FROZEN HEAT | Volume 2

gas. In unconventional production, this “produced water” also includes substantial volumes of injected water that has returned to the surface. The handling, transmission, reuse and ultimate disposal of produced water are prone to incidents of water release that can impact surface water and groundwater quality. In addition, the transmission of deeper formation fluids (water and hydrocarbons) into aquifers (via loss of “wellbore integrity” commonly associated with faulty or degraded cement seals) is a poorly constrained risk in all hydrocarbon development. Gas hydrate can also be expected to result in potentially-significant volumes of produced water which will need to be disposed of. As mentioned above, however, gas hydrates tend to exist too close to the sea floor or ground surface to coexist with liquid hydrocarbons, limiting the hydrocarbon contamination danger during production. Moreover, given that the water released during hydrate dissociation is highly purified (the combination of hydrate formation and dissociation has even been researched as a means of purifying water), the produced water will be a blend of fresh and in-situ water. The issues associated with gas hydrate produced water management will therefore be unique. For example, in the marine setting, it may be necessary to add salt to the water before returning it the environment. Air Quality Impacts: Air quality impacts can occur in a variety of ways. Fugitive emissions associated with releases during drilling and losses at pipelines and associated compressor stations are poorly constrained at present and are the subject of substantial research related to both emission detection and mitigation. Gas hydrate production, like any conventional gas production, will add to the total volume of gas being handled, and as such, could generate additional emissions. Similarly, potential impacts the most promising technique, the testing has thus far been of limited duration and does not provide a basis for consid- eration of the long-term production response of the reservoir. The next milestone in this field will likely be a series of ex- tended-duration production tests, in which the long-term production behaviour of the reservoir and the associated physical impacts can be assessed more fully. These projects would be complex, expensive, and technically challenging. However, the data acquired during long-duration produc-

tion testing are critical for the refinement and calibration of numerical reservoir simulators and for addressing persistent uncertainties in the prediction of long-term, field-scale res- ervoir responses and potential environmental impacts. The lessons from such tests could ultimately contribute to the design of specific production strategies tailored to particular geological settings around the world.

For the immediate future, gas hydrate production research will likely continue to be facilitated primarily by government

associated with utilization (combustion and release of CO 2 ) will also be the same for any gas, regardless of the reservoir from which it is produced. However, as discussed in Volume 2 Chapter 1 and Volume 2 Chapter 4, potential positive implications of additional gas hydrate utilization could occur if that gas displaces fuels that burn less cleanly. In this regard, the relative purity of hydrate-derived gas (commonly 99%methane with limited impurities, which strongly distinquishes it from other unconventional gas sources) should give it the smallest air-quality impact of any fossil fuel resource. Moreover, as suggested in Text Box 3.4, it may be possible to protect the air quality by injecting waste CO 2 gas into the hydrate-bearing formation rather than allowing the CO 2 produced while burning methane to enter the atmosphere. Methane Gas “Burps”: Gas hydrate may have been an active participant in past episodes of global climate change, resulting in substantial additions of methane gas to the atmosphere (see Volume 1 Chapters 2 and 3 for a full discussion). Such releases are inferred to have occurred over long time frames in response to global changes in water-bottom temperature and sea-level. The potential for similar releases in response to ongoing climate change is uncertain, but whatever that risk may be, there is no connection to the issue of gas production from gas hydrate because climate-sensitive hydrates (those with the potential to respond to environmental change) and reservoir-quality hydrates exist as physically distinct and separate sub-sets of the global gas hydrate distribution. There is no meaningful opportunity to either mitigate future climate- driven releases of methane from gas hydrate, nor exacerbate them, through production (see Boswell and Collett, 2011).

A GLOBAL OUTLOOK ON METHANE GAS HYDRATES 77