Study On Low-damage Polyhydroxy Alcohol Fracturing Fluid System

Hydraulic fracturing is an important measure for increasing the output of oil-gas field and augmenting injection of water-injection well. As the development of oil-gas field goes further, fracturing objects has tumed form the main oil-gas reservior to the external low-peremable oil-gas reservior currently, at the same time, the damage of water-based gum gelling fracturing fluid has become incresingly prominent problem. The paper presented a low molecular polyhydroxg alcohol as the thickener of a water-based fracturing fluid system, developed a new low-damage and low-cost water-based fracutring fluid system for low-peremable reservior reconstruction to reduce the harm of fracturing fluid to oil-gas reservior.Based on the known of organic boron, three different types of organic boron were synthesized through experiments, in which boron acid was the main agent, three different polyhydric alcohols were ligands, toluene was solvent and water-carrying agent. The effect of ratio of raw materials and solvent amount on the yield of synthetic products were discussed, the reaction conditions were optimized. The application performances of three synthetic organic boron aqueous solutions used as crosslinker were examined by taking the delayed cross-linking time and shear stablity as indictor, the organic boron OB-I with the performances of stablization to tempeture and the resistance to shear force was filtered as the main crosslinker of polyhydric alcohols fracturing fluid system. To regulate the delayed cross-linking time of OB-I, a delayed regulator and a alcohols solubility promoter were added in it and incorporated, at last, crosslinker FOB used in polyhydric alcohols fracturing fluid system was obtained.The fracturing fluid formulations suiting for the stratum tempeture of 60℃and 70℃were identified by single-factor experiment, in which a low molecular polyhydic alcohols was thickener, organic boron FOB was crosslinker, and adding pH adjusting agent. And based on this formulation of the fracturing fluid, the compund of polyhydroxy alcohol and guanidine as thickener was studied, the proportion of the complex compound and the basic formula of fracturing fluid were determined. A released acid agent HD was selected as the breaker of polyhydroxy alcohol fractaring fluid through gel-breaking experiment, the result showed, when breaker amount is 0.5% under 60℃, the fracturing fluid could be breaken from gell to water, viscosity is 2.70mPa·s.Reference to water-based fracturing fluid performance evaluation SY/T 5107-2005 and general technology condition of fracturing fluid SY/T 6376-1998, the comprehensive performances of polyhydroxy alcohols fracturing fluid and complex fracturing system were estimated, and compared with the conventional fracturing fluid. The result showed that:the polyhydroxy alcohol fracturing fluid system have perfect rheological properties, good shear stability, small filter loss, better performance of suspending sand than conventional guanidine gum fracturing fluid, low residue content and little reservoir demage, and it was suitable for the low-permeable oil-gas field reservior fracturing.