Research and Application of Non-flowback Clean Fracturing Fluid in Changqing Ultra-Low Permeability Oilfield

Guar gum and high viscosity slippery water are the most widely used fracturing liquid system in ultra-low permeability reservoir of Changqing Oilfield, and which produced amount of backflow liquid. In view of its high treatment cost, incomplete gel-breaking resulting in secondary pollution of reservoirs and other problems, a clean fracturing liquid system has been invented. The experimental results show that the gluing time of the fracturing fluid is less than 20 s at water temperature 20 ℃. At the shear rate of 100 ℃ and 170 s−1, the viscosity is more than 50 mPa·s after 60 min, and the settlement speed of 20–40 mesh quartz sand under static is 0.056 mm/s. Compared with the reservoir damage of guar gum and high viscosity slippery water, the results show that the residue content of the clean fracturing liquid is 3.8% after gel-breaking, and the damage rate to the reservoir core is 8.14%. The compatibility between the gel-breaking liquid and the formation water is good and has no impact on oil and water emul. The clean fracturing fluid system has been popularized and applied in 8 wells and increased oil production 228 tons per well in that year. The average construction displacement was 2.5 m3/d, and the viscosity of the wellhead gel-breaking was 2.7 mPa·s in all test wells. The wells were put into production 2 days later, and the blowout liquid directly entered the ground collection and transmission system with three-phase separator operated normally. The practice shows that the clean fracturing fluid can realize non-flowback in the well site, which greatly reduces the cost of discharge treatment, and has good promotion value and prospects under the current environmental protection situation.