硅氧烷增稠CO2压裂液高压流变性

压裂过程中CO2压裂液的相态和流变特性复杂多变,CO2压裂液的高压流变性是压裂设计的基础。制备一种硅氧烷类增稠剂,测试其增稠性能,并通过改变增稠剂质量分数、温度、压力研究增稠后的CO2压裂液在毛细管内流动的流变特性。结果表明:8～16 MPa条件下,硅氧烷增稠CO2压裂液表现为典型的幂律流体特性;温度和压力对硅氧烷增稠的CO2流变性影响显著,随着温度升高,硅氧烷增稠CO2的表观黏度降低,稠度系数与流变指数均减小,在30～40 ℃,CO2由液态变为超临界状态,增稠CO2的表观黏度大幅度下降;随着压力升高,硅氧烷增稠CO2表观黏度升高,稠度系数增大,流变指数减小,CO2压裂液的非牛顿性增强,压力由8 MPa升高至16 MPa,硅氧烷增稠CO2的表观黏度增大62％。
The phase state and rheological properties of CO2 as a fracturing fluid during fracturing are complex, and its viscosity is fundamental for the process design. In this study, siloxane was tested as a thickener of CO2, and its thickening behavior was investigated at high pressure. The rheological property of the thickened CO2 was measured using a capillary method, in which the effects of thickener mass fraction, temperature and pressure on the viscosity of CO2 were investigated. The experimental results show that the thickened CO2can be characterized as a typical power-law fluid under pressure of 8-16 MPa, and its viscosity are influenced significantly by the variation of temperature and pressure. With increasing temperature, the apparent viscosity of the thickened CO2, the consistency coefficient and the flow index decrease. In the temperature range of 30-40 ℃, CO2 changes from liquid to supercritical state, and its apparent viscosity decreases dramatically. As pressure increases, the apparent viscosity of the thickened CO2as well as the consistency coefficient increase, while the flow index decreases, and the non-Newtonian feature of the thickened CO2 is enhanced. The apparent viscosity of the thickened CO2 can be increased by 62％ when pressure increases from 8 MPa to 16 MPa