Experimental Study of Nanosilica Gel as a Water Shut-Off Agent in Fractured Reservoirs

Excessive water production in the oil industry is a persistent challenge, impacting operational costs and environmental concerns related to water disposal. Fractures and channels are widely recognized as significant sources of water production in reservoirs produced under a water drive mechanism. Recent investigations have shown the efficiency of nanosilica gel in mitigating water production in high-permeability formations. However, these studies have not thoroughly evaluated its performance in addressing fractures as potential pathways for water migration. Therefore, this study investigates the performance of nanosilica gel in fractures and channels, which are major sources of water production. Four carbonate core samples of 1.5-inch diameter and 3-inch length were utilized: two containing an induced fracture and the other featuring an open channel. Core samples underwent core flooding experiments, computed tomography (CT) scans, and nuclear magnetic resonance (NMR) T₂ measurements. The coreflooding system was utilized to treat carbonate samples with two gels: a nanosilica gel solution comprising 75 (wt %) nanosilica and 25 (wt %) activator, and polyacrylamide/polyethylenimine (PAM/PEI) gel of (9/1) wt %. The injection of a sufficient volume of the gel ensured successful placement and curing at a high temperature of 200 °F. The nanosilica demonstrated exceptional plugging efficiency, with a remarkable 100% reduction in permeability and enduring durability under varying differential pressures, reaching up to 1000 psi. This performance was at the same level of plugging efficiency obtained with PAM/PEI gel with 9/1 (wt %) concentration. CT scans and NMR analysis further confirm the uniform distribution of both gels and the successful displacement of brine from the fractures and channels.