Long-Term Comparison of Nanosilica and Polyacrylamide/Polyethyleneimine Gels as Water Shutoff Agents in Permeable Matrix

Summary The oil and gas industry faces numerous challenges, among which the management of excessive water production is a significant concern. Nanosilica gel is a newly developed silicate gel for water shutoff applications. No investigation has been conducted to evaluate the gel’s performance over an extended period. The objective of this study is to evaluate the long-term performance of nanosilica gel in a permeable matrix over 6 months while also comparing this performance with polyacrylamide/polyethyleneimine (PAM/PEI) gel. Coreflooding experiments were conducted to evaluate the performance of the nanosilica gel of 75/25 wt% (nanosilica/activator) and PAM/PEI gel (9/1 wt%) on carbonate core samples at 200°F. The experiment involved initial permeability assessment, gel placement, and endurance tests up to 1,000 psi. Additional measurements of computed tomography (CT) scan and nuclear magnetic resonance (NMR) were implemented: CT scans visualized density changes, and NMR measured fluid distribution in the pore system. Then, samples were aged at 167°F for 6 months, with endurance tests (up to 1,000 psi) conducted in the first, third, and sixth months to assess gel-plugging efficiency. The results demonstrated nanosilica gel’s remarkable plugging efficiency, achieving a reduction in permeability from 144.85 md to 0.001 md initially and sustaining differential pressures up to 1,000 psi with minimal leakoff rates. After 6 months, nanosilica gel maintained plugging efficiency above 99.98%, while PAM/PEI gel efficiency reduced to 99.85%. The nanosilica gel achieved slightly better long-term plugging performance than PAM/PEI gel with a maximum leakoff rate of 0.25 cm3/min in 6 months (2.165 cm3/min for PAM/PEI gel). CT scan analysis confirmed effective gel placement within the pore systems, and minimal degradation occurred over time with less significant impact on the efficiency of nanosilica gel compared with PAM/PEI gel.