Segmented NMR Antenna for High-Speed Well Logging

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Solution Overview

Problem

NMR well logging instruments face limitations in measuring accurate porosities and T2 distributions at high speeds due to speed effects, such as incomplete pre-polarization and compression of T2 distributions, which restrict their logging speed compared to other porosity tools.

Innovation Solution

The design incorporates a well logging instrument with a magnet for pre-polarizing nuclear spins and radio frequency antennas, where the receiver section is shorter than the transmitter antenna, allowing for non-overlapping measurements and mitigating speed effects by maintaining transverse magnetization during movement, enabling faster logging speeds without degrading measurement accuracy.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If NMR measurements are performed at high logging speeds, then productivity is improved, but measurement precision deteriorates due to speed effects such as incomplete pre-polarization and compression of T2 distributions

Engineering Contradiction:

Improvelogging speedVSAvoidaccuracy of porosity and T2 distribution measurements

Core Design Contradiction:

ProductivityVSMeasurement precision

Solution Approach 1:

The antenna is divided into two distinct sections: a transmitter antenna for applying RF pulses and a receiver antenna for detecting NMR signals. This segmentation allows the transmitter to cover a larger volume for faster sampling while the receiver maintains optimal signal detection capabilities, thereby enabling high-speed logging without sacrificing measurement precision.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

A dedicated receiver antenna acts as an intermediary between the transmitter antenna and the detection system. This separate receiver antenna optimizes signal reception while the transmitter focuses on excitation, allowing the system to operate at higher speeds without degrading the quality of NMR signal detection.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Measurement precision

If the antenna length is increased to improve signal reception, then measurement precision is improved, but device complexity and measurement time increase

Engineering Contradiction:

Improvesignal detection qualityVSAvoidmeasurement time

Core Design Contradiction:

Measurement precisionVSDuration of action of moving object

Solution Approach 1:

By segmenting the antenna into transmitter and receiver sections, each can be optimized for its specific function. The receiver antenna can be sufficiently long to capture strong signals without requiring the entire antenna system to be extended, thus maintaining measurement precision while reducing overall measurement time and improving logging speed.

Inventive Principle:

Principle #1Segmentation

3Device complexity

If the same antenna is used for both transmission and reception, then device complexity is reduced, but measurement precision deteriorates due to speed effects

Engineering Contradiction:

Improveantenna configurationVSAvoidaccuracy of NMR measurements

Core Design Contradiction:

Device complexityVSMeasurement precision

Solution Approach 1:

The antenna system is segmented into separate transmitter and receiver antennas. This segmentation resolves the conflict by allowing each antenna to be optimized for its specific function - the transmitter for efficient pulse application and the receiver for optimal signal detection - thereby maintaining measurement precision while enabling faster logging speeds.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The separate receiver antenna serves as an intermediary that decouples the transmission and reception functions. This intermediary structure allows the system to achieve high-speed logging without the speed-induced measurement errors that occur when a single antenna must perform both functions.

Inventive Principle:

Principle #24Intermediary (Mediator)

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 allows for accurate measurement of porosities and T2 distributions at significantly higher speeds, up to 1800 feet per hour, comparable to gamma-gamma density and neutron porosity tools, while minimizing the impact of speed-induced errors, thus enhancing the efficiency of NMR well logging.

Implementation Method 1

inducing a static magnetic field in the formation for pre-polarizing nuclear spins

Methodology Applied

Scientific EffectMagnetic field induction: Electromagnetic Induction

Implementation Method 2

applying radio frequency current pulses to the entire transmitter antenna

Methodology Applied

Scientific EffectRadio frequency electromagnetic radiation: Electromagnetic Induction

Implementation Method 3

receiving signals by the at least one of the receiver section of the transmitter antenna and the separate receiver antenna

Methodology Applied

Scientific EffectElectromagnetic signal reception: Electromagnetic Induction

Data Source

PatentUS9759832B1Apparatus and methods for fast NMR well logging without instrument speed effects

Publication Date: 2017.09.12 SCHLUMBERGER TECH CORP

AI summary

An apparatus for NMR properties of subsurface formations includes a magnet, a transmitter antenna and at least one of a receiver section of the transmit antenna or a separate receiver antenna having a length along the longitudinal dimension of the apparatus which is shorter than a length of the transmitter antenna along the longitudinal dimension. The apparatus includes circuitry for applying radio frequency current pulses to the entire transmitter antenna and for receiving signals by the at least one of the receiver section of the transmitter antenna and the separate receiver antenna.