Bond Log Theory and Interpretation. April 16th, Variable Density Log ( VDL). • Examples of good cement bond and Cement Bond. Log (CBL). 1. 2. 3. 4. 2 Sep Properly run and interpreted, cement-bond logs (CBL) provide highly reliable estimates of Cement to Pipe Bond & Formation VDL. 23 May A standard CBL (Cement Bond Logging) tool uses sound energy to determine how well bonded the Below is the explanation of bonded pipe.

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This Schlumberger tool comprised an array of eight ultrasonic transducers that allowed a limited radial inspection of the casing and its annulus. The method allows localized zones of good hydraulic seal to be identified in a way that is independent of borehole-fluid type.

In cases of poor bonding, casing-collar signals may also be interpretatin as “w” patterns anomalies Fig. This dimensionless quantity is the ratio of measured attenuation to maximum attenuation:. A “straight” waveform display is traditionally interpreted to mean no cement bonding.

Cement bond logs

By analyzing the entire waveform, an acoustic-impedance map of the cement can be constructed. New interpretation methods integrate ultrasonic and attenuation measurements from conventional tools to provide improved cement evaluation in these conditions. The VDL should be examined to ensure that the formation arrival is impacting the amplitude curve. Track 2 contains the acoustic attenuation logs for the six pads. One caveat regarding the use of the amplitude curve for bond evaluation: These are the bond between casing and cement and, to a lesser extent, that between cement and formation.

If the initial log run was not under pressure and the log indicates poor bond, the presence of a microannulus can be evaluated by running a second bond log under pressure to see if there is a difference.

Track 2 shows a cross-sectional presentation of the pipe shape. The waveform and amplitude data allow two bonds to be investigated.


Track 3 shows a cross section of the pipe wall. The resulting waveform is comprised of a casing signal and a formation signal; the casing signal arrives first, followed by the formation signal. There is poor cement condition between X and X depth units.


To support the casing shear bond To prevent fluid from leaking to the surface For isolating producing zones from water-bearing zones hydraulic bond Acoustic logs provide the primary means for evaluating the mechanical integrity and quality of the cement bond. Table 1 [1] [10]. They are interoretation grouped as “cement evaluation tools.

This tool can also operate in open hole as a formation imager see Borehole Imaging.

TR spacing typically ranges from 3 to 5 ft. It deals with the problem of gas-contaminated cement, which has been a longstanding interpretation problem in the industry. Cb response depends on the acoustic impedance of the cement, which, in turn is function of density and velocity. Essentially, the CBL reads low-amplitude values in gas-contaminated cements.

This provides good acoustic coupling and most of the acoustic energy is transmitted to the formation, resulting in little weak to no casing signals and little amplitude until the arrival of the strong formation signal.

Dark zones are the most strongly bonded. Track 1 contains ihterpretation gamma ray and two quality curves for pad contact with the borehole wall and for centralization, both of which are of high quality in this example.

However, the presence of gas in cement slurries, as an inert component or as contamination, may seriously affect ultrasonic-tool interpretation. Amplitude, measured directly or as an attenuation ratio, is the primary bond measurement and is used to provide:. In addition, each tool design also provides a conventional 5-ft VDL waveform measurement to provide information about the cement-to-formation bond. The most recent tools have a single rotating transducer that incorporates both the source and receiver of ultrasonic energy.

The received waveform is the sum of the reflected waveform from the original burst and the exponentially decaying waveform from the resonant energy that is trapped between interpreation inner and outer edges of the casing.

Track 3 contains the CBL waveform, which indicates cement-to-casing bond as well as cement-to-formation bond.

The third scenario, bond to casing only, is a common condition in which cement is bonded to the casing but not interprrtation the formation. Energy is transmitted at one pad and is received at an adjacent pad. The shorter spacing e. Acoustic logs provide the primary means for evaluating the mechanical integrity and quality of the cement bond. If cement is bonded to the casing, there will be a strong interptetation.


They operate on the principle that acoustic amplitude is rapidly attenuated in good cement bond but not in partial bond or free pipe.

Cement-bond logging tools use gated systems to measure the specific parts of the acoustic waveform needed for the primary bond-amplitude measurement.

At greater depths, the pipe is well bonded. Interpretation techniques combining these different measurements provide improved evaluation in lightweight cements, especially in the annulus, beyond the casing-cement bond. Because the pads are in direct contact with the casing—in contrast to ultrasonic measurements—measurements are unaffected by:. Tracks 4 and 5 imart clarity to the interpretation of Fig. In an evolution similar to that of openhole acoustic logs, new designs were subsequently introduced that measured signal amplitude at a near receiver and a full waveform from a far receiver.

Track 4 presents a variable-attenuation log or cement map of the casing periphery vs. Centering in the cased hole is more critical because the higher-operating frequencies i. Track 4 contains the average impedance of the image in Track 5 and a cement-bond index CBI as a quick indication of the degree of bonding.

Track 1 contains the gamma ray for correlation and acoustic travel time for quality control. A high rate of attenuation is indicative of a good cement bonding to the casing and an absence of channels within the cement. As with openhole tools, cement-bond tools require centralization to ensure accurate measurements. For example, the presence of shear-wave amplitudes on the full-waveform display is an indication of good acoustic coupling to the formation.

Use this section to provide links to relevant material on websites other than PetroWiki and OnePetro. Gates are time periods during which measurements are made—they can be either of the following:.

The cement-evaluation presentation includes casing ovality and tool eccentricity in Track 1.