Abstract
This study proposes and examines a practical technique for monitoring underground fluid migration using tidal deformation of the Earth. The gravitational attraction of the bodies in the solar system causes deformation of the Earth, and the pore pressure of the geological reservoirs changes in response to such tidal phenomena. These pore pressure changes are related to the poroelastic parameter χ, which is a function of fluid saturations in the pore space, and χ can be an indicator for monitoring the underground fluid migration.
To retrieve the pressure changes caused by the Earth tide from field-measured pressure data including long-term pressure trends and noises, a pressure-analysis algorithm based on the cubic spline interpolation and the least squares method was employed. A set of numerical experiments were performed and the results showed that a proper selection of the time-node span for the interpolation enabled retrieval of diurnal and/or semi-diurnal pressure fluctuations.
The developed algorithm was applied to actual field data, which confirmed that the diurnal and semi-diurnal features of the pressure fluctuations can be explained by the Earth tide. The estimated χ values indicated the arrival of the displacing fluid at the monitoring well, showing that fluid migration can be monitored by analyzing the χ profiles.
