Investigation On Phase Distinguish And Fluid Flow Behavior In Porous Media During Hydrates Formation And Dissociation Process

Nature gas hydrate has been into the field of vision of scientists because of its abundant reserves, widely distribution and other advantages. Furthermore, it’s called one of new energy which can replace the traditional fossil fuels in the twenty first century. The physical property of phase distinguish and fluid flow behavior of natural gas hydrates during formation and dissociation process is the base of exploitation research, therefore it made use of magnetic resonance imaging (MRI) and computed tomography (CT) imaging to observe the formation process of hydrates, to study the property of distinguishing between hydrates and solution and to discuss the migration regularity of the relatively flow between gas and water after hydrates exiting.It made a research of the formation process of hydrates in porous media including oil and water with the help of MRI experimental system. It also discussed how the nuclear magnetic relaxation time T1 and T2 changed during formation process. CO2 hydrates were the research objects, the results showed that T1 and T2 in the oil environment were obvious less than them when there were no oil in the media. With the decreasing of saturation of residual water, The relaxation rate 1/T1、1/T2 increased respectively in a linear way and in a index way which were consistent of the effect from surface relaxation mechanism to them in the BT model.It made a research of distinguishing between hydrates and solution using CT experimental system. THF hydrates were the research objects, the result showed that the distinguish effect of KI was much better than NaCl, with the concentration of KI increasing the distinguish effect was increased firstly and decreased later. The concentration corresponding to the best distinguish effect of KI was 6%. The results were also showed that with the help of CT system using contrast agents we could distinguish THF hydrates from THF solution successfully, we could observed directly and dynamically the change of the boundary curve when hydrates decomposed and the hydrates area changed in the CT images. It was proved that in use of threshold value method the saturation of THF hydrates could be calculated in dissociation process.With the condition of different saturation of hydrates it made a research of the relatively flow between gas and water using MRI system. THF hydrates were the research objects, the result showed that with the fluid flowing there was a displacement front boosting process. When the displacement front passes the model from left to right, the saturation of residual water was reduced gradually. When the displacement front boosted, the distribution of residual water was not changed. Using the flow model raised by Goodfield et.al to analyzing calculation, the result showed that the velocity of partial darcy to gas and water two phase both had three parts, the left part was the displacement front had passed, the middle part was the displacement front being part and the right part was the displacement front had not passed. With the saturation of residual water increasing gradually in the model, the result showed that in the condition of different saturation of THF hydrates the capillary dispersion rate was increased firstly and decreased later, but viscous-dominant fractional flow decreased gradually and gravity flow function was also increased firstly and decreased later. However, along with the flowing direction, the relative permeability to gas was increased gradually and the relative permeability to water was decreased gradually.