Development and Evaluation of Clear Fracturing Fluid for Low Temperature Coalbed Methane Formation

To solve the problems in fracturing low temperature coalbed methane formation, a clear fracturing fluid was developed, containing 0.4% VES, 0.15% SSN, 1.0% swelling inhibitor, 0.06% extender and 0.08% residue preventer. A low temperature contact breaker was also developed for use under 20-35 ℃. Laboratory evaluation shows that this fracturing fluid has good shear thinning capacity. The settling velocity of haydite in this fracturing fluid at 20 ℃ is 0.528 cm/min. Rate of core permeability impairment caused by this fracturing fluid is 17.1%. Formations fractured with this fluid have high fluid conductance. The fracturing fluid has low friction coefficient and some inhibition to the dispersion and migration of coal fines. After adding 0.45% low temperature contact breaker, the gel of the fracturing fluid becomes completely broken after 3-4 hours. The fracturing fluid after gel-breaking has a surface tension of 23.5 mN/m, a viscosity of 3.85 mPa·s, and a residue content of 65 mg/L. Rate of core permeability impairment caused by the gelbroken fluid which compatible very well with connate water, is only 13.5%.