Estimating Transversely Isotropic Elastic Constants from Borehole Sonic Data
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Solution Overview
Problem
Current methods for estimating all five transversely-isotropic (TI) elastic constants in hydrocarbon reservoirs are limited, often averaging anisotropic properties over large volumes and failing to provide high axial resolution, which is crucial for optimal hydrocarbon extraction and hydraulic fracture design in organic-rich shale formations.
Innovation Solution
A method that uses borehole sonic data from a single horizontal well, combining sonic data processing with reflection and refraction data from nearby stiff layers, such as limestone, to estimate all five TI-elastic constants with high axial resolution, enabling accurate characterization of anisotropic elastic properties and formation stress distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional methods are used to estimate TI elastic constants, then the estimation can be performed, but the axial resolution is low and anisotropic properties are averaged over large volumes
Solution Approach 1:
The method segments the estimation process into distinct components: processing monopole refracted headwaves for C11, processing fast-dipole waveforms for C66, processing slow-dipole waveforms for C55, and solving travel-time equations for C33 and C13. This segmentation allows high-resolution estimation of individual elastic constants without requiring complex integrated measurements.
Solution Approach 2:
The patent utilizes reflection data from horizontal proximate stiff layers (limestone stringers) to provide additional constraints on the elastic constants. By combining sonic data from multiple wave types with reflection data, the method resolves the underdetermined system and achieves high axial resolution through multi-dimensional data integration.
2Measurement precision
If high axial resolution is achieved, then local heterogeneities can be characterized, but the method requires combining multiple data types from horizontal wells
Solution Approach 1:
The method merges processing of multiple sonic wave types (monopole refracted headwaves, fast-dipole waveforms, slow-dipole waveforms) with reflection data from horizontal proximate stiff layers. This combination provides sufficient constraints to solve for all five TI elastic constants with high axial resolution while maintaining a systematic approach to data integration.
Solution Approach 2:
Horizontal proximate stiff layers (such as limestone stringers) serve as intermediary reflectors that provide additional data constraints. These layers act as natural markers that enable the inversion process to resolve elastic constants with high precision by providing reference points for travel-time analysis.
3Measurement precision
If all five TI elastic constants are estimated, then complete anisotropic characterization is achieved, but existing methods average properties over large volumes
Solution Approach 1:
The method achieves local quality by estimating elastic constants at specific axial positions along the horizontal well trajectory. By using reflection data from horizontal proximate stiff layers and processing multiple wave types, the inversion can resolve elastic constants at the scale of individual heterogeneities rather than averaging over large volumes.
Solution Approach 2:
The method performs preliminary processing of sonic waveforms to extract travel times and amplitudes for different wave types before inversion. This preliminary action organizes the data in a way that facilitates the subsequent inversion for elastic constants, enabling high-resolution estimation without requiring complex real-time processing.
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 precise estimation of TI-elastic constants as a function of depth along a lateral producer well, enhancing the reliability of hydrocarbon extraction and hydraulic fracture placement by accounting for local shale heterogeneities and improving completion strategies.
Implementation Method 1
borehole sonic data obtained from at least one subterranean borehole in a transversely isotropic formation
Implementation Method 2
A monopole transmitter emits energy equally in omni-direction away from its center
Implementation Method 3
a dipole transmitter emits energy in a particular direction
Implementation Method 4
A Stoneley wave propagates along the interface between the borehole fluid and the formation
Implementation Method 5
the monopole low frequency sonic signal may attenuate depending on characteristics of the geological formation along the borehole, such as a fracture or permeable zone
Implementation Method 6
Monopole refracted headwaves may include monopole compressional and shear headwaves
Data Source
AI summary
A method for estimating all five transversely-isotropic (TI)-elastic constants using borehole sonic data obtained from at least one subterranean borehole in a transversely isotropic formation. In an embodiment, the method includes: solving for a quasi-compressional qP-wave velocity VqP using inversion algorithms based on exact solutions of the Kelvin-Christoffel equations for plane wave velocities in arbitrarily anisotropic formations, where the five TI-elastic constants may include C11, C13, C33, C55, and C66.