Quick basics of purposes of cement & scenarios bond logs run in Variable Density Log (VDL). • Examples of good Log (CBL). 1. 2. 3. 4. Properly run and interpreted, cement-bond logs (CBL) provide highly reliable estimates of Cement to Pipe Bond & Formation VDL. Geosciences/Interpretation The Cement Bond Log (CBL) service provides a detailed evaluation of the cement bond to casing and 3`Amplitude, gamma ray, casing collar locator (CCL), and the VDL or signature waveform presentation.
|Published (Last):||17 September 2009|
|PDF File Size:||15.13 Mb|
|ePub File Size:||5.69 Mb|
|Price:||Free* [*Free Regsitration Required]|
Floating gates remain open, but recording is only triggered by an amplitude value greater than a designated threshold value. A value of less than 1. They operate on the principle that acoustic amplitude is rapidly attenuated in good cement bond but not in partial bond or free pipe.
At greater depths, the pipe is well bonded. Table 2 lists the limitations of conventional cement-bond logs. These devices measure the attenuation between two interpretstion and receivers as a way of eliminating, or at least minimizing, the effects of:. The USI cannot distinguish between gas-filled cement and fluids, but it can quantify the acoustic impedance of the cement. The application of statistical variance processing to the conjunctive use of CBL and ultrasonic impedance data has led to an interprettation cement evaluation.
Presentation of the full acoustic waveform assists in resolving bond ambiguities arising from use of an amplitude measurement alone and provides qualitative information about the cement-to-formation bond. The acoustic signal travels through borehole fluid, casing, cement, and the formation itself. This dimensionless quantity is the ratio of measured attenuation to maximum attenuation:.
It deals with the problem of gas-contaminated cement, which has been a longstanding interpretation problem in the industry. For example, foam cements, which intentionally create void spaces in the cured cement, can be misinterpreted as partial bond if normal cement is assumed.
In this case, the eccentricity comprises both tool and casing eccentricity resulting from formation movement salt flow. If there is unset cement or water behind the casing, there will be a weak reflection.
Track 3 shows cbl-dl average and minimum attenuation at each sampling level. Track 4 provides the average, minimum, and maximum values of the pipe radius that is shown in Track 5.
To do this, repeated acoustic pulses are directed at the imterpretation to make it resonate in its thickness mode and the energy level attenuation of the decaying reflected wave is measured. 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.
Energy is transmitted at one pad and is received at an adjacent pad.
In cases of poor bonding, casing-collar signals may also be identified as “w” patterns anomalies Fig. An interesting example of the complementary nature of these data has been presented by De Souza Padilha and Da Silva Araujo. In contrast, a microannulus a small gap between the casing and cement sheath may extend over long sections of casing but inyerpretation not prevent a hydraulic seal. This may occur with the presence of a microannulus or channels within the cement.
The shorter spacing e. Because the pads are in direct contact with the casing—in contrast to ultrasonic measurements—measurements are unaffected by:.
The resulting waveform is comprised of a casing signal and a formation signal; the casing signal arrives first, followed by the formation signal. Essentially, the CBL reads low-amplitude values in gas-contaminated cements.
The tool has to be centered. These tools use one or more azimuthally sensitive transducers to evaluate cement quality around the circumference of the casing.
Cement bond logs –
Track 5 is a CBL-type display. When channeling occurs, it is generally localized and nonuniform; that cbl-fdl, it occurs over relatively short intervals and can frequently be identified by variations in the amplitude response. The casing-evaluation presentation includes casing ovality, eccentricity, hole deviation, and gamma ray in Track 1. Use this section to list papers in OnePetro that a reader who wants to learn more should definitely read.
A “straight” waveform display is traditionally interpreted to mean no cement bonding. There is nearly lov pipe above an apparent top of cement at a depth of approximately X80 depth units.
Cement bond logs
The first reflection is at the casing itself. To support the casing shear bond To prevent fluid interpretaation 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 the cement bond. One cbl-vd, regarding the use of the amplitude curve for bond evaluation: Variable density is a continuous-depth time display of full-waveform amplitude presented as shades of black and white.