Experimental Study of Methane Hydrate Decomposition Kinetics in NaCl, KCl, and PVP Solutions

Natural gas hydrates are a promising energy source with considerable potential in the coming decades, and they are gaining increasing attention for their development and utilization. During hydrate extraction, it is essential to decompose hydrates to produce methane gas, while during drilling operations, hydrate decomposition should be avoided to maintain formation stability. The impact of hydrate inhibitors such as NaCl, KCl, and PVP on the decomposition of hydrates remains a controversial topic. To clarify the effects of inhibitors, we designed and proposed a novel experimental protocol, and the results show that injection of high-concentration NaCl or KCl solutions into methane hydrate samples can induce the decomposition of existing hydrates, whereas no such phenomenon was observed when a PVP solution was injected, and even with the injection of a 20% PVP solution, more hydrates continue to form slowly. In mixed solutions of NaCl and PVP, the hydrate decomposes in lower concentrations ofNaCl, indicating that PVP can promote decomposition of the hydrate. According to the Consecutive Desorption and Melting (CDM) decomposition kinetic model, inorganic salt thermodynamic inhibitors (THI) reduce parameters such as methane solubility in solution and the enthalpy of phase change in the empty hydrate lattice, and kinetic inhibitors (KI) such as PVP can lead to a decrease in the extent of surface coverage, thereby facilitating hydrate decomposition. In our study, we propose experimental methods to determine the kinetics of hydrate decomposition in inhibitor solutions and discuss the mechanisms by which inhibitors affect hydrate decomposition, providing insights for developing reasonable plans for natural gas hydrate reservoir exploitation or drilling operations.