Use of geophysics, particularly 3D seismic surface measurements, as an essential element for reservoir description has come into prominence in the last decade. This use has been driven by the shift from exploration to exploitation in many parts of the world. This occurrence is particularly widespread in the United States where most of the new reserves are generated by infill and extension drilling based on the detailed knowledge of the reservoir characteristics.

Tracking the movement of fluid saturations is a logical extension of the geophysical technology being applied to reservoir description. Several successful thermal drive reservoir monitoring projects have been reported in the literature. Because of the large number of reservoirs under gas injection or water-flood, there is a strong economic incentive to extend the application of the monitoring technology to these drive mechanisms. A few such projects have been published, some with mixed results.

Several studies show that incremental recoveries of less than 0.5% will recover the monitoring costs of many small reservoirs; and, for larger reservoirs, the comparable figure is in the neighborhood of 0.1 %.

Examples from the United States, where accurate descriptions of the compartmentalization of the reservoir is the key factor, and from the North Sea, where monitoring of the fluid fronts is a major economic issue, show that substantial progress has been made in analyzing and understanding complex reservoirs. A critical factor is the linkage and integration of all the geological, geophysical, and engineering information across the various technologies in a form which makes it readily available to those who are analyzing it.

Examples show that feasibility studies which evaluate the sensitivity of seismic, petrophysical, and engineering parameters can be useful in estimating the reliability of surface seismic methods for tracking the movement of fluid fronts during the production of a reservoir.

A gross estimate of the potential market for geophysics in reservoir description and monitoring can be made by searching for the number of reservoirs exhibiting the range of physical properties which might be reasonably detected directly or which might be detected as changes in response over appropriate time intervals. Using conservative criteria, such an estimate suggests that the size of the geophysical market in another decade could be several multiples over what it is today.

As the dense spatial coverage provided by 3D seismic measurements become better integrated with other information technologies, the potential range of conditions in which reservoirs can be successfully described and monitored will expand, even with today’s technology. Currently, there are perhaps two major limiting factors. One is the cost of 3D, three component, surface seismic measurements, a technology essential for estimating lithology and fracture orientations. The other is the degree to which seismic amplitudes can be reliably transformed into lithology and porosity attributes.

Significant progress continues to be made in steadily reducing these barriers, and the expectations are that geophysical methods will become a larger part of a rapidly growing reservoir management industry.



About the Author(s)

Mr. Graebner is currently Chief Geophysicist for HGS and Chairman of the Board of Reservoir Monitoring, Inc., a joint company formed by Halliburton Geophysical Services, Inc. (HGS) and Scientific Software-Intercomp, Inc. (SSI), to develop and carry out reservoir monitoring services using the technologies and resources of both companies.

In a career associated with petroleum exploration for more than forty years in various assignments, largely focused around directing seismic software development and research, and coordinating worldwide seismic data processing operations, he has been Senior Vice President of Geophysical Service, Inc. (GSI), Vice President of Texas Instruments Incorporated, and Vice President of HGS.

Bob was a recent President of the Society of Exploration Geophysicists and has presented and published several papers in GEOPHYSICS, GEOPHYSICAL PROSPECTING, SCIENCE, and Offshore Technology Conference publications. He and Dr. C.G. Dahm jointly received the SEG award for the best paper published in GEOPHYSICS in 1982. He has served on the Geophysical/Geological Advisory committees at the Colorado School of Mines, the University of Colorado, and Southern Methodist University.

He received a B.S. degree in Engineering Physics from the University of Colorado in 1948 and an M.S. in Physics from the same university in 1954. His entire career has been with GSI and HGS in successive positions as geophysicist on seismic field crews, member of a seismic research and development group, manager of an area geophysicist group, manager of data processing, manager of marketing, and manager of technology development.

He is a member of the Society of Exploration Geophysicists, the Dallas Geophysical Society, the Houston Geophysical Society, the European Association of Exploration Geophysicists, the Australian Society of Exploration Geophysicists, and the American Association for the Advancement of Science.



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