Study On The Average Capillary Pressure Curve Of X Gas Reservoir

The deeper the understanding of low permeability reservoir is,the more important the data on capillary pressure of reservoir becomes:it is an underlying data for studying microscopic pore structures of reservoirs;meanwhile,capillary pressure controls fluid flow,and its capillary behavior influences the percolation mechanism of multiphase flow in media of rock pore.The capillary pressure curve of rock measured by experiment is not representative enough,and it needs to be leveled off and contrasted integrally in practical application of an oil field.The application the half empirical formula-J function-is restricted and inaccurate.In view of this,the paper studies the average capillary pressure curve of a low permeable tight sandstone gas reservoir by means of laboratory experiment,model derivation and programing.The research is as follows:(1)Fully investigated the present research situation of capillary pressure domestically and abroad from three aspects:the definition of capillary pressure,the obtainment of capillary pressure curve and the application of capillary pressure curve,and drew upon the shortcomings of those researches to pave ways for the further research of the paper.(2)Analyzed the internal structure of the low permeable tight sandstone core via experiments of ordinary thin plate,cast thin plate and scanning electron microscope;studied the shape and characteristic parameters of capillary pressure curve of low permeable tight sandstone gas reservoir in China via mercury intrusion experiment.(3)Deduced the J function of the average capillary pressure based on the model of rock capillary bundle,generated J function from mercury intrusion and displacement experiment data of the low permeability tight sandstone gas reservoir,compared,analyzed and optimized various generating functions,and then the average capillary pressure curve of the reservoir was obtained.(4)Selected mercury intrusion and displacement experiment data of the low permeable tight sandstone gas reservoir,determined the average capillary pressure curve by curve encryption method,and detailed the mathematical principle of the method,the solving steps by examples and the accuracy judgment.(5)Obtained the characteristic value of rock pore structure by integral method based on the average capillary pressure data obtained from the fourth chapter of the paper,and manifested the advanced and accuracy of this method comparing with the results of traditional graphical method and the moment method.(6)Established the numerical simulation mechanism model of the low permeable tight sandstone gas reservoir,compared and analyzed the influence on the numerical simulation results(yield,gas/water ratio,formation pressure)of the gas reservoir by inputting J function of the third chapter and various average capillary pressure curves obtained in the fourth chapter by curve encryption method.The paper systematically studied the average capillary pressure curve of the low permeability tight sandstone gas reservoir from the graphic analysis on the low permeability tight sandstone core,the mercury intrusion experiment,the derivation of J function of the average capillary pressure,the comparison analysis of the generating functions,as well as the proposal of curve encryption method to obtain the average capillary pressure curve of the reservoir.The paper laid a theoretical foundation for the improvement of J function by deducing J function of half empirical formula;and provided accurate capillary pressure data for practical application in oil field by proposing curve encryption method to obtain the average capillary pressure curve of the reservoir.