EM Shielding for Deep MWD Resistivity Measurements

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Solution Overview

Problem

Electromagnetic induction well logging is hindered by conductive drill pipes, which reduce sensitivity to formation resistivities and remote boundaries, limiting the ability to effectively measure earth formations ahead of the drill bit, especially at larger angles and in horizontal wells.

Innovation Solution

A method and apparatus using a shielded transmitter and receiver system with a conductive copper shield, positioned between the transmitter and receiver coils, to attenuate parasitic effects from the drill pipe, allowing for deeper and more accurate measurements by combining signals using bucking estimation and phase difference techniques.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If large spacing (up to 20 meters) is created between transmitter and receiver, then the effect of conductive drill pipe is reduced, but the sensitivity to remote boundaries becomes low

Engineering Contradiction:

Improveeffect of conductive drill pipeVSAvoidsensitivity to remote boundaries

Core Design Contradiction:

Object-affected harmful factorsVSMeasurement precision

Solution Approach 1:

A non-conductive shield is introduced as an intermediary component between the transmitter and receiver. This shield blocks the direct electromagnetic coupling path between the conductive drill pipe and the measurement system, allowing the tool to operate with small spacing (maintaining sensitivity to remote boundaries) while eliminating the harmful effect of the conductive pipe.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Measurement precision

If small spacing is used between transmitter and receiver, then sensitivity to remote boundaries is improved, but the effect of conductive drill pipe is enhanced

Engineering Contradiction:

Improvesensitivity to remote boundariesVSAvoideffect of conductive drill pipe

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The non-conductive shield acts as a mediator that enables small spacing between transmitter and receiver (improving sensitivity to remote boundaries) while simultaneously blocking the harmful electromagnetic coupling from the conductive drill pipe. This resolves the contradiction by decoupling the two effects.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The shield provides localized electromagnetic isolation specifically in the region between the transmitter and receiver, allowing the measurement system to have high sensitivity to remote boundaries while the local area around the drill pipe is protected from its harmful conductive effects.

Inventive Principle:

Principle #3Local quality

3Object-affected harmful factors

If non-conductive shield is introduced between transmitter and receiver, then parasitic effects from drill pipe are attenuated, but device complexity increases

Engineering Contradiction:

Improveparasitic effects from drill pipeVSAvoiddevice complexity

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

The non-conductive shield can be implemented as a thin-walled tubular structure that provides effective electromagnetic isolation. This thin-film approach minimizes the added complexity and size while maintaining the function of blocking parasitic effects from the conductive drill pipe.

Inventive Principle:

Principle #30Flexible shells and thin films

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

Enhances the ability to detect resistivity boundaries up to 5 meters ahead in vertical wells and 10 meters in horizontal wells, improving geo-steering and measurement resolution while minimizing the impact of conductive drill pipes on signal sensitivity.

Implementation Method 1

A conductive copper shield is wrapped around the drill pipe between the transmitter and receiver coils. The shield attenuates parasitic electromagnetic signals generated by the conductive drill pipe through electromagnetic induction and eddy current damping, allowing accurate measurement of formation resistivity.

Methodology Applied

Scientific EffectElectromagnetic induction: Electromagnetic Induction

Implementation Method 2

The damping portion includes at least one cut that may be longitudinal or azimuthal. A non-conductive material may be disposed within the cut. Alternatively, the damping portion may include segments having cuts and segments having a non-conducting material on an outer surface thereof.

Methodology Applied

Scientific EffectEddy currents: Eddy Currents

Data Source

PatentUS8278930B2Deep MWD resistivity measurements using EM shielding

Publication Date: 2012.10.02 BAKER HUGHES CO

AI summary

Structure for deep MWD resistivity measurements suitable for both geo-steering and measurements ahead of the drill bit is disclosed. Alternating current is transmitted through a loop and an induction signal is measured by a two-coil bucking receiving system placed at some distance from the transmitter. To further reduce a parasitic effect of the currents in the pipe, a conductive copper shield wrapping around the pipe is used. The length of the shield is about one and one-half to two times longer than the longest transmitter/receiver spacing of the structure. The transmitter/receiver system is located in the center of the described electromagnetic shield.