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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Tool eccentering reduces signal amplitude and travel time Fig.
The signal is received, processed, and displayed vrl a microseismogram. The data relate to an interval that overlaps with the conventional CBL in Fig. Track 5 is a CBL-type display.
The cement-bond instrument sleeve is typically slotted to suppress and delay the tool signal that might otherwise be confused with the important casing signals. One caveat regarding the use of the amplitude curve for bond evaluation: In cases of poor bonding, casing-collar signals may also be identified as “w” patterns anomalies Fig. 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.
This Schlumberger tool comprised an array of eight ultrasonic transducers that allowed a limited radial inspection of the casing and its annulus. Measurements from these devices are influenced by the same factors as openhole televiewer devices.
These tools typically operate at higher frequencies than conventional openhole tools—between 20 and 30 kHz. 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.
Track 2 shows a cross-sectional presentation of the pipe shape. The ultrasonic tools compute the acoustic impedance of the material beyond the casing. 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.
Cement-bond logging tools use gated systems to measure the specific parts of the acoustic waveform needed for the primary bond-amplitude measurement. Table 1  . In the last scenario, partial bond, a fbl exists within an otherwise well-bonded casing. A value of less than 1. The VDL should be examined to ensure that the formation arrival is impacting the amplitude cdl. In this case, the eccentricity comprises both tool and casing eccentricity resulting from formation movement salt flow.
These are the bond between casing and cement and, to a lesser extent, that between cement and formation.
These tools use one or more azimuthally sensitive transducers to evaluate cement quality around the circumference of the casing. This article needs additional citations for cnl. A BI value of 1. Ultrasonic tools are superior to the acoustic CBLs, although they remain adversely affected by highly attenuating muds. The USI cannot distinguish between gas-filled cement and fluids, but it can quantify the acoustic impedance of the cement. Fixed-gate systems are commonly used for amplitude measurements and floating gates for travel-time measurements.
The two measurements are combined to form a result that compensates for:. Track 2 contains the acoustic attenuation logs for the six pads. Use this section to list papers in OnePetro that a cgl who wants to learn more should definitely read. 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.
The first reflection is at the casing itself. Amplitude, measured directly lo as an attenuation ratio, is the primary bond measurement and is used to provide:. Unsourced material may be challenged and removed.
The use of new high-performance low-density, foam, and complex cements is increasing. Views Read Edit View history. Use this section to provide links to relevant material on websites other than PetroWiki and OnePetro. In this situation, energy traveling through the casing is attenuated drastically because of the highly attenuating cement sheath.
Pressuring the casing improves the acoustic coupling to the formation and the cbo signal will decrease and the formation signal will become more obvious Fig. Articles needing additional references from December All articles needing additional references All articles with unsourced statements Articles with unsourced statements from December Ultrasonic tools can be operated to address two objectives concurrently: This separation allows for easier analysis of the formation-signal strength and is used to monitor cement-to-formation bonding.
At greater depths, the pipe is well bonded. Vvdl as filtrate invasion and formation alteration may produce changes in formation acoustic properties, and thus variation in acoustic logs over time,    so too, cement-bond logs may vary over time as the cement cures and its properties change.