FROZEN HEAT | Volume 2

3.3 DRILLING A GAS HYDRATE PRODUCTIONWELL

Drilling through gas-hydrate-bearing strata involves a variety of potential technical and environmental challenges. For example, some early exploration wells in the Arctic experienced shallow gas flows and borehole stability problems, including abnormal hole erosion and/or tight hole conditions (Collett and Dallimore 2002). The problems were linked mainly to the accepted drill-

ing practices in the 1970s and 1980s, which could cause signifi- cant thermal and/or mechanical disturbance of the gas-hydrate- bearing strata. This could potentially result in the release of free gas and a significant reduction in sediment strength (Figure 3.2). Similar problems have been encountered in other settings (Borowski and Paull 1997; Nimblett et al. 2005). Industry has

Gas hydrate drilling and production problems

Gas release

Gas leakage

Collapsed casing

Production facilities

Open borehole

Gas leakage

Gas hydrate

Gas hydrate

Hydrate

Free gas

Free gas

Hydrate

Hydrate

Free gas

Free gas

Hydrate

Free gas

Free gas

Cased borehole

Cased borehole

Production of hot hydrocarbons

Figure 3.2: Potential drilling and production problems: The figure shows typical gas-hydrate-related drilling and production problems encountered during drilling programs in the Arctic (from Collett and Dallimore 2002). Gas release scenario (left): over-pressured free gas is encountered unexpectedly beneath a gas hydrate layer. Gas leakage scenario (centre): possible disturbance of gas hydrate by drilling that has dissociated gas hydrate and caused free gas migration outside of the drill casing. Collapsed casing scenario (right): possible disturbance of gas hydrate caused by conventional production of warm hydrocarbon at depth.

A GLOBAL OUTLOOK ON METHANE GAS HYDRATES 63

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