Bond Log Theory and Interpretation. April 16th, Variable Density Log ( VDL). • Examples of good . Single CBL 3′ amplitude can not identify channeling. Properly run and interpreted, cement-bond logs (CBL) provide highly reliable estimates of Cement to Pipe Bond & Formation VDL. interpretation of this recently developed measurement and will detail case studies from Gulf of Mexico offshore wells comparing results from traditional. CBL /VDL.
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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. However, the presence of gas in clb slurries, as an inert component or as contamination, may seriously affect ultrasonic-tool interpretation.
The most recent tools have a single rotating transducer that incorporates both the source and receiver of ultrasonic energy. Table 2 lists the limitations of conventional cement-bond logs. Proper cement placement between the well casing and the formation is essential: Conventional cement-bond logs CBLs comprise a pulsed transmitter and several receivers of acoustic energy positioned as a vertical array of transducers.
Cement bond logs –
In the first scenario, free pipe, there is no cement bond between the casing and cement. Use this section to provide links to relevant material on websites other than PetroWiki and OnePetro.
The shorter spacing e. Gates are time periods during which measurements are made—they can be either of the following:. If cement is bonded to the casing, interpretatiion will be a strong reflection. Track 2 contains the acoustic attenuation logs for the six pads. There is nearly free pipe above interpretatioj apparent top of cement at a depth of approximately X80 depth units. Essentially, the CBL vl low-amplitude values in gas-contaminated cements.
On the basis of empirical data, the log can be calibrated directly in terms of cement compressive strength. 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. The third scenario, bond to casing only, is a common condition in which cement interprrtation bonded to the casing but not to the formation.
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.
Floating gates remain open, but recording is only triggered by an amplitude value greater than a designated threshold value. In this case, the eccentricity vdo both tool and casing eccentricity resulting from formation movement salt flow.
These tools typically operate at higher frequencies than conventional openhole tools—between 20 and 30 kHz. TR spacing typically ranges from 3 to 5 ft. 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.
Acoustic logs provide the primary means for evaluating the mechanical integrity and quality of the cement bond. The cement-evaluation presentation includes casing ovality and tool eccentricity in Track 1. Measurements from these devices are influenced by the same factors as openhole televiewer devices. This condition is indicated by the lack of later-arriving formation energy. However, in foamed cements or when exotic additives are used, these calibrations can be inaccurate. 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.
The USI cannot distinguish between gas-filled cement and fluids, but it can quantify the acoustic impedance of the cement. Ultrasonic tools are superior to the acoustic CBLs, although they remain adversely affected by highly attenuating muds.
Cement bond logs
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. Track 2 contains the amplitude curve and amplified amplitude, which indicates cement-to-casing bond.
Tracks 4 and 5 imart clarity to the interpretation of Fig. Modern acoustic cement-evaluation bond devices are comprised of monopole axisymmetric transmitters one or more and receivers two or more.
A BI value of 1. At greater depths, the pipe inteerpretation well bonded. However, they are not reliable as indicators of hydraulic sealing by the cement, because they cannot detect small channels therein. An interesting example of the complementary nature of these data has been presented by De Souza Padilha and Da Silva Araujo. There is poor cement condition between X and X depth units.