Academic literature on the topic 'Decomposition of CoCl2 hydrates'

Gas hydrates are considered a promising energy source for the 21st century, and understanding their formation and decomposition processes is crucial. This study utilized micro-fluidic technology to observe the secondary formation and decomposition of hydrates at the pore scale, comparing methane-tetrahydrofuran(THF)-water and methane-water systems. The study found that hydrates tended to form and decompose at the gas-liquid interface, and the second formation rate of hydrates was higher than the first. During depressurization, hydrates located at the solid-liquid interface decomposed first, followed by decomposition towards the interior of the hydrate. The study sheds light on the formation and decomposition characteristics of gas hydrates at the pore scale, providing some insights for the safe and efficient exploitation of gas hydrate.

Heat storage systems using reversible chemical solid-fluid reactions to store and release thermal energy operates in charging and discharging phases. During last three decades, discussions on thermal decomposition of several salt-hydrates were done (experimentally and numerically) [1,2]. A mathematical model of heat and mass transfer in fixed bed reactor for heat storage is proposed based on a set of partial differential equations (PDEs). Beside the physical phenomena, the chemical reaction is considered via the balances or conservations of mass, extent conversion and energy in the reactor. These PDEs are numerically solved by means of the finite element method using Comsol Multiphysics 4.3a. The objective of this paper is to describe an adaptive modeling approach and establish a correct set of PDEs describing the physical system and appropriate parameters for simulating the thermal decomposition process. In this paper, kinetic behavior as stated by the ICTAC committee [3] to understand transport phenomena and reactions mechanism in gas and solid phases is taking into account using the generalized Prout-Tompkins equation with modifications based on thermal analysis experiments. The model is then applied to two thermochemical materials CaCl2 and MgCl2 with experimental activation energies and a comparison is made with TGA-DSC measurement results.

In this work, different saturated methane hydrates were formed by controlling the methane gas filling pressure on the three-dimensional experimental systems. The hydrates were dissociated using by depressurization and combination method, respectively. The results indicated that, as the saturation enhancing, the gas production was enlarged, however, the gas production rate became extremely volatile, and the decomposition cycle increased. Furthermore, compared with single depressurization, the combination method has the high gas production rate and efficiency, and the short decomposition cycle. So the combination method is worthy for further study of the gas hydrate exploitation.

Abstract Hydrate formation and decomposition are important factors affecting fluid flow in porous media. To reveal the characteristics of hydrate formation and decomposition in the pores of porous media, pore-scale experiments under different types of flow in micromodel were conducted using a visual microflow experimental apparatus. The experimental results suggested that heterogeneous hydrates were formed in the pore channels, which was mainly affected by the gas-water distribution and temperature & pressure. Compared with the gas-dominated and water-dominated flow, the hydrate formation rate was the maximum under gas-water two-phase flow, and the risk of hydrate blocking the flow channel was the maximum. Moreover, the hydrates were gradually decomposed from the pressure-reduced outlet to the inlet. The methane produced by hydrate decomposition in the pore channel would gather and form a continuous gas flow channel under pressure difference, and the methane dissolved in the water phase would also gradually precipitate out as the pressure decreases to form bubbles, which would form large methane bubbles with adjacent bubbles, thus driving the surrounding water phase flow. This paper lays a foundation for future research on hydrate formation, decomposition and flow in porous media.

ABSTRACT Natural gas hydrate (NGH) is a clean and abundant emerging energy source that develops in pores of soil deposits in permafrost regions and deep seabed, which are difficult to exploit. Cavitation bubbles contain powerful energy that can effectively break hydrate and may bring higher exploitation efficiency. However, the decomposition of hydrate induced by cavitation damage is still unclear, and the damage characteristics of hydrate need further research. In this paper, a study is conducted based on experiments of laser induced cavitation damage to methane hydrate to evaluate the influence of cavitation on the decomposition of hydrate under different cavitation parameters. The results show that: 1) Cavitation exerts a strong promotion effect on the decomposition of hydrate, and microjet induced by bubble collapse is a key factor accelerating hydrate dissociation; 2) During hydrate decomposition, the generated methane bubbles have an influence on the cavitation damage effect. 3) Larger cavitation energies can lead to stronger hydrate damage, while closer standoff distances do not always lead to more sustained cavitation damage. This paper conducts a preliminary study on the influence of cavitation bubbles on the decomposition of hydrate, which provides a theoretical guidance for further research on the mechanism of cavitation effects on hydrate. INTRODUCTION Natural gas hydrate is an important unconventional energy source, which is considered to be one of the most promising alternative energy sources in the 21st century. The proven reserves of natural gas hydrates are up to 80 billion tons of oil equivalent and are predominantly distributed under seabed (Fitzgerald, G. C. et al., 2012; Li et al., 2020; Sloan, 2003; Song et al., 2021). Currently, there are many problems in the process of gas hydrate exploitation by conventional methods, such as low efficiency of gas production, poor sustainability and risk of reservoir destabilization and collapse. Thus, commercial extraction of gas hydrate cannot be achieved for the moment based on the existing technology and equipment (Luo et al., 2021; Terzariol et al., 2017; Zhang et al., 2022). The cavitation phenomenon is a destructive effect with enormous energy and was first discovered in the shipbuilding industry (Lauterborn, W. & Bolle, H. J., 1975). The high temperature and pressure generated during the collapse of a bubble can cause significant damage to the surrounding wall (Li et al., 2007; Zhou et al., 2018), which has a strong damaging effect on hydrated soft sediments (Zhang et al., 2022). In recognition of the powerful destructive effect of cavitation, Li et al. proposed a new idea of integrated method of drilling radial horizontal wells by cavitation jets with screen tubing completion to extract hydrates based on the characteristics of unconformable gas hydrate resources in the South China Sea (Li et al., 2020). In particular, the hydro-jet erosion effect plays an important role in improving the efficiency of jet breaking underwater and increasing the production of hydrate. Peng et al. optimized a contraction-expansion cavitation nozzle and verified the cavitation erosion ability of cavitation jets based on laboratory experiments (Peng, K., 2018). Zhang et al. conducted a macroscopic study for the cavitation jet's erosion performance on natural gas hydrates and verified that the cavitation jet has a stronger destructive effect than classic water jets (Zhang et al., 2020). Existing studies and results argue for the effectiveness of cavitation jets for efficient gas hydrate fragmentation, while most of the work is conducted based on macroscopic jet experiments, and the results are difficult to characterize the specific effects of cavitation on hydrate. Few experimental studies have been conducted to investigate the effect of the bubble collapse process on the hydrate breakage.

Abstract Deepwater natural gas hydrates have attracted widespread attention as a clean energy resource, but their decomposition process will significantly change the physical and mechanical properties of the formation, posing a threat to the stability of the casing during drilling. Deepwater natural gas hydrates have attracted widespread attention as a clean energy resource, but their decomposition process will significantly change the physical and mechanical properties of the formation, posing a threat to the stability of the casing during drilling. Based on the multi-physics coupling theory, this study comprehensively analyzes the impact of hydrate decomposition on formation stability and the bearing capacity of the conductor. A coupled model integrating gas-water two-phase flow, thermal fields, and mechanical fields is constructed using finite element software to simulate the stability changes of the conductor passing through hydrate-bearing formations. The results indicate that during the early stages of hydrate decomposition, pore pressure in the near-well region rises rapidly, and the stress on the bottom and surrounding formation of the conductor increases significantly, resulting in intensified formation settlement and substantial conductor displacement. As the decomposition proceeds, the pore pressure and stress distribution tend to be stable, and the conductor displacement changes gradually slow down; the decomposition rate, pore pressure, and temperature changes show obvious time correlation, with violent fluctuations in the initial stage and gradually stabilizing over time. This study elucidates the dynamic mechanism of hydrate decomposition's impact on conductor stability and provides theoretical support for optimizing deepwater drilling design and natural gas hydrate development.