Experimental Study on Nano Polymer Microspheres Assisted Low Salinity Water Flooding in Low Permeability Reservoirs

Abstract

Abstract Water flooding in low permeability reservoirs generally results in severe channeling and a large amount of remaining oil. Polymer microspheres and low-salinity water are proven practical approaches for profile control and oil displacement, respectively, and their combination is expected to achieve both effects. This paper evaluates the co-injection of nano-polymer microspheres and low salinity water and its impacts on oil displacement in low permeability reservoirs. Firstly, the influence of injection velocity and injection concentration on the plugging effect of nano-polymer microspheres was evaluated by core displacement experiments. Secondly, the nano-polymer microsphere solutions were prepared using 10-time and 100-time diluted formation water to evaluate the impacts of the co-injection of nano-polymer microspheres and low-salinity water. Meanwhile, the Nuclear Magnetic Resonance T2 spectrum and imaging test were used to reveal the extent of residual oil in pores of various sizes during core flooding as well as the mechanism of oil displacement. The experimental results showed that, compared with nano-polymer microsphere flooding, the composite system of low salinity water and nano-polymer microsphere increased the recovery rate from 17.8% to 24.4%. The subsequent waterflooding stabilization injection pressure increased from 1.40 MPa to 2.43 MPa, and the corresponding plugging efficiency increased from 49.3% to 67.9%. The NMR study indicated that, in the polymer microsphere drive stage, the produced oil mainly came from the large pore spaces, accounting for 75% on average. With a lower solution salinity, the percentage of crude oil produced from the medium pore space to the total oil produced in the microsphere drive stage increased from 15% to 23%. The lower the salinity, the higher the oil produced from small- and medium-sized pores. Our results showed that polymer microspheres eliminated water channeling and changed flow direction, forcing the low-salinity water to enter smaller pores and improving the sweep and oil displacement efficiency. This study confirms the potential of synergistic flooding with low salinity water and nano-polymer microspheres in enhancing oil recovery in low permeability reservoirs. This study is the first to visually assess the impacts of nano-polymer- assisted low-salinity water flooding using NMR online tests. We confirmed that this combined technology successfully achieved both profile control and oil displacement. The nano-polymer-assisted low-salinity water flooding holds the advantages of low cost and simple construction, implying great potential in low permeability reservoirs.