Seismic Wave Stimulation May A Be Low-Cost Procedure For Enhanced Recovery

(Tech Connections Column, July 2001, American Oil and Gas Reporter)

Seismic wave stimulation technology has the potential for being a low-cost procedure for enhanced oil recovery, but field results have been mixed, at least partially because of a lack of consensus on the mechanisms responsible for increased recovery. However, knowledge is at a critical stage, and industry may soon know “when, where and how it works,” so it can be applied reliably. The following information should help operators make informed decisions on this evolving technology.

Proposed mechanisms include:

• Changes in wettability;
• Coalescence and/or dispersion of oil droplets;
• Reduced viscosity;
• Surface tension; and
• Increased permeability.

Pore pressure changes are believed important, since production increases have occurred even when mechanical strain levels were quite low. There is agreement that the source frequency range should be low enough to allow energy to propagate to the reservoir, which may be up to several thousand feet from the source well, with little loss of amplitude resulting from attenuation in the medium.

R&D work has focused on mechanisms, understanding the why/when/where/how questions, and modeling. With proper understanding of the contributing mechanisms and appropriate mathematical models, responses in different geologies and formations as a function of porosity, fluid and matrix properties can be modeled.
The Lawrence Berkley National Laboratory and industry partners have conducted several field tests. To date, three sources have been tested in three different formations: in a sandstone in Colorado, and in diatomite and shale formations in California. In all of these tests, no seismic energy above background was observed. It is thought that monitoring equipment was too far away. Future tests will place sensors much closer (within a 100 feet).

Oil & Gas Consultants International Inc. (OGCI) is partnering with the Osage Tribe, field operator Calumet Oil Company, and Phillips Petroleum Company to test vibration stimulation in the North Burbank Unit in a U.S. Department of Energy-funded project. Seismic Recovery LLC, a subsidiary of OGCI, will test its patented whirling orbital vibrator. The tool uses backward-whirling motion to create both compression and shear seismic waves from 5 to more than 500 Hz. The direct mechanical contact with the formation allows the device to be used in reservoirs with a gas cap–a situation that would dampen a fluid pressure pulse technique. Phillips will conduct laboratory tests using its proprietary sonic core apparatus to determine fluid flow response to a range of vibration frequencies. Drilling was imminent, as soon as mid-July. Once baseline data are gathered, vibration stimulation will begin.

Applied Seismic Research tried its in-situ seismic stimulation tool in Lost Hills during two tests last year. In a continuous 12-day stimulation test conducted during July 2000, oil cut was increased with no overall increase in fluids. A longer 38-day test performed during October-November 2000 in a group of 60 wells, increased oil cut and oil production by 11 and 17 percent, respectively. Because many of the wells had undergone various types of workovers and fracture stimulation, a control group of 26 wells that had not been disturbed by stimulation procedures was also monitored. By the end of the second stimulation treatment, oil cut and oil production from the 26 control wells had increased by 29 and 26 percent, respectively. Data did indicate that stimulation needed to be continuous.

British Petroleum is exploring pressure pulsing for EOR, well-bore cleanup, pipeline problems, and drilling. In preparing for field trials, it has screened reservoirs looking for onshore, low gas content, and “softer” rocks to allow fluid-rock coupling. Five candidate reservoirs have been selected out of 300. AERA Energy has tried seismic stimulation (in cooperation with Los Alamos National Lab in its Lost Hills, San Ardo, and Belridge fields, and two or three additional field tests are planned. Marathon conducted a test in the Tensleep in Wyoming, a high viscosity oil reservoir. Tool failure and lack of resources kept the test from being completed. The formation was hard and fractured, resulting in water cycling problems. The resulting reduction in injectivity was attributed to mobilization of high viscosity oil. Marathon is considering another test of the technology.

Information from three commercial suppliers–Applied Seismic Research, PerfClean, and Sonic  Production Systems–is contained within the referenced state-of-the-art summary. Some other known suppliers were unable to respond.

Editor’s Note: The preceding was excerpted from a state-of-the-art summary developed by Susan Jackson (primary author), RMC Inc. for DOE’s National Petroleum Technology Office, published in June 2001 PTTC Network News. Visit http://www.pttc.org for additional information.