Recent Advances in Methods of Gas Recovery from Hydrate-Bearing Sediments: A Review

Abstract

Safe, efficient, and economical gas recovery from hydrate-bearing sediments (HBS) is a severe issue that determines if natural gas hydrate (NGH), as an alternative energy in the future as fossil fuels approach depletion, is applied. Researchers worldwide are committed to developing a safe, efficient, and economical method of gas recovery from HBS. However, until now, most methods are still being validated and not have not been identified to exploit NGH commercially. Therefore, it is appropriate and significant to discuss researchers’ achievements to exploit NGH and summarize their potential benefits and challenges. This paper introduces nearly all the conventional and latest NGH exploitation methods and reviews field trials’ development characteristics. On the basis of laboratory experiments and field trials, key challenges restricting safe and efficient NGH development, and the existing research gaps reflecting these challenges, are also presented from the gas production, security, and economic aspects. The unfavorable situation mainly comprises the insufficient sensible heat, extremely low thermal conductivity, and ultralow permeability of HBS, lower gas production rate and its intense fluctuations, higher water-to-gas ratio (WGR), geological deformation, and subsidence of HBS attributed to excessive sand production, driving the consideration of some possible solutions. Given this, a new method for enhanced gas production from HBS based on the combination of depressurization (DP) and an in-situ heat generation method is proposed. Benefiting from multiple theoretical enhancement mechanisms such as replenishing energy to HBS with in-situ heat generation powders, cementing and strengthening the HBS skeleton, improving the gas permeability in HBS, decreasing the WGR based on blocking water, and removing gas characteristics of hydration products, this method could be expected to achieve promising long-term performance of gas production, which will be theoretically and practically significant to study commercial gas production.

The Development of Clathrate Hydrate Science

“…The wells produced mainly CH 4 , usually by depressurising, sometimes with thermal stimulation, but the 2012 Alaska test used CO 2 /N 2 injection to replace the CH 4 with CO 2 . Recovery methods have recently been reviewed. , CO 2 sequestration in hydrate form is promoted as a possible medium for reducing emissions into the atmosphere …”

Methane Hydrate Dissociation in Quartz Sand by Depressurization Combined with Microwave Stimulation

“…Natural gas hydrate is a solid crystalline material comprising small gas molecules trapped by Van der Waals forces in a cage of water molecules connected by hydrogen bonds. , Natural gas hydrate occurs widely in low-temperature and high-pressure environments, such as seawater, lakes and other deep-water environments, and permafrost. , Methane gas is the primary component of natural gas hydrate, whose combustion products are only carbon dioxide and water. As a clean fuel, one volume of methane hydrate can decompose 164 volumes of methane gas and 0.8 volumes of water . Moreover, natural gas hydrate reserves are abundant around the world, making it a feasible future energy source. − …”

Applications of the Discrete Element Method for Gas Hydrate-Bearing Sediments: Recent Advances and Perspectives

“…Most methods of hydrate exploitation are proposed to produce methane gas by dissociating or melting hydrates, such as depressurization, thermal stimulation, and chemical inhibitor injection. , Among them, depressurization is the most promising method to realize the commercial production of NGHs . The skeleton structure of sediments is strengthened when hydrates exist in the pore spaces of sediments. , The in situ hydrate-bearing sediments (HBSs) are stable before exploitation; however, the dissociation of gas hydrates causes the degradation of the mechanical properties of HBSs, increasing the risks of geological hazards, such as submarine landslides. , Thus, a solid understanding of the mechanical properties of HBSs is fundamental to the safe and efficient exploitation of NGHs.…”

“…Most methods of hydrate exploitation are proposed to produce methane gas by dissociating or melting hydrates, such as depressurization, thermal stimulation, and chemical inhibitor injection. 2,7 Among them, depressurization is the most promising method to realize the commercial production of NGHs. 8 The skeleton structure of sediments is strengthened when hydrates exist in the pore spaces of sediments.…”