Excessive water production greatly affects the economic life of producing wells. Though a variety of chemicals are used by the industry to control water production, most of them are not accepted in the regions with strict environmental regulations. Based on this background information, a new, green, environmentally acceptable conformance sealant has been evaluated for its performance. This conformance sealant is a two-component system that incorporates colloidal silica and an activator.This work presents the results of laboratory experiments conducted to select an appropriate activator that could provide adequate gelation times. Sodium chloride brine with a specific gravity (SG) of 1.04 was identified as a better activator than the others considered. Static and dynamic gelation times were evaluated at different temperatures up to 150°C. The effects of pH and temperature on gelation times of the new conformance system were also studied. In the pH range of 5 to7, particle collision predominates and leads to faster aggregation and formation of gel. Hence, the gelation time is minimized in this range. At pH above 7, silica particles exhibit charge repulsion resulting from surface ionization in alkaline solution, which leads to longer gelation times. An increase in temperature causes an increase in the particle collision, leading to shorter gelation times.Carbonate core tests and dynamic sandpack-flow experiments were conducted to evaluate the treatment effectiveness and thermal stability of the system due to ageing. Results showed that this system can provide effective permeability reduction in sandpacks for extended periods of time. The conformance sealant forms a gelled mixture while passing through a carbonate core, plugging the pores and voids. Laboratory experiments also proved that the sealant can be easily and effectively viscosified using a xanthan-based polymer. This viscosified version could help in providing viscous diversion to cover longer intervals.