Study On Relative Permeability Of Hydrate Reservoir Based On Pore Network Model

Scientific interest in natural gas hydrates has increased greatly in recent decades due to the decline of traditional fossil fuel resources.Downhole geophysical logging tools have made significant progress in obtaining detailed information about natural gas hydrates,but methods for observing the accumulation and migration of natural gas hydrates during their formation and dissolution still need to be improved.At the same time,sand production is an important reason to balance hydrate exploitation.Different from conventional oil and gas reservoir exploitation,hydrate exploitation involves the change of reservoir mechanical properties,the change of fluid properties and phase transformation.A large amount of sand production in the process of hydrate exploitation will result in the forced suspension of exploitation.To sum up,it is of great significance to analyze the sand producing mechanism of gas hydrates and the particle transport mechanism for the efficient development of gas hydrates.In this paper,through the establishment of the pore network model,the effect of the degree of sand production on the fluid flow in the process of gas hydrate decomposition was studied.In the late period of hydrate decomposition,different sizes of hydrate particles were formed,and fallen particles were formed due to poor cementing properties of the reservoir.The effect of two parts of particles flowing with fluids on seepage process was studied.Temperaturepressure parameters and related fluid property parameters under the condition of hydrate phase equilibrium were set,paths of fluid flow were determined by capillary force,and the pore network model of three-phase flow(particle,water and gas)was established.The simulation results show that the presence of particles has an important effect on the seepage in pore-throat space.In the process of hydrate decomposition,the deposition and blockage caused by the flow of particles in the early stage of decomposition are the main factors,while the increase of pore-throat space caused by hydrate decomposition in the late stage is the main influence factor.Therefore,the corresponding isosmotic points of the relative permeability curves move first to the left and then to the right.In the late period of hydrate decomposition,the relative permeability of the reservoir constantly changes due to the constant deposition and blockage of hydrate particles and fallen particles in pores and throats and the increase of space in the pore-throat caused by fallen particles.Finally,the sensitivity analysis is used to analyze the variation rules of different parameters.