Cement Bond Evaluation Using Low-Frequency A0 Waves
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Solution Overview
Problem
Current methods for cement bond logging in cased wellbores, especially through production tubing, are limited in detecting and locating azimuthal bonding information due to their reliance on omnidirectional monopole transmitters and are ineffective with traditional 20 kHz acoustic signals, leading to challenges in evaluating cement quality behind the casing.
Innovation Solution
The use of low-frequency casing pseudo A0 waves with unipole transmitters and receivers mounted on a rotary head to scan the casing, allowing for the extraction of cement bonding information through amplitude analysis in the slowness-frequency and time-spatial domains, enabling effective cement evaluation even with production tubing present.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional 20 kHz acoustic signals with omnidirectional monopole transmitters are used, then the logging operation can be performed with simple equipment, but the ability to detect and locate azimuthal bonding information is limited
Solution Approach 1:
The omnidirectional monopole transmitter is segmented into multiple directional transmitters arranged in a array. Each transmitter emits acoustic signals in a specific azimuthal direction, allowing the system to detect bonding information from different orientations around the casing. This segmentation enables precise localization of cement bonding defects while maintaining manageable system complexity through modular arrangement.
Solution Approach 2:
The system transitions from symmetric omnidirectional transmission to asymmetric directional transmission patterns. By positioning transmitters and receivers at specific asymmetric locations and orientations, the system can selectively probe different azimuthal sectors of the casing-cement-formation interface, thereby improving detection precision for bonding information in specific directions.
2Loss of time
If production tubing is left in place during cement evaluation, then time and money are saved, but the logging operation becomes more complex and challenging
Solution Approach 1:
The logging system is designed with a nested structure where the production tubing is present within the casing, and the logging tool is deployed within the production tubing. This nested arrangement allows cement evaluation to be performed through the existing production tubing without requiring its removal, thereby saving time and cost while managing the complexity through a hierarchical spatial configuration.
Solution Approach 2:
The system uses the production tubing itself as an intermediary medium for signal transmission. Acoustic signals are transmitted through the production tubing wall to reach the casing and cement layers, and reflected signals are received back through the tubing. This intermediary approach enables logging operations with the tubing in place, avoiding the need for its removal while still obtaining necessary cement bonding data.
3Productivity
If conventional logging methods are used without production tubing, then measurement accuracy is maintained, but costly rig time is required and operations are less efficient
Solution Approach 1:
The logging system incorporates dynamic signal processing capabilities that adapt to the presence of production tubing. The system dynamically adjusts signal frequencies, transmission powers, and processing algorithms to compensate for the additional interfaces and signal attenuation caused by the tubing, thereby maintaining measurement precision while enabling operations with the tubing in place for improved productivity.
Solution Approach 2:
The system changes key parameters such as operating frequency (using lower frequencies that can penetrate tubing), signal amplitude, and processing windowing to optimize performance when production tubing is present. These parameter adjustments allow the system to maintain adequate measurement precision for cement bonding evaluation while operating through the tubing, thus improving operational efficiency without sacrificing essential measurement quality.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables accurate cement bonding evaluation by capturing the amplitude and attenuation of A0 waves, providing detailed maps of cement quality behind the casing, reducing the need for costly rig time and enhancing well integrity assessment during well abandonment operations.
Implementation Method 1
transmitting, using a sonic transmitter, a set of transmitted sonic waves directed toward and induced in the casing
Implementation Method 2
receiving, at a sonic receiver, a set of waveforms induced in a casing of a borehole
Implementation Method 3
unipole transmitters and receivers mounted on a rotary head to scan the casing
Implementation Method 4
extracting an amplitude for the target set of A0 wave from the slowness-frequency amplitude map using a slowness-frequency window determined by the slowness-frequency semblance analysis
Data Source
AI summary
Cement bonding evaluation and logging in a wellbore environment are described. The cement bonding evaluation is performed using data associated with and processed from the measurement of sonic waves directed to and dissipated by the casing present in the wellbore.