Blockage removal and permeability enhancement method for coalbed methane wells by using electric pulses

Abstract

A blockage removal and permeability enhancement method for coalbed methane wells by using electric pulses is applicable to high-efficiency exploitation of coalbed methane wells. The blockage removal and permeability enhancement method includes: constructing a positive electrode coalbed methane wellbore and a negative electrode coalbed methane wellbore from the ground to a coal bed; when the gas yield declines because cracks in the coal bed are closed gradually or blocked by granular impurities as coalbed methane extraction goes on after hydrofracturing, injecting a conductive ion solution into the positive electrode coalbed methane wellbore to fill the coal bed between the positive electrode coalbed methane wellbore and the negative electrode coalbed methane wellbore with the conductive ion solution; placing a positive electrode and a negative electrode downwards to predetermined permeability enhancement portions of the coal bed in the positive electrode coalbed methane wellbore and the negative electrode coalbed methane wellbore respectively; and breaking down, by using high-voltage electric pulses discharge, the coal bed filled with the conductive plasma solution between the positive electrode and the negative electrode, where shock waves generated from a large amount of energy act on the coal bed to cause the closed cracks in the coal bed to be opened again and extend and to remove the granules blocking the cracks, such that the number of the cracks in the coal bed is effectively increased and crack connectivity is improved.

What is claimed is: 
     
         1 . A blockage removal and permeability enhancement method for coalbed methane wells by using electric pulses, comprising the following steps:
 a. constructing a positive electrode coalbed methane wellbore ( 2 ) and a negative electrode coalbed methane wellbore ( 3 ) from the ground to a coal bed ( 1 ), carrying out hydrofracturing in the positive electrode coalbed methane wellbore ( 2 ) and the negative electrode coalbed methane wellbore ( 3 ) according to conventional techniques, and performing coalbed methane extraction in the positive electrode coalbed methane wellbore ( 2 ) and the negative electrode coalbed methane wellbore ( 3 ) after hydrofracturing is completed;   b. when the gas yield declines after three months of coalbed methane extraction in the positive electrode coalbed methane wellbore ( 2 ) and the negative electrode coalbed methane wellbore ( 3 ), arranging a conductive ion solution pumping station ( 4 ) near the positive electrode coalbed methane wellbore ( 2 ), and arranging, in the positive electrode coalbed methane wellbore ( 2 ), a conductive ion solution conveying pipe ( 5 ) connected to the conductive ion solution pumping station ( 4 ); injecting a high-voltage conductive ion solution into the positive electrode coalbed methane wellbore ( 2 ) through the conductive ion solution pumping station ( 4 ): when the conductive ion solution is detected in the negative electrode coalbed methane wellbore ( 3 ), stopping injecting the high-voltage conductive ion solution into the positive electrode coalbed methane wellbore ( 2 ); arranging derricks ( 10 ) at the opening of the two wellbores, and arranging a balancing support ( 11 ) between the two wellbores;   c. placing, by using the derrick ( 10 ), a platform ( 9 ) installed with a positive electrode ( 6 ) and a high-voltage electric pulses generator ( 8 ) downwards to a predetermined permeability enhancement portion of the coal bed ( 1 ) in the positive electrode coalbed methane wellbore ( 2 ), and placing, by using the derrick ( 10 ), a platform ( 9 ) installed with a negative electrode ( 7 ) downwards to a predetermined permeability enhancement portion of the coal bed ( 1 ) in the negative electrode coalbed methane wellbore ( 3 );   d. adjusting, by using the balancing support ( 11 ), the positions of the platforms ( 9 ) in the positive electrode coalbed methane wellbore ( 2 ) and the negative electrode coalbed methane wellbore ( 3 ), such that the positive electrode ( 6 ) and the negative electrode ( 7 ) installed on the platforms ( 9 ) in the two wellbores are in close contact with wellbore walls respectively, and the positive electrode ( 6 ) and the negative electrode ( 7 ) are arranged face to face on the same level;   e. turning on a high-voltage power source ( 12 ) to charge the high-voltage pulses generator ( 8 ) through a cable ( 13 ), wherein upon reaching a set discharge voltage, the high-voltage pulses generator ( 8 ) discharges electricity to the coal bed between the positive electrode ( 6 ) and the negative electrode ( 7 ), such that the closed cracks in the coal bed are opened again and extend under shock waves caused by discharge, the shock waves also have a shearing effect on a porous medium of the coal bed, and clay binders on the surface of coal particles are shaken off, thereby removing blockage in the coal bed;   f. after multiple times of discharge, turning off the high-voltage power source ( 12 ), moving the platform ( 9 ) installed with the positive electrode ( 6 ) and the high-voltage pulses generator ( 8 ) out of the positive electrode coalbed methane wellbore ( 2 ), moving the platform ( 9 ) installed with the negative electrode ( 7 ) out of the negative electrode coalbed methane wellbore ( 3 ), and continuing to perform coalbed methane extraction in the positive electrode coalbed methane wellbore ( 2 ) and the negative electrode coalbed methane wellbore ( 3 ); and   g. when the extraction yield of the coalbed methane declines, repeating Steps c-f to carry out electric pulses discharge and coalbed methane extraction for multiple times.   
     
     
         2 . The blockage removal and permeability enhancement method for coalbed methane wells by using electric pulses according to  claim 1 , wherein the high-voltage pulses generator ( 8 ) has a discharge frequency of 10 to 60 Hz and a voltage range of 300 to 9000 kV. 
     
     
         3 . The blockage removal and permeability enhancement method for coalbed methane wells by using electric pulses according to  claim 1 , wherein a distance between the positive electrode coalbed methane wellbore ( 2 ) and the negative electrode coalbed methane wellbore ( 3 ) is 200 to 1500 m. 
     
     
         4 . The blockage removal and permeability enhancement method for coalbed methane wells by using electric pulses according to  claim 1 , wherein the conductive ion solution pumping station is capable of outputting the high-voltage conductive ion solution within a pressure range of 30 to 300 MPa. 
     
     
         5 . The blockage removal and permeability enhancement method for coalbed methane wells by using electric pulses according to  claim 1 , wherein the number of the multiple times of discharge is 15 to 100.