DE-NT0005668

Goal
The goal of this project is to investigate the feasibility of using marine electromagnetic (EM) surveying as a tool for characterization and quantification of the occurrence of hydrate in the seafloor section. This will be done by collecting field data and quantifying the resistivity of natural gas hydrate using laboratory measurements.

Performers
University of California San Diego - Scripps Institution of Oceanography, La Jolla, CA 92093
Lawrence Livermore National Laboratory (LLNL), Livermore, CA 94511-9900
United States Geological Survey, Menlo Park, CA 94025
Massachusetts Institute of Technology, Cambridge, MA 02139.

Background
Gas hydrate holds promise as an energy resource, is a potential hazard to offshore drilling and development, can be a factor in seafloor slope stability, and remains an enormous global reservoir of methane, a potent greenhouse gas. For all of these reasons, understanding how to quantify the volume and distribution of hydrate in marine sediments is important. Although methane hydrates occur in vast quantities (the consensus estimate is 10,000 Gt), estimates of total global volume span four orders of magnitude, mainly because existing geophysical methods are not sensitive to bulk concentration of hydrate in the seafloor section. Notably, the use of the seismic bottom simulating reflector (BSR), although a sensitive indicator of the base of the hydrate stability field, is largely ineffective at predicting the amount of hydrate between the seafloor and the BSR.

Electromagnetic (EM) methods, on the other hand, are sensitive to the concentration and geometric distribution of hydrate, but the use of marine EM techniques to characterize hydrate is still in its infancy. Field trials carried out to date have been limited in scope and sophistication, and there is a lack of laboratory-derived relationships between petrophysical properties and EM measurements on which to relate conductivity to quantitative estimates of hydrate volume in the seafloor section.

This project will carry out three EM surveys in the Gulf of Mexico over areas where hydrate is known (or thought) to exist in the sedimentary section in water depths ranging from 800 to 3,000m. The project will employ state-of-the-art EM imaging equipment and techniques that will incorporate conventional offshore hydrocarbon exploration methods and newly developed methods designed specifically for the purpose of hydrate mapping. Additionally the project will build new laboratory conductivity apparatus to make the first measurements of the electrical conductivity of natural methane hydrate as a function of temperature, pressure, pore water fraction, pore water chemistry, and sediment fraction, and will use these results to calibrate the resistivity data obtained from the field surveys in terms of hydrate concentrations. It is expected that the results of this work will include three case histories that can be used to advance the use of marine EM methods to map and quantify gas hydrate in the Gulf of Mexico, and will also provide a basis for the use of EM as a complementary tool for carrying out global studies focused on directly quantifying the distribution, concentration, and total volume of hydrate accumulations.

Potential Impact
The impact of successfully demonstrating the ability of marine EM methods to quantify hydrate content in marine sediments will be significant, as no such method currently exists. Hydrate deposits are not stratigraphic and even extensive drilling provides only point measurements with no reliable methodology for interpolation or extrapolation to regions beyond the wells. However, if an area can be comprehensively surveyed using only a few days of ship time, or if continuous profiling can be carried out, this would represent the first steps toward the possibility of a direct assessment of the global inventory of hydrate and could contribute to the discovery of economically viable hydrate concentrations. The method to be developed also holds potential for monitoring the sequestration of carbon dioxide in seafloor sediments, where the formation of CO₂ hydrate has been proposed as a natural capping mechanism to prevent escape of sequestered CO₂.

Accomplishments
This project was only initiated in early October 2008 but has already achieved a major technical objective. As part of a comprehensive study to develop marine electromagnetic methods for gas hydrate detection and mapping, the project has carried out an 18-day cruise on the R.V. Roger Revelle in the Gulf of Mexico from 7th--26th October 2008. During this experiment a total of 94 ocean bottom electromagnetic (OBEM) recorders were deployed at four survey areas (Alaminos Canyon block 818, Walker Ridge block 313, Green Canyon block 955, and Mississippi Canyon block 118) and the Scripps Undersea Electromagnetic Source Instrument (SUESI) was towed through the survey areas a total of 103 hours. Data transmission was accomplished via a 200 A, 50 m dipole antenna at heights of 70—100 m above the seafloor. The field expedition vessel also towed a 3-axis electric field recorder behind the SUESI antenna at a constant offset of 300 m. Field data collection activities were highly successful with acquisition of high quality data on almost all deployments and with only two deployments failing to collect data.

The survey over the Walker Ridge area was an addition to the originally proposed 3 survey program which was incorporated into the expedition (under the guidance of DOE) in an effort to acquire EM data at sites that are planned for evaluation via drilling and logging as a part of the Chevron led DOE JIP project scheduled for the spring / summer of 2009. This addition will ensure a more comprehensive suite of data sets for these areas of marine hydrate occurrence.

Current Status
Efforts are under way to document field activities through the development of the cruise report, assemble cruise data, and carry out basic quality control assessment of the data. The project has also initiated preliminary design studies for the conductivity cell to be used in lab based evaluation of hydrate conductivity characteristics. Activities planned for completion within Phase 1 of the project (year one) include:

• Production of an initial cruise report
• Design of the conductivity and pressure cell
• Generation of a merged EM/navigation data set
• Construction of the conductivity/pressure cell
• Performance of calibration tests for the cell using water standard
• Installation of the conductivity/pressure cell in Menlo Park and initialization of hydrate measurements
• Preliminary interpretation of field data.

Project Start: October 1, 2008
Project End: September 30, 2011

Project Funding Information:
Phase 1 – 12 months, DOE Contribution: $622,131, Performer Contribution: $615,584
Phase 2 – 12 months, DOE Contribution: $112,592, Performer Contribution: $54,784
Phase 3 – 12 months, DOE Contribution: $93,809, Performer Contribution: $0
Planned Total Funding (if project continues through all project phases):
DOE Contribution: $828,532, Performer Contribution: $670,368

Project Funding (FEW0160)
DOE Contribution: $82,354

Contact Information:
NETL – William Fincham (william.fincham@netl.doe.gov or 304-285-4268)
SCRIPPS – Steve Constable (sconstable@ucsd.edu or 858-534-2409)
Lawrence Livermore National Laboratory (LLNL) – Jeffery L. Roberts (Roberts17@llnl.gov) or 925-422-7108

Additional Information

The Kick-Off Presentation for this project is available by request. It is a PDF file that is approximately 35MB.

Link to the Scripps GOM Hydrates Field Program Website [external site]