Nanocomposite‐enhanced polymeric weak gel for conformance control in high‐salinity and high‐temperature reservoir condition

Abstract Polymeric hydrogels, known as blocking gel or disproportionate‐permeability‐reducer, have been highly successful in improving sweep efficiency and reducing excessive water cut by adjusting reservoir heterogeneity (Al‐Muntasheri and Zitha. Gel under dynamic stress in porous media: new insights using computed tomography. SPE Saudi Arabia Section Technical Symposium; 2009. Al‐Sharji, Grattoni, Dawe, et al. Pore‐scale study of the flow of oil and water through polymer gels. SPE Annual Technical Conference and Exhibition; 1999. Bai. Preformed particle gel for conformance control: factors affecting its properties and applications. SPE Reservoir Eval Eng. 2007;10:415–422). However, it remains an extremely challenging task to develop polymeric weak gel for in‐depth conformance control, simply because most in situ synthetic weak hydrogels suffer from loosely structured network and lack of efficient energy dissipation mechanism in harsh temperature environment (Bai, Leng, and Wei. A comprehensive review of in‐situ polymer gel simulation for conformance control. Pet Sci. 2022;19(1):189–202. Bhattacharya and Samanta. Soft‐nanocomposites of nanoparticles and nanocarbons with supramolecular and polymer gels and their applications. ACS Appl Mater Interfaces. 2016;8(19):21512. Bai, Zhou, and Yin. Comprehensive review of polyacrylamide polymer gels for conformance control. Pet Explor Dev . 2015;42(4):525–532). This paper introduces a low‐cost, high‐temperature resistant, polymer covalent weak gel system. Polyethylenimine (PEI) and polyethylenimine‐modified nano‐SiO 2 nano‐crosslinker were used as crosslinkers, and the performance of the gel system under high temperatures was systematically evaluated. The studied gel properties include gel formation time, gel strength, thermal stability, infrared spectroscopy, rheological properties, long‐term stability, and microstructure. Acrylamide/2‐acrylamido‐2‐methyl propane sulfonate (named QC‐9 in this paper) is used in the gel system at concentrations as low as 2250 mg/L, and the gel time can be controlled within 3–12 h by adjusting the ratio of the polymers and crosslinkers. The gel exhibits a viscosity of 100–200 mPa·s, withstands temperatures up to 130°C, and has a salt tolerance of 214818.52 mg/L, with a viscosity retention rate of ≥80% after 70 days. At a shear rate of 1 Hz, the elastic modulus ( G ′) after aging for 70 days is 1.07 Pa, and the viscous modulus ( G ″) is 0.25 Pa. The test results indicate that the gel system remains in the high‐viscosity range. Thermogravimetric Analysis tests indicate that the structural destruction temperature of the composite gel is 140°C, the activation energy of the nanocomposite crosslinking polymer weak gel is 5.2 and 16.5 kJ/mol higher for the evaporation of free water and the escape of bound water, respectively, compared to that of the PEI‐crosslinking microgel. Finally, scanning electron microscopy and atomic force microscopy were used to observe the gel's microstructure. Compared to traditional PEI crosslinked gel systems, the organic/inorganic nanocomposite crosslinked gel system has a dense, thickened network structure. Highlights Low‐cost, high‐temperature polymer gel with PEI‐modified nano‐SiO 2 . Adjustable gel formation and viscosity. High salt tolerance and long‐term viscosity retention. Stable up to 140°C with higher activation energy than PEI‐crosslinked microgel. Dense network structure with superior thermal stability.