Laboratory Experiment on Coalbed-Methane Desorption Influenced by Water Injection and Temperature

Abstract

Summary Traditional coalbed-methane (CBM) exploitation technologies, including ordinary drills, enhanced drills, water jets, and hydrofracture in the coalbed, are widely used in modern coal mining and involve high-pressure water. Because the CBM-desorption capacity decreases when using high-pressure water, the CBM output efficiency is lower than expected. To investigate the decrease in CBM desorption after water injection and the increase in CBM output after temperature is raised, an experimental system was built to simulate ideal conditions for one water-injection well per production well. The apparatus comprised a gas-liquid-injection system, a coal-sample container, a temperature-control device, a measurement system, and other auxiliary devices. Experiments on the effects of water injection and temperature on CBM desorption were carried out. The results revealed that the CBM-desorption capacity mainly depends on the water-injection pressure at constant temperature. The capacity decreased by at least 50% at less 2 MPa and became stable if the water pressure exceeded 8 MPa. Furthermore, the desorption capacity rapidly increased when the temperature was increased after water injection. Desorption reached a plateau once the temperature reached the boiling point of water, and the percentage desorption (PD) at 90°C was greater than that for free broken coal. The results demonstrate that heated hydrofracture is an effective technology with good efficiency for CBM exploitation.