Research on the Promotion of Ultrasonic Vibration on the Development of Coal Pore Fractures and Permeability

Abstract

Ultrasonic stimulation can effectively improve the water injection conditions of coal seams. For exploring the mechanism of ultrasonic stimulation to improve the water permeability of the coal mass, the evolution of the coal mass fracture after ultrasonic stimulation was investigated by low-temperature nitrogen adsorption experiments and microscopic observation, and the changes in the pore size and relative specific surface area of the coal mass were quantitatively analyzed. The changes in the effective permeability of water-bearing coal samples stimulated by ultrasonic waves were investigated by seepage experiments. The research results showed that ultrasonic stimulation produced mesopores in the size scale range of 2-10 nm and concentrated the distribution of the mesopores, thereby increasing the pore volume and the specific surface area of the coal mass. The ring pressure gradually closed the fissures and decreased the permeability of the coal body. The injection pressure can effectively improve the effect of ultrasonic stimulation on fracturing. There is a critical value for ultrasonic stimulation, below which more small pores will be produced, and above which small pores will be rapidly converted into large pores and the permeability of the coal body will be increased.

Keywords: Ultrasonic excitation, Coal seam water injection, Pores, Cracks, Effective permeability