Synthesis and performance evaluation of an efficient nano-particle viscosity reducer for enhanced heavy oil recovery in Pingfangwang Oilfield

Abstract

Unconventional resources, such as heavy oil, have become strategic alternatives to conventional reservoirs. The Pingfangwang Oilfield, a major heavy oil production site within the Shengli Oilfield in China, contains formation oil with a viscosity of 500–800 mPa·s, an oil recovery rate of 0.2–0.3 %, and a recovery factor of 20–30 %. Given the crude oil parameters and reservoir characteristics of the Pingfangwang Oilfield, this study developed a highly efficient active nano viscosity reducer. The active nano viscosity reducer exhibited a microscopic dispersion size of ∼20 nm, with a surface enriched with long-chain alkanes and polar amide groups. Laboratory results indicated that 0.3 wt% of the active nano viscosity reducer lowered the oil–water interfacial tension to 19.65 mN/m. After treatment, the water contact angle on the core surface ranged from 135.4° to 141.2°, thereby effectively enhancing interfacial activity. In comparison with conventional surfactants and commercial nanomaterials, the active nano viscosity reducer achieved an oil film stripping efficiency of >90 %, and the viscosity reduction rate in the reservoir environment exceeded 90 %. To elucidate its viscosity reduction mechanism, a molecular simulation system was developed according to the composition of the heavy oil in the field, using GROMACS software. Simulations revealed the mechanism by which the active nano viscosity reducer reduced heavy oil viscosity. Specifically, the viscosity reducer molecules disrupted the stacking structure of asphaltene molecules, formed stronger hydrogen bonds, and effectively inserted themselves into the structure, thereby breaking the asphaltene network and lowering the viscosity. This study offered both theoretical foundation and technical support for the efficient development of heavy oil in the Pingfangwang Oilfield through the application of an active nano viscosity reducer and insights into its mechanism.