Mechanical Destabilization and Cage Transformations in Water Vacancy-Contained CO₂ Hydrates

Abstract

Clathrate hydrates show wide applications in energy recovery and storage, CO2 capture and storage, and other sustainable technologies. Water vacancy in clathrate hydrates is a common defect; however, its effects on the mechanical properties of clathrate hydrates, especially CO2 hydrates, have not been well studied. Herein, the mechanical characteristics of CO2 hydrates with three different types of water vacancy defects are investigated for the first time through molecular dynamics simulations with several popular water force fields. It turns out that the mechanical properties of CO2 clathrate hydrate vary with the type of water vacancy and water force field. Upon critical strains, a variety of unconventional cages of 425862, 425863, 425864, 4151062, 4151063, and 4151064 form, of which 4151062 predominates and is identified to be transient and a clathrate intermediate in forming 425862, 425863, and 425864. Moreover, diverse cage transformations of 51262 ↔ 4151063, ↔ 4151062, ↔ 425863, ↔ 425864 and 512 ↔ 4151062, ↔ 425862 occur via two distinct transformation mechanisms including insertion/removal and rotation of a pair of water molecules. This study provides new perspectives on the mechanics and microstructural transformations of CO2 hydrate, which are crucial for evaluating the formation and mechanical stability of CO2 hydrate-bearing sediments as well as the CO2 geological storage by hydrate-based technologies.

Review and Perspectives of Energy-Efficient Methane Production from Natural Gas Hydrate Reservoirs Using Carbon Dioxide Exchange Technology

“…13 A study on the influence of water vacancy on mechanical properties was conducted by Liu and team. 14 They also affirmed that the replacement method does not significantly affect the sediment's geomechanical properties, whereas the change in water vacancy slightly reduces the lattice constant of replacing the CO 2 hydrate. The samples exhibited different stress behavior concerning the change in water vacancies, and the unconventional new cage transformations appearing due to the change were defined as metastable.…”

“…They considered the dominant factor responsible for the heteroclathrate deformation to be the hydrogen bonds . A study on the influence of water vacancy on mechanical properties was conducted by Liu and team . They also affirmed that the replacement method does not significantly affect the sediment’s geomechanical properties, whereas the change in water vacancy slightly reduces the lattice constant of replacing the CO 2 hydrate.…”

“…They were introduced from the early 1970s and are known for their low computation requirements and high efficiency. MD simulation studies include hydrate nucleation and dissociation behavior, effect of hydrate inhibitors, , effect of nanoparticles, characteristics of heteroclathrates, mechanical stability, thermal conductivity, etc. Monte Carlo simulations adopted from early 1980s are mostly used to study the storage efficiency of hydrate forming gases as well as to estimate the CH 4 reserves in place .…”

“…There are three known hydrate structures sI, sII, and sH hydrate . Notations, such as 5 12 , 5 12 6 2 , 5 12 6 4 , 5 12 6 8 , and 4 3 5 6 6 3 , indicate the type of hydrate cages encountered through hydrate characterization experiments. − Natural gas hydrates can guarantee the sustainability of fuel and are less polluting.…”

Predicting mechanical properties of CO2 hydrates: machine learning insights from molecular dynamics simulations

“…In this structure, CO 2 occupy the larger cages, while the methane molecules occupy the smaller cages. Liu et al [35] utilized several commonly used water force fields and conducted MD simulations to investigate the mechanical properties of CO 2 clathrate hydrates with three different types of water vacancy defects. The results revealed that the mechanical performance of CO 2 clathrate hydrates varies with the type of water vacancy and water force field.…”