Rotating Unipole Acoustic Source for Formation Anisotropy Measurement
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Solution Overview
Problem
Current acoustic logging systems face limitations in accurately measuring anisotropic properties of earth formations due to operational and environmental factors, particularly in measuring shear velocity and directional stress, especially in drilling environments where frequencies are restricted.
Innovation Solution
A system employing a unipole acoustic source and synchronously rotatable receiver stations within a borehole to measure shear velocity as a function of azimuthal angle, detecting abrupt changes to determine anisotropy parameters, including the direction of minimum/maximum stress, using high-frequency operations for LWD and wireline logging systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional monopole or dipole acoustic sources are used in MWD/LWD systems, then formation acoustic properties can be measured, but measurement precision is limited due to operational and environmental factors restricting source frequencies
Solution Approach 1:
The patent changes the fundamental parameter of the acoustic source from conventional monopole/dipole to a rotating unipole source. This parameter change enables the system to measure formation anisotropy at frequencies suitable for LWD/MWD operations (above 100 Hz) while achieving the necessary measurement precision for anisotropy characterization. The rotating unipole source creates a time-varying acoustic field that encodes directional information, resolving the contradiction between frequency constraints and measurement accuracy.
2Productivity
If acoustic logging systems operate in drilling environments, then real-time formation evaluation is achieved, but measurement precision deteriorates due to operational and environmental factors
Solution Approach 1:
The system performs preliminary measurements of formation acoustic properties using the rotating unipole source during drilling operations. By continuously rotating the unipole source and measuring the time-varying acoustic responses at multiple receiver stations, the system preliminarily characterizes formation anisotropy parameters (shear velocity, stress direction) in real-time. This preliminary action enables subsequent corrections to seismic images and drilling mechanics estimates, resolving the contradiction between real-time evaluation and measurement precision.
3Measurement precision
If unipole acoustic source operates at high frequency for LWD systems, then anisotropy parameters can be determined, but device complexity increases compared to conventional systems
Solution Approach 1:
The rotating unipole source mechanism serves multiple functions: it generates acoustic energy, encodes directional information through rotation, and enables anisotropy measurement at frequencies suitable for LWD operations. By making the source rotate synchronously with the drill string, the system achieves anisotropy measurement capability without requiring separate measurement tools, thus reducing overall device complexity while maintaining high measurement precision.
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 precise determination of anisotropy parameters, improving the accuracy of seismic imaging and drilling mechanics estimation by effectively measuring shear velocities and stress directions in anisotropic formations, even in challenging drilling conditions.
Implementation Method 1
a unipole acoustic source; measure responses of said receiver stations in azimuthal angular segments; process said responses to determine shear velocity of said formation as a function of azimuthal angle
Implementation Method 2
determine said parameter quantifying anisotropy of said formation using said shear velocities as a function of said azimuthal angle by detecting an abrupt change in shear velocity, wherein said parameter includes an angular direction of minimum/maximum stress of said formation
Data Source
Figure 1~2B
Figure 2A
Figure 3~4
AI summary
A logging system for measuring anisotrophic properties of the materials penetrated by a borehole. A downhole or "logging tool" element of the system comprises a source section (23) that comprises either a unipole or a dipole acoustic source. The receiver section (22) comprises a plurality of receiver stations (24) disposed at different axial spacings from the acoustic source. Each receiver station comprises one or more acoustic receivers. The system requires that the source and receiver sections rotate synchronously as the logging tool is conveyed along the borehole. Receiver responses are measured in a plurality of azimuthal angle segments and processed as a function of rotation angle of the tool. The logging system can be embodied as a logging-while-drilling system, a measurement-while-drilling system, and a wireline system that synchronously rotates source and receiver sections. All embodiments require that the acoustic source operate at a relatively high frequency.