Decomposition Kinetics and Self-Preservation of Methane Hydrate Particles in Crude Oil Dispersions: Experiments and Theory

• Published in: Energy & fuels Vol. 33; no. 12; pp. 12353 - 12365
• Main Authors: Sizikov, Artem A, Vlasov, Valeriy A, Stoporev, Andrey S, Manakov, Andrey Yu
• Format: Journal Article
• Language: English
• Published: American Chemical Society 19-12-2019
• ISSN: 0887-0624; 1520-5029
• DOI: 10.1021/acs.energyfuels.9b03391

The self-preservation phenomenon may be used for storage and transportation of natural gas in the form of gas hydrate. In this work, decomposition kinetics and self-preservation of methane hydrate dispersions in two types of crude oils were studied. Hydrate particle sizes in both dispersions did not exceed 30 μm. The experiments were performed at constant temperatures from −4 to −20 °C without preliminary deep-freezing of the samples. The kinetic curves of the methane hydrate decomposition were recorded as depending on methane pressure in the autoclave vs time. In the experiments with the first dispersion, it was shown that at the decomposition degree of 50%, the hydrate decomposition rates decreased by 1–2 orders of magnitude in comparison to the rates at the start of the decomposition process; therefore, hydrate self-preservation took place. Estimated thickness of the ice shell providing self-preservation did not exceed 1.3 μm at the decomposition degree of 50%. Self-preservation was less pronounced in experiments with the second dispersion. It may be explained by the presence of the surfactant in the second dispersion, which was added to stabilize the water-in-oil emulsion from which the dispersion was obtained. Possible mechanisms and the effect of various factors on the efficiency of self-preservation are discussed in this work. A mathematical model of hydrate decomposition process taking into account self-preservation of hydrate particles in the dispersion is suggested. A time-dependent (decreasing) diffusion coefficient of methane in ice shell was used in the model.