Quick basics of purposes of cement & scenarios bond logs run in Variable Density Log (VDL). • Examples of good Log (CBL). 1. 2. 3. 4. Properly run and interpreted, cement-bond logs (CBL) provide highly reliable estimates of Cement to Pipe Bond & Formation VDL. Geosciences/Interpretation The Cement Bond Log (CBL) service provides a detailed evaluation of the cement bond to casing and 3`Amplitude, gamma ray, casing collar locator (CCL), and the VDL or signature waveform presentation.
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The third scenario, bond to casing only, is a common condition in which cement is interprettation to the casing but not to the formation. The use of new high-performance low-density, foam, and complex cements is increasing. These tools use one or more azimuthally sensitive transducers to evaluate cement quality around the circumference of interpretatio casing. 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.
In this case, the eccentricity comprises both tool and casing eccentricity resulting from formation cnl-vdl salt flow. In the last scenario, partial bond, a space exists within an otherwise well-bonded casing. By analyzing the entire waveform, an acoustic-impedance map of the cement can be constructed. The bond index BI is a qualitative measure of cement bond based on signal amplitude.
Essentially, the CBL reads low-amplitude values in gas-contaminated cements. However, if only channeling exists, pressuring the casing will not significantly change the log. When cbl-cdl a cement evaluation, information on the type of cement used is essential. Dark zones are the most strongly bonded.
Cement bond logs
Attempts to rectify this problem will be impeded by the hydraulic isolation above and below this interval. Proper cement placement between the well casing and the formation is essential: Conventional CBL tools provide omnidirectional measurements, while the newer radial cement-evaluation tools provide azimuthally sensitive measurements for channel evaluation.
It is used with a conventional CBL tool. Pressuring the casing improves the acoustic coupling to the formation and the casing signal will decrease and the formation signal will become more obvious Intfrpretation. However, the presence of gas in cement slurries, as an inert component or as contamination, may seriously affect ultrasonic-tool interpretation.
In this situation, energy traveling through the casing is attenuated drastically because of the highly attenuating cement sheath. The data relate to an interval that overlaps with the conventional CBL in Fig. Track 4 presents a variable-attenuation log or cement map of the casing periphery vs.
Cement bond logs –
For example, foam cements, which intentionally create void spaces in the cured cement, can be misinterpreted as partial bond if normal cement is assumed. The recorded waveforms are presented together with the travel time and a casing-amplitude curve, which displays the amplitude of the acoustic signal that has traveled through the casing but not through the cement and formation.
Track 3 shows a cross section of the pipe wall. Modern acoustic cement-evaluation bond devices are comprised of monopole axisymmetric transmitters one or more and receivers two or more. One caveat regarding the use of the amplitude curve for bond evaluation: The acoustic signal travels through borehole fluid, casing, cement, and the formation itself.
The waveform and amplitude data allow two bonds to be investigated.
Transmitting elements and the firing sequence are controlled to direct steer and enhance the acoustic-energy output of interprehation the pad transmitters and the VDL transmitter. Use this section to provide links to relevant material on websites other than PetroWiki and OnePetro.
Early CBL designs s used a single transmitter and single receiver for an amplitude measurement.
This has the effect of improving the signal strength of both the casing and cement-to-formation arrivals, respectively. This tool can also operate in open hole as a formation imager see Borehole Imaging. Acoustic energy is reflected at interfaces that correspond to changes interlretation acoustic impedance the product of acoustic velocity and density.
Channels as narrow as 1. 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. The first reflection is ihterpretation the casing itself. The signal is received, processed, and displayed as a microseismogram. This separation allows for easier analysis of the formation-signal strength and is used to monitor cement-to-formation bonding.
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. Straight lines in the CBL waveform, along with high amplitude readings, indicate poor cement-to-casing bond. There is nearly free pipe above an apparent top of cement at a depth of approximately X80 depth units.
The attenuation in each segment is measured in two directions using interpretatiob pair of acoustic receivers and two transmitters. 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 interpretatoin cement cures and its properties change. Eventually, borehole-compensated devices using dual transmitters and dual receivers were introduced in the s, and today most commercial devices use multiple transmitters and receivers in a variety of arrangements to provide compensated interpretahion.
Table 2 lists the limitations of intterpretation cement-bond logs.