标题：DEVELOPMENT OF A NOVEL SUPERCRITICAL CO_2 FRACTURING FLUID THICKENER POLYDIMETHYLSILOXANE-VINYL ACETATE AND THE INVESTIGATION OF ITS THICKENING MECHANISMS
摘要：Supercritical carbon dioxide (SC CO_2) has been used in fracturing processes under mild conditions, but its low viscosity impeded the sand carrying efficiency and reservoir fracturing range. To tackle the existing technical challenge of low CO_2 viscosity in supercritical CO_2 fracturing, this paper presents the latest research & development (R&D) and thickening mechanism of the new silicon-based thickener polydimethylsiloxane-vinyl acetate (PDMS-VAc) for substantially thickening SC CO_2. PDMS-VAc can be prepared by using emulsion polymerization of methylcyclosiloxane, vinyl tri- ethoxysilane, and vinyl acetate at the mass ratios of 2:1:3. The functional groups and chemical structures of PDMS-VAc were evidenced by FT-IR spectroscopy and 1H NMR spectroscopy. The thickening mechanism of PDMS-VAc in SC CO_2 was explored in terms of the macromolecular irregularity theory of thickener and the dissolution theory of SC CO_2. Without the aid of any co-solvents, the viscosity of PDMS-VAc in SC CO_2 was 6.20 mPa-s at 2 wt.% thickener concentration while temperature and pressure were 50 °C and 12MPa. This thickener can increase the viscosity of SC CO_2 by 134 times, which is equal to or even exceeds the thickening effects of similar products commonly used in the oilfields. The thickening property was increased first and then decreased when the thickener concentration was increased from 1 wt.% to 5 wt.%. When the temperature and pressure were increased from 35 °C to 80 °C and 8 MPa to 20 MPa, respectively, the thickening performance of PDMS- VAC in SC CO_2 was increased first and then decreased.
