Effect of nano-SiO2 on the flowback-flooding integrated performance of water-based fracturing fluids

Nanomaterials have the characteristics of reducing water molecular clusters and improving surface properties. Therefore, it can effectively enhance the oil displacement (or imbibition) effect while developing low permeability and unconventional reservoirs. Volume fracturing based on horizontal wells has become the primary technology in developing unconventional reservoirs. In this paper, we investigated the effect of nano-SiO2 on the rheology, flowback, and subsequent oil displacement performance of fracturing fluid. Results showed that nano-SiO2 had little impact on the swelling and dispersion properties of the two thickeners (i.e., guar gum and emulsion polymer). The apparent viscosity of these two thickener solutions decreased by less than 15% after aging for 24 h. Nevertheless, nano-SiO2 particularly influenced the rheological properties of guar gum based fracturing fluid. That is to say, the increase in the amount of nano-SiO2 gradually reduced the temperature and shear resistance of the fracturing fluid. When the concentration of nano-SiO2 reached 5%, the temperature and shear resistance of fracturing fluid decreased by 40%-60% in the temperature range of 80 to 100 & DEG;C. However, nano-SiO2 had little effect on the fracturing fluid's breaking time and the solution's viscosity after breaking, and the surface tension of the solution slightly increased after breaking. The fracturing fluid added with nano-SiO2 improved the performance of inhibiting clay swelling after the gel was broken. In addition, the solution after gel breaking had an excellent demulsification effect on emulsified crude oil when the concentration of nano-SiO2 was less than 0.2%. While the concentration of nano-SiO2 was greater than 0.5%, the increase in nano-SiO2 concentration gradually strengthened the emulsification between crude oil and gel-breaking fluid. Nano-SiO2 also had an excellent oil displacement effect, and it increased the recovery efficiency of primary water flooding by 9.99-13.34 percentage points. IThe field test of nanoparticle flooding and fracturing integrated technology was carried out for two wells in the Mahu tight oil reservoir of Xinjiang Oilfield, NW China. The pilot tests of the two wells were very successful, and the cumulative oil production on the 180th day after the fracturing operation was 20-50% higher than that of the comparison well. & COPY; 2023 Elsevier B.V. All rights reserved.