Time-Lapse Muon Budgets for Density Change in a Geological Carbon Storage Reservoir

This paper computes the muon attenuation, exposure and resolution budget for imaging a geological carbon storage reservoir with cosmic-ray muons. Sight lines through 800 metres of sandstone reservoir rock at a density of 2.3 grams per cubic centimetre present an opacity of 1.84e+05 grams per square centimetre (1840 metres of water equivalent), which sets a minimum muon energy of 516.6 GeV and a transmitted vertical intensity of 0.002836 per square metre per second per steradian. For a detector of 2 square metres with the stated acceptance and efficiency, divided among 20 image elements, the stated feature produces a flux contrast of 0.07023 and reaches five standard deviations in 811.3 days of counting, while the target precision of 0.02 per image element requires 400.1 days. A deployment of 365 days delivers a per-element precision of 0.02094, corresponding to a thickness sensitivity of 16.75 metres. The combined angular resolution is 4.073 milliradians, of which tracking contributes 2.828 milliradians and multiple scattering at the threshold momentum 2.931 milliradians. The budget is compared with published muography of the same class of target, for which studies of muon monitoring for carbon storage have proposed detectors in boreholes or tunnels beneath reservoirs, with sensitivity analyses based on the small density decrease as carbon dioxide displaces brine. Every number is computed by the accompanying script from the stated inputs. Computed, not measured.