In the process of oil and gas extraction and transportation, the aggregation and deposition of hydrate particles within oil and gas pipelines is a primary cause of pipeline blockage, with adhesion being the fundamental cause of hydrate particle aggregation. With the development of crude oil and natural gas transportation technology, the application of pipeline internal coating technology is becoming increasingly widespread. It is essential to compare the physical properties and practicality of various coating materials and conduct preliminary screening. Adhesion experiments on coating materials suitable for the conditions of oil and gas pipeline transport have been conducted. The experimental results indicate that the PTFE/PPS composite coating has advantages in reducing the adhesive force of hydrate particles under low temperatures and different degrees of subcooling. As the degree of subcooling increases, the adhesive force between the hydrate particles and the PTFE/PPS composite coating substrate gradually increases from 8.36 mN·m⁻¹ to 10.26 mN·m⁻¹. With a 3 °C increase in subcooling, the adhesion force increases by 1.92 mN·m⁻¹, which is about 68% lower on average compared to an uncoated substrate. Epoxy resin E-51 coatings and polyurea coatings also demonstrate certain anti-hydrate adhesion properties, but their performance is slightly inferior compared to the PTFE/PPS composite coating. These research results can provide an important reference for hydrate prevention technology in oil and gas transportation pipelines.

The accurate prediction of wellbore temperature and pressure is important for safe drilling. However, annulus temperature and pressure changes are more complicated due to phase transition. To study this problem, a prediction model of temperature and pressure in deep water riserless drilling is established by considering hydrate cuttings decomposition, interphase mass transfer, and phase transition heat. Based on this model, the effects of hydrate cuttings decomposition on the temperature and pressure of drilling in a hydrate reservoir are explored. The results show that the influence of hydrate cuttings decomposition increases significantly with an increase in the inlet temperature. The influence of hydrate cuttings decomposition on temperature and pressure decreases with an increase in displacement. A small range in the variation of density and penetration rates has little impact on the annulus pressure but mainly affects the temperature. The influence of hydrate cuttings decomposition increases with an increase in the penetration rate. In normal drilling conditions, hydrate cuttings decomposition has little impact on annulus temperature and pressure, but under the conditions of a high inlet temperature, high hydrate saturation, low displacement, and high penetration rate, it is necessary to consider the impact of hydrate cuttings decomposition. This study can provide reference for the prediction of temperature and pressure in deep water hydrate reservoir riserless drilling.

Mass transfer and phase transition have an important effect on the velocity of bubble migration in deepwater wellbores, and accurate prediction of bubble migration velocity is crucial for calculating the safe shut-in period of deepwater oil and gas wells. Therefore, the effect of bubble dissolution mass transfer and hydrate phase transition on bubble migration behavior in the deepwater environment have attracted extensive attention from researchers in the fields of energy, marine chemistry, and marine engineering safety. In this work, a new model of bubble migration velocity in deepwater is developed, which considers the effect of hydrate phase transition and gas-water bidirectional cross-shell mass transfer during bubble migration. Based on the observation data of bubble migration in deepwater, the reliability of the model in predicting bubble migration velocity is verified. Then, the model is used to calculate and analyze the bubble migration velocity and bubble migration cycle under different initial bubble size, different annular fluid viscosity, and density. The results show that the initial size of bubble and the viscosity of annulus fluid are the main factors affecting the migration velocity of the bubble, but the density of annulus fluid has little effect on the migration velocity of the hydrated bubble and clean bubble. In addition, the migration velocity of the clean bubble gradually increases during the migration process from the bottom to the wellhead, while the migration velocity of the hydrated bubble is divided into a gradually decreasing stage and a slowly increasing stage. The gas consumption and the thickening of hydrate shell in the gradually decreasing stage play a dominant role, and the increase of bubble volume caused by the decrease of pressure in the slowly increasing stage is the most important factor. The formation of the hydrated bubble can significantly reduce the migration velocity of the bubble and effectively prolong the safe shut-in period. This study provides a reference for quantitative description and characterization of complex bubble migration behavior with phase change and mass transfer in deepwater environment.

Deep-water gas well testing is a key technology for obtaining reservoir production and physical property parameters. However, gas hydrates could easily form and cause blockage in the low-temperature and high-pressure environment on the seafloor. Therefore, it is extremely important to inhibit hydrate growth in deep-water operations. Ionic liquid is a type of hydrate inhibitor with both thermodynamic and kinetic effects. However, its intrinsic inhibiting mechanism is still unclear. By using molecular dynamics simulation, the growth process of methane hydrate in the 1-ethyl-3-methylimidazole chloride (EMIM-Cl)-containing system at the pressure of 15 MPa and temperature of 273.15 K was studied. The system energy and angular order parameters (AOP) were extracted as the evaluation indicators. It was found that the time for the complete growth of methane hydrate in the EMIM-Cl-containing system was about 10 ns, longer than that in the pure water, indicating that EMIM-Cl showed an obvious inhibition effect to hydrate growth. The results also implied that the joint action of hydrogen bond and steric hindrance might be the inhibition mechanism of EMIM-Cl. Some six-membered rings in hydrate crystal large cage structures evolved from five-membered rings under the effect of EMIM, which partly contributed to the delay of hydrate formation.