Dr. Robert Woolsey of the University of Mississippi and a small group of like-minded scientist and engineers from research institutions around the country have long wanted to study gas hydrates. But it took a cataclysmic event to get the level of support they needed from government and industry to make a start at unraveling their mystery. Woolsey heads up the Gulf of Mexico Gas Hydrates Research Consortium, managed by the Center for Marine Resources and Environmental Technology (CMRET) at the university.

Gas hydrates are found in the deep continental margins around the world, typically at water depths greater than 1,640 ft (500 m) with temperatures less than 39.2°F (4°C). They are ice-like crystalline solids formed from a mixture of water and natural gas, commonly methane.
In the late ’90s when Shell was involved in drilling preparations at its Ursa discovery in the Gulf of Mexico, the sudden encounter of a high-pressure shallowwater flow resulted in the loss of the template, the drill site and ultimately millions of dollars. Many in the field attribute the problem most likely to an unexpected encounter with hydrates. Certain US governmental agencies with responsibilities in these areas were suddenly keen to support research focused on learning more about gas hydrates and how to avoid them and their potential catastrophic effects on bottom-founded installations and drilling activities.

Once that happened, doors that were previously closed were at least partially opened for the support of research. Woolsey and his team wondered if they could establish a permanent laboratory and monitoring station on the ocean bottom to study hydrates more or less continuously over a longer period of time, maybe several years? Thus the concept for the Gas Hydrates Seafloor Observatory was born.

The Department of Interior’s Minerals Management Service (MMS), a long-time supporter of the CMRET, was the first to support the observatory concept, primarily for the investigation of hydrates and their effects on seafloor stability. The Department of Energy’s National Energy Technology Laboratory was next to provide support, expanding on its interest in hydrates as a future energy resource of considerable potential. More recently, the National Oceanographic and Atmospheric Administration’s National Undersea Research Program joined in support, focusing on hydrates and associated gas venting to the water column and eventually to the atmosphere with potential impact on global climate.

Recently, the MMS arranged for the dedication of two-thirds of Block 118 in Mississippi Canyon to establish the seafloor laboratory to observe gas hydrates and the hydrocarbon system of the hydrate stability zone.

Research to date

Events like Ursa and many other lesser drilling encounters have given good indication that the stability problems hydrates present are very real at depth as well. However, Woolsey and his compatriots originally had trouble reproducing similar responses in their onshore labs.

“A leading chemical engineer at Mississippi State, Rudy Rogers, finally cracked that thing for us,” Woolsey said. Rogers demonstrated that bacteria in the vicinity of the hydrates created “biosurfactants” that act as catalysts which facilitate the reaction between the methane gas and the sea water. They provide a nucleation site, primarily on marine clays, which enhance the crystallization of hydrates under otherwise marginal thermal conditions. He also demonstrated that the surfactants, while having an affinity for marine clays, had no such affinity for silica sand, a condition that may well prove to have profound effects and provide an explanation for the problematic shallowwater flows.

The observatory/monitoring station

The university has sub-contracted with prominent researchers from some 15 other universities to provide parts of the overall monitoring station and research program. A variety of instrumented arrays will measure geochemical processes, microbial activities associated with the gas hydrate system, and various types of geophysical ocean acoustic and seismic measurements. A series of vertical seismic arrays will extend from the seafloor into the water column, and horizontal sensor arrays will be laid on the seafloor.

“The intent is to study the gas hydrate system in a calendar time sense, like 4-D reservoir monitoring,” said Bob Hardage, senior research scientist at the University of Texas’ Bureau of Economic Geology and consortium four-component (4-C) seismic systems team leader. “The general objective is to get all of this instrumentation on the seafloor and do several years of data collection to try to understand what a gas hydrate system in the Gulf of Mexico does from year to year.” The seismic work is further supported by the ocean acoustic expertise of Ross Chapman, University of Victoria, BC, with an ocean acoustic line array that can utilize sea surface noise from waves and passing ships to image sub-bottom reflectors to the base of the hydrate stability zone and beyond. The overall seismic/acoustic program is managed by Tom McGee, senior scientist and geophysicist, CMRET.

Other data collected will include thermal gradient data, which will be monitored via a multi sensor borehole array fitted with 4-C seismic sensors as well as thermistors. Pore fluid chemistry will be studied under the direction of Jeff Chaton, Florida State University, eventually via a bottom-deployed mass-spectrometer, with continuous sample streams provided by osmotic pumping from horizons of interest within the sedimentary section. A number of other vent and lower water column/ boundary layer, hydrocarbon sensor arrays will be employed in a similar autonomous fashion under the supervision of the consortium bio-geochemical program team leader, Chris Martens, University of North Carolina.

Ideally at least part of the station will be operational this summer.

Other research

Though the modeling of the events of gas hydrate formation and dissociation in context with oceanic and geologic events is the main thrust of this study, Woolsey said that the permanent set of geophysical and bio-geochemical arrays on the seafloor will provide other information as well. “There is a tremendous amount of hydrocarbon that vents to the seafloor, and there are microbes that do a good job of cleaning up mother nature’s mess,” he said.

He noted that work done several miles east of the ConocoPhillips’ Joliett platform indicates a vent which researchers have fondly dubbed “Old Faithful” because of the apparent volume and regularity of its venting episodes. “It’s mainly gas, but there’s a mix of liquids too,” Woolsey said. “If you’re out there in a boat on the surface, it smells like a refinery. From the vantage point of a submersible it looks like an underwater volcano. But if you go back down there a few days later, you see little if any hydrocarbons on the seafloor. And the bacteria look all fat and happy.”

This could have important ramifications in the recognition of an important fundamental source of nutrients for the marine flora and fauna food chain, and a viable means of well-produced saltwater disposal from offshore platforms, he said. ?Another side benefit from the research is the fact that the acoustic monitoring being done on the seafloor can detect large storm waves. The Woolsey team is hoping to rig some of the regional NOAA data buoys that collect wind and wave information with these sensors to beam the information to satellites and then to shore. The seismic monitoring can also pick up earthquakes at depth, which can have ramifications for seafloor stability.

“I think we should be very concerned about the potential instability of some of the very steep slopes,” he said. “Mississippi Canyon was formed by huge slumps of 100 or more square miles (260 sq km) in area. A slump of that magnitude could generate a rather substantial tsunami with catastrophic impact on the Gulf Coast.”