Study on Low Damage Seawater Base Fracturing Fluids

A salt-resistant thickening agent, BCG-1S, was developed for use inseawater base fracturing fluids.The BCG-1S is made from acrylamide, unsaturated functional monomers DM16 and AMP1 through polymerization and hydrolysis, using ammonium persulfate-sodium bisulfite as initiator.Below 10℃ 0.55%BCG-1S viscosities in 10 min.Settlent rate of single particle is 0.0324mm/s at 30℃.The viscosified tap water or seawater can tolerate contamination of 4, 000 mg/L Ca²⁺ and 2, 000 mg/L Mg²⁺.A seawater base fracturing fluid is formulated with the BCG-1S, BCG-5(a metallic ion chelator), B-55(a viscosifier), B-13(a high temperature stabilizer) and BCG-10(an encapsulated gel breaker) etc.This fracturing fluid has good carrying capacity and high temperature stability(up to 140℃).No sedimentation of solid particles is found in the fracturing fluid sample at 25℃ after 7 d, and the viscosity of the fluid remains almost unchanged.The fracturingfluid, after gel breaking, has residue content of less than 5 mg/L and surface tension of less than 26 mN/m, indicating thorough gel breaking.The flow conductivity of the fractures generated by this fracturing fluid is only reduced by 8.45%by the gel breaker solution used, which is acceptable.