Research on the Influence of Depressurization on the Decomposition of Nondiagenetic Hydrate in the Process of Solid Fluidized Mining

Natural gas hydrate is an efficient and clean resource that contains a lot of heat energy. The decomposition products of natural gas hydrates are mainly methane, and the combustion products are CO2 and water, which belong to clean energy. In this study, an experimental device and method for simulating the synthesis and decomposition of marine nondiagenetic hydrates during solid fluidized mining are established to study the decomposition rule and influencing factors of marine nondiagenetic hydrates. The reservoir crushing and stirring device is designed to simulate the crushing process at the inlet during solid fluidized mining; a liquid compensating device is designed to remove the free gas in the reactor before the decomposition of hydrates so that the decomposition reaction rate of hydrates in the initial stage can be accurately measured. Experimental research is carried out on the influence of the depressurization on the decomposition of hydrate particles during the mining process. The experimental results show that for nondiagenetic hydrates, the greater the pressure drop, the faster the decomposition reaction, and the more obviously the system temperature drop, but the pressure drop is not as large as possible. In the actual mining process, the pressure drop must be reasonably controlled to avoid causing the water layer to freeze and the “self-protection effect” of hydrates, which will cause negative effects on mining operations. Compared with conventional depressurization mining, the nondiagenetic hydrates mined by solid fluidized mining technology are more sensitive to the pressure drop. In this article, considering the comprehensive influence of multiple variables, a decomposition rate model of marine nondiagenetic hydrates is established, and the reaction rate constant equation of hydrate decomposition in the process of solid fluidization mining is derived on the basis of experimental results. This article gives a theoretical basis for studying the decomposition kinetics of marine nondiagenetic hydrates.