Resistivity Logging Ratio Signals for Anisotropic Formation Inversion
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Solution Overview
Problem
Existing resistivity logging technologies face challenges in accurately measuring formation resistivity, anisotropy, dip, and strike angles due to complex interactions in anisotropic formations and non-perpendicular boreholes, often relying on simplified models that result in suboptimal measurement quality.
Innovation Solution
A resistivity logging method and system utilizing ratio-based signals to determine formation parameters like horizontal resistivity, anisotropy, dip, and strike angles, employing a multi-component electromagnetic logging tool with tilted antennas and advanced signal processing techniques to account for tool orientation and environmental effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If simplified models are used to interpret electromagnetic logging measurements, then measurement speed is improved, but measurement precision deteriorates
Solution Approach 1:
The patent transforms the complex non-linear inversion problem into a linear least-squares problem by changing the parameterization approach. Instead of directly inverting for formation parameters using simplified models, the method computes ratio-based signals that linearly relate to formation properties, enabling accurate results with computationally efficient linear inversion techniques.
Solution Approach 2:
The patent introduces ratio-based signals as intermediary quantities that mediate between the raw electromagnetic measurements and the formation parameters. These ratio signals serve as intermediate representations that capture formation properties while being insensitive to certain environmental variations, enabling more accurate and efficient inversion.
2Measurement precision
If complex models accounting for all formation parameters are used, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent extracts and separates the determination of different formation parameters (horizontal resistivity, vertical resistivity, anisotropy, dip, strike) into distinct computational steps based on different ratio signals. This allows each parameter to be determined independently using optimized inversion approaches, reducing the complexity of simultaneously solving for all parameters together.
3Ease of operation
If traditional logging tools are used in anisotropic formations with dipping beds, then ease of operation is maintained, but measurement precision deteriorates
Solution Approach 1:
The patent employs dynamic signal processing that adapts to the actual formation conditions by computing multiple ratio-based signals with different sensitivities. The inversion process dynamically determines the optimal combination of signals for each measurement depth, allowing the system to automatically adjust to anisotropic and dipping formation conditions without requiring manual intervention.
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
The method provides improved accuracy in resistivity measurements and geosteering capabilities by accounting for complex formation properties and tool orientation, leading to more reliable formation parameter determination and reduced sensitivity to environmental and tool-related errors.
Implementation Method 1
a transmitter transmits an electromagnetic signal that passes through formation materials around the borehole and induces a signal in one or more receivers
Data Source
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Figure 8A~8D
AI summary
Electromagnetic resistivity logging systems and methods yielding formation anisotropy and dip from a signal set that closely approximates the response of a idealized tool. One illustrative method embodiment derives from an azimuthally-sensitive tool's measurements a full set of orthogonal direct couplings (Vxx, Vyy, Vzz) and a cross-coupling sum (Vxz+Vzx) or (Vyz+Vzy). These values are converted into a signal set as a function of borehole position, the set including: a first signal representing a ratio between Vzz coupling components at different spacing distances, a second signal representing a ratio between Vxx and Vzz coupling components, a third signal representing a ratio between Vyy and Vzz coupling components, a fourth signal representing a ratio between Vxx and Vyy coupling components, and a fifth signal representing a ratio between a cross-coupling sum and a sum of the direct couplings. From this signal set, formation parameters can be accurately determined by inversion.