Monitoring with earth tides at the CO2CRC Otway Project

Abstract

Tidal forces from the Sun, Moon and other astronomical bodies cause daily tides in the solid earth. Atmospheric tides and ocean-loading tides have similar effects. The variable tidal stresses cause variations in pressure in fluid-saturated rocks. These changes are familiar to hydrologists and their amplitude can be used to estimate the properties of aquifers. Rock-mechanical properties determine the tidal response, and this suggests that saturation with CO2 might be detectable. We report monitoring of earth tides, from six deep wells near an artificially-created CO2 plume. This were complemented with surface seismic surveys, delineating the plume. There were strong responses of the earth tides' amplitudes to the creation and propagation of the plume. We were able to quantify the range of the effect of the earth tides and show that diurnal and semi-diurnal tides contain complementary information. Earth tides may be a useful supplementary method of monitoring CO2 plumes created by geological storage.

Keywords: Geological storage, earth tides,monitoring, CO2