New Generation Silicate Gel System for Casing Repairs and Water Shutoff

Abstract

Abstract The SPI gel system is a low cost, multi-component silicate based gel, mixed at surface and pumped as a single stage with controlled gel times ranging from a few hours to several days to form a variety of resilient gels from hard, "ringing" to soft, weak gels. This new environmentally friendly, "green" gel system uses low chemical concentrations and no heavy metals for a low overall cost. SPI gel systems were developed to solve water conformance problems on injector and producer wells, for casing leak repairs and other applications. The SPI pre-gelled system has a low viscosity for deep penetration of leaks and tight formations and it can be designed for special applications. Well over 1000 lab tests were performed to evaluate the SPI gel system at the RTA Systems laboratory. Further rheological testing was conducted and is in progress at the Tertiary Oil Recovery Project at the University of Kansas. Lab tests are continuing to establish a minimum 5-year life of the SPI silicate gels for permitted injection well repairs for regulatory Mechanical Integrity Testing (MIT) requirements. This paper presents the laboratory discovery work and the early 3rd party confirmation work. These gels are now being field-tested for waterflood conformance and casing repairs. Introduction Permeability and reservoir heterogeneity variations significantly affect the sweep efficiency or reservoir conformance of oil recovery processes. Over the last 40 years, several methods1–4 were proposed for improving reservoir conformance using crosslinked polymers to mitigate the problems associated with reservoir heterogeneity. Two methods are commercially used to crosslink polyacrylamides based on the controlled availability of multivalent metal ions (generally chromium) resulting in the crosslinked polyacrylamide. Key issues with the crosslinked polyacrylamide systems includeenvironmental and safety issues over the heavy metal crosslinking agent chromium,limited penetration depth,polymer shear degradation,polymer absorption on the reservoir surface, (4) polymer gel time, (5) polymer precipitation under harsh reservoir conditions. Application of silicates in different industrial areas is enormous and well documented. Injection of silicate solutions into reservoirs with the aim at enhancing the recovery factor through a diverting effect was first proposed in 1922.5Acidic gel systems are the oldest and most commonly employed techniques that employ silicates. These gels are more accurately described as precipitation type gels since they are extremely brittle with no elasticity. In the early 1960's, sodium silicate and glyoxal were combined to make various hard cement-like coatings on substrates. At low concentrations, a firm gel was obtained that lacked cohesiveness and was not as hard as cement. In 1964, Gandon6 took the mission one step further citing sodium silicate reactions with other organic compounds to make cement like substances used to create very hard consolidated soils for constructing bridge and dam structures. In the last 50 years, numerous inventors7–9 patented various sodium silicate systems to make gels for use in plugging high permeability areas of oil and gas producing reservoirs. Krumrine and Boyce's paper10 compiles numerous papers and patents on sodium silicate chemistry as applied to oil field and grouting applications. They also drew attention to a controversial fact that the silicate use was inequitably neglected in commercial applications in favor of polymer treatments in practice at the time.