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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This condition is indicated by the lack of later-arriving formation energy. The data is collected by the tool and recorded on a log which is used by the oil producing company as an indicator of zonal isolation in the well. This page was last edited on 11 Novemberat Tool response depends on the acoustic impedance of the cement, which, in turn is function of density and velocity.
Variable density is a continuous-depth time display of full-waveform amplitude presented as shades of black and white. Eventually, borehole-compensated devices using dual transmitters and dual receivers were introduced in the s, and today most commercial devices use multiple transmitters and receivers in a variety of arrangements to provide compensated measurements. These tools typically operate at higher frequencies than conventional openhole tools—between 20 and 30 kHz.
The USI cannot distinguish between gas-filled cement and fluids, but it can quantify the acoustic impedance of the cement. Track 3 shows a cross section of the pipe wall.
variable-density log – Schlumberger Oilfield Glossary
The ultrasonic tools compute the acoustic impedance of the material beyond the casing. Articles needing additional references from December All articles needing additional references All articles with unsourced statements Articles with unsourced statements from December The cement-evaluation presentation includes casing ovality and tool eccentricity in Track 1.
For example, foam cements, which intentionally create void spaces in the cured cement, can be misinterpreted as partial bond if normal cement is assumed. A BI value of 1.
Cement bond logs
New interpretation methods integrate ultrasonic and attenuation measurements from conventional tools to provide improved cement evaluation in these conditions. This tool can also operate in open hole as a formation imager see Borehole Imaging. In the last scenario, partial bond, a space exists within an otherwise well-bonded casing. The resulting waveform is comprised of a casing signal and a formation signal; the casing vdll arrives first, followed by the formation signal.
The data relate to an interval that overlaps with the conventional CBL in Fig. Track 5 is a CBL-type display. Channels as narrow as 1.
Cement Bond Logging Tools
A similar response can be caused by the presence of fbl gas in shallow, high-porosity zones. The attenuation in each segment is measured in two directions using a pair of acoustic receivers and two transmitters.
When conducting a cement evaluation, information on the type of cement used is essential.
The bonding between cement and formation is investigated through a CBL-type receiver array for wave-train presentation Fig. An interesting example of the complementary nature of these data has been presented by De Souza Padilha and Da Silva Araujo.
If there is unset cement or water behind the casing, there will be a weak reflection.
Cement bond logs –
By analyzing the entire waveform, an acoustic-impedance map of the cement can be constructed. The bond index BI is a qualitative measure of cement bond based on signal amplitude.
The tool has to be centered. Track 2 contains the acoustic attenuation logs for the six pads.
The result is that little energy is transferred to the annular fluid and virtually none is transferred to the formation.