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Japanese get sustained gas hydrate production but higher rates needed
Alan Bailey for Petroleum News
Two methane hydrate production tests in the Eastern Nankai Trough, offshore Japan, demonstrated the stable production of natural gas and water for several days through the drawdown of pressure in the hydrates, according to the latest edition of the National Energy Technology Laboratory’s Fire in the Ice publication. However, although the gas production rates could be sustained, the rates were too low for commercial viability. The Japanese plan further testing, trying out techniques that might raise the production rates to economic levels.
North Slope testing One focus of upcoming production testing is the North Slope Hydrate 01 well, drilled by BP in the winter of 2018-19 in the western part of the Prudhoe Bay unit on behalf of Japan Oil, Gas and Metals National Corp., the U.S. Geological Survey and Petrotechnical Resources of Alaska. The intent is to drill two additional wells nearby, to enable the testing of sustained gas production from hydrates in the subsurface. The North Slope has huge quantities of methane hydrate deposits around the base of the permafrost.
Methane hydrate is a solid in which molecules of methane, the primary component of natural gas, are concentrated inside a lattice of water molecules. The hydrates greatly concentrate methane, relative to accumulations in conventional gas reservoirs. The material remains stable within a range of relatively low temperatures and high pressures. Raising the temperature or reducing the pressure causes the material to disassociate into water and methane gas. Potential gas production has mainly focused on pressure reduction, although there are other techniques that can be used.
High production rate needed The Japanese research team has determined that economically viable gas production from hydrates requires a methane production rate per well of at least 1.8 million cubic feet per day from a hydrate site containing at least 350 million cubic feet of the gas. The maximum production rate achieved in the Eastern Nankai Trough tests was around 700,000 cubic feet per day. And tests have indicated that production rates tend not to increase over time, the Fire in the Ice article says.
The testing revealed two issues. One was an excess of water production, along with the methane production. The other was a pressure drop across the interface between the wellbore surface and the well sand control device, with this pressure drop inhibiting the drawdown of the pressure in the rock formation holding the hydrates. The next phase of the methane hydrate research program will focus on finding solutions to these problems. This continuing research, seeking better production technologies, will include improved reservoir modeling. The research will also involve carrying out a marine survey, to identify appropriate future test sites.
The testing of improved production techniques will involve using the test wells being drilled on the North Slope, the Fire in the Ice article says.
Additional activities Additional activities in the Japanese research will include environmental impact studies, economic analyses and the integration of new technologies into the research program. Japan Methane Hydrate Operating Co. Ltd. is joining Japan Oil, Gas and Metals, and the National Institute of Advanced Industrial Science and Technology, AIST, in the Japanese methane hydrate research consortium. Separate from this consortium, AIST is continuing a program of surveys and studies into seafloor methane hydrate production and recovery, the Fire in the Ice article says.
- ALAN BAILEY
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