Preparation and application of a composite super ultra-low surface tension cleanup additive

In order to solve the reservoir damage caused by the serious "liquid resistance" effect of fracturing fluid in the process of ultra-low permeability reservoir flowback, the composite test of fluorocarbon surfactant and hydrocarbon surfactant was carried out. The synergistic effect, wettability and thermodynamic spreading of surfactant were studied to evaluate the drainage efficiency of composite drainage aids, forming an ultra-low surface cleanup additive with very low surface tension and interface tension meeting the general technical requirements of fracturing fluid. The results show that the surface tension of aqueous solution is less than 19.00 mN/m, the interfacial tension is less than 1.50 mN/m, the contact angle is 86.30 ° and the drainage rate of aqueous solution is 91.51%. Meantime, the ultra-low surface tension aid has good compatibility with fracturing fluid and other additives. The ultra-low surface tension drainage aid has been applied in two horizontal wells of Changqing ultra-low permeability oil field, the flowback rate is 73.19%～78.15%. Compared with the conventional one, the flowback rate was increased by 16.30% ～ 18.78% and has a better drainage effect.