High water production greatly affects the economic life of producing wells and is a serious problem in the oil industry. Excessive water cut is also responsible for many oilfield-related damage mechanisms, such as scale deposition, fines migration, corrosion, etc. Nanomaterials, such as nanosilica, in combination with chelating agents, could be used for plugging and sealing water-or gas-producing zones (bottom-water coning, gas coning, natural fractures, etc.), thus improving oil recovery.
The nanosilica used in design of water shutoff is an inorganic material with properties of no dissolution or aggregation in a liquid environment. Moreover, the entire system, including the chelating agent, is compatible with reservoir fluids and is environmentally acceptable. The particle size of nanosilica greatly influences the structural properties of the material. These aspects, in turn, exhibit a strong effect on chemical reactivity. The smaller particle size of nanosilica than previously used silica products generates increased surface area and interface atoms, which in turn increases the surface free energy and associated structural perturbations.
This paper presents the development of a novel, environmentally acceptable conformance sealant that incorporates nanosilica and an activator. Different chelating agents, which are also non-toxic and biodegradable, are used as activators in this conformance evaluation. The newly developed system can effectively prevent water and gas flow in BHSTs up to 300°F. The static gelation times were evaluated at different temperatures up to 300°F. An increase in temperature caused an increase in the particle collision, which led to lower gelation times. The effects of pH and concentration of activators on gelation times of the new conformance system were also studied. The gelation time could be controlled by adjusting the concentration of the activator, which is advantageous because it allows the sealant to remain pumpable over predictable periods of time.