Logging Tool Pad Body Reduces Current Leakage

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Solution Overview

Problem

Electrical earth borehole logging tools face challenges with electric current leakage and signal degradation due to high frequencies and large standoff distances between the tool mandrel and the earth formation, especially in conductive formations, which affect resistivity imaging accuracy.

Innovation Solution

The solution involves a logging tool with a pad body, transmitters, and measure electrodes, where the ratio of transmitter area to measure electrode area and impedance between the pad body and the logging tool body are optimized to reduce current leakage, and a processor estimates resistivity parameters using the measured impedance and transmitter potential.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If higher frequencies of operation are used, then imaging quality improves, but current leakage to the tool mandrel increases

Engineering Contradiction:

Improveimaging qualityVSAvoidcurrent leakage

Core Design Contradiction:

Measurement precisionVSLoss of energy

Solution Approach 1:

A pad body is introduced as an intermediary component between the transmitters and the tool mandrel. The pad body provides electrical isolation, preventing current leakage to the mandrel while maintaining the beneficial effects of higher frequency operation for improved imaging quality

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The tool is segmented into electrically isolated components: transmitters mounted on the pad body, measure electrodes electrically isolated from both transmitters and mandrel, and the pad body itself acting as an isolated platform. This segmentation prevents unwanted current paths while preserving signal integrity

Inventive Principle:

Principle #1Segmentation

2Adaptability or versatility

If larger standoff distance exists between tool mandrel and formation, then tool design flexibility improves, but signal quality degrades

Engineering Contradiction:

Improvetool design flexibilityVSAvoidsignal quality

Core Design Contradiction:

Adaptability or versatilityVSMeasurement precision

Solution Approach 1:

The pad body acts as an intermediary that maintains consistent electrical coupling to the formation even when standoff distance varies. This allows the tool to accommodate different borehole conditions and design requirements without compromising signal quality

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The system maintains effective electrical coupling by optimizing the configuration parameters of transmitters and measure electrodes on the pad body, allowing operation across varying standoff distances through parameter adjustment rather than requiring fixed geometric relationships

Inventive Principle:

Principle #35Parameter changes

3Loss of energy

If transmitters and measure electrodes are electrically isolated, then current leakage reduces, but device complexity increases

Engineering Contradiction:

Improvecurrent leakage reductionVSAvoidelectrical isolation requirements

Core Design Contradiction:

Loss of energyVSDevice complexity

Solution Approach 1:

Multiple electrical isolation functions are merged into a single integrated pad body structure. The pad body simultaneously serves as the mounting platform for transmitters, the electrical isolation barrier, and the structural interface with the formation, simplifying the overall design while achieving current leakage reduction

Inventive Principle:

Principle #5Merging (Combining)

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 configuration effectively minimizes current leakage and enhances resistivity imaging sensitivity, providing accurate resistivity parameter estimation and improved imaging quality even at higher frequencies and larger standoff distances.

Implementation Method 1

A measured electric current flows in a circuit that connects a current source to the transmitter, through the earth formation to the return electrode and back to the current source in the tool

Methodology Applied

Scientific EffectElectrical current flow: Conduction (electrical)

Implementation Method 2

In inductive measuring tools, an antenna within the measuring instrument induces a current flow within the earth formation

Methodology Applied

Scientific EffectElectromagnetic induction: Electromagnetic Induction

Implementation Method 3

The magnitude of the induced current is detected using either the same antenna or a separate receiver antenna

Methodology Applied

Scientific EffectElectromagnetic detection: Electromagnetic Induction

Data Source

PatentUS8862406B2Electrical imager operating in oil-based mud and low resistive formation

Publication Date: 2014.10.14 BAKER HUGHES CO

AI summary

This disclosure relates to apparatuses and methods for reducing current leakage between a measure electrode and a logging tool body during borehole investigations in an earth formation involving electric current and non-conductive drilling fluid. The apparatus may include one or more transmitters disposed on a pad body, configured to inject an electric current into the earth formation, and coupled to the mandrel and one or more measure electrodes. The measure electrodes may be configured to receive current from the formation and coupled to a back plate of the pad body. The apparatus may be configured to maintain a selected ratio between pad body to logging tool body impedance and transmitters to logging tool body impedance sufficient to reduce current leakage between the earth formation and the logging tool body. The transmitter/mandrel and measure electrode/back plate may be electrically isolated from one another. The method may include using the apparatus.