Research On The Effect Of Dynamic Capillary Pressure Of Oil-water Two-phase Flow In Low Permeability Reservoir

Oil-water two-phase flow is a very important phenomenon in the development of oil and gas fields,and capillary pressure plays a central role in the two-phase flow.Since the beginning of the last century,many studies have dealt with determining the capillary pressure-saturation relationship Pc(Sw)and have shown non-uniqueness in the Pc(Sw)relationship,which can either be attributed to a direction dependence or to a rate dependence,e.g.the rate of change of saturation.In this paper,the dynamic effect of capillary pressure is studied systematically.Based on the experimental data,this paper analyzed the factors that influence the dynamic coefficient and found that the influence factors including porous medium,displacement fluid properties and water saturation in porous media.And the denser the porous media,the larger the dynamic coefficient;moreover,dynamic coefficient is positively correlated with fluid density,and negatively correlated with fluid viscosity ratio;at the same time,with the increase of wetting phase saturation,dynamic coefficient decreases gradually.Due to the low permeability reservoirs have the characteristics of low porosity and low permeability,small pore throat,the effect of dynamic capillary pressure is noticeable in oil-water flow process underground,based on this,this paper buildup water flooding model.By analyzing,it turns out that: with the dynamic capillary pressure in the model,the resistance of water flooding becomes larger,resulting in the formation o f energy diffusion slows down,and the oil and water interface velocity decreases,leading to the higher formation pressure;if increasing the formation permeability or decreasing the viscosity ratio of oil/water,it will enhanced the fluid flow ability,and then the dynamic effect of capillary pressure will be also reduced.As the dynamic effect in mercury injection experiment,the paper puts forward the method to eliminate the dynamic effect.This paper got the dynamic coefficients in different saturations according to the measured initial data;then obtained the dynamic terms in different saturations based on the calculated dynamic coefficients;and finally got the static capillary pressure after eliminating the dynamic terms.At last,the rational analysis between the results and the initial data would be introduced.It turns out that the method can not only eliminate the dynamic effects of Conventional Mercury Penetration Experiment,but also shorten the experimental period drastically,which is particularly apparent for extra-low permeability or tight sandstone oil reservoirs.At last,the paper established a two-dimensional mathematical model,considering dynamic capillary pressure,and the influence of dynamic capillary pressure on flowback efficiency and other parameters is analyzed.Then,it turns out that: when the dynamic capillary pressure effect is considered,the flowback rate of fracturing fluid can be reduced.When the formation permeability is increased or the viscosity ratio of oil and water is reduced,the flowback efficiency of fracturing fluid can be improved.This paper studies the influences of dynamic capillary pressure effect on the low permeability reservoir development,and puts forward the dynamic correction method of capillary pressure curves,it provides a new way to evaluate the effect of dynamic capillary pressure on the reservoir development and the rapid and accurate acquisition of static capillary pressure curve,which has important theoretical and practical value.