Gas hydrate production and related issues

Methane gas, a low carbon energy source, can provide an energy supply for many years if produced from naturally occurring CH4 hydrate reservoirs. The various CH4 recovery methods (e.g. depressurisation, thermal stimulation, inhibitor injection or a combination of these methods: Sloan, 1998) have already been investigated and are reported in the literature.

These production methods may induce instability in the hydrate rich sediments. The likely mechanism is that hydrate decomposition at the base of the hydrate stability zone convert consolidated sediments into loose gas-charged sediments. This causes a decrease in the shear strength and facilitates the occurrence of landslides, tsunamis or other natural disasters, such as the 1986 Lake Nyos disaster (Rogers, 1996). After massive landslides on the continental slopes, mud volcano eruptions could cause massive hydrate dissociation and the release of CH4 into the atmosphere, which would contribute to climate change. Natural gas pipelines laid from production platforms to shore may warm sea floor sediments and decompose surrounding hydrates. A concern of the oil and gas industry is also the fact that drilling through hydrate zones might destabilize supporting foundations for platforms and production wells. Disruptions to the ocean floor from hydrate decomposition could also result in surface slumping or faulting, endangering work crews and the environment. Loss of seawater buoyancy because of hydrate-released gas could endanger floating structures (Hovland and Gudmestad, 2001).

Co2 Hydrate Stability Zone
Figure 3. A. Seafloor CH4 hydrate stability zone. B. Permafrost CH4 hydrate stability zone.

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