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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Cement bond logs
Properly run and interpreted, cement-bond logs CBL provide highly reliable estimates of well integrity and zone isolation. 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.
When conducting a cement evaluation, information on the type of cement used is essential. Track 3 shows a cross section of the pipe wall. Use this section to list papers in OnePetro that a reader who vsl to learn more should definitely read. The VDL should be examined to ensure that the formation arrival is impacting the amplitude curve. Track 1 contains 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.
One caveat regarding the use of the amplitude curve for bond evaluation: To support the casing iterpretation bond To prevent fluid inteerpretation leaking to the surface For isolating producing zones from water-bearing zones hydraulic bond Acoustic logs provide the primary means for evaluating the mechanical integrity and quality of cdl cement bond.
The pad spacing is such that the first arrival is the wave that has passed through the casing. Proper cement placement between the well casing and the formation is essential: Tool eccentering reduces signal amplitude and travel time Fig. 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.
It deals with the problem of gas-contaminated cement, which has been a longstanding interpretation problem in the industry. Channels as narrow as 1. Tracks 4 and 5 imart clarity to the interpretation of Fig. These are the bond interpretatioj casing and cement and, to a lesser extent, that between cement and formation.
They are often grouped as “cement evaluation tools. In addition to specialized cement-bond devices, modern openhole array tools are designed to also provide conventional cement-evaluation measurements in cased intepretation. The waveform and amplitude data allow two bonds to be investigated.
CEMENT BOND LOG INTERPRETATION
The casing-evaluation presentation includes casing ovality, eccentricity, hole deviation, and gamma ray in Track 1. This tool can also operate in open hole as a formation imager see Borehole Imaging.
Essentially, the CBL reads low-amplitude values in gas-contaminated cements. Track 6 provides the average, minimum, and maximum values of the pipe thickness that is the image shown in Track 7, where red indicates pipe thinning and blue indicates pipe thickening. Ultrasonic tools can be operated to address two objectives concurrently: 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.
The bonding between cement and formation is investigated through a CBL-type receiver array for wave-train presentation Fig. The tool has to be centered.
They operate on the principle that acoustic amplitude is rapidly attenuated in good cement bond but not in partial bond or free pipe. 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. When channeling occurs, it is generally localized and nonuniform; that is, it occurs over relatively short intervals interpretatiion can frequently be identified by variations in the amplitude response.
The acoustic signal travels through borehole fluid, casing, cement, and the formation itself. Positive waveform amplitudes are interpretatipn as dark bands and negative amplitudes as gray or white bands; contrast is proportional to amplitude. Use this section to provide links to relevant material on websites other than PetroWiki and OnePetro.
TR spacing typically ranges from 3 to 5 ft. Because the pads are in direct contact with the casing—in contrast to ultrasonic measurements—measurements are unaffected by:.
However, they are not reliable as indicators of hydraulic sealing by the cement, because they cannot detect small channels therein.
Track 4 provides the average, minimum, and maximum values of the pipe radius that is shown in Track 5. These devices measure the attenuation between two transmitters and receivers as a way of eliminating, or at least minimizing, the effects of:.
Cement bond logs –
Track 5 is a CBL-type display. Table 1  . Whenever possible, amplitude data should be used in conjunction with the other measurements presented on the log e. The two measurements are combined to form a interpreration that compensates for:.