Self-Preservation of Gas Hydrate Particles Suspended in Crude Oils and Liquid Hydrocarbons: Role of Preparation Method, Dispersion Media, and Hydrate Former

The effect of self-preservation of small (few dozens of micrometers) methane hydrate particles in suspensions of a hydrate in crude oils was discussed in our previous work (A. S. Stoporev et al., Energy Fuels, 2014, 28, 794-802). In this work, we present new experimental data on (1) self-preservation of methane hydrate suspensions prepared with the use of different experimental methods, (2) self-preservation of methane hydrate suspended in different hydrocarbons and oil + hydrocarbon mixtures, and (3) self-preservation of gas hydrate-in-oil suspensions formed by different hydrate forming gases. It has been demonstrated that the efficiency of self-preservation of methane hydrate particles can be strongly increased by mixing with crude oil. The powder of methane hydrate with particle sizes of 50-150 mu m was mixed with crude oil under conditions providing the hydrate stability (1 degrees C, pressure of >3 MPa). The oil was mixed with the hydrate by vigorous shaking. Furthermore, the sample of the hydrate suspension was cooled to liquid nitrogen temperature and was recovered from the autoclave. Two stages of the hydrate decomposition occurred at atmospheric pressure. The first one started at approximately 75 degrees C, which is close to the equilibrium temperature of the methane hydrate under atmospheric pressure (-80 degrees C). The entire remaining hydrate decomposed at the second stage at degrees C, i.e., at the ice melting point. Independent experiments proved that the same powder of methane hydrate without oil decomposed under atmospheric pressure in one stage started at approximately 75 degrees C. No self-preservation occurred in this case. The experiments on study of self-preservation of methane hydrate suspensions in toluene, decane and mixtures of these solvents with crude oil were performed. These suspensions were synthesized from emulsions of water in the respective organic liquids. No self-preservation occurred in the case of pure toluene and decane. At the same time, the addition of 25-50 wt % of crude oil to these solvents resulted in clearly expressed self-preservation of methane hydrate in the corresponding suspensions. In addition, it was demonstrated that the effect of self-preservation of hydrate-in-oil suspensions could be observed for ethane, propane, and carbon dioxide, as well as for hydrocarbon mixture gas hydrates (in all cases, the sizes of the hydrate particles did not exceed a few dozen micrometers).