WG 3 will review environmental challenges associated with methane production from gas hydrates. Environmental risks are moderate compared to other deep-water operations since gas hydrates and the associated formation fluids do not contain toxic substances. Moreover, blow-out events are not a concern since gas hydrate deposits have low in-situ pressures and are maintained at or below hydrostatic pressure during the entire production process. However, gas hydrates can constitute environmental risks by affecting seafloor stability and releasing methane into the water column. Sediments deposited at continental slopes are in some cases stabilized by gas hydrates cementing the grain fabric. Gas production from these deposits may induce slope failure causing severe damage to seabed installations and benthic ecosystems and methane gas emissions into the marine environment. Methane is an important greenhouse gas and any release of methane to the atmosphere would have an impact on climate change. The lifetime of methane in the atmosphere is much shorter than of CO2, but CH4 is more efficient at trapping radiation than CO2. On a 100 year time scale, the comparative impact of CH4 on climate change is about 28 times greater than CO2 (IPCC, 2013). Leakage of methane gas may also occur during the production process since the overburden sealing gas hydrate deposits from the marine environment has a limited thickness. It is important to recall that methane-hydrate accumulations are often associated with gas seeps (Berndt et al., 2014; Marin-Moreno et al., 2013; Phrampus et al., 2014; Roemer et al., 2012a; Roemer et al., 2012b; Roemer et al., 2014; Sahling et al., 2014; Smith et al., 2014; Torres et al., 2002; Westbrook et al., 2009). These seeps may influence the development of oceanic ecosystems on the seafloor. When considering gas production from methane-hydrate accumulations, the question regarding the fate of potential methane release consistently arises as leaks may occur. Such release may have impacts on the ecosystem associated with methane-hydrate settings. In fact, the areas surrounding hydrate deposits, particularly those outcropping on or close to the seabed, often support a large microbial/benthic community based on direct interaction with the hydrate itself or from gas release. These communities are delicate and could be seriously affected by changes in gas release rates, or exploitation of near seabed hydrates. In a similar manner exploitation of deeper hydrates that results in release of methane gas to the seabed may result in dramatic changes to any indigenous microbial/benthic community and whilst small gas releases may possibly stimulate the microbial community it is highly likely that large gas releases will have a negative impact. Finally, methane may be present in the water column, and depending on depth and temperature it may occur as hydrate, free gas, or dissolved gas. Gas may be released directly at the seafloor due to dissociation of hydrate or as a result of dissolution or dissociation of dislodged hydrate as it rises through the water column (methane hydrate is less dense than seawater). Methane will dissolve in the water column as it rises resulting in elevated methane concentrations, and gas bubbles will expand as the pressure drop as the bubble rises through the water column (Zhang, 2003). Whilst it may be unlikely that methane will reach the atmosphere (except for catastrophic releases; de Garidel-Thoron et al., 2004) the spatial extent (and concentration) of methane in the water column will depend upon the depth and the local current and the rates of microbial methane consumption (i.e., Boetius and Wenzhöfer, 2013; Steeb et al., 2015). Therefore, in a production scheme, there is a need to better characterize the potential environmental challenges, and efficiently quantify the amount of methane discharged into the water column as well as its influence on the living communities in the surrounding area. To minimize the environmental risks, gas hydrate deposits located in the Black Sea could serve as production test sites since this marginal sea harbors anoxic bottom waters inhibiting the development of benthic ecosystems.
MIGRATE (Marine gas hydrate - an indigenous resource of natural gas for Europe). ESSEM (Earth System Science and Environmental Management) COST Action ES1405. WG 3: Environmental challenges. First annual report,
Spagnoli F
2016
Abstract
WG 3 will review environmental challenges associated with methane production from gas hydrates. Environmental risks are moderate compared to other deep-water operations since gas hydrates and the associated formation fluids do not contain toxic substances. Moreover, blow-out events are not a concern since gas hydrate deposits have low in-situ pressures and are maintained at or below hydrostatic pressure during the entire production process. However, gas hydrates can constitute environmental risks by affecting seafloor stability and releasing methane into the water column. Sediments deposited at continental slopes are in some cases stabilized by gas hydrates cementing the grain fabric. Gas production from these deposits may induce slope failure causing severe damage to seabed installations and benthic ecosystems and methane gas emissions into the marine environment. Methane is an important greenhouse gas and any release of methane to the atmosphere would have an impact on climate change. The lifetime of methane in the atmosphere is much shorter than of CO2, but CH4 is more efficient at trapping radiation than CO2. On a 100 year time scale, the comparative impact of CH4 on climate change is about 28 times greater than CO2 (IPCC, 2013). Leakage of methane gas may also occur during the production process since the overburden sealing gas hydrate deposits from the marine environment has a limited thickness. It is important to recall that methane-hydrate accumulations are often associated with gas seeps (Berndt et al., 2014; Marin-Moreno et al., 2013; Phrampus et al., 2014; Roemer et al., 2012a; Roemer et al., 2012b; Roemer et al., 2014; Sahling et al., 2014; Smith et al., 2014; Torres et al., 2002; Westbrook et al., 2009). These seeps may influence the development of oceanic ecosystems on the seafloor. When considering gas production from methane-hydrate accumulations, the question regarding the fate of potential methane release consistently arises as leaks may occur. Such release may have impacts on the ecosystem associated with methane-hydrate settings. In fact, the areas surrounding hydrate deposits, particularly those outcropping on or close to the seabed, often support a large microbial/benthic community based on direct interaction with the hydrate itself or from gas release. These communities are delicate and could be seriously affected by changes in gas release rates, or exploitation of near seabed hydrates. In a similar manner exploitation of deeper hydrates that results in release of methane gas to the seabed may result in dramatic changes to any indigenous microbial/benthic community and whilst small gas releases may possibly stimulate the microbial community it is highly likely that large gas releases will have a negative impact. Finally, methane may be present in the water column, and depending on depth and temperature it may occur as hydrate, free gas, or dissolved gas. Gas may be released directly at the seafloor due to dissociation of hydrate or as a result of dissolution or dissociation of dislodged hydrate as it rises through the water column (methane hydrate is less dense than seawater). Methane will dissolve in the water column as it rises resulting in elevated methane concentrations, and gas bubbles will expand as the pressure drop as the bubble rises through the water column (Zhang, 2003). Whilst it may be unlikely that methane will reach the atmosphere (except for catastrophic releases; de Garidel-Thoron et al., 2004) the spatial extent (and concentration) of methane in the water column will depend upon the depth and the local current and the rates of microbial methane consumption (i.e., Boetius and Wenzhöfer, 2013; Steeb et al., 2015). Therefore, in a production scheme, there is a need to better characterize the potential environmental challenges, and efficiently quantify the amount of methane discharged into the water column as well as its influence on the living communities in the surrounding area. To minimize the environmental risks, gas hydrate deposits located in the Black Sea could serve as production test sites since this marginal sea harbors anoxic bottom waters inhibiting the development of benthic ecosystems.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
