Experimental study on ultrasonic irradiation for enhancing coalbed methane recovery

Area of Science:

• Geosciences
• Energy Engineering
• Materials Science

Background:

• Low-permeability coal reservoirs pose challenges for efficient gas recovery.
• Traditional methods often struggle with gas adsorption and migration in coal.

Purpose of the Study:

• To investigate the effectiveness of a novel ultrasonic irradiation method for enhancing gas recovery from coal.
• To analyze the impact of ultrasonic irradiation on coal permeability, desorption, and internal structure.

Main Methods:

• Development of a specialized triaxial stress ultrasonic irradiation test apparatus for coal.
• Conducting permeability and desorption experiments on coal samples under varying ultrasonic conditions.
• Utilizing X-ray computed tomography (CT) to visualize crack expansion.
• Developing a permeability and desorption model incorporating effective sound pressure.

Main Results:

• Ultrasonic irradiation gradually improved coal permeability, with variations influenced by irradiation duration.
• The Klinkenberg effect was observed, showing a complex relationship between permeability and gas pressure.
• Higher sound intensity significantly enhanced coal desorption, yielding greater gas volumes.
• X-ray CT revealed expansion of meso- and macro-cracks in coal samples post-irradiation.
• Coal temperature and strain exhibited a distinct "J-shaped" curve during the process.

Conclusions:

• Ultrasonic irradiation is a viable method to enhance gas recovery from low-permeability coal reservoirs.
• The developed model accurately describes the improvement in coal seam gas production capacity under ultrasonic treatment.
• Understanding the interplay of permeability, desorption, and fracture dynamics is crucial for optimizing gas extraction.