The goal of this project is to evaluate the direct-current electrical resistivity (DCR) method for remotely detecting and characterizing the concentration of gas hydrates in the deep marine environment. This will be accomplished by adapting existing DCR instrumentation for use on the sea floor in the deep marine environment and testing the new instrumentation at Mississippi Canyon Block 118.
Baylor University, Waco, TX 76798
Advanced Geosciences Inc., Austin, TX 78726
Specialty Devices Inc., Wylie, TX 75098
Marine occurrences of methane hydrates are known to form in two distinct ways. By far the most common occurrence is associated with the vertical migration of biogenetic gas into the near-bottom hydrate stability zone. Hydrates that form in this way are normally, but not always, associated with bottom simulating seismic reflections (BSR). In these cases the BSR signature indicates that gas hydrates are present over large areas, but seismic information alone is not enough to determine where concentration levels may be high enough to warrant future production consideration. The second kind of marine hydrate deposits form by the vertical migration of thermal gas from deep source rocks and conventional gas reservoirs. Thermally-derived hydrates are normally associated with gas seeps that occur where deep-seated faults intersect the sea-floor. They are generally not laterally extensive, but because the gas seeps are sites of highly focused methane discharge, greater concentrations of hydrate are possible. As a result of this concentration, thermal hydrate deposits may be the first in the marine environment to be considered for production. However, because thermal hydrates are seldom associated with BSR signatures, neither their presence nor their concentration can be reliably determined by seismic methods alone.
There is a growing consensus that additional geophysical information in the form of sub-bottom electrical resistivity data will be needed to confirm the presence and determine the concentration of gas hydrate. While the presence of hydrate in the sediment pore spaces causes only minor changes in seismic velocities, the electrical properties of sediment are greatly influenced by the presence of either hydrate or free gas. Hence, the occurrence of a high resistivity anomaly in a subsurface region associated with a seismic velocity anomaly would indicate the presence of free gas. Anomalously high resistivity in a region with essentially normal seismic velocities is indicative of the presence of hydrate. The question that remains is “What kind of electrical method will be most applicable to future hydrate exploration needs?”
This project will attempt to further the development of marine electrical profiling by adapting DCR methods developed for land-based and shallow-water environmental studies to hydrate characterization in the deep-marine environment.
The proposed geophysical method is potentially simpler, less expensive, and more easily extended to 3-D and 4-D surveys than geophysical methods previously applied to the study of gas hydrate deposits. If the experiments are successful and the DCR method demonstrates the ability to detect and characterize gas hydrate distribution at the test site, then the method could become another very important tool for hydrate characterization. When used in conjunction with existing and new seismic methods, this could represent a novel “combined technique” methodology for more effectively locating and characterizing marine hydrate occurrences. Its use in reconnaissance surveys could be particularly important when exploring for thermal hydrate deposits not associated with BSR signatures. Its use for long-term monitoring would be particularly important in monitoring hydrate production, much as 4-D seismic data are currently being used to monitor petroleum production.
The project has been completed. The final report is available below under "Additional Information".
Phase 1 - DOE Contribution: $138,199
Phase 2 - DOE Contribution: $115,650,
Planned Total Funding - DOE Contribution: $253,849
Phase 1 - Performer Contribution: $21,957
Phase 2 - Performer Contribution: $46,928
Planned Total Funding - Performer Contribution: $68,885
In addition to the information provided here, a full listing of project related publications and presentations as well as a listing of funded students can be found in the Methane Hydrate Program Bibliography [PDF].
Final Project Report [PDF-4.29MB] - March, 2013
September 2007 Project Review [PDF-4.47MB]
Kick-off meeting presentation [PDF-3.28MB] - January 9, 2007
Technology Status Assessment [PDF-57KB] - December, 2006 - "Geophysical Exploration Methods for Gas Hydrates"