A comprehensive study on the enhancements of rheological property and application performances for high viscous drag reducer by adding diluted microemulsion

Slickwater fracturing has become the mainstream fracturing technology for unconventional reservoirs. High viscous friction reducer (HVFR) is considered as the substitute for conventional slickwater fracturing fluid to overcome the poor proppant carrying capability and reduce the fluid types to lower the treatment cost. In this study, diluted microemulsion (DME) is selected as a novel additive for HVFR. Comprehensive experiments were conducted to evaluate the performance enhancement of HVFR in terms of rheological properties, temperature stability, salinity stability, proppant carrying capacity and spontaneous imbibition. Experimental results show that DME can effectively increase the resistance to salinity, temperature and shear for HVFR. The drag reduction rate of HVFR with DME is up to 74% at the temperature of 90 °C. The proppant settling velocities with the addition of DME for different mesh sizes can be reduced from 47.3% to 66.7% compared to the HVFR system. With the addition of DME, oil recovery through spontaneous imbibition is improved by 24.9%. Based on the results of NMR scans and electron microscopy, HVFR and DME can form quasi-crosslinked structures when the DME acts as the adsorption point. This structure can enhance the strength of the polymer chains and generate a tighter polymer network, which can effectively improve the viscosity and viscoelasticity of the slickwater. This study suggests that DME can be selected as a promising additive for HVFR and proposes a comprehensive evaluation method to screen the additives for slickwater.