Near-Bit Resistivity Sensor Using Rotating Magnet Array
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Solution Overview
Problem
Conventional electromagnetic well logging tools face limitations in accurately measuring resistivity and conductivity of earth formations, particularly when looking ahead of the drill bit, due to interference from geological noises and the direct alternating-current field, which affects the accuracy of fluid content and bed boundary measurements.
Innovation Solution
The use of a rotating magnet array with induction receiver coils or toroid coils with a high magnetic permeability core, positioned near the drill bit, generates a time-varying magnetic field to induce alternating currents in the formation, allowing for measurements of electromagnetic signals and magnetic fields without direct electrical power, thus reducing interference and enhancing the ability to measure properties ahead of the drill bit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional electromagnetic well logging tools are used to measure resistivity and conductivity of earth formations, then measurements can be obtained, but accuracy is reduced due to interference from geological noises and direct alternating-current field
Solution Approach 1:
The patent extracts and removes the harmful direct alternating-current field component from the measurement system by using a rotating magnet array that generates only a time-varying magnetic field without direct electrical power connection, thereby eliminating the source of interference that affects measurement accuracy
Solution Approach 2:
The patent introduces a rotating magnet array as an intermediary mechanism between the power source and the formation. This intermediary converts electrical energy to mechanical rotation, which then generates the magnetic field indirectly, preventing direct electrical contact and the associated interference in the formation measurements
2Adaptability or versatility
If measurements are taken closer to the drill bit to look ahead, then ability to measure properties ahead of bit is improved, but interference from geological noises increases
Solution Approach 1:
The rotating magnet array serves as an intermediary that generates a controlled time-varying magnetic field, acting as a shield against unpredictable geological noises. This intermediary mechanism provides a stable, known excitation source that enables reliable measurements even when positioned close to the drill bit for ahead-of-bit looking
3Power
If direct electrical power is used to generate electromagnetic field, then field generation is effective, but direct alternating-current field interference occurs
Solution Approach 1:
The patent replaces the direct electrical power system with a mechanical rotation system. Instead of applying electrical power directly to generate the electromagnetic field, the system uses mechanical rotation of permanent magnets to generate the time-varying magnetic field, thereby substituting a mechanical mechanism for an electrical one and eliminating direct alternating-current field interference
Solution Approach 2:
The patent employs periodic action by rotating the magnet array at a controlled frequency to generate the time-varying magnetic field. This periodic mechanical rotation creates the necessary electromagnetic excitation in a controlled manner, avoiding the continuous direct alternating-current field that causes interference
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 more accurate and distant measurements of formation properties ahead of the drill bit, reducing uncertainty from geological noises and avoiding direct alternating-current field interference, thereby improving the estimation of resistivity and conductivity.
Implementation Method 1
generating an alternating current in a volume of interest of the formation surrounding the borehole with a time varying magnetic field in the volume produced by rotating the sensor assembly about the axis of rotation
Implementation Method 2
The plurality of receiver sensors may comprise induction receiver coils each wound around corresponding permanent magnets of the plurality of permanent magnets
Data Source
AI summary
Systems, methods, and devices for evaluation of an earth formation intersected by a borehole using a logging tool. Tools include sensor assemblies with permanent magnets mounted at a first radial distance from an axis of rotation of the sensor assembly, as well as receiver sensors. The sensor assembly is configured to generate an alternating current in a volume of interest of the formation surrounding the borehole with a time varying magnetic field in the volume produced by rotating the sensor assembly about the axis of rotation. Methods include making EM signal measurements or magnetic field measurements with receiver sensors responsive to the alternating current and estimating at least a formation property of the volume using the measurements.