Experimental Research On Dynamic Effect Of Capillary Pressure In Low Permeability Core

Water injection development is an effective exploitation measure for low-permeability reservoirs.However,due to low rock permeability and high oil seepage resistance,reservoir energy transfer is difficult and production declines quickly.Capillary pressure is one of the important factors affecting the effect of water flooding.The traditional capillary pressure model considers the capillary pressure when the oil-water interface reaches the equilibrium state.Recent studies have found that the capillary pressure has a dynamic effect in the process of oilwater two-phase dynamic seepage,which will change with the displacement speed,but the influence factors and mechanism of the dynamic effect There are still many problems that need to be further studied and improved.Taking a low-permeability water-wet reservoir as an example,firstly,the effect of mercury intrusion rate on the mercury intrusion capillary pressure curve of low-permeability cores is analyzed through the high-pressure mercury intrusion test.Then,a dynamic capillary pressure curve test device is designed based on the semi-permeable baffle method,a systematic capillary pressure dynamic effect evaluation method is established,and pseudo-dynamic coefficients are introduced to quantitatively characterize the strength of the capillary pressure dynamic effect.The oil-water dynamic capillary pressure curves under different displacement rates,different rock permeability,different oil-water viscosity ratios,and different initial water saturations were tested.Based on the experimental data,the dynamic capillary pressure mathematical model was established and the sensitivity of the corresponding parameters was established.analysis.Finally,the influence of different capillary pressure curves on the development of low-permeability reservoirs is studied by using water cut equation derivation and numerical simulation.Studies have shown that the increase of mercury ingress rate will cause the gentle section of the mercury injection capillary pressure curve of low-permeability cores to move upward,the peak of the pore size distribution curve shifts to the left,and the corresponding small pore distribution frequency increases.The pseudo-dynamic coefficient is positively correlated with displacement speed and oil-water viscosity ratio,and negatively correlated with permeability.The larger the pseudo-dynamic coefficient,the stronger the dynamic effect.When the initial water saturation is greater than the irreducible water saturation,the dynamic capillary pressure curve moves upward as a whole,that is,the larger the initial water saturation,the weaker the dynamic effect of the capillary pressure.The non-dimensional analysis of the influencing parameters of the dynamic capillary pressure is carried out to establish a function model of the pseudo-dynamic coefficients,which can better fit the experimental data.Based on this,a mathematical representation model of the dynamic capillary pressure is constructed.For lowpermeability water-wet reservoirs,considering the dynamic capillary pressure to accelerate the rise of water cut,too fast water injection and too large injection-production well spacing will reduce the degree of production and deteriorate the development effect.