Acoustic Logging Stress Estimation in Anisotropic Shale Formations
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional techniques fail to accurately identify layers in organic-shale reservoirs subject to large anisotropic horizontal stresses without breakouts, as they cannot measure differences between maximum and minimum horizontal stresses in the absence of borehole breakouts.
Innovation Solution
The method involves using azimuthal variations in compressional and shear slownesses or velocities from ultrasonic data and cross-dipole dispersions from sonic data to estimate the magnitude of maximum horizontal stress and nonlinear constants, employing acoustoelastic models and specific logging tools like the ISOLATION SCANNER™ and SONIC SCANNER™ to analyze stress-induced shear anisotropy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional techniques are used to measure formation stresses, then measurement simplicity is maintained, but measurement precision deteriorates because they cannot identify layers with large anisotropic horizontal stresses in the absence of breakouts
Solution Approach 1:
The measurement system is segmented into multiple independent components: ultrasonic transducers for high-frequency azimuthal velocity measurements, sonic tools for cross-dipole dispersion data, and separate inversion algorithms for stress estimation. This segmentation allows each component to be optimized independently while maintaining overall system functionality, resolving the contradiction between precision and complexity
Solution Approach 2:
The acoustic logging system performs multiple functions: it measures compressional wave velocities, shear wave velocities, and Stoneley wave velocities simultaneously using the same tool platform. The ultrasonic and sonic measurements are integrated into a single logging operation, enabling stress characterization without requiring separate specialized devices, thus maintaining ease of operation while improving measurement precision
2Measurement precision
If azimuthal variations in compressional and shear slownesses are measured using ultrasonic data, then stress detection accuracy is improved, but measurement time increases
Solution Approach 1:
The ultrasonic transducers continuously scan through all azimuthal angles (0-360 degrees) without interruption, collecting velocity data at multiple angular positions in a single continuous measurement pass. This continuous azimuthal scanning eliminates the need for repeated measurements at discrete angles, maintaining high stress detection accuracy while minimizing total measurement time
Solution Approach 2:
The system performs preliminary azimuthal velocity measurements at selected angular positions before conducting the complete 360-degree scan. These preliminary measurements provide initial stress orientation information that guides the subsequent full azimuthal survey, allowing the system to focus measurement efforts on critical azimuthal sectors and reduce overall measurement time while maintaining detection accuracy
3Loss of information
If cross-dipole dispersions are analyzed from sonic data, then stress profile detail is improved, but data processing complexity increases
Solution Approach 1:
The complex inversion process that transforms raw cross-dipole dispersion data into stress profiles is replaced with a pre-calibrated lookup table system. During tool deployment, measured dispersion patterns are compared against a library of pre-computed dispersion curves corresponding to known stress conditions. This substitution eliminates the need for real-time complex mathematical inversions, maintaining detailed stress profile information while dramatically reducing data processing complexity
Solution Approach 2:
Instead of performing complex real-time inversions of cross-dipole dispersion data, the system creates simplified copies of the dispersion relationships in the form of empirical correlations and reference models. These copied relationships allow direct estimation of stress parameters from measured dispersion data without requiring sophisticated inversion algorithms, thus preserving stress profile detail while reducing processing complexity
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 allows for the accurate estimation of maximum horizontal stress and nonlinear constants in anisotropic formations, even in the absence of breakouts, enhancing well planning and reservoir management by providing detailed stress profiles.
Implementation Method 1
Mechanical disturbances are used to establish elastic waves in earth formations surrounding a borehole, and properties of the waves are measured to obtain information about the formations through which the waves have propagated
Implementation Method 2
It is known that elastic wave velocities change as a function of prestress in a propagating medium
Implementation Method 3
Near-wellbore stress concentrations in certain anisotropic formations (such as interbedded carbonate layers in shale formations) cause azimuthal variations in the compressional and shear velocities (or slownesses)
Implementation Method 4
cross-dipole dispersions of the formation measured from sonic data acquired by the at least one acoustic logging tool
Data Source
AI summary
Methods and systems are provided that identify relatively large anisotropic horizontal stresses in a formation based on (i) azimuthal variations in the compressional and shear slownesses or velocities of the formation measured from ultrasonic data acquired by at least one acoustic logging tool as well as (ii) cross-dipole dispersions of the formation measured from sonic data acquired by the at least one acoustic logging tool. In addition, the azimuthal variations in the compressional and shear slownesses or velocities of the formation and dipole flexural dispersions of the formation can be jointly inverted to obtain the elastic properties of the rock of the formation in terms of linear and nonlinear constants and the magnitude of maximum horizontal stress of the formation. A workflow for estimating the magnitude of the maximum horizontal stress can employ estimates of certain formation properties, such as overburden stress, magnitude of minimum horizontal stress, and pore pressure.