基于含硅类增稠剂的新型超临界CO2压裂液的流变特性及岩心伤害评价

针对超临界CO2压裂液黏度低、携砂能力差的应用现状合成了含硅类增稠剂，并研究了超临界CO2压裂液的流变特性及岩心伤害情况，旨在为增稠剂的优选以及现场压裂施工提供参考依据。通过溶液聚合法室内合成了聚甲基倍半硅氧烷PMSQ和聚甲基倍半硅氧烷-醋酸乙烯酯PMSQ-VAc二元共聚物增稠剂，采用红外光谱测试验证了增稠剂样品的主要官能团，运用高压长管管流实验法测试了超临界CO2压裂液的增黏效果及其流变特性，最后评价了超临界CO2压裂液在人造裂缝天然长岩心中的滤失性、岩心伤害率。研究结果表明，随着温度、压力的升高，2种增稠剂的增黏效果均先增大后减小；随着增稠剂注入量的增大，2种CO2压裂液的黏度先增大后减小；在超临界CO2流体中，PMSQ-VAc的增黏效果相对较好，可使其黏度最大达到3.892 mPa·s；在渗透率为0.551 mD的岩心中，PMSQ-VAc与超临界CO2流体混合后压裂液的滤失系数为1.435×10-2 m/min1/2，滤失速度为0.010 m/min，岩心的伤害率为16.33%~25.36%，滤失系数和滤失速度较小，伤害程度属弱。

A New Supercritical CO2 Fracturing Fluid Containing Silicon Thickener: It's Rheological Property and Core Damage Evaluation

A silicon thickener has been developed to deal with the problems that supercritical CO2 fracturing fluid is faced with, such as low viscosity and poor sand carrying capacity. The rheological properties and core damage of supercritical CO2 fracturing fluid were studied to provide a reference for the selection of thickeners and field fracturing operation. Two thickeners have been developed through solution polymerization; one is polymethylsilsesquioxane (PMSQ) and the other, a copolymer of polymethylsilsesquioxane and vinyl acetate (PMSQ-VAc). The main functional groups of the two thickeners were characterized with IR spectroscopy. The viscosifying effect of the two thickeners in supercritical CO2 fracturing fluids and the rheological property of the fracturing fluids treated with the thickeners were measured with high pressure pipe flow experiment through long pipe. The filtration property and damaging capacity of supercritical CO2 fracturing fluids flowing through long natural cores with artificial fractures were also valuated. It was found in these studies that the thickening effect of the PMSQ thickener and the PMSQ-VAc thickener first increased and then decreased with temperature and pressure. As the concentration of the thickeners increased, the viscosity of the two CO2 fracturing fluids first increased and then decreased. Compared with PMSQ, PMSQ-VAc has better thickening effect in supercritical CO2 fluid; the viscosity of supercritical CO2 fluid can be increased by PMSQ-VAc to 3.892 mPa·s. In cores with permeability of 0.551 mD, supercritical CO2 mixed with PMSQ-VAc had a low filtration coefficient of 1.435×10-2 m/min1/2, a low filtration rate of 0.010 m/min and percent core damage of 16.33%-25.36%, which is weak.