| Aim at the characteristics of low permeability and strong adsorption of coal reservoir in China, and the current situation of limited effect and scope of intensifying gas desorption, seepage and extraction rate by the stress released-method, such as borehole, hydraulic cutting and hydraulic fracturing, etc, and in the electric, electromagnetic, vibration or heat field. The electrochemical method was proposed and studied systematically to intensify gas desorption and seepage from anthracite in this paper, having gotten expected effect. The work and achievements are mainly that:(1) The experimental apparatus of intensifying gas desorption and seepage from coal by electrochemical method was developed, which is the first test device in the field of electric seepage of fluid through coal. Based on electro-osmosis theory, the test method of intensifying gas desorption and seepage was proposed, which provide a new measure for liquid driving by electro-osmosis and carrying gas seepage through coal.(2) The multi-scale measurements of pore-fracture structure of modified coal were finished. The surface area, average pore diameter, porosity, fracture connectivity and fracture numbers of coal modified in different electrolyte concentration and potential gradient were measured. The electrochemical treatment decrease surface area, increase porosity and open the mineral-filled pore-fractures. The effect laws of electrochemical treatment parameters on pore-fractures of coal were ascertained. Using fractal method, the influence of modification on heterogeneity of pore-fracture structure was characterized.(3) The surface properties of coal in the process of electrochemical treatment were studied. The wettablity, electrokinetic and surface groups of coal modified in different electrolyte concentration and potential gradient were measured. The influence of modification on capillary force and electro-osmosis force were analyzed. The microcosmic change mechanism of surface properties of coal was dissected.(4) The experiment of intensifying gas desorption from coal by electrochemical method was conducted. The ultimage desorption ratio increase from 61.84% to 82.28%, while desorption time was shortened 3/4. The effects of pH, electrolyte concentration and positive gradient on desorption properties of coal in the process of electrochemical treatment were studied. The primary and secondary sequence of influence degree of three factors was analyzed. The mechanism of intensifying gas desorption from coal was revealed.(5) The experiment of intensifying gas seepage from coal by electrochemical method was conducted. The effects of electrolyte concentration, positive gradient, pore pressure and volumetric stress on seepage properties of coal in the process of electrochemical treatment were studied. The effect of intensifying gas seepage is better when pore pressure is less than 3MPa or the volume stress is more than 16MPa. The seepage velocity and permeability coefficient of coal in the process of electrochemical treatment increased 3.12～28.57 times, and show an increased linear rule with the increase of potential gradient and show an inverted U type with the decrease of electrolyte concentration. The gas seepage equation in couple of pressure and electric treatment were established. |
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