Optimization of low-temperature fracturing fluid and its application in the tight sandstone gas in the Linxingshenfu Block of the Ordos Basin

A series of studies were carried out to optimize the fracturing fluid to be used in the low-temperature reservoirs in the Linxingshenfu Block of the Ordos Basin. After the reservoir characteristics were understood based on a great number of core experiments and logging data, experiments were carried out on the gel breaker system for its optimization, and low-temperature catalyst was adopted for fast gel breaking under low temperature, so as to realize fast flowback and reduce fracturing liquid-formation contact duration. Meanwhile, the gel breaker of 30−80 ℃ high-activity biological enzyme was adopted to reduce the content of residual gel breaker efficiently so as to realize the thorough removal of residual gel and ensure the flow conductivity of fractures. Considering the effect of the injection of fracturing fluid on the reservoir temperature, the dosages of various gel breakers were designed in the stepwise mode so as to realize the gel breaking in a shorter time. Then, thickener, clay stabilizer and cleanup additive were optimized based on the reservoir physical properties. And thus, a set of economic and efficient fracturing fluid system was prepared. This system has been applied in 100 layers in over 30 production wells of Linxingshenfu Block. It is shown that the base fluid has the viscosity of 18−27 mPa · s and the crosslinking time of 35−55 s. After the fracturing is completed, the well is closed for 1 h and then opened for flowing, when the viscosity of flowback fluid is 5 mPa · s, indicating complete gel breaking. Its initial production and cumulative production are obviously higher than those of simple oxidizing gel breaker which is not designed specifically, and many wells present high yield, proving that the optimized fracturing fluid system is well applicable in the Linxingshenfu Block.