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Partnership plans methane hydrate testing
New well is part of a three-well project to test and evaluate sustained gas production from hydrates under North Slope permafrost Alan Bailey Petroleum News
The Department of Energy’s National Energy Technology Laboratory has published information relating to a new methane hydrate well that was completed in January in the western part of the Prudhoe Bay unit on the North Slope. The drilling of the well forms part of a project aimed at testing the production of natural gas from hydrates, as a potential future commercial gas resource. NETL formed a partnership with Japan Oil, Gas and Metals National Corp., the U.S. Geological Survey and Petrotechnical Resources of Alaska for the drilling of the well. BP, operator of the Prudhoe Bay unit, oversaw the drilling.
Stratigraphic test well A presentation on the NETL website provides some insights into the objectives and plans for the project. Apparently the new well has been designed as a stratigraphic test well, to evaluate the subsurface methane hydrate resource at the site. Depending on the results of this evaluation, the intent is to drill two additional wells nearby: a well for sustained testing of gas production from hydrates, and a well for characterizing the hydrates and collecting data. The stratigraphic test well that has now been drilled would become a second data gathering well.
Methane hydrate is a solid in which molecules of methane, the primary component of natural gas, are concentrated inside a lattice of water molecules. Huge quantities of the material, which remains stable within a certain range of relatively high pressures and low temperatures, are known to exist around the base of the permafrost under the North Slope. There are also extensive hydrate accumulations in other parts of the world, including in the seabed of the Gulf of Mexico and offshore Japan. The hydrates greatly concentrate the gas, relative to accumulations in conventional gas reservoirs.
Gas can be released from hydrates through some combination of elevating the temperature or reducing the pressure of the hydrate resource. Although there have been demonstrations of short-term hydrate production, no one has yet conducted a sustained, long-term production test.
Hydrates on the North Slope The NETL presentation comments that the Alaska North Slope is a “natural laboratory” for the assessment of methane hydrate production technology.
The hydrates under the North Slope, while extensive, exist in a series of discrete sand reservoirs at various depths and locations. A production well would obviously need to be located in a situation where it can penetrate one or more of these reservoirs.
There have been two methane hydrate wells drilled on the Slope. One, the Mount Elbert well, drilled in 2007, enabled the gathering of gas hydrate cores and evaluated the production characteristics of the hydrates that the well penetrated. The second, the Ignik Sikumi well, drilled in 2011-12, tested short term gas production using a couple of production techniques.
The objective of the current project is to test the feasibility, practicalities and characteristics of longer-term gas production.
Planning the project The NETL presentation says that the methane hydrate research team had considered a test site on unleased land on the North Slope but had discounted that possibility because of high logistics costs, the lack of support infrastructure, an uncertain regulatory environment and relatively high geologic risk. Instead, the team, in cooperation with the Prudhoe Bay unit working interest owners, has opted for a location on the North Slope gravel road system, in the western part of the unit. The location is clearly understood from a geologic perspective, has multiple hydrate reservoir zones and would minimize any interference with operation in the unit.
The expectation is that the project location would enable production testing for at least six months, and optimally 18 to 24 months, the presentation says.
The testing will focus on gas production through depressurization of the hydrates, a technique that testing in the Ignik Sikumi well had indicated to be particularly favorable. However, the focus will be on the science of hydrate production rather than demonstrating production rates. And thermal, mechanical and chemical well stimulation technologies will be available, as necessary. The intent is to use proven oilfield technology where possible.
Hydrate targets The chosen site has three sand horizons containing hydrates, and the wells are designed to penetrate all three of these horizons. The plan is to conduct the testing in one horizon that appears particularly prospective, with the fallback possibility of testing a second prospective horizon. Following the drilling of the new stratigraphic test well DOE said that the well had confirmed the presence of hydrates in two reservoirs that are suitable for testing, and that temperature and acoustic monitoring devices had been fitted in the well as a precursor to future field experiments.
SAExploration Inc. has applied for a permit to conduct a vertical seismic survey around the well site - apparently one of the instruments placed downhole in the well was a geophone for recording seismic signals.
Further wells The next phase of the project will include the drilling of the other two wells. A geo-data well, offset about 80 meters from the first well would acquire data for characterizing the test reservoir and enabling the characterization of test results. This well would be of similar design to the first well, but possibly with larger tubulars to allow the deployment of a suitable pressure corer device for characterizing the hydrates, the presentation says.
The third well, the production test well, would be positioned between the two other wells and would be designed with an appropriate completion and with tubulars that can accommodate artificial lift technology.
Subsequent production testing would lead to the gathering of data and data evaluation that would shed further light on the practicalities and feasibility of hydrate production.
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