The U.S. Department of Energy's (DOE) National Energy Technology Laboratory (NETL), as part of an international partnership, has taken a significant step forward in investigating the resource potential of natural gas hydrates within the Prudhoe Bay Unit (PBU) on the Alaska North Slope.
Gas hydrates are naturally occurring combinations of natural gas and water that form in specific conditions of relatively cold temperatures and relatively high pressures. They are known to occur in abundance in northern Alaska, as well as in the shallow sediments of deepwater continental margins around the world, including well documented deposits in the Gulf of Mexico and off the southeastern coast of Japan.
Alaska is the only location in the world where gas hydrate recoverability can be feasibly tested and monitored over the desired timeframes. Alaska’s North Slope holds an estimated 54 trillion cubic feet of technically-recoverable gas in hydrate form according to the USGS.
In cooperation with the PBU owners, DOE/NETL, working in partnership with the Japan Oil, Gas and Metals National Corporation, the U.S. Geological Survey (USGS), and Petrotechnical Resources-Alaska, successfully drilled and logged an initial test well (Stratigraphic Test Well) in the greater Prudhoe Bay oil field that has confirmed the occurrence of gas hydrates in two reservoirs that are suitable for potential future testing.
The initial well was suspended with temperature and acoustic-monitoring devices that will allow it to serve as a monitoring well for future field experiments. Significant subsurface data was secured including a full suite of geophysical measurements and 39 sidewall pressure cores during the operation.
Because of the December 2018 work, two high-quality gas hydrate reservoirs with characteristics typical of many global accumulations (arctic and marine) were confirmed via extensive, research-level logging-while-drilling data. The deeper reservoir at about 54 degrees Fahrenheit could provide optimal conditions for reservoir experiment and a shallower reservoir at approximately 40 degrees Fahrenheit could enable iterative testing of gas hydrate production response. Reservoir samples were retrieved to enable production test well design.
The effort builds upon prior gas hydrate field research conducted by both the United States and Japan, in Canada in 2002, 2007, and 2008; Alaska in 2007 and 2012; and offshore Japan in 2013 and 2017. The work of the United States and Japan has confirmed the occurrence of gas hydrates in both the U.S. and in Japan, identified many technical details of its occurrence and nature, and demonstrated the technical feasibility of producing natural gas from the reservoir.
The location of this site in the greater PBU provides the necessary infrastructure to conduct field experiments of sufficient duration to reveal how gas hydrates release natural gas in response to reservoir depressurization. Such long-term testing cannot be feasibly done either offshore or in an undeveloped Arctic area onshore.
The collaborative effort has benefitted from the support of the Alaska Department of Natural Resources to facilitate gas hydrate evaluation in Alaska and BP Alaska, which operated the well on behalf of the Prudhoe Bay Unit owners.
Click here to access papers summarizing the 2018 Stratigraphic Test Well program that will be presented at the 10th International Conference on Gas Hydrates in Singapore currently scheduled for 18-23 July, 2021.