The Cement Bond Log (CBL) service provides a detailed evaluation of the casing collar locator (CCL), and the VDL or signature waveform presentation. The variable-density log is commonly used as an adjunct to the cement-bond log, and offers better insights into its interpretation; in most cases microannulus. A digital sonic tool that provides conventional openhole sonic measurements, standard CBL amplitude and Variable Density log (VDL), and attenuation.
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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. The use of new high-performance low-density, foam, and complex cements is increasing. Views Read Edit View history. If there is unset cement or water behind the casing, there will be a weak reflection. The cement-bond instrument sleeve is typically slotted to suppress and delay the tool signal that might otherwise be confused with the important casing signals.
The shorter spacing e.
Cement bond log
Interpretation techniques combining these different measurements provide improved evaluation in lightweight cements, especially in the annulus, beyond the casing-cement bond. If lof 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.
The first reflection is at the casing itself. Use this section to list papers in OnePetro that a reader who wants to learn more should definitely read.
Eventually, borehole-compensated devices using dual transmitters and lg receivers were introduced in the s, and llg most commercial devices use multiple transmitters and receivers in a variety of arrangements to provide compensated measurements. These are the bond between casing and cement and, to a lesser extent, that between cement and formation. In this case, the eccentricity comprises both tool and casing eccentricity resulting from formation movement salt flow.
Cement bond log – Wikipedia
Early CBL designs s used a single transmitter and single receiver for an amplitude measurement. Courtesy of Baker Atlas.
A cement bond log documents the evaluation of the integrity of cement work performed on an oil well. At the same time, the annulus outside the cement sheath provides poor acoustic coupling. For example, foam cements, which intentionally create void spaces in the cured cement, can be misinterpreted as partial bond if normal cement is assumed.
There is nearly free pipe above an apparent top of cement at a depth of approximately X80 depth units.
variable-density log – Schlumberger Oilfield Glossary
This article needs additional citations for verification. The data relate to an interval that overlaps with the conventional CBL in Fig.
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. Variable density is a continuous-depth time display of full-waveform amplitude presented as shades of black and white. This separation allows for easier analysis of the formation-signal strength and is used to monitor cement-to-formation bonding.
The casing-evaluation presentation includes casing ovality, eccentricity, hole deviation, and gamma ray in Track 1. Just as filtrate invasion and formation alteration may produce changes in formation acoustic properties, and thus variation in acoustic logs over time,    so too, cement-bond logs may vary over time as the cement cures and its properties change. As a result, a free-pipe acoustic signal is:. Track 1 contains the gamma ray for correlation and acoustic travel time for quality control.
Cement-bond logging tools use gated systems to measure the specific parts of the acoustic waveform needed for gdl primary bond-amplitude measurement.
The attenuation in each segment is measured in two directions using a pair of acoustic receivers and two transmitters. December Learn how and when to remove this template message.
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 vd, quality of the cement bond.
Track 3 shows the average and minimum attenuation at each sampling level. A “straight” waveform display is traditionally interpreted to mean no cement bonding.
,og result is that little energy is transferred to the annular fluid and virtually none is transferred to the formation. Whenever possible, amplitude data should be used in conjunction with the other measurements presented on cdl log e.
Track 4 provides the average, minimum, and maximum values of the pipe radius that is shown in Track 5. However, the presence of gas in cement slurries, as an inert component or as contamination, may seriously affect ultrasonic-tool interpretation.