Using Well Operation Noise To Estimate Shear Modulus Changes From Measured Tube Waves – A Feasibility Study

Geophysical monitoring techniques are commonly used to image the subsurface and potential changes. These monitoring techniques are important for CO2 storage projects to ensure a safe operation. A detailed image of the subsurface can be achieved from borehole seismic where mostly transmitted and reflected waves are investigated. However, these measurements are time consuming and costly as receivers and sources need to be moved within the well during the acquisition. We investigate the monitoring potential of tube waves, which propagate along the interface between the well and geological formation. An experiment is conducted where the signal from a rotating metal pipe in a borehole is recorded in a nearby observation well. The tube wave velocity can be measured with a high precision, around ± 1.2 m/s, during the experiment, which is an important measure to evaluate the potential of the method. Therefore, it might be possible to use noise sources like CO2 injection phases to monitor changes of the formation surrounding the well. This would reduce the time and cost needed for borehole seismic as only receivers at a constant position are required. Further field test are needed to investigate the feasibility at larger scales and for real injection cases.