Reservoir simulation

Reservoir simulation is an area of reservoir engineering in which computer models are used to predict the flow of fluids (typically, oil, water, and gas) through porous media.

Uses

Reservoir simulation models are used by oil and gas companies in the development of new fields. Also, models are used in developed fields where production forecasts are needed to help make investment decisions. As building and maintaining a robust, reliable model of a field is often time-consuming and expensive, models are typically only constructed where large investment decisions are at stake. Improvements in simulation software has lowered the time to develop a model. Also, models can be run on personal computers rather than more expensive workstations.

For new fields, models may help development by identifying the number of wells required, the optimal completion of wells, the present and future needs for artificial lift, and the expected production of oil, water and gas.

For ongoing reservoir management, models may help in improved oil recovery by hydraulic fracturing. Specialized software may be used in the design of hydraulic fracturing, then the improvements in productivity can be included in the field model. Also, future improvement in oil recovery with pressure maintenance by re-injection of produced gas or by water injection into an aquifer can be evaluated. Water flooding resulting in the improved displacement of oil is commonly evaluated using reservoir simulation.

The application of enhanced oil recovery (EOR) processes requires that the field possesses the necessary characteristics to make application successful. Model studies can assist in this evaluation. EOR processes include miscible displacement by natural gas, CO₂ or nitrogen and chemical flooding (polymer, alkaline, surfactant, or a combination of these). Special features in simulation software is needed to represent these processes.

Reservoir simulation is used extensively to identify opportunities to increase oil production in heavy oil deposits. Oil recovery is improved by lowering the oil viscosity by injecting steam or hot water. Typical processes are steam soaks (steam is injected, then oil produced from same well) and steam flooding (separate steam injectors and oil producers). These processes require simulators with special features to account for heat transfer to the fluids present and the formation, the subsequent property changes and heat losses outside of the formation.

A recent application of reservoir simulation is the modeling of coalbed methane (CBM) production. This application requires a specialized CBM simulator. In addition to the normal fractured (fissured) formation data, CBM simulation requires gas content data values at initial pressure, sorption isotherms, diffusion coefficient, and parameters to estimate the changes in absolute permeability as a function of pore-pressure depletion and gas desorption.

Fundamentals

Traditional finite difference simulators dominate both theoretical and practical work in reservoir simulation. Conventional FD simulation is underpinned by three physical concepts: conservation of mass, isothermal fluid phase behavior, and the Darcy approximation of fluid flow through porous media. Thermal simulators (most commonly used for heavy-oil applications) add conservation of energy to this list, allowing temperatures to change within the reservoir. Finite difference models come in both structured and more complicated unstructured grids, as well as a variety of different fluid formulations, including black oil and compositional.

Other types of simulators include finite element and streamline.

Applications

Several reservoir simulators have been written over the years. Vendor software includes (alphabetically):
* ECLIPSE, by SIS, a division of Schlumberger
* Exodus and ExoTherm, by T.T.& A/PetroStudies Consultants Inc.
* GASMOD, by [http://www.phhpc.com/simulation/ PHH Petroleum Consultants LTD]
* GPRS by Energy Resources Engineering Department, Stanford University
* GREAT and WFlood by SiteLark
* MKT, by TimeZYX
* REVEAL, by Petroleum Experts, Inc.
* Sensor, by Coats Engineering, with original funding from Phillips Petroleum Company (now ConocoPhillips)
* STARS,IMEX and GEM by Computer Modeling Group
* SURE, by SMT
* Tempest, by Roxar
* tNavigator, by [http://www.rfdyn.com Rock Flow Dynamics]
* VIP and Nexus, by Landmark, a division of Halliburton
* 3DSL, by Streamsim Technologies

So-called "in-house" packages have been developed by several major oil and gas companies, including (again, alphabetically):
* CHEARS, by Chevron
* EMpower, by ExxonMobil
* MoReS, by Royal Dutch Shell
* POWERS, by Saudi Aramco
* BOAST, by [http://www.doe.gov USA DoE]
* BOAST-FEM, by Husam Yaghi and John M. Tyler

The structural and reservoir property information required for many simulations is often provided by geologic modelling software. Many reservoir simulators are part of a software suite that assists data input and results analysis. Separate systems that rely on reservoir simulators also exist. They assist the performance of such tasks as history matching, making multiple simulations and analysis of forecasts.

References

* Aziz, K. and Settar, A., Petroleum Reservoir Simulation, 1979, Applied Science Publishers.
* Ertekin, T, Abou-Kassem, J.H. and G.R. King, Basic Applied Reservoir Simulation, SPE Textbook Vol 10, 2001.
* Fanchi, J., Principles of Applied Reservoir Simulation, Gulf Publishing, 1997.
* Mattax, C.C. and Dalton, R. L, Reservoir Simulation, SPE Monogram Volume 10, 1990.
* Holstein, E. (Editor), Petroleum Engineering Handbook, Volume V(b), Chapt 17, Reservoir Engineering, 2007.
* Warner, H. (Editor), Petroleum Engineering Handbook,Volume VI, Chapter 6, Coalbed Methane, 2007.

* Additional publications available from the Society of Petroleum Engineers (http://www.spe.org)

ee also

* Geologic modeling
* Petroleum engineering