Systematic Approach to Develop a Colloidal Silica Based Gel System for Water Shut-Off

Abstract Undesirable water production can significantly affect the economic life of producing wells. Excess water production results in loss of productivity, corrosion, and scaling. Also, the need for water handling facilities and reinjection of unwanted water can further add to the total cost of the project, which consequently increases the cost of production. In offshore operations, produced water can have an adverse impact on the environment. The use of a colloidal silica based fluid system was developed for water shutoff application. A systematic experimental study was conducted to evaluate the effect of key parameters on the gelation properties of this system; that is: particle size, pH, temperature, and silica concentration. Also, the effect of different salts, as an activator agent, were tested to initiate in-situ gelation of colloidal silica. The performance of this system was evaluated by conducting static gelation tests as well as high pressure and high temperature viscosity measurements up to 150°C. Colloidal silica solutions exhibit low viscosity. Proper selection of suitable activators can lead to in-situ gelation and formation of a high viscous gel to block the pore space. The permanent sealing of formation porosity can be achieved by building the viscosity of colloidal silica. The colloidal silica gelation time can be tailored by varying the activator type and concentration to match the field operation requirements. Kinetics of colloidal silica gelation at elevated temperatures showed quicker viscosity buildup. The gelation time can be varied by controlling the initial pH of the system. A stable system and good dispersion was achieved for the colloidal silica solution without using an activator, as confirmed from the Zeta potential results. Increasing the salt concentration and temperature or lowering the pH of the system results in unstable system that triggers the gelation process. The existence of more than one of the above factors (i.e., salt, temperature, and lower pH) results in further reduction in gelation time. Colloidal silica has a low viscosity and can penetrate deeper into the formation matrix before transforming into a gel. The fluid system presented in this paper was developed to address the needs of water shutoff applications. The environmentally friendly system is comprised of two components; colloidal silica and an activator.