Natural Gas Hydrates: Development and Test of Innovative Methods for Gas Production From Hydrate Bearing Sediments

Summary It is anticipated that increasing pressure for cleaner burning fuels and lower carbon dioxide (CO2) emissions will cause a shift in global energy demand from oil to natural gas. In the near future, natural gas is expected to replace crude oil as the fuel of choice for energy production and transportation. In Trinidad and Tobago, natural-gas production has already surpassed crude-oil production. Natural gas accounts for 80% of the country's energy export, but the reserves-to-production ratio is only 7 years (year 2022). Consequently, the Ministry of Energy has taken steps to supplement the natural-gas resource base by supporting initiatives that can potentially bolster the nation's proven gas reserves. Such initiatives include invitations to tender on deepwater blocks offshore Trinidad and Tobago's gas-rich east coast. Even though initiatives are under way to boost conventional natural-gas reserves, effort was not placed on identifying and/or characterizing unconventional gas resources such as natural-gas hydrates. Furthermore, the potential hazards of submarine gas hydrates on deepwater exploration and production (E&P) activities on Trinidad and Tobago's east coast were not assessed. The results presented in this manuscript provide oil-and-gas operators with a means of proactively managing the risk associated with natural-gas hydrates. More importantly, this study acts as a necessary precursor to future studies in characterizing and, later, harnessing the energy potential of Trinidad-and-Tobago's natural-gas-hydrate deposits.

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A Thermal Chemical Reaction System for Natural Gas Hydrates Exploitation

Frontiers in Energy Research ◽

10.3389/fenrg.2021.804498 ◽

2022 ◽

Vol 9 ◽

Author(s):

Yanan Wang ◽

Zhenxin Sun ◽

Qingping Li ◽

Xin Lv ◽

Yang Ge

Keyword(s):

Natural Gas ◽

Heat Generation ◽

Gas Hydrates ◽

Catalyst Concentration ◽

Reaction System ◽

Gas Production ◽

Reactant Concentration ◽

Natural Gas Hydrates ◽

Hcl Concentration ◽

Thermochemical Reaction

The methodology of using CO2 to replace CH4 to recover the natural gas hydrates (NGHs) is supposed to avoid geological disasters. However, the reaction path of the CH4–CO2 replacement method is too complex to give satisfactory replacement efficiency. Therefore, this study proposed a thermochemical reaction system that used the heat and the nitrogen released by the thermochemical reactions to recover NGHs. The performance of the thermochemical reaction system (NaNO2 and NH4Cl) regarding heat generation and gas production under low temperature (4°C) conditions was evaluated, and the feasibility of exploiting NGHs with an optimized formula of the thermochemical reaction system was also evaluated in this study. First, the effects of three catalysts (HCl, H₃PO₄, and NH2SO3H) were investigated at the same reactant concentration and catalyst concentration. It was confirmed that HCl as a catalyst can obtain better heat generation and gas production. Second, the effect of HCl concentration on the reaction was investigated under the same reactant concentration. The results showed that the higher the HCl concentration, the faster is the reaction rate. When the concentration of HCl was greater than 14 wt%, side reactions would occur to produce toxic gas; hence, 14 wt% was the optimal catalyst concentration for the reaction of NaNO2 and NH4Cl at low temperatures. Third, the heat generation and gas production of the thermochemical reaction systems were evaluated at different reactant concentrations (1, 2, 3, 4, 5, and 6 mol/L) at 14 wt% HCl concentration. It was found that the best reactant concentration was 5 mol/L. Finally, the feasibility of exploiting NGHs with the optimal system was analyzed from the perspectives of thermal decomposition and nitrogen replacement. The thermochemical reaction system provided by this study is possible to be applied to explore NGHs’ offshore.

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Reverse Time Migration of Vertical Cable Seismic Data to Image Hydrate-Bearing Sediments With High Resolution

Frontiers in Earth Science ◽

10.3389/feart.2021.751202 ◽

2021 ◽

Vol 9 ◽

Author(s):

Linfei Wang ◽

Huaishan Liu ◽

Zhong Wang ◽

Jin Zhang ◽

Lei Xing ◽

...

Keyword(s):

High Resolution ◽

Natural Gas ◽

Gas Hydrates ◽

Velocity Analysis ◽

Reverse Time ◽

Reverse Time Migration ◽

Time Migration ◽

Natural Gas Hydrates ◽

High Resolution Images ◽

Hydrate Bearing Sediments

Marine vertical cable seismic (VCS) is a promising survey technique for submarine complex structure imaging and reservoir monitoring, which uses vertical arrays of hydrophones deployed near the seafloor to record seismic wavefields in a quiet environment. Recently, we developed a new type of distributed VCS system for exploration and development of natural gas hydrates preserved in shallow sediments under the seafloor. Using this system and air-gun sources, we accomplished a 3D VCS yield data acquisition for gas hydrates exploration in the Shenhu area, South China Sea. In view of the characteristics of VCS geometry, we implement reverse time migration (RTM) on a common receiver gather to obtain high-resolution images of marine sediments. Due to the unique acquisition method, it is asymmetrical for the reflection path between the sources and the receivers in the VCS survey. Therefore, we apply accurate velocity analysis to common scatter point (CSP) gathers generated from common receiver gathers instead of the conventional velocity analysis based on common depth point gathers. RTM with this reliable velocity model results in high-resolution images of submarine hydrate-bearing sediments in deep water conditions. The RTM imaging section clearly shows the bottom simulating reflector (BSR) and also the reflection characteristics of the hydrate-bearing sediments filled with consolidated hydrates. Moreover, its resolution is relative to that of acoustic logging curves from the nearby borehole, and this imaging section is well consistent with the synthetic seismogram trace generated by the logging data. All these results reveal that VCS is a great potential technology for exploration and production of marine natural gas hydrates.

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