CBL-VDL LOG INTERPRETATION PDF

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.

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Track 3 shows a cross section of the pipe wall.

This separation allows for easier analysis of the formation-signal strength and is used to monitor cement-to-formation bonding. Radial-cement-evaluation devices were developed to overcome some limitations of conventional integpretation tools and to permit more accurate evaluation of cement distribution behind casing by providing the precise location of partial bond and channeling.

In the first scenario, free pipe, there is no cement bond between the casing and cement. It is used with a conventional CBL tool. Track 3 contains the CBL waveform, which indicates cement-to-casing bond as well as cement-to-formation bond.

This dimensionless quantity is the ratio of measured attenuation to maximum attenuation:. In contrast, a microannulus a small gap between the casing and cement sheath may extend over long sections of casing but may not prevent a hydraulic seal. This condition is indicated by the lack of later-arriving formation energy.

CEMENT BOND LOG INTERPRETATION

A BI value of 1. The acoustic signal travels through borehole fluid, casing, cement, and the formation itself. The USI cannot distinguish between gas-filled cement and fluids, but it can quantify the acoustic impedance of the cement.

The height of the collar disturbance is a function of measurement TR spacing amplitude, 3-ft interval; variable density, 5-ft interval courtesy of Baker Atlas. To support the casing shear bond To prevent fluid from 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.

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In this situation, energy traveling through the casing is attenuated drastically because of the highly attenuating cement sheath.

Cement bond logs

The second reflection may be at the outside of the casing. A high rate of attenuation is indicative of a good cement bonding to the casing and an absence of channels within the cement. These cased-hole wireline tools measure:. TR spacing typically ranges from 3 to 5 ft.

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. Courtesy of Baker Atlas. This Schlumberger tool comprised an array of eight ultrasonic transducers that interprtation a limited radial inspection of the casing and its annulus.

Just as filtrate invasion and formation alteration may produce changes in formation acoustic properties, and thus variation in acoustic logs over time, [6] [7] [8] so too, cement-bond logs may vary over time as the cement cures and its properties change.

When cbl-vdll occurs, it is generally localized and nonuniform; that is, it occurs over relatively short intervals and can frequently be identified by variations in the amplitude response. Acoustic logs provide the primary means for evaluating the mechanical integrity and quality of the cement bond. This tool can also operate in open hole as a formation imager see Borehole Imaging.

If the initial log run was not under pressure and the log indicates poor bond, the presence of a microannulus can be evaluated by running a second bond log under pressure to see if there is a difference. In the second scenario, good bond, cement is properly bonded to casing and to the formation.

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The first reflection is at the casing itself.

The resulting waveform is comprised of a casing signal and a formation signal; the casing signal arrives first, followed by the formation signal. A common practice is to run cement-bond logs with the casing under pressure cbk-vdl expand the casing ibterpretation the cement, thereby decreasing any microannulus that might exist. Interpretation techniques combining these different measurements provide improved evaluation in lightweight cements, especially in the annulus, beyond the casing-cement bond.

Track 4 provides the average, minimum, and maximum values of the pipe radius that is shown in Track 5. Transmitting elements and the firing sequence interpretahion controlled to direct steer and enhance the acoustic-energy output of both the pad interpretationn and the VDL transmitter.

This map can indicate the presence of interpeetation and their orientations. 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. The pad spacing is such that the first arrival is the wave that has passed through the casing.

Straight lines in the CBL waveform, along with high amplitude readings, indicate poor cement-to-casing bond. Conventional cement-bond logs CBLs comprise a pulsed transmitter and several receivers of acoustic energy positioned as a vertical array of transducers.

Channels as narrow as 1. Ultrasonic tools are superior to the acoustic CBLs, although they remain adversely affected by highly attenuating muds. Centering in the cased hole is more critical because the higher-operating frequencies i.

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