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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Amplitude, measured directly or as an attenuation ratio, is the primary bond measurement and is used to provide:. Track 1 kog the gamma ray and two quality curves for pad contact with the borehole wall and for centralization, both of which are of high quality in this example. Tracks 4 and 5 imart clarity to the interpretation of Fig.

The second reflection may be at the outside of the casing. Use this section to list papers in OnePetro that a reader who wants to learn more should definitely read. The USI cannot distinguish between gas-filled cement and fluids, but it can quantify the acoustic impedance of the cement. Retrieved from ” https: A sonic tool is typically run on wireline by a service company that detects the bond of the cement to the casing and formation via a principle based on resonance.

TR spacing typically ranges vdo 3 to 5 ft.

This separation allows for easier analysis of the formation-signal strength and is used to monitor cement-to-formation bonding. Lpg “straight” waveform display is traditionally interpreted to mean no cement bonding.

The signal is received, processed, and displayed as a microseismogram. This map can indicate the presence of channels and their orientations.

Views Read Edit View history. 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. 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.

Cnl 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. The acoustic signal travels through borehole fluid, casing, cement, and the formation itself. Ultrasonic tools can be operated to address two objectives concurrently: It is used with a conventional CBL tool.


Cement-bond logging tools use gated systems to measure the specific parts of the acoustic waveform needed for the primary bond-amplitude measurement.

Cement bond logs

From Wikipedia, the free encyclopedia. The waveform and amplitude data allow two bonds to be investigated. A value of less than 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 application of statistical variance processing to the conjunctive use of CBL and ultrasonic impedance data has led to an improved cement evaluation. Fixed gates are set generally at the wellsite to open, remain open, and close at designated times; opening time for the gate is a lg of the casing size and the borehole-fluid velocity.

Track 2 contains the acoustic attenuation logs for the six vsl.

Acoustic logs do not measure cement quality directly, rather, this value is inferred from the degree of acoustic coupling of the cement to the casing and to the formation. In cases of poor bonding, casing-collar signals may also be identified as “w” patterns anomalies Fig. Dark zones are the most strongly bonded. The shorter spacing e.

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.

Cement bond logs –

To do this, repeated acoustic pulses are directed at the casing to make it resonate in its thickness mode and the energy level attenuation of the decaying reflected wave is measured. Transmitting elements and the firing vdo are controlled to direct steer and enhance the acoustic-energy output of both the pad transmitters and the VDL transmitter.

Acoustic energy is reflected at interfaces that correspond to changes in acoustic impedance the product of acoustic velocity and density. Centering in the cased hole is more critical because the higher-operating frequencies i. In this example, the partial bonding is sufficient to provide hydraulic isolation.

Vrl Schlumberger tool comprised an array of eight ultrasonic transducers that allowed a limited radial inspection of the casing and its annulus. However, if only channeling exists, pressuring the casing will not significantly change the log.


variable-density log – Schlumberger Oilfield Glossary

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. If cement is bonded to the casing, there will be a strong reflection. 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.

Modern kog cement-evaluation bond devices are comprised of monopole axisymmetric transmitters one or more and receivers two or more. Tool eccentering reduces signal amplitude and travel time Fig. Fixed-gate systems are commonly used for amplitude measurements and floating gates for travel-time measurements.

It deals with the problem of gas-contaminated cement, which has been a longstanding interpretation problem in the industry. 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.

Track 1 contains the gamma ray for llog and acoustic travel time for quality control. The method allows localized zones of good hydraulic seal to be identified in a way that is independent of borehole-fluid type. Pressuring the casing improves the acoustic coupling to the vvl and the casing signal will decrease and the formation llg will become more obvious Fig. Good cement bond to casing produces a rapid damping higher impedance of this resonance; poor cement bond results in longer resonance decay lower impedance.

Track 2 shows a cross-sectional presentation of the pipe shape.

Cement Bond Logging Tools

New interpretation methods integrate ultrasonic and attenuation measurements from conventional tools to provide improved cement evaluation in these conditions. If the gate opening is too large, there may be interference between early and late-arriving signals. Track 3 shows a cross section of the pipe wall.