页岩气低伤害超临界CO2凝胶压裂液研究

针对常规水压裂液会对页岩造成伤害，容易产生水锁，不易返排，还造成水资源消耗和污染环境等问题，制备了低伤害二氧化碳凝胶压裂液。将自备的F2EU和F4EU增稠剂加入到超临界CO₂基液中，探究两种增稠剂的加入量对CO₂凝胶压裂液黏度的影响，综合考虑成本与效果，优选了2%的F4EU增稠剂，可将CO₂的黏度增至15.4 mPa·s。研究了温度、压力以及剪切速率对凝胶压裂液黏度的影响。实验结果表明，随着温度升高黏度总体降低，但中间出现一个短暂升高阶段；随着压力上升压裂液黏度增加；随着剪切速率的增加压裂液黏度下降，属于一种典型的剪切变稀的假塑性流体。F4EU超临界CO₂凝胶压裂液的平均伤害率为1.39%，远远小于常规压裂液对岩芯的伤害率。实验表明，F4EU超临界CO₂凝胶压裂液在页岩气压裂开采中具有良好的应用前景。

Low Damage Supercritical CO2 Gel Fracturing Fluid for Shale Gas

Considering that conventional hydraulic fracturing fluid could cause damage to the shale, easy to produce water lock, not easy to flowback, and cause problems such as water consumption and environmental pollution, low damage carbon dioxide gel fracturing, the self-made F2EU and F4EU thickeners were added to the supercritical CO₂ base solution to research the effect of the dosage of the two thickeners on the viscosity of supercritical CO₂ gel fracturing fluid. Taking into account the cost and the efficiency, the optimum thickener was 2% F4EU, which could increase the viscosity of CO₂ to 15.4 mPa·s. The effects of temperature, pressure and shear rate on the viscosity of gel fracturing fluid system was studied. The experimental results showed that the system viscosity decreased with the increase of temperature, but there was a brief rising stage in the middle and the fracturing fluid system viscosity increases with the increase of pressure; but the fracturing fluid viscosity decreased with the increase of shear rate, which proved to be a typical shear thinning pseudoplastic fluid. The average damage rate of F4EU thickened supercritical CO₂ gel fracturing fluid was 1.39%, which was much less than the damage rate of conventional fracturing fluid. The researches showed the F4EU thickened supercritical CO₂ gel fracturing fluid would have a good application prospect in shale gas production.