Rheological evaluation of a sodium silicate gel system for water management in mature, naturally-fractured oilfields

Abstract

Abstract Excess water production is a common problem in mature and hydrocarbon rate declining oil and gas fields. Increased water production rates reduce oil and gas production, increase the cost related with fluid lifting, handling and disposal of produced water, and negatively influence the hydrocarbon production economics. Among the various existing techniques for water control, silicate gel systems are known to be an effective and environmentally friendly method for managing water production. The gel systems usually contain two main components, the liquid silica and activator. The low-viscosity (almost like water) system, which is mixed and pumped from surface in a liquid form, is designed to gel under reservoir conditions, thus allowing sufficient time for the pumped fluids to reach the designated location from the treatment well. This work focuses on the laboratory qualification of a commercially available sodium silicate system for designing and implementing field water shutoff treatments in mature, naturally-fractured carbonate formations. Lab rheology measurements are carried on sodium silicate gel samples using the Anton Paar Rheometer MCR302. Two test modes are run with the specific purposes: the Dynamic-Mechanical (DMA) mode is employed to determine the onset of gelation (sol–gel transition time or gel point) and the viscosity increase versus time; the Amplitude Sweep (AS) mode is used to assess the formed gel's shear strength at a given viscosity. Gel point and gel strength play an important role in designing successful water shutoff treatments since the first determines the required time for the injected gelant system to gel into reservoir and other determines the forces the formed gel can withstand under shear conditions. The effects of silicate and activator (NaCl solution) concentrations, presence of divalent ions (e.g., Ca 2+ , Mg 2+ ), temperature, and gelant dilution on sol–gel transition time are investigated. A general correlation is derived that describes the relation between sol–gel transition times and silicate solution concentration, activator concentration, temperature, degree of water dilution, and concentration of divalent ions. This correlation can be used to design the recipe of the silicate system for applications in fields with treatment region temperatures in the range of 40–60°.