Refracted Ultrasonic Standoff Measurement for Borehole Geometry
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Solution Overview
Problem
Borehole geometry evaluation in subterranean formations is challenging due to irregular borehole shapes, especially in weak, highly stressed, or fractured rock, where caliper measurements are unreliable and ultrasonic pulse-echo techniques face energy coupling issues in soft formations.
Innovation Solution
An apparatus and method using refracted acoustic waves, specifically ultrasonic waves transmitted at a critical incidence angle, to measure standoff and borehole geometry by calculating travel time and combining measurements from multiple azimuths and depths, enabling accurate geometry data collection even in soft formations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If ultrasonic pulse-echo techniques are used to measure borehole geometry, then measurements can be obtained in hard formations, but energy coupling is insufficient in soft formations leading to unreliable measurements
Solution Approach 1:
Instead of using pulse-echo techniques that rely on reflected energy, the invention uses transmitted acoustic waves that travel through the borehole fluid and are detected by receivers. This inverts the measurement approach from reflection-based to transmission-based, enabling reliable measurements in soft formations where energy coupling is difficult.
Solution Approach 2:
The invention introduces borehole fluid as an intermediary medium to couple acoustic energy between the transmitter and borehole wall. The fluid acts as a mediator that facilitates energy transfer in soft formations where direct coupling is insufficient, allowing acoustic waves to propagate effectively.
2Measurement precision
If caliper measurements are used to evaluate borehole geometry, then local diameter measurements can be obtained, but the measurements are unreliable in irregular borehole shapes
Solution Approach 1:
The invention transitions from two-dimensional caliper measurements to three-dimensional acoustic imaging by using multiple receivers at different positions and combining travel time measurements. This dimensional enhancement allows accurate geometry characterization of irregular borehole shapes that cannot be captured by simple caliper measurements.
Solution Approach 2:
The invention changes the measurement parameter from direct physical contact (caliper) to acoustic travel time. By measuring the time for acoustic waves to travel from transmitter to receivers through the borehole fluid, the system can accurately determine borehole geometry without physical contact, adapting to irregular shapes.
3Reliability
If traditional ultrasonic techniques are used in highly stressed or fractured rock, then measurements can be obtained in stable boreholes, but the measurements fail in weak or fractured rock conditions
Solution Approach 1:
The invention replaces mechanical contact-based caliper measurements with acoustic wave-based measurements. This substitution eliminates the need for physical contact with the borehole wall, allowing reliable measurements in weak or fractured rock conditions where mechanical systems would fail or provide inaccurate data.
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 provides reliable borehole geometry data, enhancing mechanical stability assessment and improving logging measurements by effectively calculating standoff and geometry in challenging rock conditions, outperforming traditional ultrasonic pulse-echo techniques.
Implementation Method 1
at least one transmitter operable to generate an acoustic wave that is refracted along a wall of the borehole
Implementation Method 2
generate an acoustic wave that is refracted along a wall of the borehole
Implementation Method 3
at least one receiver operable to receive the refracted wave
Data Source
AI summary
Refracted ultrasonic waves are utilized to calculate tool standoff. An ultrasonic transmitter sends a wave toward (and into) the borehole wall at a critical incidence angle for refracted waves. The refracted wave travels along the borehole wall and continuously radiates energy back into the borehole at the critical angle. The refracted wave is detected by a receiver, and the travel time of the refracted acoustic wave from transmitter to receiver is measured and used to calculate standoff. By making repeated measurements at various azimuths (for instance, as the tool rotates), one or more caliper measurements can be made. The caliper measurements can be combined to yield two-dimensional geometry of the borehole. Measurements made at different azimuths and depths yield three-dimensional borehole geometry. Arrays of transmitter-receiver pairs can be used to obviate the need for varying azimuth.