Downhole Capacitive Electrode System for Orthogonal Field Measurement
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Solution Overview
Problem
Conventional methods for measuring and generating electrical fields in boreholes face challenges due to galvanic contact issues and distortion caused by casing, leading to noise and electrode failure, limiting the ability to accurately probe subsurface electrical conductivity.
Innovation Solution
A system with an electrode in electrical contact with the Earth, using capacitive coupling to measure or generate electrical fields orthogonal to the borehole axis, minimizing galvanic contact and distortion, and incorporating a shield to reduce noise from borehole fluid.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional galvanic contact methods are used to couple electrical circuits to the Earth in boreholes, then electrical field measurement can be performed, but electrode noise increases and electrode failure occurs due to streaming potentials and motion artifacts
Solution Approach 1:
The patent replaces the mechanical galvanic contact system with an electromagnetic coupling system. Instead of using physical electrodes in direct contact with borehole fluids and formations (which cause noise and failure), the invention uses electromagnetic sources and sensors that couple to the Earth through the borehole wall, eliminating mechanical contact artifacts while maintaining electrical field measurement capability
Solution Approach 2:
The patent introduces the borehole wall and surrounding formation as intermediaries between the electromagnetic source and the Earth's subsurface. The electromagnetic field couples through these intermediate structures without requiring direct electrode contact with the borehole fluid or formation, thereby eliminating streaming potentials and motion-related noise
2Measurement precision
If electrodes are placed on the outside of casing to avoid galvanic contact issues, then measurement noise decreases, but field distortion increases due to casing proximity
Solution Approach 1:
The patent moves the electromagnetic source and sensor from the radial dimension (inside or outside casing) to the axial dimension (along the borehole axis). By positioning sources and sensors at different depths along the borehole axis rather than at different radial positions, the system achieves both low noise and minimal field distortion simultaneously
3Ease of manufacture
If surface-based EM sources are used for geophysical soundings, then field generation is simple, but field attenuation and measurement uncertainty increase with depth
Solution Approach 1:
The patent pre-positions electromagnetic sources and sensors within the borehole at the desired measurement depth before conducting the survey. This preliminary placement eliminates the need for surface-based sources to generate fields that must penetrate deep into the Earth, thereby reducing attenuation and improving depth resolution while maintaining operational simplicity
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 accurate measurement and generation of electrical fields orthogonal to the borehole axis, reducing noise and extending the survey area, allowing for more effective subsurface mapping and increased depth of investigation.
Implementation Method 1
using capacitive coupling to measure or generate electrical fields orthogonal to the borehole axis, minimizing galvanic contact
Implementation Method 2
incorporating a shield to reduce noise from borehole fluid
Implementation Method 3
an electrical field produces electrical currents in the earth that have an associated magnetic field
Implementation Method 4
a time varying magnetic field induces electrical currents that result in an electrical field
Data Source
AI summary
The invention relates to measuring and generating electrical fields downhole. In one embodiment a system is provided that includes an amplifier connected to a first electrode in electrical contact with the Earth via an operative capacitive coupling. An additional electrode and amplifier are disposed in the borehole opposite the first electrode and constitute a first pair of electrodes spaced in a direction orthogonal to the axis. A second electrode is part of a group of counter electrodes spaced from each other and disposed outside the borehole. The first pair of electrodes and the amplifiers are configured to be one of a source that generates an electrical field in a direction substantially orthogonal to the axis of the borehole and a sensor that measures an electric field substantially orthogonal to the axis of the borehole.