Progress in enhanced oil recovery technologies through chemical flooding in high-temperature and high-salinity reservoirs in Shengli Oilfield

Shengli Oilfield has abundant chemical flooding resources. However， the implementation of chemical flooding technologies is difficult due to strong reservoir heterogeneity， high reservoir temperature， high formation water mineralization， high calcium and magnesium ion content， and high crude oil viscosity. After years of research and development， the theory of chemical flooding for high-temperature and high-salinity reservoirs has been established， forming a series of chemical flooding technologies such as polymer flooding， alkali-free binary compound flooding， heterogeneous compound flooding， and viscosity-reducing compound flooding. These technologies have significantly enhanced oil recovery in reservoirs with a formation temperature of 85 °C， a formation water mineralization of 30 000 mg/L， a calcium and magnesium ion concentration of 1 500 mg/L， and a crude oil viscosity of 1 000 mPa·s. In terms of basic theory， the mechanism of heterogeneous compound flooding was elucidated with “deformation passage， fluid flow diversion， balanced displacement， and coordinated transfer and washing” to enhance oil recovery， and an essential understanding of “simultaneously increasing viscosity and elasticity” and “significantly reducing adhesion work” was obtained during chemical flooding in high-viscosity reservoirs. In terms of technical application， in response to the technical difficulties of significantly enhancing oil recovery in offshore oilfields， an efficient binary compound oil displacement system was constructed， and a fully enclosed injection process was designed， forming a binary compound flooding technology for offshore oilfields. For reservoirs after polymer flooding and high-temperature and high-salinity reservoirs， a viscoelastic particle oil displacement agents were invented， and a heterogeneous compound flooding system was constructed. In addition， heterogeneous compound flooding technology was developed. For high-viscosity reservoirs， highly viscoelastic polymers and efficient surfactants were developed， and a viscosity-reducing compound flooding system was constructed， forming an alkali-free binary compound flooding technology. As of October 2023， the chemical flooding technologies have achieved the produced geological petroleum reserve of 6.3 × 108 t， an accumulated oil production of 7 701 × 104 t， and an accumulated oil increase of 3 604 × 104 t for high-temperature and high-salinity reservoirs in Shengli Oilfield， providing significant support for the sustained and high-quality development.