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Heavy and Thermal Oil Recovery Research

Reservoir Definition

The central idea of reservoir definition is to apply reservoir engineering techniques to improve our ability to understand reservoir rock and fluid properties and reservoir architecture, and the flow paths and flow barriers that arise from this architecture. Our interest in this topic is not just reservoir information, such as the distribution of permeability, but how geology and flow patterns determine the success of a recovery process.

Building a Reservoir Model is a complex task that requires the integration of information at various scales.

We are pursuing two tasks on this topic. History matching using reservoir simulators plays an important role in reservoir engineering. It is important for prediction and data interpretation. In many cases we have tracer or water breakthrough information at producers and pressure information. These data contain much information about the permeability distribution of the reservoir, but it is difficult to infer this distribution. Most approaches to this inverse problem begin with a conventional reservoir simulator and manipulate parameters at the grid-block level corresponding to conventional simulation grids. There are many grid blocks, thus the optimization is slow, and conventional finite difference reservoir simulators are slow. Streamline based reservoir simulators have been developed recently that execute much more rapidly, relative to conventional finite difference based simulation, and are quite accurate in that numerical dispersion is minimized. In streamline simulation, the three-dimensional flow simulation is broken down into a number of one-dimensional flow problems. We have applied the concepts of streamlines to infer permeability fields based on tracer breakthrough, water cut, and injection/production pressure information.

A Streamline Map used in History-Matching

The basic idea is to switch the optimization to the streamline level rather than optimizing parameters associated with individual grid blocks. For instance, the effective permeability along a streamline might be adjusted to match reference data rather than the permeability of each grid block. With streamlines, we compute the time of flight of a fluid volume along a streamline, and so we also know the breakthrough times for each individual streamline. The streamline or series of streamlines that under or over predict reservoir performance are thus easily identified. The streamline properties, for instance permeability, are adjusted to match the reference production curve pressure histories. In this way, we dramatically reduce the size of the optimization problem. Work to date has been encouraging and will continue.

The second task is an investigation of reservoir parameters that affect so-called "edge-water drive" (EWD). In EWD, water is injected along the flanks of an oil reservoir, buoyancy aids in the displacement of oil, and oil is produced near the crest. The most significant application of this drive pattern is probably offshore where the number of injection and production wells is more limited than onshore. For success of the process, the dip angle between the flanks and the crest of the formation must be significant to enhance buoyant displacement of oil. Likewise, there must be significant horizontal communication through the reservoir to drive oil toward the crest. In this work we will use scaling analysis and reservoir simulation to identify the most important parameters affecting edge-water drive performance. These parameters include areal extent of the reservoir, formation dip, absolute permeability, the ratio of vertical to horizontal permeability, geometry of injectors, and injection rate.


References

Akin, S., Castanier, L. M. and Brigham, W. E. (1999). "Effect of Temperature on Heavy Oil/Water Relative Permeabilities." SPE 54120, 1999 SPE International Thermal Operations Symposium, Bakersfield, CA, 17-19 Mar. 1999.

Hornbrook, J. W., Castanier, L. M. and Pettit, P. A. (1991). "Observation of Foam/Oil Interactions in a New, HIgh-Resolution Micromodel." SPE 22631, 66th Annual Technical Conference and Exhibition of the Society of Petroleum Engineers, Dallas, TX, October 6-9, 1991.

Kovscek, A. R., Patzek, T. W. and Radke, C. J. (1995). "A Mechanistic Population Balance Model for Transient and Steady-State Foam Flow in Boise Sandstone." Chemical Engineering Science 50(23): 3783-3799.

Kovscek, A. R., Johnston, R. M. and Patzek, T. W. (1997). "Evaluation of Rock/Fracture Interactions During Steam Injection Through Vertical Hydraulic Fractures." SPE Production and Facilities May: 100-105.

Kumar, M. and Beatty, F. D. (1995). "Cyclic Steaming in Heavy Oil Diatomite." SPE 29623, SPE 65th Western Regional Meeting, Bakersfield, CA, March 8-10, 1995.

Maini, B. B., Sarma, H. K. and George, A. E. (1993). "Significance of Foamy-Oil Behaviour in Primary Production of Heavy Oils." Jour. of Canadian Pet. Tech. 32(9): 50-54.

Schembre, J. M., Akin, S., Castanier, L. M. and Kovscek, A. R. (1998). "Spontaneous Water Imbibition into Diatomite." SPE 46211, 1998 Western Regional Meeting of the Society of Petroleum Engineers, Bakersfield, CA, May 10-13, 1998 SPE.

Smith, G. E. (1988). "Fluid Flow and Sand Production in Heavy-Oil Reservoirs Under Solution-Gas Drive." SPE Production Engineering May: 169-180.


Energy Resources Engineering Department, School of Earth Sciences, Stanford, CA
kovscek@stanford.edu

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