Borehole Image Correspondence And Automated Alignment

Borehole images are often misaligned due to a depth offset in the acquisition sensors of a wireline tool. We propose an algorithm that identifies matching feature points and aligns the image. One of the main challenges is that imaging pads have no azimuthal overlap. This has been solved by extrapolating the pixels on the boundary to create a synthetic overlap that facilitates feature matching. Feature matching is implemented in two stages: first by finding a local correspondence among feature points and second by performing a global minimization with additional regularization constraints on the estimated shifts. The method has been successfully used to align several imaging logs in less than 1 minute whereas a manual alignment would take 6 hours.