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A set of scaling criteria of a polymer flooding reservoir is derived from the governing equations, which involve gravity and capillary force, compressibility of water, oil, and rock, non-Newtonian behavior of the polymer solution, absorption, dispersion, and diffusion, etc. A numerical approach to quantify the dominance degree of each dimensionless parameter is proposed. With this approach, the sensitivity factor of each dimensionless parameter is evaluated. The results show that in polymer flooding, the order of the sensitivity factor ranges from 10 −5 to 10 0 and the dominant dimensionless parameters are generally the ratio of the oil permeability under the condition of the irreducible water saturation to water permeability under the condition of residual oil saturation, density, and viscosity ratios between water and oil, the reduced initial oleic phase saturation and the shear rate exponent of the polymer solution. It is also revealed that the dominant dimensionless parameters may be different from case to case. The effect of some physical variables, such as oil viscosity, injection rate, and permeability, on the dominance degree of the dimensionless parameters is analyzed and the dominant ones are determined for different cases.

Gas production from hydrate reservoir by the combination of warm water flooding and depressurization is proposed, which can overcome the deficiency of single production method. Based on the combination production method, the physical and mathematical models are developed to simulate the hydrate dissociation. The mathematical model can be used to analyze the effects of the flow of multiphase fluid, the kinetic process of hydrate dissociation, the endothermic process of hydrate dissociation, ice-water phase equilibrium, the convection and conduction on the hydrate dissociation and gas and water production. The mechanism of gas production by the combination of warm water flooding and depressurization is revealed by the numerical simulation. The evolutions of such physical variables as pressure, temperature, saturations and gas and water rates are analyzed. Numerical results show that under certain conditions the combination method has the advantage of longer stable period of high gas rate than the single producing method. natural gas hydrate reservoir, warm water flooding, depressurization, numerical simulation Citation:Bai Y H, Li Q P. Simulation of gas production from hydrate reservoir by the combination of warm water flooding and depressurization.

The vast amount of hydrocarbon gas encaged in gas hydrates is regarded as a kind of future potential energy supply due to its wide deposition and cleanness. How to exploit gas hydrate with safe, effective and economical methods is being pursued. In this paper, a mathematical model is developed to simulate the hydrate dissociation by depressurization in hydrate-bearing porous medium. The model can be used to analyze the effects of the flow of multiphase fluids, the intrinsic kinetic process of hydrate dissociation, the endothermic process of hydrate dissociation, ice-water phase equilibrium, the variation of permeability, the convection and conduction on the hydrate dissociation and gas and water production. The numerical results agreed well with the 1-D and 2-D experiments. The numerical results for 3-D hydrate reservoir show that in the first stage of depressurization gas can be produced effectively from hydrate reservoir. With the depletion of reservoir energy because of endothermic process of hydrate dissociation the gas rate decreases rapidly. Then, methods such as thermal stimulation and inhibitor injection should be considered to replace depressurization. depressurization, gas hydrate reservoir, numerical simulation, physical experiment