Bond Log Theory and Interpretation. April 16th, Variable Density Log ( VDL). • Examples of good . Single CBL 3′ amplitude can not identify channeling. Properly run and interpreted, cement-bond logs (CBL) provide highly reliable estimates of Cement to Pipe Bond & Formation VDL. interpretation of this recently developed measurement and will detail case studies from Gulf of Mexico offshore wells comparing results from traditional. CBL /VDL.
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In addition, each tool design also provides a conventional 5-ft VDL waveform measurement to provide information about the cement-to-formation bond. The vdk in each segment is measured in two directions using a pair of acoustic receivers and two transmitters.
Variable density is a continuous-depth time display of full-waveform amplitude presented as shades of black and white. These tools typically operate at higher frequencies interprftation conventional openhole tools—between 20 and 30 kHz.
Cement bond logs –
Table 2 lists the limitations of conventional cement-bond logs. Radial-cement-evaluation devices were developed to overcome some limitations of conventional cement-bond tools and to permit more accurate evaluation of cement distribution behind casing by providing the precise location of partial bond and channeling.
On a variable-density log, free pipe and fluid arrivals if present are easily identified as straight dark and light lines indicating homogenous acoustic properties at either side of the display Fig. It deals with the problem of gas-contaminated cement, which has been a longstanding interpretation problem in the industry.
Consequently, there is no acoustic coupling with the formation and most of the transmitted acoustic energy is confined to the casing and the borehole fluid. Track 4 provides the average, minimum, and maximum values of the pipe radius that is shown in Track 5. Conventional cement-bond logs CBLs comprise a pulsed transmitter and several receivers of acoustic energy positioned as a vertical array of transducers. A “straight” waveform display is traditionally interpreted to mean no cement bonding.
Acoustic energy is reflected at interfaces that correspond to changes in acoustic impedance the product of acoustic velocity and density. A common practice is to run cement-bond logs with the casing under pressure to expand the casing against the cement, thereby decreasing any microannulus that might exist. 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.
The use of new high-performance low-density, foam, and complex cements is increasing. In these situations, users are advised to consult with the logging service company regarding the appropriate calibrations. Tool eccentering reduces signal amplitude and travel time Fig. The result is that little energy is transferred to the annular fluid and virtually none is transferred to the formation. Acoustic logs provide the primary means for evaluating the mechanical integrity and quality of the cement bond.
The pad spacing is such that the first arrival is the wave that has passed through the casing.
These cased-hole wireline tools measure:. Channels as narrow as 1. Good cement bond to casing produces a rapid damping higher impedance of this resonance; poor cement bond results in longer resonance decay lower impedance. 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 interpretatioon second bond log under pressure to see if there is a difference.
The data relate to an interval that overlaps with the conventional CBL in Fig. Positive waveform amplitudes are shown as dark bands and negative amplitudes as gray or white bands; contrast is proportional to amplitude. For vld, the presence of shear-wave amplitudes on the full-waveform display is an indication of good acoustic coupling to the formation.
Properly run and interpreted, cement-bond logs CBL provide highly interpretatioh estimates of well integrity and zone isolation. Channeling is significant because it prevents a hydraulic seal.
CEMENT BOND LOG INTERPRETATION
Track 5 is a CBL-type display. In the last scenario, partial bond, a space exists within an ijterpretation well-bonded casing. Data from these tools are presented as individual log curves or as azimuthal images “maps” of cement quality generated by interpolating between the individual azimuthal measurements Fig.
The most recent tools have a single rotating transducer that incorporates both the source and receiver of ultrasonic energy.
Ultrasonic tools are superior to the acoustic CBLs, although they remain adversely affected by highly attenuating muds. In this example, the interpreetation bonding is sufficient to provide hydraulic isolation.
The data for circumferential inspection of the casing, as described above, and for the evaluation of cement bonding are obtained on the same logging pass.
Dark zones are the most strongly bonded. Track 6 provides the average, minimum, and maximum values of the pipe thickness that is the image shown in Track 7, where red indicates pipe thinning and blue indicates pipe thickening.
Track 3 shows the average and minimum attenuation at each sampling level. Track 3 shows a cross section of the pipe wall.
Cement bond logs
They are often grouped as “cement evaluation tools. 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.
Table 1  .