Flow-Rate-Controlled Hydrate Formation Kinetics during Shallow Methane Leakage from Muddy Reservoirs: Experimental Validation and Enhanced Saturation Prediction

Abstract

Abstract Shallow methane leakage is a topic of great concern for governments and the public worldwide. Upward methane leakage can induce hydrate formation, enabling high-density carbon sequestration but also causing significant changes in fluid saturation and reservoir properties. However, existing studies lack key conclusions about the dynamic prediction of saturation during upward methane migration. Therefore, the formation characteristics and saturation prediction of methane hydrates in muddy cores at different flow rates were studied. The results show that lower gas flow rates are more conducive to hydrate formation, which is attributed to sufficient gas–liquid contact and enhanced mass transfer. The maximum increase in hydrate saturation is 47.43%, and the maximum decrease in permeability (increase in damage coefficient) is 65.99% (27.48%). Methane hydrate formation leads to a decrease in permeability and induces an increase in the inlet pressure nonpressurization gradient, with a maximum pressure difference of 5.85 MPa. At the same time, the permeability and hydrate saturation comply with K = K0((1 – Sh)/(1 + 2Sh))2.5, and the measured values are all within the 95% prediction band. On the basis of the coupled relationship between hydrate saturation and inlet pressure during the flow process, a new hydrate saturation prediction method is proposed (R2 > 0.98). Orthogonal experiment results show that the gas flow rate has the greatest influence on the hydrate saturation, while the outlet pressure has the least influence. This study provides a constructive solution for predicting the hydrate saturation during the upward leakage process of methane.