Enhancing gas recovery from natural gas hydrate reservoirs in the eastern Nankai Trough: Deep depressurization and underburden sealing

Possible Influx of Seawater during Gas Production from Unsealed Gas Hydrate Reservoirs has Economic and Environmental Implications

“…In this study, a poor sealing and an “aquifer” at the bottom of the hydrate-bearing zone scenario was investigated and high water production rates were observed to be controlled by the bottom pressure . These findings are consistent with previous observations of seawater dissociating and releasing natural gas from gas hydrate-bearing sediments. − …”

“…In our study, we did not account for the economic implications of seawater flux but speculated that, due to the high water/gas ratios (Figure ), a scenario with seawater influx would have negative implications and not be economically viable. However, we caution that even if a seal was initially present, its integrity of such a shallow clay layer may be compromised by both underpressure and possible reservoir compaction, e.g., For the silt scenarios, i.e., Cases A and C, sealing solutions like injecting gel or sealing chemical agents might be suggested to improve production performance. − , Thus, our findings may have significant environmental and economic implications for the design of gas production from hydrate reservoirs.…”

“…While these field tests were generally successful in releasing gas from hydrate over short time spans of several days to weeks, the impact of long-term depressurization and hydrate dissociation is not yet understood. Several modeling studies have focused on the geomechanical challenges related to compaction and subsidence of the reservoir during fluid withdrawal. , Several studies have investigated how permeable overburdens and underburdens could influence gas production from gas hydrates. − Nevertheless, the impact of overburden and the effect of gas production from gas hydrates on seafloor fluid flow have not yet been studied for the gas hydrate reservoir located at the Hikurangi Margin, New Zealand. In this study, we present results from conceptual modeling that suggest that the production of gas from hydrates using depressurization may lead to an influx of seawater from above through the seafloor to the reservoir, unless a seal is present, which could have economic and environmental implications for the Hikurangi Margin, New Zealand.…”

Critical Review on Carbon Dioxide Sequestration Potentiality in Methane Hydrate Reservoirs via CO2–CH4 Exchange: Experiments, Simulations, and Pilot Test Applications

“…Several studies revealed that stepwise depressurization of CH 4 by CO 2 mixed gas produces more CH 4 while CO 2 is stored as a hydrate in bearing sediments. However, factors for enhancing CO 2 sequestration and CH 4 production were unclear. − Reference analyzed the essential parameters to be considered in enhancing high CO 2 storage in CH 4 hydrate-bearing sediments and CH 4 gas production. These parameters were the CH 4 /CO 2 ratio mixtures, residual water saturation ( S rw ), and shut-in period.…”

Reservoir Stimulation Technologies for Natural Gas Hydrate: Research Progress, Challenges, and Perspectives

“…Gu et al 123 proposed a method that combined deep depressurization with underburden sealing to further improve productivity. The production effects at different sealing rates were investigated by using numerical simulations.…”