Lignocellulosic hydrogel for profile control and water plugging in high salt reservoirs

Profile control is an effective method for enhancing oil recovery. In-situ crosslinked gels offer advantages such as easy pumping and controllable gel formation time when used as agents for profile control. However, conventional in-situ crosslinked gels suffer from the drawback of shrinkage under high salinity, and the crosslinking agent is typically organometrics, leading to permanent damage to the reservoir. Therefore, it is very important to develop a plugging agent that is resistant to high salinity and causes minimal damage. In this study, sodium lignosulfonate, known for its excellent thermal stability and biocompatibility, was crosslinked with carboxymethyl cellulose and β-cyclodextrin to create a hydrogel gf. The structures of the hydrogel were characterized using FTIR, XRD, viscosimeter and SEM. The temperature resistance, salt resistance, shear resistance, long-term stability and plugging ability of the gel gf-5 were evaluated. The results showed that, compared with the traditional underground crosslinked gel pg-1, gf-5 showed better application performance. Even at a high salinity level of 200,000 mg/L in the aqueous solution, the viscosity of gf-5 was 96830 mPa·s. Additionally, the Ca2+ present in the mineralized water formed calcium hydroxide particles with hydroxide, acting as rigid support points. This phenomenon enhanced the strength and toughness of the gel. Furthermore, the gel system maintained a stable structure at 60–90 ℃ for 120 days. In sand-packed tubes with varying permeability, the sealing rate exceeded 96 %, and the breakthrough pressure reached 8.593 MPa. SEM images demonstrated that the gel effectively enveloped the sand and adhere to the porous medium.