In-Situ Pore Plugging Using Nanosilica-Based Fluid System for Gas Shutoff to Maximize Oil Production

Abstract

Summary A nanosilica (NS)-based fluid system was evaluated for forming in-situ glass-like material inside the matrix for permanent gas shutoff. The innovative aspect of this technique is how it turns NS into a substance that resembles glass-like material to block pores. This method involves two steps: First is pumping low-viscosity aqueous NS mixture into the formation and allowing it to gel up. Second is allowing gas production to dehydrate the NS gel to form in-situ glass-like material inside the formation. In this paper, an NS-based fluid system was assessed for pumping strategy and performance evaluation. An NS-based fluid system consists of a mixture of colloidal silica and activators. It possesses low viscosity, which assists in deeper penetration during placement. With time and temperature, it can lead to in-situ gelation to form a rigid gel to block the pore space. The NS-based fluid system was optimized using gelation tests and coreflooding tests to evaluate its performance under high-pressure, high-temperature conditions. The formation of in-situ glass-like material inside pores was analyzed using a scanning electron microscope (SEM). The 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 faster viscosity buildup as compared to a lower temperature. Before gelation, the viscosity for the NS-based fluid system was recorded as less than 5 cp at a 10 s–1 shear rate, whereas after gelation, the viscosity was increased to more than 500 cp at a 10 s–1 shear rate. Using coreflooding tests, N2 gas permeability of the Berea sandstone core was completely plugged after pumping the five times pore volume (PV) of NS-based fluid system at 200°F. During NS-based fluid system injection through the core, differential pressure was increased to only 10 psi showing better injectivity than viscous polymeric gel. The SEM images showed the presence of glass-like material filling the porosity, which showed an in-situ generation of glass-like material inside pores. After the successful placement of NS-based fluid system in one of the gas wells having sandstone formation, gas production was reduced by 65%. Polymeric fluids systems are viscous in nature, and difficult to pump deeper inside the formation, also with time, polymers tend to degrade making ineffective shutoff treatment over a period. The NS-based fluid system presented in this paper is robust, thermally stable, environmentally friendly, and can serve as an alternative to currently used conformance polymers for gas shutoff applications.