Preparation and characterization of supramolecular gel suitable for fractured formations

Abstract

The excellent mechanical properties of supramolecular gel could adapt to the complex reservoir environment and had broad application prospects in the field of oil and gas drilling and production engineering. In this paper, a supramolecular gel based on hydrophobic association and hydrogen bonding was prepared by micellar copolymerization, which could be used to plug fractures and pores in formations. Supramolecular gel was a gel network system with high performance characteristics formed by self-assembly of non-covalent bond interaction. The rheological properties, mechanical mechanics, temperature resistance and swelling ability of supramolecular gel were studied. The results showed that the supramolecular gel had a dense three-dimensional network structure with open and interconnected pore structures, which could exhibit good rheological properties and strong viscoelastic recovery ability. The mechanical properties of the supramolecular gel were excellent, it had a tensile stress of 0.703 MPa and an elongation at break of 1803%. When the compressive strain was 96%, the compressive stress could reach 14.5 MPa. Supramolecular gel also showed good temperature resistance and swelling properties. At the aging temperature of 135 °C, supramolecular gels still maintained good gel strength, and it only took 12 h to reach the equilibrium swelling ratio of 35.87 in 1% NaCl solution. It was also found that supramolecular gel in low concentration saline (1% NaCl solution) showed relatively faster swelling than high concentration saline (25% NaCl solution). The swelling process of the supramolecular gel was non-Fick diffusion (type Ⅱ). This indicated that the organic/inorganic permeability network was well formed. Therefore, the diffusion rate of small molecules could be guaranteed to be equal to the relaxation rate of large molecules before and after the phase transition temperature. In addition to the diffusion of water molecules, the swelling process of the supramolecular gel was also affected by the relaxation of gel network and polymer chain segment, the interaction between water molecules and polymer network and the groups of polymer network and other factors. Supramolecular gel particles could be used as plugging materials for drilling fluids, which had excellent ability to plug formation fractures and pores. The plugging ability of the supramolecular gel was up to 6.7 MPa for 0.5 mm fracture width, and 9.6 MPa for porous media with 5 mD permeability. Compared with HT-PPG gel particles commonly used in oil fields, supramolecular gel particles had better plugging ability on fractures and porous media. The development and application of supramolecular gel had far-reaching significance for promoting the functional application of polymer materials in drilling and production engineering.