Search

Carbon neutrality is now a common strategic target worldwide, with geological storage seen as the mainstream scheme to address CO 2 emissions and the greenhouse effect. Depleted natural gas hydrate reservoirs (DNHR), with their high-pressure, low-temperature environment, could capture CO 2 in the form of hydrates, being an innovative way for carbon storage. A lab-scale reactor was used in this work to simulate CO 2 injection into the reservoir after gas hydrate exploitation. As expected, it was found that the low-temperature environment of the depleted reservoir at the end of gas production provided a high driving force and accelerated the rate of CO 2 hydrate formation. Consequently, the maximum gas storage capacity was increased by 66% by optimizing the injection timing and reducing the gas injection flow rate to enable enough hydrate formation. Besides, the formation of CO 2 hydrate in the DNHR could also help stabilize the reservoir to achieve a more efficient CH 4 production and CO 2 storage. This study provides a novel strategy for gas hydrate exploitation as well as subsequent geological storage of CO 2 in depleted natural gas hydrate reservoirs by making full use of their favorable conditions. • Depleted gas hydrate reservoirs capture carbon dioxide in the form of hydrates. • Optimizing the injection process and timing can effectively improve CO 2 storage efficiency. • Spatial evolution of carbon dioxide hydrate in DNHR. [ABSTRACT FROM AUTHOR]

The utilization and transportation of clean energy require efficient energy storage solutions. Gas hydrate represents a promising way for high-density storage under mild conditions. In particular, hydrate induced by confined space has the advantage of being environmentally friendly with rapid nucleation and high mass transfer efficiency. However, the cost of artificial pore-construction methods has hindered its widespread application. In this study, we report a novel approach of hydrate storage in the -SO 3 − modified flexible balsa wood as a naturally porous material. The surface sulfonate groups were successfully grafted by coupling agents which was verified by various techniques. The material's natural porous hierarchical structure allows for efficient fluid flow in porous media, enabling a reduction in induction time by ∼88% and a storage capacity of up to 150.6 v/v by adjusting the load water amount. The 100 wt% water-loaded wood materials exhibited the highest water conversion efficiency. Moreover, the recoverable mechanical properties make it reusable without performance degradation. The inner pore structure and hydrate morphologies were further investigated by X-ray microscopy to clarify the hydrate growth mechanism. The interconnected pores and channels make the hydrate grow in layers inside. In addition, the performance could be adjusted by simply changing the hydrophobicity to regulate the gas flow which may contribute to the large storage systems. The use of natural biomass porous materials provides an environmentally friendly and economically feasible strategy for gas storage. [Display omitted] • The modified flexible balsa wood was synthesized and applied in energy storage. • Methane hydrate induction time was reduced by ∼88% and the storage capacity was enhanced to 150.6 v /v. • The 400 wt% water loaded case exhibited the best storage performance. • The hydrate started to form in axial parenchyma structures verified by X-ray microscopy. • Tunable storage performance based on hydrophobic and hydrophilic modification. [ABSTRACT FROM AUTHOR]

Natural gas hydrates are a potential future energy modality with the advantages of clean burning and large resource reserves and have attracted worldwide attention. Natural gas hydrates formation and dissociation impact the skeletal structure and mechanical properties of porous media sediments. In addition, there is a synergistic effect between the migration of fine clay particles in porous media and hydrate behavior. In this study, methane hydrate was examined in-situ using a low-field nuclear magnetic resonance system in the presence of two suspensions of clay particles with different stability. The results showed that clay particles impacted methane hydrate formation and dissociation and the pore structure of porous media. Hydrate nucleated preferentially in large pores, causing them to split into smaller pores; the presence of clay particles, especially illite, improved the water conversion rate. The results indicated that water content in large pores increased after hydrate dissociation but was discontinuous among different pores. When illite was present, the distribution was more continuous; when montmorillonite was present, the water distribution of the large pores was similar to that of the original state. This work increases our understanding of the kinetics, water migration, and pore structure alteration of methane hydrate formation and dissociation in sediments with clay particles and provides support for the safe and efficient development of natural gas hydrates. • Clay particles impacted methane hydrate formation and dissociation • Hydrate nucleated preferentially in large pores • Clay particles, especially illite, improved the water conversion rate • Water content in large pores increased after hydrate dissociation but was discontinuous among different pores [ABSTRACT FROM AUTHOR]

• Presence of fine particle could block the pores and hinder gas production. • Water content determines the behavior of fine particle aggregation. • Distribution pattern of fine particles directly affects the gas production efficiency. Natural gas hydrates are widely distributed in silty marine sediments containing fine particles less than 75 μm in size. The effects of WC (water content) on the behavior of fine particle migration and their role in gas and water production do not appear well understood. This work found that the WC slightly affected the gas production pattern in uniform sandy reservoirs. Yet upon a mixture of coarse and fine particles, the fine particles would instantly aggregate at the nearby pore throat reducing the reservoir permeability and prolonging the production by more than 3 times. Surprisingly, 16% of the fine particles at the edge and 19% at the middle were found to migrate with the fluid flow upon increasing water content, resulting in a less hindered initial gas production but a following more complete blockage or even production failure. This behavior can be consolidated in the scenario of a sand-kaolin mixture. The findings could provide new knowledge on the particle migration behavior upon gas and especially water production and guide the strategy design on dealing with the sand problem in the field test. [ABSTRACT FROM AUTHOR]