新型CO2压裂用增稠剂的增稠性能及机理

为了改善CO₂压裂液的黏度，需要加入适合该体系的增稠剂，笔者以八甲基环四硅氧烷与四甲基四乙烯基环四硅氧烷为原料，六甲基二硅氧烷为封端剂，五甲基二硅氧烷为支链添加剂，四甲基氢氧化铵与氯铂酸为催化剂合成了一种支链聚硅氧烷CO₂增稠剂，并对该增稠剂的结构进行红外光谱（FT-IR）分析。此外，对加入支链聚硅氧烷增稠剂的CO₂压裂液的性能进行了研究。结果表明，在20℃、7%的加量下，加入相同分子量的聚二甲基硅氧烷CO₂压裂液的黏度为1.66mPa×s，而加入硅氧烷增稠剂CO₂压裂液的黏度为6.67 mPa×s，硅氧烷增稠剂增稠效果明显；CO₂压裂液的黏度随着增稠剂浓度的增加而显著改善，增稠剂的浓度在1%~3%时，随压力从8 MPa升高到14 MPa，含支链聚硅氧烷增稠剂的CO₂压裂液黏度升高明显。然而，压裂液的黏度随温度的增大明显降低。新型支链聚硅氧烷增稠剂比聚二甲基硅氧烷的增稠效果明显优异，与国外产品的增黏效果相差较小。同时提出了聚硅氧烷对CO₂压裂液的增稠机理。 

Thickening Performance and Thickening Mechanism of a Viscosifier for CO2 Fracturing Fluid

CO2 fracturing fluid requires suitable viscosifiers to increase its viscosity. A branched polysiloxane was developed for use in CO2 fracturing fluid as a viscosifier. The branched polysiloxane is synthesized with octamethylcyclotetrasiloxane and tetramethylt etravinylcyclotetrasiloxane as raw materials, hexamethyldisiloxane as blocking agent, pentamethyldisiloxane as branching additive, and tetramethylammonium hydroxide and chloroplatinic acid as catalyst. The molecular structure of the viscosifier was characterized using FT-IR method, and CO2 fracturing fluid treated with the viscosifier studied for its performance. It was found that, at 20 ℃, the viscosity of a CO2 fracturing fluid treated with 7% polydimethylsiloxane was 1.66 mPa·s, while the viscosity of another CO2 fracturing fluid treated with 7% synthesized branched polysiloxane viscosifier of the same molecular weight (as that of the polydimethylsiloxane) was 6.67 mPa·s, showing that the branched polysiloxane viscosifier is a better viscosifier for CO2 fracturing fluid. The viscosity of the CO2 fracturing fluid increases with increase in the concentration of the branched polysiloxane viscosifier in the fracturing fluid. At viscosifier (branched polysiloxane viscosifier) concentration of 1% to 3%, when pressure is increase from 8 MPa to 14 MPa, the viscosity of the CO2 fracturing fluid increased remarkably. On the other hand, the viscosity of the CO2 fracturing fluid decreases greatly as temperature increases. The branched polysiloxane viscosifier synthesized in this study is able to better increase the viscosity of CO2 fracturing fluid than polydimethylsiloxane, and has thickening ability that is almost the same as that of viscosifiers manufactured abroad. This paper also discusses the thickening mechanisms of the branched polysiloxane.