FROZEN HEAT | Volume 2

While gas hydrates have considerable potential as an en- ergy resource, the challenges to realizing their commercial production are not trivial. This is largely due to the fact that gas hydrates occur in a solid form, with the gas molecules (usually methane) trapped within a crystalline lattice of water molecules. Many early concepts for producing methane from gas hydrates were based on mining technologies, in which solid masses of gas hydrate or gas hydrate-bearing sediment would be physically removed from the sea floor. However, major international gas hydrate research programs now tend to dismiss mining approaches on the grounds of significant detrimental environmental consequences and of economic and technical impracticality. However, recent field studies worldwide have confirmed that concentrated deposits of gas hydrates can occur in res- ervoir settings that are consistent with potential extraction using existing hydrocarbon exploration, drilling, and pro- duction technologies (Collett et al. 2009). These settings are where gas hydrates reside within the pore spaces of discrete, permeable to highly permeable, laterally continu- ous units rich in sand and or coarse-grained silts. (Moridis et al. 2009). This would involve accessing the reservoir via drilled wells, manipulating local pressure-temperature con- ditions to force the solid hydrate crystal to dissociate into its water and gas components, and then producing the re- leased gas to the surface.

The advantage of using conventional hydrocarbon produc- tion technologies is that there is a great deal of worldwide experience on the subject, covering the spectrum from ex- ploratory drilling to production. Based on this experience, it appears likely that gas hydrate production in marine or per- mafrost environments will involve the following existing hy- drocarbon production approaches that are designed to enable production while minimizing environmental impact: • Establishment of safe foundation conditions for the well in- frastructure through detailed pre-production study of the well- site geology in order to recognize and avoid potential hazards and provide a full understanding of the potential impact of production on the ground supporting the well infrastructure; • Installation and cementing of casing strings to maintain well stability while drilling into the target gas hydrate pro- duction interval; • Installation of production casing and downhole comple- tion equipment to enable testing and production of hydro- carbon-bearing intervals; • Effective well control and zonal isolation during production; • Minimization of the impact of gas extraction on the sur- face and subsurface environment; and • Monitoring of the response of the gas hydrate field to pro- duction. This chapter describes some of the most recent suggested approaches to meeting these requirements for gas hydrate production.

A GLOBAL OUTLOOK ON METHANE GAS HYDRATES 61