FROZEN HEAT | Volume 2

3.5 TIME FRAME FOR GAS HYDRATE DEVELOPMENT

Commercial production of gas from gas hydrates has not yet occurred. Several production research and develop- ment studies have, however, been carried out, most notably

at the Mallik site in Canada (see summary in Dallimore et al. 2012) and in the Nankai Trough (Yamamoto et al. , 2014). While this research has clearly identified depressurization as

Box 3.5 Environmental Impacts of Gas Hydrate Production: Comparison to Existing Conventional and Unconventional Gas Development

Hydrocarbon resources are commonly described as either “conventional” or “unconventional”. Conventional resources are those that exist in the subsurface as liquids or gases under high pressure and within permeable reservoirs such that commercially-viable production (extraction) rates can be achieved simply by drilling into the reservoir. In fact, a primary concern with conventional reservoirs is in controlling and limiting the production rate, particularly in the early phases. Failure to maintain this well control can result in well blow-outs and uncontrolled hydrocarbon release to the environment. In contrast, reservoir quality in unconventional reservoirs is typically very low, and as a result, additional engineering means are required to improve reservoir quality around well bores to achieve desired flow rates. Gas hydrates, which require some combination of reservoir depressurization, heating, and/or chemical injection to be productive, are therefore unconventional reservoirs. While the vast majority of hydrocarbons produced for energy continue to come from conventional reservoirs, production from unconventional resources, most notably shale gas in the United States, is growing rapidly. It cannot be assumed, however, that all unconventional resources will be associated with the same environmental risks. The following discusses general types of environmental risks with respect to the issue of gas hydrate production.

unconventional development, particularly where resources are deeply buried and under high pressure. Gas hydrates, which are by definition shallow (and thus relatively low-pressure) resources, are therefore very unlikely to support uncontrollable flow rates. In fact, a primary challenge in gas hydrate production is not only establishing flow, but sustaining it. Because gas hydrate reservoirs only produce recoverable methane when artificially (and temporarily) removed from their natural pressure condition (a condition that is imposed by the simple presence of the overlying sediment for onshore gas hydrates, and by the water column for offshore gas hydrates), any cessation in the energy input used to achieve pressure reduction will immediately re-establish gas hydrate stability conditions and halt the methane release (see Nagakubo et al. , 2011; Moridis et al. , 2014). Lastly, liquid hydrocarbons are not known to pool at the shallow sediment depths at which gas hydrates occur, so the risk of inducing oil spills while recovering methane from gas hydrate is minimal. Water Consumption: Unconventional production, such as shale gas, shale oil, oil shale, and tar sands are characterized by large water demands during extraction. Gas hydrate drilling and production, as now envisioned, would require minimal water useage as the primary stimulation method will be the imposition of reduced pressure through simple partial evacuation of the wellbore, as opposed to water-intensive thermal stimulation or permeability-creation through artificial fracturing.

Loss of well control/spills: This risk, which is significant in conventional resource development, can also occur in

Water Quality Impacts: All hydrocarbon production results in the co-production of reservoir brines along with the oil and

FROZEN HEAT 76