Influences of unsaturated fluids on hydrate-bearing sediments under high-pressure seepage environment

Sediments and fluids characteristics are the two important factors affected the formation and accumulation of methane hydrate in deposits. In order to study methane hydrate occurrence in sediments, the influences of unsaturated fluids on hydrate-bearing sedimentary strata under high-pressure seepage environment must be discussed. The difference of fugacity has been adopted to be the driving force in this reaction. The hydrate intrinsic kinetic constant has been written in an Arrhenius-type equation. A two-dimensional (horizontal, vertical) model coupling the aspects of unsaturated flow fluids-sedimentary characteristics-hydrate formation kinetics has been established. The evolution of porous hydraulic parameters such as water content, to-saturation coefficient, pore water pressure and hydrate saturation have been discussed. Under the conditions setting in the simulation, the results show that the pore water pressure becomes larger with time during the reaction proceeding. Under the same conditions, the increase of strata temperature and hydrate saturation will increase the pore water pressure. The hydrate saturation causes less influence; while the sediments matric suction, to-saturation coefficient and hydrate intrinsic kinetic constant will vary inversely with the pore water pressure; and the to-saturation coefficient has more strong effects.