×

Cereus Nusonix CBL – in depth

Cement evaluation logging

New generation of Cement Evaluation that can't be adjusted in-field

Cement evaluation presented in field as it looks downhole

 

With the current out-dated methods, cement evaluation measurements have been adjusted in-field to meet expectations as opposed to the actual well conditions.

Cereus Ultrasonics now presents a method of the future, based on existing methods of evaluating cement bond condition. The Cereus Ultrasonics Nusonix cement evaluation imaging tool can be run in 41/2” tubing to 133/8” casing. The results are based on direct measurements and not derived or from machine-learnt statistics.

What’s the difference between the Nusonix CBL method and traditional methods?

The basic calculations are similar, but with ultra-high fidelity acoustics, more information can be gained to complete the picture to avoid having to estimate the final result …

Ultrasonic CBL Imaging Principles – Now in the past

• Narrow bandwidth Ultrasonics
• Reduced transmitted pulse resolution
• One single resonance detected
• Frequency = casing thickness
• Amplitude = reflected energy Z2
• Cement bond impedance, Z1, computed/derived/adjusted to fit expectation

The bandwidth of current systems is limited by the lack of control of the transducer which needs to be chosen based on casing thickness for a particular job.

A narrow bandwidth signal is broad in the time domain – very hard to identify individual back-wall reflections:

The frequency domain of the front-face return (head) of the waveform shows a dip at the resonant frequency (or a harmonic there-of).  The frequency of this dip is a function of the wall thickness:

The period after the head (tail) of the waveform where the back-wall reflections should be is selected:

This selected area is then analysed in the frequency domain, which produces a single peak:

The level of this peak and derived values are then used to produce an acoustic impedance and cement bond evaluation.

Ultrasonic Cement Evaluation Imaging Principles – Cereus Ultrasonics, the future

The ultra-high-fidelity signals used in the Nusonix tool are narrow in the time domain:

… while broad in the frequency domain (180kHz to 2500kHz in this example):

This ultra-high fidelity allows individual back-wall reflections to be observed (red selected area):

In the time domain the rate at which the reflections decay provides an indication of the reflection coefficient of the casing/cement boundary:

This can then be converted to an acoustic impedance.

In the frequency domain the separation between harmonic frequencies is used to determine the casing wall thickness – many resonance peaks, providing enhanced accuracy:

Some systems require a head change, whereas the Nusonix can operate in pipes from 41/2” tubing to 133/8” casing without changing or adjusting the rotating head.

One tool, one hardware configuration, one tool set-up configuration, many jobs!

Internal Radius
Thickness
Cement Evaluation

— ONE TOOL —

Complete tool weight: 42kg [95.5lb] – Complete tool length: 4.04M [131/4‘]  – Tool diameter (excl. centralisers): 54mm [21/8“]

 

 

 

Client Challenge:

To determine the capability of the Nusonix tool in CBL mode to log known 41/2” casing samples, having various induced micro-fracs and micro-annuli repairs undertaken using casing expansion processes.

The reference samples were provided by Shell.

Cereus Solution & Results:

The Cement Evaluation mode using the Cereus “Energy Absorption Ratio” provides clear evidence of the induced micro-annulus as well as showing the presence of the expansion, the thickness at the tip (allowing burst pressures to be calculated) and the quality of the cement bond at the tip after the repair.

Nusonix provides highly repeatable measures of the tubing deformation and the resulting visibility of the restoration of a pressure seal (lateral red/orange stripes at base and tip of the deformation).

Key Outputs:
Sample with induced
micro frac:
Blue: Bad bond
Red: Good bond
Nusonix CBL mode showing
good bond at the repair:

Cereus CBL technique – Energy Absorption Ratio (EAR)

High level of absorption – Red – Good cement bond

Lower level – progressively Blue – Bad cement bond

 

4 ½” casing – Annular repair

The annular repairs were made with the use of a Local Expander, a tool developed by Renegade, in partnership with Shell:

The Nusonix tool was run into the test sample and the results plotted.

Test piece with 4 local expansions.  The top 3 expansions were logged:

Thickness, Internal Radius and External Radius:

Vertical scale: mm; horizontal scale: °, colour scale: mm

The white areas on the plots are due to the slopes of the expanded repairs.  These reflect the acoustic signal away from the transducer.  The signal becomes perpendicular again at the tip of the expansion.

CBL Data; Energy Absorption Ratio (EAR):

Vertical scale: mm; horizontal scale: °, colour scale: mm

As with the thickness plot above, the grey areas on the plots are due to the slopes of the expanded repairs.

Grey– No data
Dark brown – Good Bond
Red – No bond

 

Repeatability:

An earlier colour scheme has been used, but the quality of the repeatability is clear.

Vertical scale – Millimeters:

Good data returns as the slope appears flatter at the peak of the bulge:

For even more information or a quote, contact us.  Leasing and purchase options available.

Contact