Effect of a Modified Silicone as a Thickener on Rheology of Liquid CO₂ and Its Fracturing Capacity

Abstract

The low viscosity of pure liquid CO2 hindered the development of CO2 fracturing technology. A modified silicone polymer was prepared as a CO2 thickener to investigate the effect of temperature, pressure, shear rate and thickener content (wt.%) on the apparent viscosity and rheology of thickened liquid CO2. In addition, CO2 fracturing capacity was evaluated with the numerical simulation of extended finite element. The results displayed that an apparent viscosity of up to 1.3 mPa·s at 303 K and 18 MPa was attained over liquid CO2 using the thickener of 3 wt.% and Toluene of 9 wt.% as additives. Compared to the commercial linear polydimethylsiloxane, a better apparent viscosity was obtained from the mixture of this prepared thickener, Toluene and CO2. The apparent viscosity decreases with increasing temperature and shear rate. By contrast, an improving apparent viscosity was revealed with an increase in the pressure from 8 to 14 MPa and thickener content from 1 to 3 wt.%. The rheological index decreased with increasing thickener content with pressure but the rise in temperature led to an increasing rheological index. The mesh structure theory of the thickener, CO2 and Toluene molecules was in this paper gives a good explanation for the discrepancy between CO2 viscosity with the thickener content, temperature, pressure, or shear rate. Compared to pure CO2, the numerical simulation of CO2 fracturing demonstrated an excellent fracturing capacity by using the thickened CO2 fracturing fluid in shale reservoirs. This investigation could provide the basic reference for the development of CO2 fracturing technology.

Keywords

• polydimethylsiloxane
• CO₂ thickener
• CO₂ fracturing technology
• oil and gas development engineering