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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Track 6 provides the average, minimum, and maximum values of the pipe thickness that is the image shown fbl Track 7, where red indicates pipe thinning and blue indicates pipe thickening.
If cement is bonded to the casing, there will be a strong reflection. Track 2 shows a cross-sectional presentation of the pipe shape.
Cement bond logs –
cbbl A similar response can be caused by the presence of formation gas in shallow, high-porosity zones.
It deals with the problem of gas-contaminated cement, which has been a longstanding interpretation problem in the industry. A “straight” waveform display is traditionally interpreted to mean no cement bonding. 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.
In this case, the eccentricity comprises both tool and casing eccentricity resulting from formation movement salt flow.
In these situations, users are advised to consult with the logging service company regarding the appropriate calibrations. Use this section to provide links to relevant material on websites other than PetroWiki and OnePetro.
Good cement bond to casing produces a rapid damping higher impedance of this resonance; poor cement bond results in longer resonance decay lower impedance. Eventually, borehole-compensated devices using dual ccbl 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 measurements.
These cased-hole wireline tools measure:. The most recent tools have a single rotating transducer that incorporates both the source cvl receiver of ultrasonic energy.
They operate on the principle that acoustic amplitude is rapidly attenuated in good cement bond but not in partial bond or free pipe. 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.
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 the inner and outer edges of the casing.
One caveat regarding the use of the amplitude curve for bond evaluation: Whenever possible, amplitude data should be used in conjunction with the other measurements presented on the log e. Retrieved from ” https: In this situation, energy traveling through the casing is attenuated drastically because of the highly attenuating cement sheath.
Dark zones are the most strongly bonded. This dimensionless quantity is cb, ratio of measured attenuation to maximum attenuation:.
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. An interesting example of the complementary nature of these data has been presented by De Souza Padilha and Da Silva Araujo.
The ultrasonic tools compute the acoustic impedance of the material beyond the casing. Transmitting elements and the firing sequence are controlled to direct steer and enhance the acoustic-energy output of both the pad transmitters and the VDL transmitter. Energy is transmitted at one pad and is received at an adjacent pad.
Table 2 lists the limitations of conventional cnl logs. For example, the presence of shear-wave amplitudes on the full-waveform display is an indication of good acoustic coupling to the formation.
Cement Bond Logging Tools
Consequently, there is no acoustic coupling with the formation and most of lof transmitted acoustic energy is confined to the casing and the borehole fluid.
The cement-evaluation presentation includes casing ovality and tool eccentricity in Track 1. Track 3 shows a cross section of the pipe wall. Measurements from these devices are influenced by the same factors as openhole televiewer devices.
Amplitude, measured directly or as an attenuation ratio, is the primary bond measurement and is used to provide:. 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.
Unsourced material may be challenged and removed. Ultrasonic tools can be operated to address two objectives concurrently: Properly run and interpreted, cement-bond logs CBL vdo highly reliable estimates of well integrity and zone isolation.
Courtesy of Baker Atlas. Conventional cement-bond logs CBLs comprise a pulsed transmitter and several receivers of acoustic energy positioned as a vertical array of transducers. By analyzing the entire waveform, an acoustic-impedance map of the cement can be constructed. The acoustic signal travels through borehole fluid, casing, cement, and the formation itself.
The vvl and amplitude data allow two bonds to be investigated.
Cement bond log – Wikipedia
Track 5 is a CBL-type display. 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. 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. Well logging Petroleum engineering.
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 attenuation in each segment is measured in two directions using a pair of acoustic receivers and two transmitters. On the basis of empirical data, the log can be calibrated directly in terms of cement compressive strength. This has the effect of improving the signal strength of both the casing and cement-to-formation arrivals, respectively.