Experimental Studies on Methane Hydrate Formation in Uniform Porous Media

Methane hydrate is a fascinating physical occurrence of methane and water in solid-state. Methane Hydrates have been under investigation for several decades due to its importance in energy and environment, and its various applications in physical sciences and technologies. I developed models in the laboratory to gain insight into (i) secondary hydrate formation in the porous medium, which involves crystallization with hysteresis, and (ii) multi-phase (gas-water) occurrence and flow in the presence of hydrates in the porous medium. In the first part, methane hydrate is formed in a sand pack that undergoes cooling-heating cycles over a range of temperatures. Five cycles are designed so that hysteresis can be observed in the sand pack. Each cycle has a different melting temperature which, leads to varying intensity of temperature relaxation effect on the hysteresis. Evidence of hysteresis is observed in three separate temperature readings of thermocouples. The formation of hydrates is dependent on the thermal cooling rate of the sand pack, and the melting temperature of the previous cycle. A temperature increase is observed in the whole system, and this increase is driven by temperature peaks indicating significant hydrate formation near the thermocouples. These peaks have substantial effects on the entire system. By comparing each cycle’s temperature peaks, hysteresis is observed at the temperature readings of the short thermocouple. The same hysteresis pattern follows for the location of the temperature peaks. A new mechanistic model, following the residual cage theory, is proposed for the prediction of secondary hydrate formation time as a function of the melting temperature.\nIn the second part, methane hydrate is formed in the sand pack in a transparent x-ray vessel. The gas relative permeability in the presence of methane hydrate is measured using two different steady-state flow experiments: single-phase (gas) flow, multi-phase (water-gas) simultaneous flow. Water and gas co-flow experiments cause issues that complicate the results, while the single-phase gas flow method gives good results. Therefore, in measuring relative permeability in the presence of gas hydrates, single-phase gas flow measurements are recommended. A new empirical equation is given correlating the relative permeability to hydrate saturation.