Xinyao Su

During deepwater drilling, testing, production, or hydrate mining, the circulating medium in the wellbore may contain solid particles, such as rock chips and sand, in addition to drilling fluids, gas, and water. In the high-pressure, low-temperature conditions of deep water, gas intrusion can easily combine with free water in the drilling fluid to form hydrates, increasing the drilling risk. Therefore, understanding the formation patterns of hydrates in drilling fluids is of significant importance for the prevention and control of hydrates. This study utilized a small-scale high-pressure reactor to investigate the impact of the stirring rate, NaCl, and methanol additives, as well as the sand content on the hydrate formation process and gas consumption. The results indicate that the hydrate formation process can be divided into an induction stage, a rapid formation stage, and a slow formation stage. The induction stage and rapid formation stage durations are significantly reduced under stirring conditions. In NaCl and methanol solutions, hydrate formation is inhibited, with the induction stage duration increasing with higher concentrations of NaCl and methanol. There was no apparent rapid formation stage observed. The final gas consumption decreases substantially with increasing concentrations of NaCl and methanol, reaching no significant hydrate formation at a 20% concentration. The sand content has a significant impact on the slow formation stage, with the final gas consumption increasing within a certain range (in this work, at a sand content of 20%), and being notably higher than in the pure water system under the same conditions.

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.