An Experimental Study on the Interaction between Hydrate Formation and Wax Precipitation in Waxy Oil-in-Water Emulsions

Abstract

The coupled formation of wax crystals and hydrates is a critical issue for the safety of deep-sea oil and gas exploration and subsea transport pipeline flow. Therefore, this paper conducts an experimental study on the characteristics of methane hydrate formation in a water-in-oil (W/O) system with different wax crystal contents and explores the influence of different initial experimental pressures on the induction period and maximum rate of hydrate formation. The wavelet function was introduced to process the reaction rate and calculate the maximum speed of hydrate formation. Notably, the higher the pressure, the smaller the maximum rate of hydrate formation. We observed that wax crystal precipitation increases the viscosity of the emulsion, which limits the diffusion of gas in the liquid phase during hydrate nucleation and thus delays the hydrate nucleation. The methane gas precipitation also affects the remaining fraction’s wax content and therefore affects the wax precipitation. Secondary hydrate formation was observed several times during the experiment, increasing the risk of pipeline blockage. Overall, this work provides insights into the effect of wax crystal precipitation on hydrate behaviour that could facilitate flow assurance applications in subsea multiphase pipelines and inform the safe transportation of oil and gas pipelines.