Bond Log Theory and Interpretation. April 16th, Variable Density Log ( VDL). • Examples of good cement bond and Cement Bond. Log (CBL). 1. 2. 3. 4. 2 Sep Properly run and interpreted, cement-bond logs (CBL) provide highly reliable estimates of Cement to Pipe Bond & Formation VDL. 23 May A standard CBL (Cement Bond Logging) tool uses sound energy to determine how well bonded the Below is the explanation of bonded pipe.

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The data relate to an interval that overlaps with the vld CBL in Fig. 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.

Tool eccentering reduces signal amplitude and travel time Fig. Acoustic logs provide the primary means for evaluating the mechanical integrity and quality of the cement bond. The cement-evaluation presentation includes casing ovality interpretaiton tool eccentricity in Track 1. Track 2 contains the amplitude curve and amplified amplitude, which indicates cement-to-casing bond.

Cement bond logs

They operate on the principle that acoustic amplitude is rapidly attenuated in good cement bond but not in partial bond or free pipe. 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.

The ultrasonic tools compute the acoustic impedance of the material beyond the casing. Track 1 contains the gamma ray for correlation and acoustic travel time for quality control. The method allows localized zones of good hydraulic seal to be interprettaion in a way that is independent of borehole-fluid type.

Acoustic energy is reflected at interfaces that correspond to changes in acoustic impedance the product of acoustic velocity and density. Ultrasonic tools can be operated to interpregation two objectives concurrently: This tool can also operate in open hole as a formation imager see Borehole Imaging. The waveform and amplitude data allow two bonds to be investigated. A similar response can be caused by the presence of formation gas in shallow, high-porosity zones.

Whenever possible, amplitude data should be used in conjunction with the other measurements presented on the log e. In addition, each tool design also provides a conventional 5-ft VDL waveform measurement to provide information about the cement-to-formation bond. If cement is bonded to interprftation casing, there will be a strong reflection.

The most recent tools have a single rotating transducer that incorporates both inherpretation source and receiver of ultrasonic energy. This Schlumberger tool comprised an array of eight ultrasonic transducers that allowed a limited radial inspection of the casing and its annulus.

In this situation, energy traveling through the casing is attenuated drastically because of the highly attenuating cement sheath.

Cement bond logs –

The first reflection is at the casing itself. Because the pads are in direct contact with the casing—in contrast to ultrasonic measurements—measurements are unaffected by:. This separation allows for easier analysis of the formation-signal strength and is used to interpetation cement-to-formation bonding. 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.

These are the bond between casing interpretafion cement and, to a lesser extent, that between cement and formation. On a variable-density log, free pipe and fluid arrivals if present are easily identified as straight dark and light lines indicating interpretatiin acoustic properties at either side of the display Fig.

Amplitude, measured directly vsl as an attenuation ratio, is the primary bond measurement and is used to provide:. The height of the collar disturbance is a function of measurement TR spacing amplitude, 3-ft interval; variable density, 5-ft interval courtesy of Baker Atlas. Straight lines in the CBL waveform, along with high amplitude readings, indicate poor cement-to-casing bond.

In contrast, a microannulus a small gap between the casing and cement sheath may extend over long sections of casing but may not prevent a hydraulic seal. Dark zones are the most strongly bonded.

In the second scenario, good bond, cement is properly bonded to casing and to the formation. Conventional CBL tools interpreetation omnidirectional measurements, while the newer radial cement-evaluation tools provide azimuthally sensitive measurements for channel evaluation.


These tools use one or more azimuthally sensitive transducers to evaluate cement quality around the circumference of the casing. In cases of poor bonding, casing-collar signals may also be identified as “w” patterns anomalies Fig. Track 5 is a CBL-type display. Track 2 shows a cross-sectional presentation of the pipe shape.

Essentially, the CBL reads low-amplitude values in gas-contaminated cements. 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.

A “straight” waveform display is traditionally interpreted to mean no dbl bonding. New interpretation methods integrate ultrasonic and attenuation measurements from conventional tools to provide improved cement evaluation in these conditions.

Proper cement placement between the vdk casing and the formation is essential: As a result, a free-pipe acoustic signal is:. Gates are time periods during which measurements are made—they can be either of the following:. The two measurements are combined to form a result that compensates for:. Fixed gates are set generally at the wellsite to open, remain open, and close at designated times; opening time for the gate is a function of the casing size and the borehole-fluid velocity.

Use this section to list papers in OnePetro that a interpretattion who cnl to learn more should definitely read.