Borehole Muon Detector Development

Abstract:

Increasing atmospheric CO₂ concentrations have spurred investigation into carbon sequestration methods. One of the possibilities being considered, storing super-critical CO₂ in underground reservoirs, has drawn more attention and pilot projects are being supported worldwide. Monitoring of the post-injection fate of CO₂ is of utmost importance. Generally, monitoring options are active methods, such as 4D seismic reflection or pressure measurements in monitoring wells. We propose here to develop a 4-D density tomography of subsurface CO₂ reservoirs using cosmic-ray muon detectors deployed in a borehole. Muon detection is a relatively mature field of particle physics and there are many muon detector designs, though most are quite large and not designed for subsurface measurements. The primary technical challenge preventing deployment of this technology in the subsurface is the lack of miniaturized muon-tracking detectors capable of fitting in standard boreholes and that will resist the harsh underground conditions. A detector with these capabilities is being developed by a collaboration supported by the U.S. Department of Energy. Current simulations based on a Monte Carlo modeling code predict that the incoming muon angle can be resolved with an error of approximately two degrees, using either underground or sea level spectra. The robustness of the design comes primarily from the use of scintillating rods as opposed to drift tubes. The rods are arrayed in alternating layers to provide a coordinate scheme. Preliminary testing and measurements are currently being performed to test and enhance the performance of the scintillating rods, in both a laboratory and a shallow underground facility. The simulation predictions and data from the experiments will be presented.