CBL VDL LOG PDF
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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Track 4 contains the average impedance of the image in Track 5 and a cement-bond index CBI as a quick indication of the degree of bonding. In this situation, energy traveling through the casing is attenuated drastically because of the highly attenuating cement sheath.
This dimensionless quantity is the ratio of measured attenuation to maximum attenuation:. They operate on the principle that acoustic amplitude is rapidly attenuated in good cement bond but not in partial bond or free pipe. In the last scenario, partial bond, a space exists within an otherwise well-bonded casing. Views Read Edit View history. When conducting a cement evaluation, information on the type of cement used is essential. 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 bonding between cement and formation is investigated through a CBL-type receiver array for wave-train presentation Fig. The result is that little energy is transferred to the annular fluid and virtually none is transferred to the formation. In these situations, users are advised to consult with the logging service company regarding the appropriate calibrations.
Articles needing additional references from December All articles needing additional references All articles with unsourced statements Articles with unsourced statements from December Please help improve this article by adding citations to reliable sources. In the first scenario, free pipe, there is no cement bond between the casing and cement.
Gates are time periods during which measurements are made—they can be either of the following:. This has the effect of improving the signal strength of both the casing and cement-to-formation arrivals, respectively. Floating gates remain open, but recording is only triggered by an amplitude value greater than a designated threshold value. The most recent tools have a single rotating transducer that incorporates both the source and receiver of ultrasonic energy.
Variable density is a continuous-depth time display of full-waveform amplitude presented as shades of black and white.
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. This article needs additional citations for verification. This separation allows for easier analysis of the formation-signal strength and is used to monitor cement-to-formation bonding.
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. The data for circumferential inspection of the casing, as described above, and for the evaluation of cement vdll are obtained on the same logging pass.
Track 5 is a CBL-type display. llg
Cement Bond Logging Tools
Properly run and interpreted, cement-bond logs CBL provide highly reliable estimates of well integrity and zone isolation. Conventional CBL tools provide omnidirectional measurements, while the newer radial cement-evaluation tools provide azimuthally sensitive measurements for channel evaluation.
The attenuation in each segment is measured in two directions using a pair of acoustic receivers and two transmitters. Essentially, the CBL reads low-amplitude values in gas-contaminated cements. There 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 second reflection may be at the outside of the casing. These tools typically operate at higher frequencies than conventional openhole tools—between 20 and 30 kHz.
At greater depths, the pipe is well bonded. 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. There is poor cement condition between X and X depth units. It is used with a conventional CBL tool.
The casing-evaluation presentation includes casing ovality, eccentricity, hole deviation, and gamma ray in Track 1. The bond index BI is a qualitative measure of cement bond based on signal amplitude. Amplitude, measured directly or as an attenuation ratio, is the primary bond measurement and is used to provide:.
The USI cannot distinguish between gas-filled cement and fluids, but it can quantify the acoustic impedance of the cement. 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.
In addition, each tool design also provides a conventional 5-ft VDL waveform measurement to provide information about the cement-to-formation bond.
Cement Bond Logging Tools | Schlumberger
Attempts to rectify this problem will be impeded by the hydraulic isolation above and below this interval. December Learn how and when to remove this template message. Retrieved from ” https: As with openhole tools, cement-bond tools require centralization to ensure accurate measurements.
Straight lines in the CBL waveform, ccbl with high amplitude readings, indicate poor cement-to-casing bond.
If the gate opening is too large, there may be lov between early and late-arriving signals. This condition is indicated by the lack of later-arriving formation energy. The VDL should be examined to ensure that the formation arrival is impacting the amplitude curve. Good cement bond to casing produces a rapid damping higher impedance of this resonance; poor cement bond results in longer resonance decay lower impedance. Channeling is significant because it prevents a hydraulic seal.
This map can indicate the presence of channels and their orientations.
In addition to specialized cement-bond devices, modern openhole array tools are designed to also provide conventional cement-evaluation measurements in cased hole. TR spacing typically ranges from 3 to 5 ft. Tool eccentering reduces signal amplitude and travel time Fig.