However, this equivalent wellbore radius rw, eq can be used for a reservoir simulator only if the fracture is entirely included in one gridblock and rw, eq is smaller than the equivalent wellblock radius r0. So, it is necessary to study the techniques for the fractured well modelling with coarse grids. In this paper, we will propose a new method for the simulation of fractured wells. This method is based on the well model rather than on the gridding technique. For the well modelling in reservoir simulation, a numerical productivity index (PI) is usually introduced to relate the wellbore pressure, the well block pressure and the well flow rate, since the singularity around the well causes different values between the wellbore pressure and the wellblock pressure. In most of the well models, the well trajectory and its position are not really considered. So these well models are limited for the complex well modelling, and are inappropriate for the fractured well modelling. Recently, a new kind of well model was proposed, which takes into account well configurations by using equivalent transmissibilities to improve the flow calculation in the well vicinity. This well model will be extended to model fractured wells in this paper. In this paper, we will study particularly high conductivity fractures, and these fractures can be considered as a part of the well. To establish a well model, it is necessary to know a steady-state or pseudo-steady state pressure distribution around the well. In section 2, the integral formulae are introduced to represent the pressure distribution for a steady-state problem. This formula is general and is valid for any well configuration and any kind of fractures. In particular, we will present some applications to hydraulically fractured wells. Modelling of Fractured Wells A steady-state flow problem is considered to get the pressure solution around the wells and the fractures. This solution will be used for numerical PI and equivalent transmissibility calculations. The integral formulas are used for the pressure representation. These formulas were introduced for complex well modelling and are also suitable for fractured well modelling. P. 813

Dynamic effective permeability of a laminated structure with cross flow in the transient flow process and its application to reservoir simulation

Distinguished Author Series articles are general, descriptive representations that summarize the state of the art in an area of technology by describing recent developments for readers who are not specialists in thetopics discussed. Written by individuals recognized as experts in the area, these articles provide key references to more definitive work and presentspecific details only to illustrate the technology. Purpose: to informthe general readership of recent advances in various areas of petroleumengineering. "Today, desktop computers and a wide range of reservoir. simulation systemsprovide the engineer with an economic means to solve complex reservoir.engineering problems with efficiency." Introduction This paper describes the state of the art in reservoir simulation for thenonexpert, focusing primarily on advances that have occurred since a similarpaper was published by Coats1 in 1982. For completeness, a historyof simulation is given first, followed by a brief and simple review of thesimulation process. Advances in simulation technology are then described, highlighting those in reservoir description and simulation of naturallyfractured reservoirs, hydraulic fracturing, and horizontal wells. The future ofreservoir simulation is discussed last. Many papers have been presented since Coats' review in 1982. Rather thanrepeat the exhaustive list provided in the SPE indices, a reduced set ofpertinent references is given. I offer my apologies in advance to the authorsof the many excellent papers contributed during the past decade that are notmentioned here. History of Simulation In the broadest sense, reservoir simulation has been practiced since thebeginning of petroleum engineering. By the late 1940's, the potential ofreservoir simulation was recognized and several companies embarked on thedevelopment of both analog and numerical models to enhance the existinganalytical solutions, material balances, and ID Buckley-Leverett displacementcalculations. By the late 1950's, major commitments to fundamental research on thenumerical solution of flow equations began to bear fruit. The results werecrude, but certainly useful, computer programs for simulating reservoirs. Theseprograms represented a major advance and used the solution of sets offinite-difference equations to describe 2D and 3D, transient, multiphase flowin heterogeneous-porous media. For the first time, reservoir engineers couldsolve complex problems. The driving force for development of numerical-simulation systems was theability to predict the future performance of a reservoir under various "whatif" conditions so that better reservoir-management decisions could be made. This force still drives the use of reservoir simulation today. Current businessincentives for virtually all reservoir-simulation applications fall into one ormore of the following categories: economics; credibility and reliability;decision-making; arbitration and unitization; performance monitoring;nonelective studies resulting from safety, environmental, or regulatoryconcerns; and communications and personnel utilization.2 Throughout the 1960's, reservoir-simulation development was devoted largelyto three-phase, black-oil reservoir problems. Recovery methods that weresimulated included pressure depletion and various forms of pressuremaintenance. Many computer programs were developed to address most of thegeneral reservoir problems encountered. These programs operated on mainframecomputers and used decks of cards for input. During the 1970's, the picture changed remarkably because of theproliferation of research in EOR processes, advances in numerical-solutiontechniques, and the decreased size and increased speed of computers. Mathematical simulators were developed that extended beyond conventionalprimary and secondary recovery into such areas as chemical flooding, steamflooding, and in-situ combustion. Research during this period resulted insignificant advances in characterizing the physics of hydrocarbon displacementsunder the influences of temperature, chemical agents, and complexmulticomponent phase behavior. Simulators had to reflect chemical adsorptionand degradation, reaction kinetics, interfacial-tension-reduction effects, andmore complex equilibrium phase behavior. The range of reservoir-simulation application continued to expand during the1980's. Reservoir description, finally becoming a major topic on its own, advanced to the use of geostatistics to describe heterogeneities and to providereservoir definition not expressed in reservoir models. The technology to modelnaturally fractured reservoirs, including compositional effects, was alsodeveloped, with extensions into the simulation of hydraulic fracturing andhorizontal wells. and application to such complex processes as reservoirmonitoring.

The East Swan Hills Unit No. 1 is located on the eastern flank of the Swan Hills Beaverhill Lake "A" and "B" Pools. The reservoir is now in an advanced stage of depletion like many of Alberta's oil reservoirs. Optimization of a geologically complex reservoir, such as is found in the Beaverhill Lake, is a major undertaking and requires a multi-disciplinary approach. To evaluate waterflood performance a study consisting of petrophysical data reduction, geological mapping, spreadsheet analysis of recovery and reservoir simulation was carried out. This paper highlights three major contributions which were essential in the analysis.The significance of geological mapping which has identified layerirlg/ heterogeneity within the Swan Hills formation and the potential in the underlying Slave Point formation.Manual waterflood calculations have enhanced the understanding of the reservoir and confirmed Slave Point production, prior to proceeding with numerical simulation.The methodology used to simulate a multilayer reservoir under waterflood is described. Incremental recovery is predicted by improved waterflooding in selected areas of the Unit. A program consisting of injection testing, production testing, single well tracers and selective cased-hole logging has been designed, prior to proceeding with field implementation. Introduction The East Swan Hills Unit is located in the province of Alberta approximately 200 km northwest of Edmonton as shown in Figure 1. This field was discovered in early 1963 with primary production commencing in the same year. Commingled production is derived primarily from the Swan Hills formation as well as from the underlying Slave Point formation. There are 76 wells in the Unit. The field was produced by primary fluid expansion drive since there was no gas cap or no acquifer support. Unitization occurred in 1967 for the purposes of waterflooding. Peak oil production of 1959 m3/day occurred in 1969 after which oil production declined at 20% per year. An aggressive workover program was initiated in 1984 to arrest the production decline. The program was successful as indicated by the oil production rate which has remained flat over the last five years. The current oil rate is 100 m3/day with a water cut of 90%. As the Unit was approaching its economic limit, it was concluded that a detailed reservoir engineering study should be carried out to determine if improved waterflooding could be achieved. This paper documents the results of the study and the methodology used.. The paper has been divided into three main sections: Geological - Petrophysical Studies, Conventional Reservoir Engineering Review and Reservoir Simulation. The Optimization Program developed from these three studies is then discussed. Finally, the conclusions of the paper are presented. Geological- Petrophysical Studies Method of Study When the East Swan Hills pool was being developed and unitized a fairly simple geological model was used. Two reservoirs, the Swan Hills member and the Slave Point member were recognized, These became known colloquially as the "Light Brown" and "Dark Brown". respectively. The Light Brown member was known to be of substantially better reservoir quality; hence most development was aimed at this pay.

The objective of this paper is to provide reservoir engineers fresh insight and a new approach to the description of heavy oil and water relative permeability functions in reservoir simulation. This paper proposes a plausible mechanism of heavy oil flow in porous media influenced by the effect of water-oil emulsification to address the inability of simulation models to replicate primary oil production rates during cold producing operations. A number of heavy oil reservoirs that naturally flow without stimulation show higher field oil production rates than often can be predicted by numerical simulation. To match the field production, reservoir simulation engineers often exhaust all valid parameter changes in the numerical model and resort to questionable changes on parameter values that usually enjoy high confidence level by physical measurements. To overcome these shortcomings, we first identify in situ water-oil emulsification, a plausible mechanism of heavy oil flow in water-oil systems, and then offer a practical approach to modeling water oil relative permeability for heavy oil-water systems. Beyond water-oil relative permeability curve adjustments, the parameters that are changed by simulation engineers during reasonable history matching may consist of an unrealistic increase in oil saturation and/or a significant decrease in oil viscosity. Both parameters are usually measured in labs and should not be altered significantly. In addition, sometimes during simulation model calibration, the increase in absolute permeability goes so high that it cannot be supported by any logic or physical measurement. The new relative permeability modeling approach for heavy oil and water systems considers the fact that naturally occurring heavy oil contains a large quantity of emulsifying agent and the density contrast between heavy oil and water is so low that heavy oil in porous media may flow by a continuous oil and stable emulsion phase. A part of the total oil flow occurs via oil phase that is similar to light oil and water system and the other part flow via a quasi-stable emulsion/water phase. This practical approach for heavy oil water relative permeability modeling removes the difficulties that a simulation engineer often faces during heavy oil water history matching and calibration. The new modeling approach presented in this paper is successfully applied in modeling cold heavy oil production performance for a heavy oil reservoir in California. One field example is provided in this paper and some results are presented to estimate heavy oil water relative permeability from standard lab data.

Flux Corrected Transport (FCT) is a technique developed to reduce numerical diffusion around shock fronts which has not previously been used in reservoir engineering. The first section of this paper describes the application of FCT techniques to solving a one dimensional waterflooding problem, and shows how to include FCT in an IMPES simulator. A second feature of our program is the implicit timesplit treatment of capillary pressure effects. A comparison between laboratory data and simulator results is included, and good agreement is obtained.

This paper describes application of Project INTERSECT, a next generation highly scalable reservoir simulator on real large scale field models. High resolution reservoir simulation is required to better define and describe fluid flow and enable improved field development and tactical operational planning. Massively parallel computing techniques overcome limitations of problem size and space resolution. This paper demonstrates that large-scale simulation models can be performed on commodity hardware taking advantage of evolution in multicpu hardware architecture and software engineering. This allows both geologists and reservoir engineers to include more realistic geologic and engineering detail for better and more reliable production optimization. Intense computer simulation is essential for effective reservoir management. The advances in reservoir characterization techniques and the industry drive towards the ‘smart oilfield’ with rapid model updates will require more efficient model processing to achieve timely field operational decisions. Parallel reservoir simulators have the potential to solve larger, more realistic problems than previously possible. The size and application of reservoir simulation problems have been limited by the availability of computing hardware, reservoir simulation architecture and of solution methods for solving large-scale heterogeneous problems. The next generation reservoir simulator demonstrates that key modeling challenges has been overcome by a software architecture and capability to model more realistic subsurface and surface models. Applications of the new reservoir simulator illustrates how typical reservoir engineering options such as local grid refinement, local grid coarsening, multilateral wells and aquifer modeling affect the overall parallel performance and scalability using highly heterogeneous large-scale models. Application of new modeling techniques highlight increased accuracy of modeling results and more reliable field development planning and reservoir management decisions.

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.