ABSTRACT

We have analyzed ultrasonic flexural data acquired in a North Sea well using a commercial tool optimized for generating such data, and found how one might separate refractions along successive layers of casings, and from these separated refractions, characterize successive pipes and annuli. From the timing of refracted events, we determined the shape of a pipe, and by examining the amplitudes of these refracted events — a measure of the conductance of a pipe wall to transverse movement — we characterized the material in the annuli around a pipe. Data from two separate depth intervals were analyzed, demonstrating that a well plan might not give a sufficiently accurate description of the well. In the deeper interval in which the inner pipe was supposed to be free, we found that the annulus was most likely filled with sedimentation and debris. We could also see that the inner 7 in tubing was touching, or nearly touching, the outer 9⅝ in casing over the entire interval. For the shallower interval, below a certain depth, we saw that the 7 in tubing appeared to be touching the 9⅝ in casing approximately every 7–8 m. From measurements inside the 7 in tubing, we estimated the deformation of the outer 9⅝ in casing to be up to a maximum of nearly 5 cm, meaning that the minimum inner diameter of the outer pipe was close to the outer diameter of the inner pipe. Whereas some features revealed by the analyses were “good-to-know” — such as minor pipe deficiencies and deformations — other features might be critical for planned overhaul, or for operations related to abandonment, e.g., touching points were potential sticking points. Knowing where they were may be critical in determining the best depth to cut a pipe before pulling.

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