Numerical simulation on natural gas hydrate formation within porous media using constant volume method

Synthesizing samples of hydrate-bearing sediment in laboratories is an effective way to investigate the properties of gas hydrate occurring in nature. However, it is time-consuming and hard to manipulate. Numerical simulations can easily and quantitatively simulate hydrate formation in sediment by controlling any formation conditions. Therefore, in this work the numerical simulation method was introduced to study the formation process and distribution of gas hydrates in lab-scale sediment under the conditions of constant volume and water bath cycling. The results show that the hydrate sample with relatively uniform distribution can be produced in the well-mixed gas-brine system. However, a long reaction time is still required to ensure that gas hydrates have synthesized completely even though the system temperature and pressure tend to be stable. When an interlayer (i.e., the permeability or the porosity in the intermediate part is different from its up and below parts) occurring in the sediment, both the permeability and the porosity of interlayer have effects on the formation of gas hydrate at the lab scale, but the final saturation distribution of gas hydrates in the medium is almost the same to that in homogeneous sediment. This could be mainly because the hydrate formation rate is rapid at the early stage, and the interlayer affects the mass transfer in the system significantly, as is opposite in the later period because of the slow reaction rate. After maintaining a long reaction time, the results tend to be consistent. © 2015, Science Press. All right reserved.