Seismic reflection imaging of fractures using least-squares migration and linear-slip theory : laboratory and numerical tests

Characterizing the mechanical and hydraulic properties of fractures is crucial in hydrocarbon and geothermal field development. Contrary to passive microseismic measurements, active seismic measurements using a borehole, e.g., VSP or sonic logging, have a potential to address aseismic fractures. However, there is a considerable scale gap between the characteristic wavelength in VSP and in sonic logging, which hinders consistent interpretations of active and passive measurements. Recent developments of reflection imaging using microearthquakes and dipole acoustic data successfully image individual fractures or clusters of them around a borehole, which indicates the potential to fill the gap by addressing quantitative fracture properties around a borehole up to a few tens of meters away from the borehole. In this study, we couple the least-squares migration with the linear-slip theory in order to achieve high-resolution reflection imaging of fracture compliances around a borehole, which are then useful to characterize microscale structures at the fracture. Tests in the laboratory successfully characterize the spatially varying fracture compliance due to the partial inclusion of water in the fracture. Numerical modelling tests of the source-receiver configuration of acoustic dipole measurements and random background media shows the potential of the proposed approach for quantitatively imaging fractures around a borehole.