Abstract
Coal-bed methane (CBM) is a new type of clean energy, which is abundant in China. Rational development and use of CBM can not only reduce the occurrence of mine disasters but also alleviate energy shortages. However, the “high storage capacity and low-permeability” characteristics of China’s CBM have hindered the realization of industrialized CBM production. To study the effect of microwave radiation on the permeability of coal reservoirs, a seepage experiment under different stress and microwave radiation conditions was carried out by using the seepage experiment system of gas-bearing coal under microwave radiation developed by the authors. The relationship among different microwave powers, different irradiation times, different energy inputs, and coal permeability was explored. The results show that the microwave power effect and the temperature effect promote coal permeability. Under microwave radiation, the relationship between permeability and effective stress followed a negative exponential function, and all R-squared values were greater than 0.97. The permeability increased monotonically with increasing microwave power and irradiation time, and the linear fitting slope of the rate of increase in the low-effective-stress area was greater than in the high-effective-stress area. Under the same energy input, permeability increased with rising microwave power. The peak temperature of the coal sample also increased with increasing power. When the microwave power increased to a certain range, the permeability growth of the coal sample was the greatest, and the temperature gradient of the coal-sample temperature field was the steepest. The coal sample experienced the optimum microwave radiation power under the action of microwaves to achieve the permeability enhancement effect of microwaves on the coal sample. The experimental results provide a theoretical reference for applying microwave radiation technology in coal-bed methane extraction.
Highlights
Energy is the basis of economic and social development and the main factor affecting such development
Where k is the permeability; L is the length of the coal sample; qout is the gas flow rate; μ is the dynamic viscosity coefficient of the gas (Pa · s); A is the crosssectional area of the coal sample; Pin is the gas inlet pressure (MPa); and P0 is the standard atmospheric pressure (MPa)
E effective stress is an important factor affecting deformation of the coal sample. e mathematical tensor of the effective stress on the coal sample can be expressed as σi′j σij − αpδij, (2)
Summary
Energy is the basis of economic and social development and the main factor affecting such development. To develop coal-bed methane in low-permeability coal seams, researchers in China and elsewhere have carried out many research studies and achieved a certain number of results. E results showed that it is feasible to use gas displacement technology to extract coal-bed methane from low-permeability reservoirs in China. To achieve industrialized production of CBM, it is urgent to combine the research results of scientists around the world to develop a method of promoting gas dissolution and increasing permeability that can improve China’s special coal-reservoir structure. Some researchers in China have conducted experimental studies on the adsorption and desorption characteristics of gas in coal after microwave application and found that microwaves can promote desorption of coal-bed methane from coal [25, 26]. Erefore, combined with the microwave radiation triaxial percolation system developed in this study, this paper describes an experimental study on the percolation characteristics of coal seams under the impact of microwave radiation. e test results have a certain reference value for application of microwave radiation to production of coalbed methane
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