Clarifying the mechanism that results in the mechanical behavior differences of hydrate particles in different states is of great significance for understanding the agglomeration mechanism of hydrate particles and the mechanical behavior characteristics of the liquid bridge between particles in a pipeline environment dominated by oil or gas. In this study, the typical liquid bridge morphology and the consolidation characteristics of hydrate particles during the contact-pull process between hydrate particles and water droplets were observed using an improved micromechanical force testing device, as well as a force sensor with a higher sampling frequency and the electric displacement stage with a smaller step. It was found that the consolidation state of the liquid bridge changes in a complex manner in the gas phase environment, and there is a special weak consolidation state: when the hydrate shell on the surface of the liquid bridge is pulled off, a new hydrate shell will form on the surface of the unconverted water at the fracture until the liquid bridge is stretched to several times the particle diameter length and breaks. Based on the hydrate shell formation theory and the existing model of hydrate interparticle mechanics, a possible liquid bridge weak consolidation model was supplemented to explain this state to elucidate the mechanism that causes the difference in the mechanical behavior of the liquid bridge for hydrate particles in different states.

A comprehensive understanding of the intricate water/gas two-phase flow in sedimentary pores is essential for accurately predicting gas production following the in-situ dissociation of natural gas hydrates, as it is crucial for optimizing resource extraction strategies. This study constructed three typical clay slit nanopore models with distinct wettability characteristics – hydrophilic, relatively hydrophobic, and Janus hybrid-wettability – and used molecular dynamics simulations to investigate the spatial distribution and transport dynamics of two-phase fluids under varying water saturation conditions. The results revealed a significant negative correlation between water saturation and gas relative permeability. When water saturation reaches a critical threshold, the water lock effect occurs, blocking gas flow. Pore wettability plays a key regulatory role in water/gas phase dynamics via influencing the formation pathways of water locks. In relatively hydrophobic pores, weaker solid-water interactions promote the rapid clustering of water molecules, forming water locks, while hydrophilic surfaces enable water lock formation through gradual thickening of the liquid film. In Janus pores with low water saturation, strong electrostatic interactions between oppositely charged pore walls facilitate the formation of discrete water bridge networks, maintaining “gas windows” that allow gas flow, although these windows eventually close as saturation increases. The lower the water saturation, the more favorable it is for gas transport; in contrast, hydrophilic pores exhibit higher gas transport efficiency. Our findings provide valuable molecular-scale insights into how wettability governs multiphase flow transport, offering a theoretical foundation for reservoir modification and seepage control in natural gas hydrate recovery.

It remains a great challenge to understand the hydrates involved in phenomena in practical oil and gas systems. The adhesion forces between hydrate particles, between hydrate particles and pipe walls, and between hydrate particles and reservoir particles are essential factors that control the behaviors of clathrate hydrates in different applications. In this review, we summarize the typical micro-force measurement apparatus and methods utilized to study hydrate particle systems. In addition, the adhesion test results, the related understandings, and the applied numerical calculation models are systematically discussed.

The trial production of natural gas hydrate reservoirs remains poor. Reasonable reservoir reconstruction, which can improve formation permeability, is an important approach to increasing the efficiency and enhancing production. In this work, water jet slotting is proposed to reconstruct an natural gas hydrate reservoir near a wellbore. The spatial slots formed by water jet slotting not only directly constitute high-permeability channels, but also generate disturbances to the surrounding in-situ sediment. Water jet slotting disturbances to nearby sediment was investigated using a three dimensional flow-structure coupling model to evaluate the proposed reconstruction method. The reservoir at the SH2 site in the Shenhu area of the South China Sea was used as the reference. A horizontal slotting arrangement along the vertical well was adopted. The results demonstrate that water jet slotting can change the primary stress state of the sediment around the wellbore, and generate a dominant stress relaxation zone and small stress concentration zone. Within the stress relaxation zone, the in-situ compressive stress was remarkably reduced or even transformed into tensile stress, accompanied by sediment displacement and volumetric expansion strain. This is conducive to loosening the sediment around the wellbore and improving the permeability characteristics. In addition, the influence of the water jet slotting parameters including slot radius, spacing, and number on disturbances to the nearby sediment was studied. Reservoir responses to water jet slotting under balanced and unbalanced bottom-hole pressures were compared and analyzed. This study provides a reference for natural gas hydrate reservoir reconstruction using water jet slotting.