Earth tidal and barometric responses observed in the Callovo-Oxfordian clay Formation at Andra Meuse/Haute-Marne Underground Research Laboratory

Fluid pressures were recorded over 6.5 years in borehole EST207 located at the Andra Meuse/Haute-Marne Underground Research Laboratory in Bure (France). The borehole is equipped with a multipacker system monitoring 11 intervals, including 8 in the Callovo-Oxfordian clay Formation, 2 in the Dogger Formation and 1 at the Oxfordian base. Pressure data were analysed for responses to Earth tides and barometric pressure in the 11intervals. Fourier analyses on the pressure data revealed some of the Earth tidal components. Use of ETERNA software determined a better estimate of Earth tidal wave parameters (amplitudes, phases and their standard deviations) and barometric efficiency. Estimates of the tidal parameters K1, O1, P1, S1 and M2, N2, S2, K2 were made before and after barometric correction. It is suggested that in the Callovo-Oxfordian clay, the greater the clay content of the formation, the greater the barometric efficiency values. A barometric and tidal responses classification using four groups as a function of the 11 borehole intervals is in good agreement with the geological configuration. This preliminary geological interpretation will allow both the estimation of poroelastic and hydrogeological parameters of the clay formation from Earth tidal and barometric responses without classical pump test experiments, and the monitoring of these properties over a long period.