Experimental Study On Ultrasonic Testing Of CO 2 Flooding In XX Reservoir

In recent years, ultrasonic measurement technology is being more and more applied in exploration and exploitation of petroleum and natural gas. The speed variations of ultrasonic longitudinal and transverse wave in rocks are found not only related to lithological characters of rocks such as porosity, permeability and etc., but also quite closely to types of fluid in rock blowhole and saturation conditions. Nevertheless, present conventional ultrasonic measurements on rock cores are carried out under relatively sole steady condition while very few ultrasonic dynamic measurements on cores under different loading conditions are reported. On the other hand, CO2 displacement of reservoir oil is meaningful to enhanced oil recovery. Consequently, experimental measurement and study on the relationship between the speed variations of ultrasonic longitudinal and transverse wave and saturation of two fluids in rock cores in the process of CO2 displacement of reservoir oil may be of important guiding significance for CO2 displacement of reservoir oil in oil fields.Based on the sufficient investigations of present domestic and oversea relative researches, improvement to the routine core holder currently in use has been made, and a set of ultrasonic dynamic measurement with loading parameter variable for rock cores has been developed. A series of orthogonal experiments to several cores from G block of XX oil reservoir under different loading and saturation conditions has been carried and analysis on ultrasonic wave speed variation laws have been done. After experimental measurements and analysis for single phase fluids such as saturated single phase gas, single phase water and single phase oil were finished, experimental measurements and analysis for CO2 displacement of reservoir oil have been completed. Through the measurements and analysis, the following conclusions have been obtained:(1) The reliability of the developed measuring device has been verified with the fairly excellent consistency between the ultrasonic dynamical measurement results and the steady triaxial stress measurement results;(2) The ultrasonic measurement results for rock cores show that the wave speed is influenced by porosity, permeability, mechanical parameters with regard to different rock cores, while with regard to the same core, it has been found that the higher the surrounding pressure, the quicker the ultrasonic wave, and the higher the temperature, the slower the wave. Under the different temperature loading conditions, the variation amplitude for transverse wave and longitudinal wave is different from each other while the variation tendencies are observed to stay the same.(3) The measurement results to several different rock cores under different single phase saturated fluid conditions confirm that the speed of ultrasonic longitudinal wave can be largely affected by variation of saturated fluids in the pore medium of the core as that of ultrasonic transverse wave, almost never on contrast. The measurement results to the same rock core under different single saturated fluid but equal temperature and pressure conditions display that the speed of ultrasonic longitudinal wave under the water-saturated condition is quicker than that under oil-saturated condition that is larger then, than that under CO2-saturated condition, which illustrates that the smaller the density of the saturated fluid, the slower the speed of ultrasonic longitudinal wave;(4) Experimental measurement and analysis of CO2 displacement of reservoir oil for several rock cores with similar physical property from G block. The experiment results with ultrasonic transverse wave has again verified that the speed of ultrasonic transverse wave can almost never been affected by the fluid variation in the pore medium of the core. The experiment results with ultrasonic longitudinal wave present that the speed of ultrasonic longitudinal wave tends to continuous reduction with the gradual increase of CO2 saturation and gradual decrease of oil saturation in the core. Based on linear regression treatment to experimental data with the least square method, a matched empirical formula to express the relation of the speed of ultrasonic longitudinal wave with CO2 saturation has been obtained. Meanwhile, the other matched empirical formula to express the relation of the speed of ultrasonic longitudinal wave not only with CO2 saturation, but also with core porosity, outer temperature and confining pressure as well has also been derived based on the further analysis of the relation between the speed of ultrasonic longitudinal wave and core porosity counting on the with a view to the speed reduction characteristic of ultrasonic longitudinal wave. The effectiveness of the empirical formula applied in the same aimed formation of the same block has been fairly well verified with the measurement results of CO2 displacement of reservoir oil experimental experiments with the other rock cores with similar physical property from the G block.