Methane hydrate is a compound of water and methane (the major component of natural gas) that forms under pressure at cold temperatures. The amount of natural gas in methane hydrate is estimated to be far greater than all the world's conventional natural gas resources. It could potentially become a significant source of natural gas. Methane hydrate exists beneath large portions of the world's arctic permafrost, as well as within deep-sea sediments. On Alaska's North Slope, the volume of hydrate-based natural gas has been estimated at several times the volume believed to exist there in conventional gas-bearing formations.
The Hot Ice No. 1 well was drilled as part of a two-year cost-shared partnership between the U.S. Department of Energy's Office of Fossil Energy, Anadarko Petroleum Corp., Maurer Technology Inc., and Noble Engineering and Development. The project is part of the Energy Department's Methane Hydrates R&D Program, and supports the President's National Energy Policy, which calls for increasing domestic energy supplies, including more speculative "frontier" resources such as methane hydrate, to enhance national security.
"We're just beginning to understand the nature of methane hydrate distribution in the subsurface," said Brad Tomer, of the Energy Department's National Energy Technology Laboratory, which oversees the methane hydrate research program. "Each time we are able to successfully gather high-quality scientific data from the subsurface - as we did with the Hot Ice No. 1 well - we add significantly to our understanding of how hydrate forms, how it can be located, and what its resource potential might eventually be." The well also provided an opportunity to showcase several unique and previously untested Arctic drilling technologies that can be expected to play a role in future Alaskan drilling operations.
Hot Ice No. 1, located just south of the Kuparuk River field, 60 miles west of Deadhorse, Alaska, is the first dedicated hydrate well in Alaska. Spudded on March 31, 2003, drilling operations at the well were suspended because of warming weather and resumed in January 2004. On February 7, the well reached its planned total depth of 2,300 feet, about 300 feet below the zone where temperature and pressure conditions would theoretically permit gas hydrates to exist. Although significant gas shows were encountered, no methane hydrate was found.
"The absence of hydrate at the site is in itself a significant scientific finding," said Tom Williams, Vice President with Maurer Technology Inc. and a member of the team drilling the well. "Based on detailed evaluation of log data from adjacent offset wells, the Hot Ice No. 1 well was expected to encounter a significant thickness of reservoir quality sands in the Upper West Sak unit. The sands were there just as expected but we found free gas and water rather than hydrate in the hydrate stability zone. Figuring out why will require a thorough post-mortem analysis of the core, log, and seismic data from the well."
Although disappointed by the missed opportunity to evaluate a hydrate-filled formation, the researchers believe that a tremendous amount of knowledge will be gained for future hydrate exploration through analysis of the unique suite of collected data. "Clearly, the model for distribution of methane hydrate on the North Slope may be more complex than we previously thought," added Williams.
The Hot Ice #1 well successfully demonstrated for the first time a number of innovative technologies, including the Arctic Drilling Platform, a mobile hydrate core analysis laboratory, and a new application of a continuous coring rig.
Anadarko's Arctic Platform consists of 16 lightweight aluminum modules fitted together and mounted on steel legs to create a platform large enough to contain a rig, auxiliary equipment, and a mobile laboratory. Another five modules form an adjacent platform with living quarters for 40 people. The Arctic Platform design permits light and air to reach the tundra grass at a drill site during the summer months, and the relatively small and shallow holes created by the legs can be filled when drilling is completed. The system eliminates the need to build drilling pads of ice or gravel that have more impact on the tundra landscape.
Leaving the modular platform in place during the summer appears to have had no adverse impact on the environment or wildlife, lending support to the idea that such a system could be used to safely extend the drilling season on the North Slope by several months.
The mobile core lab, developed by engineers and scientists at the University of Oklahoma, makes it possible to analyze cores at a reduced temperature and in close proximity to the drill site. This is critical to the accurate characterization of hydrate in cores because methane hydrate quickly separates into methane gas and water when warmed. At Hot Ice #1, the mobile lab was successfully employed to immediately perform measurements on both the whole core retrieved from the well and on one-inch plugs taken from the full-sized core.
The well also provided an Arctic test of a state-of-the-art CAT scan tool developed by Lawrence Berkeley Laboratory specifically for pinpointing methane hydrate concentrations within cores immediately upon retrieval.
The continuous coring rig used to drill the Hot Ice #1 well proved to be a safe and efficient system for drilling and coring relatively shallow wells through permafrost intervals. In this first attempt at continuously coring permafrost to detect methane hydrate, the well was cored from a depth of 82 feet to 2,300 feet, with 93 percent of the core successfully recovered.
The well also produced a high resolution, three-dimensional vertical seismic profile (VSP) survey that should help to delineate the stratigraphy and structure that control the occurrence of hydrate in the area. The VSP recorded shallow seismic data using a dense spacing of receivers and vibrators that allows geophysicists to interpret lateral variations in potential hydrate reservoirs.
"The entire drilling system-including all the well control safeguards, the Noble DrillSmart system, and the chilled drilling fluid system, which are not normally associated with this type of rig-performed exceptionally well," added Williams. "This has been well documented, so it can be replicated to save future drilling programs a lot of time, and provide a safe and very efficient way to explore for hydrate in the future."
"Although we did not find the hydrate we expected, we were able to advance a whole suite of technologies that could ultimately make exploration for and production of the Arctic methane hydrate resource economically feasible," added Tomer. "These new technologies can be taken to future hydrate research sites where they will ultimately aid in building a better characterization of this potentially important frontier resource." In addition, the geologic knowledge gained from an ongoing comprehensive analysis of the core, log, and seismic data from the well will improve models for the genesis and distribution of hydrate accumulations on the North Slope.
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