Formulating formation mechanism of natural gas hydrates

Abstract

A large amount of energy, perhaps twice the total amount of all other hydrocarbon reserves combined, is trapped within gas hydrate deposits. Despite emerging as a potential energy source for the world over the next several hundred years and one of the key factors in causing future climate change, gas hydrate is poorly known in terms of its formation mechanism. To address this issue, a mathematical formulation is proposed in the form of a model to represent the physical insight into the process of hydrate growth that occurs on the surface and in the irregular nanometer-sized pores of the distributed porous particles. To evaluate the versatility of this rigorous model, the experimental data is used for methane (CH4) and carbon dioxide (CO2) hydrates grown in different porous media with a wide range of considerations.

Fundamental of swapping phenomena in naturally occurring gas hydrates

“…Four phases may coexist there, namely gas ( G ), aqueous ( A ), solid ice ( I ) and hydrate ( H ). With this, the following practical aspects are taken into account to characterize the hydrate phenomena: gas hydrates mostly occur in permeable marine sediments in presence of water (pure/with salt ions) 17 hydrates are likely to form in the interstitial pore space between porous particles 18 , 19 porous medium consists of irregular 3D particles with their uneven distribution pores of these particles are further irregular in size and shape these nanometer-sized pores also participate in hydrate formation and decay 1 . It is confirmed through the seismic survey studies conducted in the gas hydrate field of Alaska 20 , Blake Ridge 20 , 21 and Mackenzie Delta 22 surface renewal is inevitable because of the barrier (i.e., solid hydrate film) grown during hydrate formation and decayed during dissociation at the interface 18 pure carbon dioxide and methane, and 3–20 mol% CO 2 in air or with N 2 gas form sI hydrate structure that consists of two small 5 12 cages and six large 5 12 6 2 cages per unit cell 23 , which is evident through PXRD pattern 5 pure and mixed CO 2 (N 2 major and CO 2 minor) effectively act as the replacement agent.…”

“…The driving force is proposed in terms of chemical potential ( μ ) that considers the combined effect of temperature, pressure and composition 19 . It is expressed as where, and are the chemical potential of water in the filled hydrate and the liquid phase, respectively.…”

Nonmonotonous Lattice Distortion Model for Gas Hydrates

“…The Langmuir constant ( C ij (2) ) for the doubly occupied hydrate cages can be estimated using the following expression: Here, C ij h–g and C ij g–g are the Langmuir constants for host–guest and guest–host interactions, respectively. The quantity C ij g–g can be estimated using the Buckingham-type potential function, while C ij h–g is estimated as The term ω is the angle-averaged cavity potential that can be represented by the Kihara potential model as The parameters σ , ε , and a are the collision diameter, energy well depth, and hard core radius, respectively. For implementing this model on the hydrate, the expression is reformulated as follows: where R ′ is the cavity radius, and z ′ is the coordination number that is defined as the number of water molecules that form a unit hydrate cavity.…”

“…The term ω is the angle-averaged cavity potential that can be represented by the Kihara potential model 20 as a r a a r a 4 12 6…”

Microscopic Molecular Insights into Hydrate Formation and Growth in Pure and Saline Water Environments

“…Naturally occurring gas hydrates are mostly composed of methane and prefer to reside in the deep ocean floor sediments and permanently frozen grounds. They hold vital gas resources that are 10 times more than the global conventional natural gas reserves, and perhaps it is twice the total carbon content than all other forms of fossil fuels (i.e., coal, liquid fuels, and natural gas) in the globe. , Therefore, NGHs are regarded as a sustainable energy resource for the upcoming century. − Besides, the gas hydrates are a potential tool to separate, store, − and transport the gases; desaline or purify the seawater; and ensure trouble-free fluid flow through the pipelines located in the low-temperature regions. , Thus, it is crucial to understand the fundamental nature of the formation and growth mechanism of gas hydrates.…”