Study On In-situ Continuously-mixed Clean Fracturing Fluids In Yanchang Oilfield

Hydraulic fracturing is the main stimulation measures in Yanchang Oilfield for its extra-low permeability. As a kind of working fluid during hydraulic fracturing treatments, fracturing fluid plays an important role in affecting the treatment success and postfrac well performance. Viscoelastic surfactant fracturing fluid, which is usually called "clean fracturing fluid", has been paid great attention for its good sand-carrying capability, auto-breaking in oil reservoir and non-residue.In the paper, according to geological characteristics of Yanchang Oilfield and some problems about existing clean fracturing fluids, such as difficult to gel forming in low temperature, slow to gel-broken and cannot in-situ continuously-mixed, a novel clean fracturing fluid (YCQJ-2) was prepared by screening two quarternary ammonium salt surfactants with good solubility in low temperature and optimum ratio of the surfactants and other components. Then some breakers for clean fracturing fluids, such as n-octanol, liquid paraffin, were studied and performance of YCQJ-2was evaluated. The results showed that a viscoelastic fracturing fluid would be formed when the thickening agent mixed with fresh water in certain proportion. And the clean fracturing fluid, which has the characteristics of good rheological property, easily to be broken down, non-residue and low damage to formation(<20.0%), meets requirements for hydraulic fracturing of oil reservoirs below80℃.Three wells stimulated by YCQJ-2were tested in Yanchang oilfield, and production of the wells was higher than other wells operated by guar fracturing fluid in same well groups. The test results showed that YCQJ-2clean fracturing fluid, which has a advantage of good sand-carrying capability, gel-broken controlable and low damage, can be a substitute for the guar fluid and in-situ continuously prepared during fracturing treatment process.