For many oil & gas reservoirs, especially large reservoirs in the Middle East, the availability of vast amounts of seismic, geologic and dynamic reservoir data result in high resolution geological models. Because of the limitations of conventional reservoir simulator technologies, high resolution models are upscaled to flow simulation models by reducing the total number of cells from millions to a few hundred thousand. Flow simulators using upscaled reservoir properties produce average reservoir performance and often fall short of accurately predicting recovery.

Realizing the limitations of the conventional simulators for the giant oil and gas reservoirs, parallel reservoir simulators have been developed. The first generation of parallel simulators increased the simulator capabilities by an order of magnitude — the result was that mega (million) cell simulation became a reality. Parallel computers, including PC Clusters, were successfully used to simulate large reservoirs with long production histories, using millions of cells. Mega-cell simulation helped recover additional oil and gas due to better understanding of reservoir heterogeneity. The speed of parallel hardware also helped, making many runs to address uncertainty possible.

Despite the many benefits of parallel simulation technology for large reservoirs, the average cell size still remains in the order of hundreds of meters (m) for large reservoirs. To fully utilize the seismic data, smaller grid blocks of fifty m in length are required. This size of grid block results in billion (Giga) cell models for giant reservoirs. This is a two orders of magnitude increase from the mega-cell simulation. To simulate Giga-cell models in practical time, new innovations in the main components of the simulator, such as linear equation solvers, are essential. Also, the next generation pre- and post-processing tools are needed to build and analyze Giga-cell models in practical times.

This paper describes the evolution of reservoir simulator technology, from Mega-Cell scale to a Giga-Cell scale, presenting current achievements, challenges and the road map for Giga-Cell Simulators.

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