Study On Phase Characteristics Of Enhanced Oil Recovery By Cyclic Gas Injection In Yaha Condensate Gas Reservoir

Yaha condensate gas reservoir is the largest condensate gas reservoir which adopt high pressure cyclic gas injection development.Since the gas field enter production from October,2000,the gas production in different layers show different gas oil ratio changing and output hydrocation compositional gravity segregation,forming a fluid dynamic complex phase behavior. To determine the shape of the injection gas and condensate oil and correct understanding of phase change rule of remaining gas and remaining oil dynamic characteristics of high waxy condensate gas reservoir in the process of circulation gas injection, which is important for late development adjustment in gas field.Based on the phase study, the " whole temperature field " phase diagram test and dry gas injection expansion experiment of YH23-1-24H well five different depth of formation fluid. combining with the fluid phase equilibrium simulation theory, reservoir engineering and numerical simulation,the fluid dynamic characteristics of phase in Yaha condensate gas reservoir and gas injection process in detail and on this basis the gas injection of experimental and theoretical research of gas diffusion. The conclusions obtained are as follows:(1) The present formation fluid of YH23-1-24H well is saturation condensate gas resevior with high condensate oil content. Gravity segregation phenomenon exists in Yaha condensate gas reservoir, and the gas of deeper condensate is heavier. With the increase of depth, the phase diagram of formation fluid is moved to the right, the dew point pressure gradually increases;(2) The results of the "whole temperature field " phase diagram test show that experimental value of dew point pressure tends to be higher with the temperature decrease,and the "whole temperature field " phase diagram did not detect the critical point and does not converge, and because of experimental instrument temperature control interval is limited,"the whole temperature field" phase diagram did not detect the critical point.(3) Gas injection expansion experiments show that dry gas injection expansion well which is conducive to the solubilization of displacement. Except for the5140m sample with the injection of saturated pressure decreases, the remaining four formation saturation pressure increases with the increase of injection volume;(4) The remaining oil in formation is volatile oil phase characteristic.The saturation pressure, critical temperature and critical pressure increase with gas injection rate increases and phase diagram go to the left into the light direction.The remaining oil of5175m phase inversion occurs between60%and70%, and residual oil of5154m phase inversion occurred between30%and40%with gas injection rate increases;(5) P-X and multiple contact simulation results indicate the shallow balance oil once and multi contact miscible pressure is lower than the deep stratum balance oil;(6) The research results of phase behavior when inject dry gas in condensate show that when the gas injection pressure is near dew point, the gas condensate formation dry gas, condensate gas and condensate oil phase,and the interface becomes fuzzy and the gas-liquid interface clear and strong stability with time;(7) The results of composition profile test in the PVT tube show that the component existence of gravitational differentiation, the methane content is lower with the depth increasing, while middle components and heavy component content increased with the depth increasing, which similar to the experimental results of formation fluid of different depth.The research results clear the distribution of formation fluid of different depth, analysis the mechanism of enhanced oil recovery by gas injection and form a clear understanding of formation fluid with dry gas injection,which has a leading meaning for the late development adjustment of Yaha condensate gas reservoir.