Muon tomography has been used to seek hidden chambers in Egyptian pyramids and image subsurface features in volcanoes. It seemed likely that it could be used to image injected, supercritical carbon dioxide as it is emplaced in porous geological structures being used for carbon sequestration, and also to check on subsequent leakage. It should work equally well in any other application where there are two fluids of different densities, such as water and oil, or carbon dioxide and heavy oil in oil reservoirs.
Continuous monitoring of movement of oil and/or flood fluid during enhanced oil recovery activities for managing injection is important for economic reasons. Checking on leakage for geological carbon storage is essential both for safety and for economic purposes. Current technology (for example, repeat 3D seismic surveys) is expensive and episodic. Muons are generated by high energy cosmic rays resulting from supernova explosions, and interact with gas molecules in the atmosphere. This innovation has produced a theoretical model of muon attenuation in the thickness of rock above and within a typical sandstone reservoir at a depth of between 1.00 and 1.25 km. Because this first simulation was focused on carbon sequestration, the innovators chose depths sufficient for the pressure there to ensure that the carbon dioxide would be supercritical.
This innovation demonstrates for the first time the feasibility of using the natural cosmic ray muon flux to generate continuous tomographic images of carbon dioxide in a storage site. The muon flux is attenuated to an extent dependent on, amongst other things, the density of the materials through which it passes. The density of supercritical carbon dioxide is only three quarters that of the brine in the reservoir that it displaces. The first realistic simulations indicate that changes as small as 0.4% in the storage site bulk density could be detected (equivalent to 7% of the porosity, in this specific case). The initial muon flux is effectively constant at the surface of the Earth. Sensitivity of the method would be decreased with increasing depth. However, sensitivity can be improved by emplacing a greater array of particle detectors at the base of the reservoir.
This work was done by Max Coleman of Caltech; Vitaly A. Kudryavtsev, Neil J. Spooner, and Cora Fung of University of Sheffield; and Jon Gluyas of University of Durham for NASA’s Jet Propulsion Laboratory. NPO-48328
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Differential Muon Tomography to Continuously Monitor Changes in the Composition of Subsurface Fluids
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Overview
The document discusses a project by NASA's Jet Propulsion Laboratory (JPL) focused on using Differential Muon Tomography to monitor changes in the composition of subsurface fluids. The primary objective is to assess whether this technique can effectively quantify changes in bulk fluid compositions, particularly for applications in CO2 storage and enhanced oil recovery.
Cosmic ray muons, which are generated in the upper atmosphere by cosmic-ray particles, are utilized in this approach. These muons penetrate the Earth and their flux is attenuated by the density of the materials they pass through, allowing for the detection of changes in fluid density. This method offers a potential solution for monitoring supercritical CO2 emplacement and leakage, which is critical for geological CO2 storage projects. Current monitoring methods, such as repeat 3D seismic surveys, are expensive and episodic, highlighting the need for a more continuous and cost-effective solution.
The project aims to develop a new technology that can be integrated with existing methods, such as InSAR (Interferometric Synthetic Aperture Radar), which is already used for monitoring surface deformation related to CO2 storage. By coupling muon tomography with InSAR, JPL seeks to enhance its capabilities in this rapidly expanding field.
The document outlines the feasibility of using muon tomography for monitoring subsurface fluid changes, supported by modeling density profiles of geological sections. The researchers validated their assumptions regarding muon fluxes and computed the necessary attenuations before and after CO2 introduction. The practical implementation of this technology relies on the ability to measure sufficient muons to minimize statistical uncertainty, which is influenced by the detector area.
The proposed solution involves deploying long doped Styrofoam detectors in multilateral horizontal wells, a standard technology in oilfield drilling. This innovative approach not only aims to improve CO2 storage monitoring but also has potential applications in oil production and water flooding.
Overall, the project represents a significant advancement in geophysical monitoring techniques, leveraging natural cosmic-ray muons to provide continuous, real-time data on subsurface fluid dynamics, thereby addressing critical environmental and resource management challenges.
