Study on the Phase Equilibrium Variation Law of Methane Hydrate in Methanol + Sodium Chloride Solutions of Different Concentrations

In deepwater oil and gas drilling, as well as in gathering and transportation pipelines, the combination of low temperature and high pressure can create conditions conducive to hydrate formation. Under these circumstances, methane hydrates can quickly accumulate and deposit, leading to blockages that significantly impair the operational efficiency of the pipelines. This phenomenon poses serious risks to both the cost-effectiveness and safety of drilling operations.To ensure the safety of flow in gathering and transportation pipelines, effective prevention and control of hydrates are essential. Accurately determining the phase equilibrium conditions of hydrates and understanding the variations in hydrate phase equilibrium have become critical for maintaining flow safety in deepwater operations. This study designed experiments to ascertain the phase equilibrium conditions of methane hydrates in mixed solutions of methanol (5%, 10%, 15%, 20%) and sodium chloride (2%, 4%) at various pressures (9 MPa, 12 MPa, 15 MPa, 18 MPa). Additionally, it investigated the effects of methanol and sodium chloride concentrations on the phase equilibrium of methane hydrates.Based on the established phase equilibrium conditions, a graph depicting the phase equilibrium of methane hydrate in a methanol + sodium chloride solution was constructed and analyzed. The resulting phase equilibrium data were then thermodynamically validated and compared with the phase equilibrium conditions calculated using the commercial software Multiflash for confirmation. This study addresses gaps in existing experimental databases and offers significant theoretical support for optimizing inhibitor ratios and designing flow safety assurance schemes.