Study on hydrate formation and plugging mechanisms in mineral oil–methane–water bubble flow systems without emulsifiers

Gas hydrate formation poses a significant flow assurance challenge in oil and gas production under extreme environmental conditions. This study specifically investigates the kinetics of methane hydrate formation and the associated plugging mechanisms in multiphase flow systems containing waxy oil. Experiments were conducted in a visual flow loop under various pressure (5.2–8.2 MPa) and temperature (−1 to −3 °C) conditions. The results demonstrate that the presence of waxy oil is a critical factor for pipeline plugging, as it significantly promotes hydrate nucleation—reducing the onset time by up to 53.66%—and fosters particle aggregation, leading to a dramatic increase in slurry apparent viscosity (up to 2067%). In contrast, hydrate slurries in a pure methane–water system flowed smoothly without blockage. Visual observations revealed the macroscopic process from initial hydrate formation and viewing window coverage to aggregate-induced plugging and subsequent hydrate aging and deposition. Higher initial pressure and lower temperature accelerated hydrate formation kinetics and shortened the time to plugging. A key finding is that plugging, which occurred before or after hydrate formation ceased, was primarily due to the aggregation of hydrate particles rather than to a high hydrate volume fraction. These findings highlight the severe synergistic risk posed by hydrates and waxy oils in flow assurance.