METHOD AND A SYSTEM FOR ULTRASONIC INSPECTION OF WELL BORES

摘要

A well bore is inspected to detect cement defects that can give rise to leakage. The well bore comprises an inner metal pipe. Outside the inner metal pipe its configuration may vary with distance from the top of the well bore in terms of concentric pipes outside the inner metal pipe and presence of cement between the pipes. A probe with is lowered through the inner metal pipe. An ultrasound signal is transmitted from the probe into the inner metal pipe and responses to the transmitted signal are received at a series of ultrasound receivers at different axial positions. A selection of a spatial frequency of waves arriving along the axial direction at the ultrasound receivers and/or the apparent velocity of said waves is retrieved dependent on the configuration. The received responses are band pass filtered accordingly. By selecting the band pass filter dependent on the configuration it becomes possible to detect cement defects well outside the innermost pipe from parameters of the earliest arriving pulse from the filtered reflection signal.

主权项

1. A method of monitoring cement defects in a well bore that comprises an inner metal pipe, the well bore having different well bore configurations outside the inner metal pipe at different distances from the top of the borehole, the method comprising using a probe that comprises a support structure that extends in an axial direction of the well bore, an ultrasound transmitter and a series of ultrasound receivers mounted at successive positions along the axial direction, wherein the method comprises
moving the probe through the inner metal pipe along the axial direction of the well bore; transmitting an ultrasound signal from the transmitter into the inner metal pipe; receiving responses to the transmitted signal at the series of ultrasound receivers; band pass filtering the received responses to pass selectively a part of the response in a spatiotemporal frequency pass band corresponding to a predetermined apparent velocity component of wave travel along the axial direction at the ultrasound receivers and/or a predetermined combination of temporal and spatial frequency corresponding to the predetermined apparent velocity component.