Scale Up of Heterogeneous Three Dimensional Reservoir Descriptions
- L.J. Durlofsky (Chevron Petroleum Technology Company) | R.A. Behrens (Chevron Petroleum Technology Company) | R.C. Jones (Chevron Petroleum Technology Company) | A. Bernath (Chevron Petroleum Technology Company)
- Document ID
- Society of Petroleum Engineers
- SPE Journal
- Publication Date
- September 1996
- Document Type
- Journal Paper
- 313 - 326
- 1996. Society of Petroleum Engineers
- 5.1 Reservoir Characterisation, 5.4.9 Miscible Methods, 5.3.2 Multiphase Flow, 5.8.7 Carbonate Reservoir, 5.5 Reservoir Simulation, 5.4.1 Waterflooding, 5.2 Reservoir Fluid Dynamics, 5.5.8 History Matching, 4.1.2 Separation and Treating, 4.3.4 Scale, 5.1.5 Geologic Modeling, 5.8.6 Naturally Fractured Reservoir, 5.6.5 Tracers
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A general method for the scale up of highly detailed, heterogeneous, three dimensional reservoir descriptions is developed and applied. The method entails the nonuniform coarsening of the original detailed description, with finer resolution introduced in regions of potentially high flow rate (as identified through computationally efficient single phase flow calculations) arid coarser, homogenized property descriptions applied throughout the bulk of the model. The method is applied to the simulation of three actual reservoirs and is demonstrated to provide coarsened reservoir models which give simulation results in close agreement with those of the original fine scale description but at considerable computational savings (speedups of nearly two orders of magnitude). In addition, it is shown that the method can provide geologically realistic coarse scale reservoir descriptions, which can be subsequently history matched to field data via geologically sensible modifications.
Through the use of sophisticated geological and geostatistical modeling tools, engineers and geologists can now generate highly detailed, three dimensional representations of reservoir properties. Such models can be particularly important for reservoir management, as fine scale details in formation properties, such as thin, high permeability layers or thin shale barriers, can dominate reservoir behavior. The direct use of these highly resolved models for reservoir simulation is not generally feasible because their fine level of detail (up to millions of grid blocks) places prohibitive demands on computational resources. Therefore, the ability to coarsen these highly resolved geologic models to levels of detail appropriate for reservoir simulation (tens of thousands to one hundred thousand grid blocks), while maintaining the integrity of the model for purposes of flow simulation (i.e., avoiding the loss of important details), is clearly needed.
We previously developed and applied such a technique for the scale up of detailed cross sectional models. Given a highly detailed reservoir cross section, this method was designed to generate a coarsened model that is capable of providing simulation predictions in close agreement with results using the original, detailed reservoir description. More specifically, we require agreement in (1) the global pressure-flow rate behavior of the reservoir; (2) the breakthrough characteristics of the displacing fluid and; (3) the post-breakthrough fractional flows of all reservoir fluids. The cross sectional method achieves such a scale up by efficiently identifying the likely regions of high fluid velocities (via single phase flow calculations), which can lead to the early breakthrough of displacing fluids. These regions are then modeled in detail, using a fine scale permeability description, within the coarsened reservoir model. The remainder of the fine scale description is coarsened using a general technique, based on homogenization theory, for the calculation of effective, directional permeabilities. The resulting coarsened reservoir description is able to model both average reservoir behavior as well as some important effects due to extremes in reservoir properties (such as the early breakthrough of injected fluids), without prior knowledge of the global flow field. This indicates that the scaled up model is largely process independent. The method is implemented as an interactive workstation application, with various diagnostics to allow for an assessment of the accuracy of the coarsened reservoir model relative to the original fine scale description.
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