Production improvement mechanisms in combined low salinity water flooding and preformed particle gel treatment

Abstract

Low salinity water (LSW) flooding is an enhanced oil recovery (EOR) method that promotes oil displacement efficiency. Preformed particle gel (PPG) treatment is another EOR method that enhances oil sweep efficiency. Combining these methods concurrently yields greater oil recovery than using them individually. This paper investigates the mechanisms behind the enhanced oil recovery achieved through the combined PPG-LSW method via various experiments. The findings reveal several mechanisms contributing to the improvement in oil recovery factor during PPG-LSW treatment, including emulsion expansion, wettability alteration, alkaline solution creation, and pore plugging.Based on the emulsion tests, the suspension of PPG in LSW creates more emulsion content (4.8–7.3 %) in contact with the oil compared to the PPG suspension in high salinity water (HSW) (2.2–6.5 %) or PPG-free brines (1.8–5.5 %). pH measurements revealed that the pH of all brines and PPG suspensions increases by 1.5–2.5 unites after 7 days contacting with oil-saturated sandstone thin sections. According to wettability tests, PPG-LSW systems exhibit greater potential to alter the wettability of the oil-wet thin sections toward a more water-wet state. Flood tests conducted on highly permeable sandpack models (about 8 D) indicated that the medium-sized PPG particles (mesh size of 140–200) possess higher plugging capacity compared to smaller or larger-sized particles. According to the injection tests in parallel sandpack models, the nanocomposite PPG-LSW injection with a residual resistance factor (RRF) of 16.39 in highly permeable sandpacks showed greater plugging efficiency than tests conducted with HSW (RRF of 11.36) or ordinary PPG (RRF of 8.47).

Keywords

• EOR mechanisms
• PPG-LSW treatment
• Sandstone
• Plugging efficiency
• Nanocomposite PPG