Downhole Acoustic Logging Tool Elastic Anisotropy Measurement
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Solution Overview
Problem
Conventional downhole acoustic measurement systems can only determine three or four out of the five elastic constants of a transversely isotropic medium, requiring geophysical inferences for the remaining constant, which can be problematic.
Innovation Solution
A downhole acoustic logging tool with both axially and circumferentially spaced receivers, capable of obtaining and processing both axial and circumferential acoustic measurements to directly compute the five elastic constants of a transversely isotropic medium.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional axial acoustic measurements are used, then the measurement system is simple, but only three or four elastic constants can be determined requiring problematic geophysical inferences
Solution Approach 1:
The patent transitions from conventional single axial array measurements to a dual-array configuration with both axial and circumferential receiver arrays. This dimensional expansion in measurement geometry enables capture of acoustic wave propagation in multiple directions (axial, circumferential, and cross-axial), providing sufficient independent measurements to directly determine all five elastic constants of transversely isotropic formations without requiring geophysical inferences.
Solution Approach 2:
The receiver array is segmented into distinct functional groups: axial receivers for measuring wave propagation along the borehole axis, and circumferential receivers for measuring wave propagation around the borehole circumference. This segmentation allows each receiver set to capture specific components of elastic wave propagation, collectively enabling complete characterization of the five elastic constants through coordinated measurement of P-wave and S-wave velocities in different directions.
2Reliability
If axial and circumferential acoustic measurements are obtained, then all five elastic constants can be directly determined, but the device complexity increases
Solution Approach 1:
The system processes acoustic measurements from both axial and circumferential receiver arrays to compute P-wave and S-wave velocities in multiple directions. These velocity measurements provide feedback that is used to directly calculate all five elastic constants (c11, c33, c55, c66, c13) through established relationships between acoustic wave propagation and elastic properties, eliminating the need for iterative geophysical inferences and improving reliability.
Solution Approach 2:
The dual-array acoustic logging tool performs multiple measurement functions simultaneously: it measures P-wave velocities in axial and circumferential directions, S-wave velocities in multiple orientations, and captures cross-axial wave propagation characteristics. This multi-functionality allows a single tool configuration to provide all necessary data for complete elastic constant determination, making the increased device complexity worthwhile by achieving comprehensive formation characterization.
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
Enables the direct determination of all five elastic constants without assumptions, providing more accurate and reliable results in real-time during drilling, and over-specifying the system for improved reliability.
Implementation Method 1
acoustic signals may be generated at one or more transmitters deployed in the borehole. These acoustic signals may then be received at an array of longitudinally spaced receivers deployed in the borehole
Data Source
AI summary
A downhole acoustic logging tool includes at least one acoustic transmitter and first and second arrays of acoustic receivers deployed on a tool body. The first array of acoustic receivers includes a plurality of axially spaced apart acoustic receivers and the second array of acoustic receivers includes a plurality of circumferentially spaced apart acoustic receivers. A method for making downhole acoustic logging measurements of a subterranean formation includes causing an acoustic logging tool to obtain axial acoustic logging measurements and circumferential acoustic logging measurements. The axial acoustic logging measurements and the circumferential acoustic logging measurements are then processed to compute each of five elastic constants of a transversely isotropic medium.