SiO2 synergistic modification of siloxane thickener to improve the viscosity of supercritical CO2 fracturing fluid

Supercritical carbon dioxide (SC-CO2) fracturing technology has the advantages of CO2 storage and waterless fracturing and has great application potential in the development of unconventional oil and gas resources. However, the low viscosity of SC-CO2 limits the development of this technology. This paper investigates the synergistic effect of nanomaterials on a developed thickener (HBD-2, high branched D4H). The research results show that among the five micro/nanomaterials Cu-BTC, SiO2, MCC, MWCNTs, and TiO2, only SiO2 has a good synergistic effect on the HBD-2/SC-CO2 system, and significantly improves its thickening, temperature resistance, temperature resistance and shear resistance. At 60s−1, 305.15 K and 10 MPa, 5 wt.% HBD-2 + 1 wt.% SiO2 increased the apparent viscosity of SC-CO2 to 5.82 mPa·s(The viscosity of 5 wt.% HBD-2 under the same conditions is 4.48 mPa·s). The apparent viscosity of SC-CO2 is positively correlated with pressure and SiO2 dosage and negatively correlated with temperature and shear rate. The SiO2/HBD-2 system can effectively avoid clay swelling and can change the water wetness on the core surface to neutral wettability. In addition, we also studied the mechanism of SiO2 in HBD-2/SC-CO2 thickening system by RDF(radial distribution function). The results show that the introduction to SiO2 shifts the peak position of the system to the left and enhances the peak intensity. The macroscopic manifestation is the enhancement of the apparent viscosity of HBD-2/SC-CO2.This paper proves the feasibility of nanomaterials to synergize SC-CO2, and provides a new thread for the research and development of SC-CO2 thickeners in the future.