Large-scale physical simulation is essential for advancing our understanding of natural gas hydrates exploitation mechanism. However, cylinder-shaped simulators often face challenges in balancing large volume, controllability, and comprehensive monitoring. In this study, we developed a fan column-shaped hydrate simulator (FCHS) with an internal angle of 6°, a radius of 3 m, and an inner height of 0.3 m, resulting in an effective volume of ~142 L. Moreover, the FCHS is equipped with an integrated "thermal-pressure-acoustic" sensing system, enabling in-situ monitoring of temperature, pressure, and P-wave velocity evolution during hydrate formation and dissociation process. The experimental results indicate that a pressure gradient successfully established from the reservoir center toward its boundaries during depressurization stage, and pressure propagation is relatively slow, resulting in a radial pressure difference of 3–4 MPa within a 3 m range. Once the system reaches pressure equilibrium, the pressure difference decreases to 0.3–0.4 MPa. The depressurization at the wellbore promotes hydrate dissociation in the near-well region, resulting in the radial temperature difference reaches ~1.5 ℃ along the radial direction. The acoustic data reveals that a radial gradient in hydrate saturation gradually forms from the center to the boundary during depressurization-induced gas production. The evolutions of spatio-temporal multi-fields obtained in the FCHS are consist with that of field production. The FCHS proves to be a cutting-edge platform for experimental simulation of NGH exploitation and carbon sequestration processes.

Efficient separation of CH₄ and C₂H₆ remains a critical challenge in the recovery of light hydrocarbons from natural gas. So we developed a zeolite imidazolate framework-8 (ZIF-8)/iso-hexadecane slurry for CH₄/C₂H₆ separation, and conducted solubility measurements for pure components and equilibrium separation experiments for gas mixtures. A rigorous absorption-adsorption coupled phase equilibrium model and a single equilibrium stage mathematical model were established to describe the phase equilibrium performance of gas-slurry system. The results indicated that the model exhibits high predictive accuracy for the solubility of CH₄ and C₂H₆ in the slurry, with an average relative error of less than 3.053%. Furthermore, the whole process of absorption-adsorption-desorption was designed, and the mathematical model and multi-objective optimization framework were established. The effects of operating pressure and gas-slurry ratio on product purity, recovery ratio, and total unit energy consumption were investigated. The results showed that the C₂H₆ purity in the feed gas is enriched from 22 mol/mol to 94.69 mol/mol, the C₂H₆ recovery ratio reaches 95.21%, and the total unit energy consumption is 0.4558 kW·h·Nm⁻³ (feed gas). In addition, the effects of pressure, temperature, and ZIF-8 solid content on slurry separation performance were analyzed using the established equilibrium-stage model. The results showed that the introduction of ZIF-8 enhances the separation performance of the iso-hexadecane solvent for mixed gases. Compared to the pure solvent, the separation factor increased by an average of 72.5%, which theoretically proved the advantages of slurry separation process.

Understanding the acoustic characteristics of hydrates in various sediments is crucial for hydrate resource detection and safe and efficient exploitation, as hydrate occurrence patterns vary greatly in different sediments. In this work, sediments with different bentonite contents, water saturations, and types were prepared to investigate the characteristics of P-wave velocity (reflecting the magnitude of hydrate saturation in the sediment) and amplitude (reflecting the degree of hydrate-sediment cementation) during hydrate formation and depressurization. During hydrate formation, the P-wave velocity and amplitude have similar trends. As clay content increases, the P-wave velocity increase rates quickened. On the other hand, the increased rate of P-wave velocity slows down with the increase of water saturation in the clay-bearing sediments. Comparing various types of sediment shows that the water absorption and swelling of bentonite reduce the pore space, speeding up the cementation of the hydrate with the sediment and increasing P-wave velocity at a faster rate. Correspondence between P-wave velocity and hydrate saturation is strongly related to sediment type, clay content, and water saturation. The rapidly decreasing amplitude in the early stage of hydrate depressurization indicates that hydrate in clay-bearing sediments is weakly cemented to the sediments, which is prone to stratigraphic instability. The findings of this study offer guidance for hydrate resource assessments in clay-bearing sediments as well as geologic risk estimations during hydrate mining.

CO₂ emulsions used for EOR have received a lot of interest because of its good performance on CO₂ mobility reduction. However, most of them have been focusing on the high quality CO₂ emulsion (high CO₂ fraction), while CO₂ emulsion with high water cut has been rarely researched. In this paper, we carried out a comprehensive experimental study of using high water cut CO₂/H₂O emulsion for enhancing oil recovery. Firstly, a nonionic surfactant, alkyl glycosides (APG), was selected to stabilize CO₂/H₂O emulsion, and the corresponding morphology and stability were evaluated with a transparent PVT cell. Subsequently, plugging capacity and apparent viscosity of CO₂/H₂O emulsion were measured systematically by a sand pack displacement apparatus connected with a 1.95-m long capillary tube. Furthermore, a high water cut (40 vol%) CO₂/H₂O emulsion was selected for flooding experiments in a long sand pack and a core sample, and the oil recovery, the rate of oil recovery, and the pressure gradients were analyzed. The results indicated that APG had a good performance on emulsifying and stabilizing CO₂ emulsion. An inversion from H₂O/CO₂ emulsion to CO₂/H₂O emulsion with the increase in water cut was confirmed. CO₂/H₂O emulsions with lower water cuts presented higher apparent viscosity, while the optimal plugging capacity of CO₂/H₂O emulsion occurred at a certain water cut. Eventually, the displacement using CO₂/H₂O emulsion provided 18.98% and 13.36% additional oil recovery than that using pure CO₂ in long sand pack and core tests, respectively. This work may provide guidelines for EOR using CO₂ emulsions with high water cut.

Non-methane hydrocarbons (NMHCs) are a common type of volatile organic compounds (VOCs) pollutant in the petrochemical industry and have attracted widespread attention because of their adverse health effects and environmental impacts. In this paper, we report a new porous slurry formed with zeolitic imidazolate framework-8 (ZIF-8) and iso-hexadecane to capture the low-concentration and multi-component NMHCs (mainly ethane (C₂H₆), propane (C₃H₈), and n-butane (n-C₄H₁₀)) from the oil field exhaust. The sorption capacity of C₂H₆ in the slurry is significantly higher than that of nitrogen (N₂) and methane (CH₄). Moreover, the slurry demonstrated a clear advantage for C₂H₆ over N₂ and CH₄ in competitive adsorption through the pressure-drop curves. In the NMHCs capture experiments, the C₃H₈ and n-C₄H₁₀ concentrations after purification can be reduced to below 100 ppm, while the C₂H₆ concentration can reach approximately 180 ppm. More encouragingly, in the breakthrough tests, the slurry exhibits a perfect kinetic separation selectivity for multi-component NMHCs. Furthermore, to avoid structural collapse of ZIF-8 material during long-term use in acidic and wet environments, a certain amount of 2-methylimidazole was retained in the slurry as a protective agent in the material synthesis process. In this way, the ZIF-8 materials in the slurry can retain the stable characteristic structure in an aqueous and acidic environment and keep the capture capacity for NMHCs without degradation. We believe the porous ZIF-8/iso-hexadecane slurry is a promising capture agent for low-concentration and multi-component NMHCs with strong purification capacity and stability.

In addition to the temperature and pressure conditions, the pore fluid composition and migration behavior are also crucial to control hydrate decomposition in the exploitation process. In this work, to investigate the effects of these factors, a series of depressurization experiments were carried out in a visible one-dimensional reactor, using hydrate reservoir samples with water saturations ranging from 20% to 65%. The results showed a linear relationship between gas production rates and gas saturations of the reservoir, suggesting that a larger gas-phase space was conducive to hydrate decomposition and gas outflow. Therefore, the rapid water production in the early stage of hydrate exploitation could release more gas-phase space in the water-rich reservoir, which in turn improved the gas production efficiency. Meanwhile, the spatiotemporal evolution of pore fluids could lead to partial accelerated decomposition or secondary formation of hydrates. In the unsealed reservoir, the peripheral water infiltration kept reservoir at a high water saturation, which hindered the overall production process and caused higher water production. Importantly, depressurization assisted with the N₂ sweep could displace the pore water rapidly. According to the results, it is recommended that using the short-term N₂ sweep as an auxiliary means in the early stage of depressurization to expand the gas-phase space in order to achieve the highest production efficiency.

The development of environmental friendly low dose hydrate inhibitors like kinetic hydrate inhibitors (KHIs) is of great significance for the flow assurance in oil & gas production and transportation. In this work, a combined molecular dynamic simulation and experimental verification approach was adopted to increase the efficiency of KHIs development. The inhibition effect of a series of copolymers (N-vinylpyrrolidone and N-acrylate) on hydrate growth was studied by using both molecular dynamics simulation and experimental approaches. The simulation results demonstrated that introduction of hydrophobic ester and butyl group in PVP is beneficial for the inhibition. The length of the alkyl chain of ester group played an important role in improving inhibition performance. PVP-A, the one being introduced butyl ester group into PVP gets the best inhibition effect. In addition, inhibitors can restrict methane bubbles to re-dissolve into the liquid phase, thereby inhibiting the growth of methane hydrate. Increasing the interaction between KHIs and methane can also improve the inhibitory effect of KHIs. The experimental results confirm the reliability of the molecular dynamics simulation.