Antenna Array Configuration for Deep Resistivity Logging
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Solution Overview
Problem
Conventional resistivity logging tools require increased length to achieve deep measurements, limiting their versatility and efficiency in measuring formation resistivity at various depths without altering the tool's length.
Innovation Solution
An apparatus with a pair of transmitter antennas and a pair of receiver antennas mounted on an elongate conductive body, where the transmitters are positioned on one side of the receivers, allowing for both near and far resistivity measurements by alternating the roles of the antenna pairs and adjusting their spacing, enabling extended depth of investigation without tool length changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If transmitter-receiver spacing is increased to achieve deep resistivity measurement, then depth of investigation is improved, but tool length increases
Solution Approach 1:
The patent transitions from a linear arrangement of antennas to a planar configuration where transmitter and receiver antenna pairs are positioned side-by-side rather than end-to-end. This dimensional change allows the tool to achieve the necessary transmitter-receiver spacing for deep investigation while maintaining a compact tool length suitable for logging while drilling operations.
Solution Approach 2:
The patent employs an asymmetric arrangement where the transmitter antenna pair and receiver antenna pair are offset from each other laterally rather than being symmetrically distributed along the tool axis. This asymmetric positioning enables the transmitters to be located to one side of the receivers, creating the required spacing for deep measurement without extending the tool length in the axial direction.
2Measurement precision
If transmitter-receiver spacing is increased to achieve deep resistivity measurement, then depth of investigation is improved, but device complexity increases
Solution Approach 1:
The patent divides the antenna system into distinct transmitter and receiver pairs that can be independently positioned and configured. This segmentation allows each pair to be optimized for its specific function while maintaining a compact overall structure, avoiding the complexity that would arise from a single long linear array of antennas.
Solution Approach 2:
By positioning antennas in a lateral configuration rather than extending them axially, the patent achieves deep investigation capability without proportionally increasing the number of components or their interconnections, thereby limiting the growth of device complexity.
3Adaptability or versatility
If tool length is reduced for shallow measurements, then adaptability is improved, but depth of investigation decreases
Solution Approach 1:
The patent creates a universal antenna configuration that can perform both shallow and deep resistivity measurements by utilizing the same lateral arrangement of transmitter and receiver pairs. The side-by-side positioning allows the tool to maintain adaptability for various measurement depths without requiring multiple specialized tools or configurations.
Solution Approach 2:
The asymmetric lateral positioning of transmitter and receiver pairs enables the tool to achieve both near and far resistivity measurements from a compact structure, providing versatility across different depth ranges while maintaining a short tool length suitable for logging while drilling operations.
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
Enables precise resistivity measurements at various depths using the same tool, reducing the length required for deep investigations while maintaining measurement accuracy, and allowing for both near and far resistivity measurements without increasing the tool's length.
Implementation Method 1
The transmitters when excited with a sinusoidal current, induce a voltage in the loops formed by the drill collar and the formation. This voltage, which can be measured by a secondary winding, creates a current in the formation and the borehole mud.
Implementation Method 2
A receiver measures the current running on the drill collar at the location of the receiver. A pair of receivers can measure the difference in axial current, which is the radial current entering the formation between the two receivers.
Data Source
AI summary
An apparatus for determining the resistivity of formation surrounding a borehole comprising:an elongate conductive body;a pair of transmitter antennas comprising first and second antennas mounted on the body for inducing a current in the formation; anda pair of receiver antennas comprising first and second antennas mounted on the body for measuring an axial current running in the tool body at the location of the receivers;wherein the pair of transmitter antennas is located to one side of the pair of receiver antennas.