The conversion of CO₂ into solid hydrates for seabed storage is a promising greenhouse gas mitigation method, but the influence of reservoir types on hydrate formation remains unclear due to the complexity of marine sediments. This study examines three end-member sediments-montmorillonite, diatoms, and glass beads-representing clay-, silt-, and sand-dominated reservoirs, respectively. A series of kinetic experiments, morphological observations, and electrical sensitivity tests were conducted to assess the impact of these sediments on hydrate formation. The results show that the surface electric field and water migration properties of montmorillonite provide additional nucleation sites, promoting hydrate formation during the induction period. Gas consumption and hydrate conversion rate in the montmorillonite system were five times higher than those in the deionized water control group and ten times higher than those in the diatom and glass bead systems. While diatoms facilitated milder reactions in later stages, rapid hydrate formation in montmorillonite impeded further CO₂ mass transfer. Glass beads exhibited stringent formation conditions with Ostwald ripening effects. Hydrate films initially formed at the gas-liquid interface and spread into gas and water phases via surface tension-driven water migration. Electrical sensitivity tests revealed an inverse correlation between sensitivity and induction/reaction times across sediment types.

Oil-gas two phase wax deposition is a fairly common and open-ended question in flow assurance of multiphase transportation pipelines. This paper investigated the two main aspects of oil-gas two phase wax deposition layer: apparent thickness and crystal structure characteristics. A typical highly paraffinic oil in Bohai Sea, China, was used as the experimental material to investigate the wax deposition thickness in oil-gas two phase under the influence of different oil temperatures, superficial gas/liquid phase velocities and gas-oil ratios by using multiphase flow loop experimental device. Just as in the classical theory of wax molecular diffusion, it showed that wax deposition thickness of oil-gas two phase increased with increasing oil temperature. Analysis of the impact of different superficial phase velocities found that the actual liquid flow heat transfer and shear stripping was the gas phase dominant mechanisms determining wax deposit thickness. In addition, the crystal structure of the wax deposition layer was characterized with the help of small-angle X-ray scattering (SAXS) for different circumferential positions, flow rates and gas-oil ratios. The bottom deposition layer had a complex crystal structure and high hardness, which were subject to change over flow rate variations. Furthermore, the SAXS results provided evidence that the indirect effect of the actual liquid velocity modified by the gas phase was the main mechanism. Our study of the effect of gas phase on the wax deposition of oil-gas two phase will help shed light onto the mechanism by which this important process occurs. Our findings address a very urgent need in the field of wax deposition of highly paraffinic oil to understand the flow security of oil-gas two phase that occurs easily in multiphase field pipelines.