Energy & Fuels, Vol.34, No.5, 5766-5776, 2020
Nanocellulose-Strengthened Particle Gel for Conformance Control in Fractured Tight Formations. Part I: Preparation and Mechanical Stability
Conformance control in fractured tight formations remains a challenge because of large permeability contrasts between fractures and the matrix. Therefore, there is an emerging interest in particle gels that possess favorable mechanical properties and low production costs. To address this issue, we proposed a kind of nanocellulose-strengthened particle gel, named NC-st-PG, which was prepared by sparsely interpenetrating cellulose nanofibrils (NCF) and nanocrystals (NCC) respectively into a polyacrylamide (PAAm) matrix. The characteristics of NC-st-PG from the chemical structure to mechanical and thermal stability were investigated thoroughly. We noted that the PAAm network was noticeably strengthened and toughened by introducing stiff NC segments without compromising the elasticity of the gels. The optimum amount of NCF and NCC in the PAAm was found to be 0.1 wt %. We cycled the deformation and observed that NC-st-PG exhibited fatigue-resistance and remained highly elastic after 10 cycles of stress load and unload. In addition, the swelling and thermal decomposition of NC-st-PG were restrained by the presence of NCC and NCF. These characteristics render NC-st-PG superior stability under consecutive shearing in fractures and are indicative of the efficiency and durability of conformance treatment using NC-st-PG. The results of this study supplement earlier observations and provide an alternative to conventional gels to address conformance issues in tight formations.