Tilted Antenna Resistivity Logging Inversion for Anisotropy
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Solution Overview
Problem
Resistivity logging tools face challenges in accurately measuring anisotropic properties of earth formations due to geometric spreading and absorption, requiring improved methods to account for formation anisotropy and relative dip angles for precise resistivity logging.
Innovation Solution
The use of tilted transmit and receive antennas in resistivity logging tools, combined with processor-based inversion parameters derived from antipodal sum and difference signals, allows for efficient determination of horizontal resistivity, vertical resistivity, and relative dip angles, while accounting for anisotropy and orientation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional vertical antennas are used for resistivity logging, then the measurement setup is simple, but the ability to detect anisotropic properties and formation dip angles is insufficient
Solution Approach 1:
The patent employs tilted antennas at specific angles (e.g., 45 degrees) relative to the vertical axis, creating an asymmetric antenna configuration that enables sensitivity to formation anisotropy and dip angles. This asymmetric arrangement allows the measurement system to detect directional variations in resistivity that vertical antennas cannot detect.
Solution Approach 2:
The invention transitions from a single vertical dimension (vertical antennas only) to multiple dimensions by incorporating antennas tilted at various angles in three-dimensional space. This dimensional expansion enables the system to capture electromagnetic responses from multiple orientations, providing the necessary data to characterize anisotropic formations and determine formation dip.
2Measurement precision
If multiple antennas at different orientations are deployed to measure anisotropy, then measurement accuracy improves, but data processing complexity increases
Solution Approach 1:
The patent implements an iterative inversion process where the system compares measured electromagnetic responses with synthetic responses generated from formation models, adjusts the model parameters, and repeats the process until convergence. This feedback mechanism systematically solves the complex inversion problem, extracting accurate formation parameters from multi-orientation antenna data.
Solution Approach 2:
The invention transforms the complex multi-parameter inversion problem by changing parameters into a more manageable form. The system uses parameter transformations and normalization techniques to convert raw electromagnetic responses from multiple antenna orientations into formation parameters (resistivity, anisotropy ratio, dip angle) through systematic mathematical relationships.
3Measurement precision
If tilted antennas are used to account for formation dip, then resistivity log accuracy improves, but the inversion problem becomes more complex
Solution Approach 1:
The patent applies preliminary transformations to the raw electromagnetic data before performing the main inversion process. The system pre-processes the multi-orientation antenna responses by calculating derived parameters and normalizing the data, which simplifies the subsequent inversion problem and reduces computational complexity while maintaining accuracy.
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 accurate and efficient measurement of anisotropic properties, improving the precision of resistivity logs by accounting for directional sensitivity and formation orientation, thereby enhancing the ability to detect hydrocarbons in petroleum well drilling.
Implementation Method 1
The transmitter antenna is used to create electromagnetic fields in the surrounding formation
Implementation Method 2
the electromagnetic fields in the formation induce an electrical voltage in each receiver antenna
Data Source
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Figure 7~8C
AI summary
Various resistivity logging tools, systems, and methods are disclosed At least some tool embodiments include transmit and receive antennas that measure the electromagnetic response of the formation, at least one of which is tilted to provide a directional sensitivity A processor converts the response (measured as a function of the tool's rotation angle) into a set of inversion parameters, which are then used to estimate the anisotropic properties of the formation The set of inversion parameters includes at least one parameter based on an antipodal sum of the response signal, and may further include parameters based on an antipodal difference and an average of the signal response Antipodal sum and difference values at different rotational orientations can be included in the set of inversion parameters, and they may be normalized to reduce environmental effects Some tool embodiments collect the relevant formation measurements using parallel or perpendicular tilted antennas