Resistivity Imaging Phase-Sensitive Detection Floating Reference

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Solution Overview

Problem

Galvanic imaging devices in oil-base mud are sensitive to the oil-filled gap between the electrode and the geologic formation, leading to obscured formation resistivity measurements due to high ground resistance and mud cake properties, making it difficult to produce high-definition images.

Innovation Solution

The use of phase-sensitive detection with a floating reference signal, where mud-filled chambers are used to measure the electric field between electrodes and conductive plates, allowing for accurate impedance measurements independent of the oil-filled gap, by introducing an alternating current and measuring phase differences and impedance amplitudes.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If small buttons with radius 1-2 mm are used to improve spatial resolution, then the tool spatial resolution is improved, but the ground resistance increases to 10,000-10,000,000 Ohm

Engineering Contradiction:

Improvespatial resolutionVSAvoidground resistance

Core Design Contradiction:

Manufacturing precisionVSMeasurement precision

Solution Approach 1:

A conductive plate is introduced as an intermediary element between the electrode and the formation. The plate has a larger surface area than the electrode, which reduces the ground resistance while maintaining the spatial resolution determined by the electrode size. The plate serves as a mediator that distributes the current over a larger area, reducing the resistance without compromising the imaging resolution.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The solution transitions from a point-contact electrode to a planar conductive plate structure. By adding the dimensional aspect of the plate's surface area, the system achieves lower ground resistance while the electrode's smaller dimensions maintain the spatial resolution. This dimensional expansion allows simultaneous optimization of both resolution and resistance.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

2Measurement precision

If phase sensitive detection with floating reference is used to reduce the influence of oil-filled gap, then the measurement accuracy is improved, but the device complexity increases due to additional mud chambers and conductive plates

Engineering Contradiction:

Improveformation resistivity measurementVSAvoiddevice structure

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

Mud-filled chambers are introduced as intermediary structures that contain conductive plates. These chambers serve as reference measurement paths that are insensitive to the oil-filled gap between the electrode and formation. By measuring the electrical properties through the mud-filled reference path and comparing it with the formation measurement, the system eliminates the harmful effects of the oil gap while the added structural complexity is confined to these reference chambers.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Measurement precision

If alternating current is introduced to enable phase sensitive detection, then the ability to differentiate formation measurement from reference signal is improved, but the energy consumption increases

Engineering Contradiction:

Improvesignal differentiationVSAvoidenergy consumption

Core Design Contradiction:

Measurement precisionVSUse of energy by moving object

Solution Approach 1:

Alternating current is used instead of direct current to enable phase-sensitive detection. The periodic nature of the AC signal allows differentiation between the formation measurement and the reference signal through phase comparison. This periodic action enables the system to extract formation resistivity information while rejecting the influence of the oil-filled gap, with energy consumption managed through efficient AC circuit design and appropriate frequency selection.

Inventive Principle:

Principle #19Periodic action

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 characterization of geologic formations by differentiating the formation measurement from the reference signal, reducing the influence of the oil-filled gap and improving spatial resolution in resistive mud environments.

Implementation Method 1

introducing an alternating current and measuring phase differences and impedance amplitudes

Methodology Applied

Scientific EffectAlternating current:

Implementation Method 2

measuring phase differences and impedance amplitudes

Methodology Applied

Scientific EffectImpedance measurement: Electrical Impedance Tomography

Implementation Method 3

phase-sensitive detection with a floating reference signal

Methodology Applied

Scientific EffectPhase sensitive detection: Homodyne Detection

Implementation Method 4

an electric field may be maintained between the conductive plate and the electrode; The floating reference represents the electric field in the gap

Methodology Applied

Scientific EffectElectric field: Electric Field

Data Source

PatentUS8773135B2Resistivity imaging using phase sensitive detection with a floating reference signal

Publication Date: 2014.07.08 BAKER HUGHES CO

AI summary

A device, method and system for measuring characteristics of a geologic formation using a floating reference signal having a mud chamber, an electrode disposed within the mud chamber, and an electrically conductive plate disposed within the mud chamber, the plate separated from the electrode. An alternating current source is provided on the electrode, whereby an electric field is be maintained between the electrode and the conductive plate. An opening in the mud chamber allows drilling fluids to pass there through.