SBIR-STTR Award

The DOE is evaluating deep borehole disposal of nuclear waste, where waste packages are emplaced in the lower sections of holes drilled 3 to 5 km deep in crystalline rock. A variety of plug and backfill materials are placed in the boreholes above the waste packages as structural and sealing members. This Phase I projectl will develop an approach to forming high performance plugs of molten metal and rock with exceptional seal features, requiring minimal drill rig time. The technology uses high energy thermal sources to melt the media and bond to the borehole wall material. This approach can also address immediate leakage problems caused by abandoned oil and gas wells. Poor well sealing has caused contamination in surface and subsurface water supplies, and negatively impact the performance of reservoir regions planned for CO2 sequestration and injection. Two thermal sources will be evaluated in the Phase I effort: an electric plasma arc-melter, and controlled energetic thermite mixtures that would be reacted in place. The plasma technology has been demonstrated previously for soil stabilization and in-situ vitrification of hazardous waste. The design considered for this application is a DC torch capable of 15,000K arc temperature. The torch would be positioned at the plug location, energized, and raised at a controlled rate while granular media is added to the melt. Once the desired volume of plug has been formed, the torch is withdrawn, backfilling proceeds, and the plug cools slowly by conduction. The second approach is a controlled, energetic reaction using thermite, a self-oxidizing granular metal, to melt into the borehole wall to form a plug. An engineered charge of thermite fuel and additives would be lowered to the desired plug location, ignited by a high temperature spark, and the reaction proceeds until the fuel is consumed, forming a metal and oxide solid plug. This effort will evaluate the performance requirements and emplacement environment of the deep borehole program. Numerical models will develop predictions of the thermal and structural conditions in the plug and media. The thermite technology will be evaluated in small and intermediate scale tests of mix ratios and composition to demonstrate reaction control rate and consistency of performance. The plasma torch viability assessment will address engineering aspects of the deep borehole application. The result of the Phase I effort will be an assessment of the viability of the two different approaches, and a recommendation of which technology is suitable for Phase II development and large scale field testing.

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.