Newswise — A Baylor University researcher has used a new search method that he adapted for use on the seafloor to find a potentially massive source of hydrocarbon energy called methane hydrate, a frozen form of natural gas, in a portion of the Gulf of Mexico.
Dr. John Dunbar, associate professor of geology at Baylor, and his team used an electrical resistivity method to acquire geophysical data at the site, located roughly 50 miles off the Louisiana coast. The Baylor researchers were able to provide a detailed map of where the methane hydrate is located and how deep it extends underneath the seafloor.
Located in an area called the Mississippi Canyon, the site is about 3,000-feet-wide, 3,000-feet under water, and has both active and dormant gas vents. Scientists have been researching the site since 2001, but have not been able to ascertain where the hydrate is located nor how much is there until now.
“The conventional search methods have been fairly effective in certain situations, but the resistivity method is a totally different approach,” Dunbar said. “The benefit to the resistivity method is it shows the near-bottom in greater detail, and that is where the methane hydrate is located in this case. This research shows the resistivity method works and is effective.”
Dunbar and his research team injected a direct electrical current into the seafloor to measure the resistivity of the sediment beneath the sea floor. The measurement of resistivity – the ability of a material to resist conduction of electricity – showed the researchers where the methane hydrate is located. To do this, Dunbar and his team dragged a “sled” – a device with a nearly one-kilometer-long towed array – back and forth over the site, injecting the electrical current. Sediment containing methane hydrate within its pores showed higher resistivity, compared to sediment containing salt water. While the measurement of resistivity has been used for some time, the method has seldom been used at deep depths.
The new method showed researchers that the methane hydrate was located only in limited spots, usually occurring along faults under the sea floor. Dunbar said the method also showed the methane hydrate is not as abundant as previously thought at the site.
The U.S. Department of Energy has awarded Dunbar more than $115,000 to continue researching the site. Dunbar and his team will reconfigure the towed array and shorten the length of it to about 1,500 feet. They also will cluster sensors around certain areas on the array, which will give researchers a clearer picture of how deep the methane hydrate extends and will allow them to create a three-dimensional picture of the underwater site.
An ice-like solid, methane hydrate is found beneath the seafloor in many locations across the globe, usually at depths greater than 3,000 feet. The most common place to find gas hydrate mounds in the Gulf of Mexico are along the intersections of faults with the seafloor. According to the U.S Geological Survey, the nation’s methane hydrate deposits are estimated to hold a vast 200 trillion cubic feet of natural gas. If just one percent of those deposits are commercially produced, it would more than double the country’s natural gas reserves.
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