Geoscale - Reservoir simulation on a geological scale

Direct simulation of complex grid models of highly heterogeneous and fractured porous media - a technology that bypasses the need for upscaling

Background: Standard reservoir simulators used by industry today often suffer from very long runtimes and are seldom able to utilize the detailed description of the reservoir geology and petrophysical charateristics available in high-resolution geomodels. Indeed, to simulate the flow of reservoir fluids it is common to upscale the geological model to a coarser simulation model that contains much less details. Upscaling is a time-consuming and often inaccurate process, and the need to work with a simulation and a geological model is a bottleneck in the workflow between geologists and reservoir engineers.

Project goal: The main goal of the project has been to develop new numerical methods that facilitate flow simulations directly on highly detailed geological models using a standard PC, thereby simplifying modelling workflows. Alternatively, by using the same technology to simulation models, one may drastically reduce the simulation times and open up for greater interactivity.

New technology - multiscale pressure solvers: In the project we have developed a new type pressure solvers based on a multiscale element formulation. The method is thoroughly tested, also on real-field faulted models, mainly for incompressible two-phase flow, but also for three-phase black-oil models. The numerical tests show that the multiscale pressure solver used as an upscaling method is more accurate and robust than industry-standard and state-of-the-art upscaling methods. Similarly, when used as a direct solver on highly detailed geomodels, the multiscale solver is typically 10-100 times faster than standard pressure solvers. A particular advantage our multiscale method is one does not need to explicitly form a coarse simulation model, which may be both complicated and time consuming. Avoiding the upgridding phase greatly simplifies workflows for model updating. Finally, we have also developed several new methods for fast simulation of fluid transport (streamlines, optimal ordering, non-uniform and flow-based coarsening, etc). These methods accompany the multiscale pressure solvers and facilitate very fast reservoir simulation or super-fast evaluation of flow patterns and connectivities in the reservoir. Using this technology, one can compute well-pairs and drainage volums for models with about 1 million cells within a few seconds on a standard desktop PC.

Benchmark results: Using the novel multiscale pressure solver as part of a streamline simulator, we were able to run 2000 days of production for a grid model with 1,1 million cells (Model 2  from the 10th SPE Comparative Solution Project) in about 2 1/2 minutes on a standard desktop PC without the use of any kind of parallelisation. This is about 7-8 times faster than commercial streamline simulators and about 50-100 times faster than conventional reservoir simulators. 

Key publications:

1. J. E. Aarnes, S. Krogstad, and K.-A. Lie. Multiscale mixed/mimetic methods on corner-point grids. Computational Geosciences, Vol. 12, No. 3, pp. 297-315, 2008.  DOI: 10.1007/s10596-007-9072-8
2. J. E. Aarnes, S. Krogstad, and K.-A. Lie. A hierarchical multiscale method for two-phase flow based upon mixed finite elements and nonuniform coarse grids, Multiscale Modelling and Simulation, Vol. 5, No. 2, pp. 337-363, 2006. DOI: 10.1137/050634566.
3. J. E. Aarnes, V. Kippe, and K.-A. Lie. Mixed multiscale finite elements and streamline methods for reservoir simulation of large geomodels. Advances in Water Resources, Vol. 28, Issue 3, pp. 257-271, 2005. DOI: 10.1016/j.advwatres.2004.10.007.
4. V. Kippe, J. E. Aarnes, and K.-A. Lie. A comparison of multiscale methods for elliptic problems in porous media flow. Computational Geosciences, Vol. 12, No. 3, pp. 377-398, 2008. DOI: 10.1007/s10596-007-9074-6.