Development of triaxial seepage equipment for coal and rock under the coupling of pressure-motion and electro-motion

A self developed triaxial seepage equipment for coal and rock under the coupling of pressure-motion and electro-motion is introduced,and the experiments on coal with different potential gradients in the seepage equipment are performed based on the electroosmosis property of coal and rock and double electric layer principle. The equipment is composed of loading service,triaxial compression chamber,pore pressure control system,electrochemical treatment system and data measuring system. The maximum axial pressure is 30 MPa,the maximum confining pressure is 10 MPa,the maximum pore pressure is 10 MPa,and the maximum potential gradient is 15 V / cm. The dimensions of test- ed cylinder samples are 75 mm×150 mm,and the system is resistant to mild acids and solvents. The advantages and innovations of the experiment system include that the seepage experiments can be performed with the coupling of pres- sure-motion and electro-motion under triaxial stress condition. The electroosmosis coefficient can be measured and the effect of improving permeability can be revealed. The new multi-functional loading platens are designed to fix plate e- lectrode and pass fluid. The new triaxial compression chamber is designed to realize insulation and high stiffness. The results of seepage experiments show that the rate of flow increases linearly with the increase of potential gradient. The permeability coefficient is 3. 597×10-10 cm2 / (Pa·s) and the electroosmosis coefficient is 8. 211×10-5 cm2 / (V·s), which show that the rate of flow provided by unit electric potential difference is nearly 2. 49×105 times by unit pressure difference. The two-phase flow section,the residual water saturation,relative permeability and gas effective permeabili- ty increase in the treatment of electrochemical method. Therefore,the effect of coal seam water injection can be im- proved,the water saturation of coal-bed methane reservoir can be reduced and the gas production cycle can be extend- ed in the treatment of electroosmosis.