|
Consortium locates gas hydrates in GOM Government and industry project finds saturated deposits in reservoir sands at two out of three sites drilled in offshore expedition Alan Bailey Petroleum News
In another key step towards the possible future development of gas hydrates, a potential major source of natural gas, a research team has found highly saturated deposits of the material in reservoir-quality sands under the Gulf of Mexico, the U.S. Department of Energy announced May 14. During a 21-day expedition using the semi-submersible rig Helix Q4000 the team drilled through gas hydrates in a variety of different rock types and located resource quality hydrates in two out of three reservoir sand locations that the team had targeted.
“Prior to this expedition there was little documentation that gas hydrate occurred in resource-quality accumulations in the marine environment,” DOE said.
The DOE National Energy Technology Laboratory is collaborating in this joint industry project with entities including the U.S. Geological Survey, the U.S. Minerals Management Service and an industry research consortium led by Chevron, DOE said.
Gas hydrate (or more correctly methane hydrate) contains methane molecules, the primary component of natural gas, trapped in a lattice of water molecules to form a white, rime ice-like solid that is stable in relatively low temperatures and elevated pressures, such as exist in some submarine settings or perhaps a couple of thousand feet under Arctic tundra. When decomposed by altering the pressure or temperature, the solid hydrates release about 164 times their original volume in natural gas.
Initial phase In 2005, in an initial phase of the Gulf of Mexico investigation, the joint industry project conducted a drilling and coring program that tested possible drilling hazards relating to the presence of gas hydrates in clay-dominated material immediately under the seafloor.
A major focus of subsequent work has been the refinement of techniques for locating gas hydrate deposits in the subsurface. In 2006 the project team began investigating numerous possible gas hydrate locations using detailed geologic interpretations, coupled with sophisticated techniques for analyzing 3-D seismic data, to delineate and prioritize drilling sites.
That led to this year’s drilling project, a project using state-of-the-art logging-while-drilling tools that enable downhole logs to be run while drilling is in progress, thus enabling the hydrates to be detected in the subsurface rocks, while also leading to three-dimensional images of the hydrate-bearing sediments. And the drilling results confirmed the effectiveness of the techniques used to determine the drilling locations.
“During the expedition, gas hydrate was found at saturations ranging from 50 percent to more than 90 percent in high-quality sands,” DOE said. “The deposits were also found in close accordance with the project’s pre-drill predictions, providing increased confidence in the gas hydrate exploration and appraisal technologies.”
Potential development The drilling in the Gulf of Mexico represents a move towards the possible development of submarine gas hydrates that are thought likely to be more technically challenging to produce than Arctic land-based hydrates, such as those near the existing oil and gas infrastructure on the North Slope.
In fact DOE has been working with several teams in northern Alaska, investigating ways of locating gas hydrate deposits on land and evaluating the eventual possibility of gas hydrate production, a possibility rendered appealing by estimates of vast volumes of methane locked up in the hydrates and the emerging popularity of natural gas as a clean-burning fuel.
In 2007 BP in collaboration with DOE successfully drilled a gas hydrate stratigraphic test well at Mount Elbert on Alaska’s central North Slope, recovering about 100 feet of hydrate bearing core and leading to plans for a gas hydrate production test. DOE is also working with ConocoPhillips on the North Slope to test the use of carbon dioxide to displace methane from the hydrates, a technique that would serve the dual purpose of producing natural gas and sequestering unwanted carbon dioxide.
And at the western end of the North Slope, DOE is working with the North Slope Borough and Petrotechnical Resources of Alaska to drill an initial well to test for possible gas hydrates in a gas field near Barrow.
Greater understanding The various gas hydrate projects are enabling researchers to edge towards a greater understanding of what might be involved in commercial gas hydrate exploitation. And, on the basis of gas hydrate production modeling combined with successful tests in the Mount Elbert well and in another gas hydrate well, the Mallik well in the Mackenzie Delta, USGS has determined that sustained recovery of natural gas from gas hydrates is technically feasible — in October the agency published a technically recoverable hydrate resource estimate for Alaska’s North Slope.
However, a determination of whether gas hydrate production will prove economically viable remains some distance in the future.
| 