Preparation and enhancement mechanisms of a novel modified nanographite hybrid polymer gel for profile control in deep reservoirs

This study presents the development of modified nanographite (MG) as a crosslinking agent to enhance the temperature and salt resistance of gel systems and enable their use in deep oil and gas reservoirs. The novel nanographite hybrid crosslinked gel was formed by combining polyacrylamide (PAM) as the polymer matrix with hexamethylenetetramine (HMTA), hydroquinone (HQ), and MG as the crosslinking agents. The effects of the MG concentration on the gelation time, gel strength, and thermal stability were investigated, and the plugging ability of the nanographite hybrid crosslinked gel system was evaluated. The results demonstrated that the gelation time of the hybrid gel system comprising 0.8 wt% PAM, 0.6 wt% HMTA, 0.6 wt% HQ, and 0.2 wt% MG was 4 hours, and the maximum tolerance temperature was 154.9 °C. Furthermore, the addition of MG more than doubled the storage modulus (G') and loss modulus (G'') of the gel system. Compared to the conventional gel system without MG, the hybrid gel exhibited remarkable bound water contents as high as 21.14%, which represented a more than 5-fold improvement. Microstructural analyses revealed that the hybrid gel network contained numerous MG sheets, leading to a denser network structure compared to that of the conventional gel. The presence of the MG greatly increased the network strength and crosslinking density of the hybrid gel, thereby improving its thermal stability, temperature resistance, and salt resistance. Additionally, the hybrid gel exhibited excellent plugging performance, achieving a core plugging rate of 96.2%.