Cement bond log

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A cement bond log documents the evaluation of the integrity of cement work performed on an oil well.^[1] In the process of drilling and completing a well, cement is injected through the wellbore and rises up the annulus between the steel casing and the formation.^[2]

A sonic tool is typically run on wireline by a service company that detects the bond of the cement to the casing and formation via a principle based on resonance. Casing that is not bound has a higher resonant vibration than that which is bound, causing the imparted energy from the sonic signal to be transferred to the formation.^{[citation needed]} In this sense, the amplitude of the waveform received is the basic measurement that is evaluated.

The data is collected by the tool and recorded on a log which is used by the oil producing company as an indicator of zonal isolation in the well. There are production reasons and legal reasons (governed by a petroleum regulatory body in each individual state) that dictate the well must have specific areas of isolation.^{[citation needed]}