Development of Thermally Formed Plugs for Deep Borehole Waste Disposal Applications

The DOE is evaluating deep borehole disposal of nuclear waste, where waste packages are emplaced in deep boreholes in crystalline rock formations. Improved well seals and plugs are needed for the challenging conditions at depth, particularly with the performance assurance required for long durations of nuclear waste isolation. Similar needs exist in the oil and gas, CO2 injection, and geothermal energy extraction fields as wells are set deeper into harsh chemical and thermal environments. Conventional well sealing cements are challenged by the conditions at depth, due to their vulnerability to chemical degradation and limited service temperature. High performance plug and seal components can be formed in place using self-propagating high temperature synthesis (SHS) processes. Solid phase metal/oxide reactions, supplemented by engineered mixtures of minerals and oxides, form ceramic like sealing features in wells. The plugs are developed by lowering hermetic packages of reactive material into the well, and reacting the charges to form molten material which fills and solidifies in the target region of the well. The reaction produces strong, low permeability, high corrosion resistant plug material. The initial viability assessment demonstrated formulations capable of achieving high compressive strength (over three times that of cement), low permeability (less than 100 Darcy) with the inherent corrosion resistance and service temperature characteristics of ceramics. The initial Phase II effort refined the plug formulations to optimize reaction product properties. Numerical simulations predicted the thermal effects of the plug on its surroundings. The plug emplacement system was designed (and is presently in fabrication), compatible with wireline systems. Small scale and full diameter plug formation tests have been performed in scaled experiments. The Phase IIa effort refines the understanding of thermite systems and additives, tailoring them for applications in uncased boreholes. Such settings are being considered for deep borehole disposal of nuclear waste. Detailed property measurements and scaled experiments will characterize the performance of these plug materials and the nature of the plug/rock interface. Comprehensive thermal, structural, and fluid numerical analyses of the plug and surrounding rock will aid in predicting coupled processes and sealing performance. Poor well sealing has caused contamination in surface and subsurface water supplies, and negatively impacts the performance of reservoir regions planned for CO2 sequestration and injection. This technology will offer sealing capabilities unattainable by traditional cement based techniques. Demonstration tests in CO2, geothermal, and conventional oil and gas wells are anticipated in subsequent phases. Key words: Nuclear waste, plugging and abandonment, sealing plugs, wellbore integrity, deep borehole disposal, thermite. This project will develop high performance sealing plugs for use in deep borehole disposal of nuclear waste and commercial wells. The technology provides a high strength, high corrosion resistant well sealing material superior to conventional cements.