Muon tomography for geological repositories

The project addresses the key issue in the global environment challenge concerning geological repositories, namely monitoring the structure of and possible changes in the repositories due to various processes. One particular aspect to be studied is the monitoring of the carbon dioxide migration in the repository during injection and geological storage. Storage of supercritical CO2 under the surface is seen by geologists as currently the best way of preventing further increase of the gas emissions into the atmosphere. Recent pilot schemes have shown that the injection of CO2 in large quantities (>1 Mt/year) on industrial scale is viable and more projects in the UK and worldwide are in the planning stage. Monitoring migration of the supercritical CO2 and its further dissolution into the brine and precipitation is a crucial part of the process of CO2 storage. Current monitoring techniques, such as 4D seismic surveys, are episodic and expensive. An alternative novel technique involves cosmic-ray muons which can be observed at large depths underground with their flux depending on the density and composition of materials through which they pass. Measuring muon fluxes below the reservoir can provide a continuous and inexpensive monitoring technology.
Measuring muon flux and its angular distribution underground is not a difficult task and has been done by many experiments at various depths. However, for geological repositories the muon detectors should be positioned in small boreholes (about 20 cm diameter) at a temperatures up to 50C. This imposes some constraints on the detector design and operational conditions.
The aim of the current proposal is to investigate whether the proposed novel technique can be used for monitoring geological repositories, in particular CO2 migration. We plan to build a small prototype muon detector that will be capable of measuring the muon direction and, at the same time, be deployable in the harsh environment of a borehole. Such a detector should satisfy certain requirement for deployment: a) robust; b) resistant to high temperatures (up to 50C); c) operation should be temperature independent; d) it should have small cross-sectional area to fit into the borehole; e) it should measure the angles with a few degree accuracy or better; f) it should easily discriminate between muons and background gamma-rays and electrons from radioactivity. Our plan is to design and construct a detector made of scintillator rods viewed on both sides by photomultiplier tubes. We aim to test its angular resolution using cosmic-ray muons at the surface.

This proposal is aiming to address key scientific and technological challenges in understanding the structure and evolution of geological repositories. If successful, this project will deliver a relatively low-cost methodology for monitoring geological repositories over substantial time scales (hundreds of years) helping humankind deal with the important problems causing climate change and its effects on the life on the Earth. The programme and its potential impact extend far beyond the technological advances that the successful completion of the project can bring to science and society.
Built on scientific and technological ideas developed in particle physics and particle astrophysics within STFC remits (muon detectors for cosmic rays and active veto systems for experiments for rare event searches such as dark matter WIMPs and neutrinos, detectors for particle tracking at colliders and neutrino physics), as well as on interdisciplinary projects run together with EPSRC (e.g. muon, gamma-ray and neutron detectors for nuclear security), NERC (e.g. SKY project at Boulby mine for climate change), our project has an opportunity to further advance the existing detector technology and expand it to new areas of science and industrial applications.
Understanding the structure and evolution of geological repositories is a key task for a successful implementation of numerous plans for using them as a storage place for various types of waste, in particular for storage of carbon dioxide. Mapping the combined rock and interstitial fluid density continuously and inexpensively would provide a major breakthrough in our ability to develop and realise an essential technology for geological storage of waste, in particular carbon dioxide. Currently the only methods available to monitor such sites are time-lapse seismic acquisition and a small suit of similar technologies. These are very expensive, episodic in their application and do not exclusively measure density changes associated with dense phase CO2 injection and subsequent migration.
The participants of the project together with a large group of scientists working on the muon tomography applications in various areas of science at Sheffield, Durham and Boulby have strong record in the knowledge transfer activity and are running or about to run a large variety of projects with government organisations, industry and businesses. A number of companies have already taken an interest in the muon tomography work for application as a monitoring technique in the emerging carbon storage industry.
Through our established links with industry we plan to keep these companies informed about our activities and achievements. The representatives of these companies will be invited to some of our meetings and we plan to attend conferences and other events with the participation of industrial companies where we will present our results. The businesses dealing with the development of the carbon capture and storage technologies will be prime beneficiaries of our research.
Bearing in mind an interdisciplinary character of the proposed research we will establish a programme of knowledge transfer between particle physics/astrophysics and geology/Earth science. Based on existing partnership within the muon tomography project between different departments in Sheffield and Durham we will further extend the knowledge exchange by giving seminars on topics linked to cosmic rays and particle detectors to geologists and Earth scientists, as well as seminars on carbon capture and storage and its monitoring to particle physicists and astrophysicists.
We will work together with businesses on the improvement to existing scintillators, PMTs and electronics to make it more suitable, if necessary, for borehole deployment and track reconstruction. This, in return, will provide better instrumentation for future particle physics and particle astrophysics experiments.