Experimental study on ultrasonic reduction of irreducible water saturation in low permeability reservoir

Irreducible water saturation is an important factor affecting the development effect of low permeability reservoir. Using the self-developed ultrasonic generator, kerosene was used as simulated oil, the natural low-permeability siltstone cores with different physical properties in Zhongyuan Oilfield were selected for indoor oil displacement experiment, and the effect of ultrasonic action on the saturation of irreducible water in low-permeability reservoirs was evaluated. It was found that ultrasound can further reduce the saturation of irreducible water on the basis of oil flooding. The influence of different frequencies of ultrasound on the saturation of reservoir core irreducible water is different, and there is an optimal range of ultrasonic frequency: 17 kHz ~ 125 kHz. Increasing the ultrasonic power can effectively reduce the saturation of the core irreducible water in the low-permeability reservoir, and increasing the ultrasonic power can compensate for the adverse effects caused by the increase in frequency. With the increase of ultrasonic power, the thickness of the water film first decreases rapidly, and then gradually stabilizes, the highest drop could be 67.19%. The effect of ultrasound on the reduction of the saturation of irreducible water gradually deteriorates, with the increase of temperature, and at a higher temperature of 70 °C, the ultrasonic effect can still reduce the saturation of irreducible water. The effect of ultrasound on the saturation of irreducible water at low temperature is more intense, compared with high temperature, the irreducible water saturation can be reduced by 9.26%, and the ultrasonic effect is more suitable for low temperature treatment. The effect of ultrasound on the reduction of saturation of irreducible water in reservoirs with poor physical properties is more obvious.These studies are helpful for the systematic understanding of the effect of ultrasound on low permeability reservoirs and have positive implications for improving the development effect of low permeability reservoirs.