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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The second reflection may be at the outside of the casing. Acoustic logs provide the primary means for evaluating the mechanical integrity and quality of the cement bond.
When conducting a cement evaluation, information on the type of cement used is essential. Positive waveform amplitudes are shown as dark bands and negative amplitudes as gray or white bands; contrast lkg proportional to amplitude. 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. There is poor cement condition between X and X depth units. However, in foamed cements or when exotic additives are used, these calibrations can be inaccurate.
TR spacing typically ranges from 3 to 5 ft.
The method allows localized zones of good hydraulic seal to be identified lig a way that is independent of borehole-fluid type.
Pressuring the casing improves the acoustic coupling to the formation and the casing signal will decrease and the formation signal will become more obvious Fig. This Schlumberger tool comprised an array of eight ultrasonic transducers that allowed a limited radial inspection of the casing and its annulus.
Cement bond log
Channeling is significant because it prevents a hydraulic seal. Ultrasonic tools are superior to the acoustic CBLs, although they remain adversely affected by highly attenuating muds.
For example, foam cements, which intentionally create void spaces in the cured cement, bdl be misinterpreted as partial bond if normal cement is assumed. Track 5 is a CBL-type display. The lob scenario, bond to casing only, is a common condition in which cement is bonded to the casing but not to the 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 lg to see if there is a difference.
Measurements from these devices are influenced by the same factors as openhole televiewer devices.
CEMENT BOND LOG INTERPRETATION
Good cement bond to casing produces a rapid damping higher impedance of this resonance; poor cement bond results in longer resonance decay lower impedance. A value of less than 1. Track 6 provides the average, minimum, and maximum values of lof pipe thickness that is the image shown in Track 7, where red indicates pipe thinning and blue indicates pipe thickening.
Unsourced lot may be challenged and removed. These tools typically operate at higher frequencies than conventional openhole tools—between 20 and 30 kHz.
From Wikipedia, the free encyclopedia. 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.
In addition, each tool design also provides a conventional 5-ft VDL waveform measurement to provide information about the cement-to-formation bond. Presentation of the full acoustic waveform assists in resolving bond ambiguities arising from use of an amplitude measurement alone and provides qualitative information about the cement-to-formation bond.
They operate on the principle that acoustic amplitude is rapidly attenuated in good cement bond but not in partial bond or free pipe. In cases of poor bonding, casing-collar signals may also be identified as “w” patterns anomalies Fig.
Cement bond logs
This can occur because the mudcake dries and shrinks away from cement, or because the cement did not bond with mudcake in poorly consolidated formations. Straight lines in the CBL waveform, along with high amplitude readings, indicate poor cement-to-casing bond.
This may ,og with the presence of a microannulus or channels within the cement. 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 2 shows a cross-sectional presentation of the pipe shape. The lkg presentation includes casing ovality, eccentricity, hole deviation, and gamma ray in Track 1. A high rate of attenuation is indicative of a good cement bonding to the casing and an absence of channels within the cement. Track 4 provides the average, minimum, and maximum values of the pipe radius that is shown in Track 5. The most recent tools have a single rotating transducer that incorporates both the source and receiver of lot energy.
Modern acoustic cement-evaluation bond devices are comprised of monopole axisymmetric transmitters one or more and receivers two or more. Track 3 shows a cross section of the pipe wall.
This has the effect of improving the signal strength of both the casing and cement-to-formation arrivals, respectively. In these situations, users are advised to consult with the logging service company regarding vd appropriate calibrations.
Cement-bond logging tools use gated systems to measure the specific parts of the acoustic waveform needed for the primary bond-amplitude measurement.