DE-FC26-06NT42959

Goal
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 seafloor in the deep marine environment and testing the new instrumentation at Mississippi Canyon Block 118.

Phase 1. Proposed bottom-tow resistivity system. (a) Existing DeepSea Sled. (b) Bottom-tow resistivity profiling with resistivity instrument in glass sphere pressure housings.

Performer
Baylor University, Waco, TX 76798 Field Test Site: Mississippi Canyon Block 118, Gulf of Mexico

Background
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 exploitation. 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 seafloor. 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 exploited. 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 subbottom electrical resistivity data will be needed to confirm the presence and constrain 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.

Potential Impact
The proposed geophysical method is potentially simpler, less expensive, and more easily extended to 3D and 4D 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 4D seismic data are currently being used to monitor petroleum production.

Accomplishments

• The pressure housing for the seafloor DC resistivity (DCR) system electronic components was completed in February, 2007.
• Electronic components for DCR system were completed in March 2007 and assembled into pressure housing in June, 2007.
• The seafloor electrode array for DCR system completed in March 2008.
• The control/power interface between the DCR and the Specialty Devices Inc. ROV was completed and tested in May 2008.
• Initial sea trial of the DCR system at Mississippi Canyon Block 118 was conduced in June 2008. The instrument was successfully lunched and lowered to the seafloor. On the seafloor, the DC resistivity system was powered-up by command from the surface ship, but communication with the instrument was lost during the initialization procedure. Upon recovery, it was discovered that the electrode array had been attacked by sharks and cut in half. The test verified that the control/power interface between the ROV and DC resistivity system works, but no resistivity data were collected.

Current Status
Advanced Geoscience Inc. (AGI) is currently fabricating a replacement electrode array.

The project team plans to conduct a field test of the repaired DCR system in a lake near Waco, Texas during the Winter of 2009. During Spring 2009, the system will be deployed at the Mississippi Canyon 118 site in the Gulf of Mexico for a full-scale field test. The final task (within Phase 1) will include an analysis of the DCR data acquired during the deep-tow survey and a topical report.

If activities in the initial field test prove successful, the performer plans to reconfigure the DCR system for a semi-permanent installation at one site on the seafloor at MC118 where a long term survey will take place aimed at investigating changes in the hydrate system (in the context of changing conditions in the area surrounding the evaluation site) over a period of almost two years – Project Phase 2.

Project Start: October 1, 2006
Project End: September 30, 2009

Project Cost Information:
Phase 1, DOE Contribution: $138,199, Performer Contribution: $21,957
Phase 2, DOE Contribution: $115,650, Performer Contribution: $46,928

Contact Information:
NETL – William Fincham (william.fincham@netl.doe.gov or 304-285-4268)
Baylor University – John Dunbar (John_Dunbar@baylor.edu or 254-710-2191)

Additional Information:
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].

Quarterly Report [PDF-223KB] January - March, 2008

September 2007 Project Review [PDF-4.47MB]

Quarterly Report [PDF-218KB] April - June, 2007

Kick-off meeting presentation [PDF-3.28MB] - January 9, 2007

Quarterly Report [PDF-658KB] October - December, 2006

Technology Status Assessment  [PDF-57KB] - December, 2006 - "Geophysical Exploration Methods for Gas Hydrates"