Pressure relief and permeability enhancement technology of gas-liquid composite fracturing in low permeability coal seam

Abstract

In order to solve the problem of difficult extraction of low permeability high gas coal seams, based on the existing research results, a coal seam gas-liquid composite fracturing pressure relief and permeability enhancement technology was proposed through theoretical analysis. The technology mainly relies on the high-pressure acid and high-pressure alkali liquid injected into the borehole to crack the coal seam, while the high-pressure CO2 gas generated by the liquid reaction plays a role in displacing and increasing the permeability; the technology has the dual effect of pressure relief and permeability increase, and cuts off the preparation stage of outburst; the ground stress field and gas pressure field are reduced and homogenized after the coal seam fracturing and permeability increase, and the extraction efficiency is improved. The outstanding features of the technology are: the reaction products are neutral and easy to dissolve, a small amount of acidification and permeability increasing products support the effect and weaken the fracture closure; the reaction temperature rises to avoid excessive CO2 adsorption and permeability reduction; the technology combination is flexible and changeable.

Keywords

• coal and gas outburst
• low permeability
• gas-liquid two-phase
• compound fracturing
• mechanism