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Timothy S. Collett1,
Scott R. Dallimore2
(1) U.S. Geological Survey, Denver, CO
(2) Geological Survey of Canada, Ottawa, ON
Abstract: Identification and remediation of gas hydrate induced drilling and production hazards
Gas hydrates pose significant hazards to drilling and production operations in both deep marine and onshore Arctic environments. Specific case histories of gas-hydrate-related problems are better documented for onshore Arctic regions, and thus they may serve as useful analogs for some marine gas hydrate settings. Operators involved in Arctic exploration and development activities have described numerous problems associated with gas hydrates, including uncontrolled gas releases during drilling, collapsed casings, and gas leakage to the surface outside of the casing. When the drill bit penetrates a gas hydrate accumulation, under normal Arctic or marine drilling conditions, the drilling mud can become highly gasified. The hydrate adjacent to the wellbore will continue to decompose and gasify the drilling mud as long as drilling introduces heat into the formation. Recent drilling in the Russian Yamburg field, in the Cirque ara on the North Slope of Alaska, and in a nearshore marine well in the Mackenzie Delta of Canada have all shown the potential severity of hydrate-induced drilling problems, which included gas kicks, blowouts, and, in one case, a severe fire. The production of hot fluids from depth through shallower gas-hydrate-bearing intervals can also raise formation temperatures, resulting in further hydrate decomposition. If the dissociated free-gas becomes trapped behind the casing, reservoir pressures may substantially increase and cause casing strain, or free-gas leakage to the surface outside of the casing. Remediation of hydrate-related problems has generally followed tow courses of action: (1) prevention of hydrate dissociation or (2) promotion of hydrate dissociation. Both approaches involve regulating mud weights, utilizing mud additives, and adjusting mud temperatures to control the dissociation of in-situ gas hydrates.
AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana