Sidebar: Twenty years ago this month: BP’s project to address technical, money issues
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BP Exploration (Alaska) Inc. and Anadarko Petroleum Corp. both have gas hydrate projects underway on Alaska’s North Slope. (See separate story on Anadarko.)
The BP project, aimed at characterizing and quantifying the gas hydrate resource in the Prudhoe Bay and Kuparuk River area, is funded by the U.S. Department of Energy. Others contributing to the study include the U.S. Geological Survey, the University of Arizona in Tucson and the University of Alaska Fairbanks, BP petroleum geologist Bob Hunter told an American Association of Petroleum Geologists meeting in Anchorage in May.
The U.S. Geological Survey has estimated the North Slope basin gas hydrate resource at 590 trillion cubic feet in place, he said, “including the better-known Eileen trend gas hydrates (more than 40 tcf in place) and the lesser-known Tarn trend which may contain up to 60 tcf in place.”
These, he said, are “high quality reservoirs beneath existing facility infrastructure” where there is associated geological and geophysical data including extensive three-dimensional seismic.
Gas stored in clathratesHydrates are “naturally occurring ice-like solids which are composed of water and gas that trap gas molecules in a very efficient cage-like structure called a clathrate,” Hunter said. Clathrates store up to 164 volumes of methane gas - the most common gas hydrate - per unit of clathrate. Gas hydrates are stable offshore and in from 400 to 4,000 feet subsurface in Arctic permafrost, he said.
Both water and gas must be present to form the clathrate structure and gas hydrates, Hunter said: gas has migrated from deeper accumulations on the North Slope into regionally extensive reservoir-quality shallow sands and hydrates can help form their own trap.
But before the resource can be converted into reserves, he said, “significant technical and economic issues remain to be resolved.”
The project that BP is leading “will focus on reservoir characterization and productivity of the gas hydrate, mainly in the Eileen trend.” In phase one, 2002-04, the goal is to characterize the reservoir and fluids and calculate in-place resource.
“We will also study … the drilling, completion and production methodologies which then would apply to … phase two, to drill and production test.”
In the second phase, studies of reservoir fluids characterization will continue, the best areas for data acquisition will be selected and there will probably also be a short-term production test of the gas hydrate.
“We will drill, complete, acquire data and production test a dedicated gas hydrate well or well of opportunity” at Prudhoe Bay or Milne Point, Hunter said.
Long-term production testing in third phaseIf phase two is successful, the third phase would continue earlier studies “proceed into additional probable long-term production testing operations and field test the best possible production methods for gas hydrates in association with moveable gas,” he said.
If phase three is successful, it could lead to a pilot development program.
The technical and economic issues which need to be resolved are very significant, Hunter said. Gas hydrates are an unconventional resource and unconventional resources typically require special technology to extract. Technical challenges include productivity, he said: “the primary unknown variable remains recovery factor.” Innovations in well completions will also be necessary, and non-conventional and multilateral well technology will probably be required, Hunter said.
“This could involve a significant amount of capital investment and technology investment. But what attracts us and the DOE to this research is the potential resource is very large.”