| Hydraulic fracturing is one of the most important measures to increase the output of oil-gas field and augment injection of water-injection well. This paper mainly aims at tackling the damage problems on the low permeability, alkaline sensitivity reservoir of fracturing fluid and its broken glue during fracturing. A composite cross-linking agent which can be crosslinked with carboxymethyl hydroxypropyl guar gum under acidic conditions was synthetized. Three organic zirconium crosslinking agents were synthetized separately with zirconium oxychloride, citric acid and diethanolamine, triethanolamine, glycerol. And the crosslinking performance on carboxymethyl hydroxypropyl guar gum of them was studied under the conditation that pH was3and crosslinking ratio for carboxymethyl hydroxypropyl guar gum to organic zirconium was100:1.6. The results consist of the final materials are determined to be triethanolamine, citric acid and zirconium oxychloride. The optimum reaction conditions is:the molar ratio of oxygen chlorinated zirconium, citric acids and triethanolamine is2:1:7, the reaction temperature is from80℃to90℃, the time is4to6hours. Under the above conditions, organic zirconiums with better crosslinking properties on carboxymethyl hydroxypropyl guar gum, such as good temperature tolerance, good gel state and relatively short glue freezing time, can be obtained.Impact of the amount of thickening agent, temperature, crosslinking ratio, acidity and gel breaker on gel-crosslinking and gel-breaking were studied, while the thickener was carboxymethyl hydroxypropyl guar gum and crosslinking agent was synthetic organic zirconium. And finally freezing conditions of carboxymethyl hydroxypropyl guar gum under acidic condition was determined. Adding cleanup additive, corrosion inhibitor, iron ion stabilizer and clay stabilizer as fracturing fluid additives to the system, and then we got the basic formula of acid fracturing fluid:the mass fraction of carboxymethyl hydroxypropyl guar gum is0.4%,0.5%and0.6%, that of clay stabilizer DC-1is1.0%, that of corrosion inhibitor DSH-1is0.5%, that of cleanup additive DCZ-1is0.6%, that of iron ion stabilizer DCTW-3is0.2%, pH value is3.0, the crosslinking ratio is100:1.6to100:2.0, and that of ammonium persulfate as gel breaking agent is1.0%.In order to improve the fracturing performance, synthetic organic zirconium crosslinking agent, ethanedial and zirconium oxychloride were mixed to get compound organic zirconium crosslinking agent. Effect of the amount of thickening agent, crosslinking ratio, gel breaker, and acidity on gel-crosslinking and gel-breaking were studied, while the thickener was mixture of carboxymethyl hydroxypropyl guar gum and partially hydrolyzed polyacrylamide, and crosslinking agent was composite organic zirconium. The fracturing fluid system under acidic condition with mixture of carboxymethyl hydroxypropyl guar gum and partially hydrolyzed polyacrylamide as the thickening agent, composite organic zirconium as crosslinking agent was obtained. The basic formula of fracturing fluid is:the mass fraction of carboxymethyl hydroxypropyl guar gum is0.4%, that of partially hydrolyzed polyacrylamide is0.2%, that of clay stabilizer DC-1is1.0%, that of corrosion inhibitor DSH-1is0.5%, that of cleanup additive DCZ-1is0.5%, that of iron ion stabilizer DCTW-3is0.2%, pH value is3.0, the crosslinking ratio is100:1.8to100:2.2, and that of ammonium persulfate as gel breaking agent is1.0%.Refering to Recommended practices on measuring the properties of water-based fracturing fluid SY/T5107-2005and General technical specifications of fracturing fluid SY/T6376-2008, comprehensive performance evaluation of two acid fracturing fluid systems were made. The results show that:these two acid fracturing fluid have pefect rheological properties, good shear stability,exellent performance of encapsulation, small filter loss, less broken glue residue, and less damage to the core matrix permeability than industry standards. |
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