NMR Antenna Arrays for Fast Logging Without T2 Compression
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Solution Overview
Problem
Existing NMR logging techniques face challenges in achieving fast logging speeds due to incomplete pre-polarization and T2 relaxation time compression, leading to inaccuracies in porosity and fluid characterization.
Innovation Solution
The use of a novel antenna design with separate transmitter and receiver antennas, combined with a multi-frequency RF pulse sequence, allows for non-overlapping measurements and minimizes the T2 speed effect by ensuring the receiver antenna remains within the excited region during motion, thus enabling faster logging speeds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single antenna is used for both transmission and reception in NMR logging, then the device complexity is reduced, but the T2 relaxation time compression and incomplete pre-polarization occur due to instrument motion, leading to measurement inaccuracies
Solution Approach 1:
The antenna system is segmented into separate transmit and receive antennas. The transmit antenna is dedicated to generating RF pulses for exciting nuclear spins, while the receive antenna is dedicated to detecting NMR signals. This segmentation allows each antenna to be optimized for its specific function and enables the receiver to remain stationary within the excited region during instrument motion, eliminating T2 compression effects.
Solution Approach 2:
A separate receive antenna acts as an intermediary between the transmit antenna and the formation. It is positioned within the excited region and remains stationary during instrument motion, serving as a stable detection point that captures NMR signals without being affected by the motion-induced T2 compression that would occur if the same antenna used for transmission also performed reception.
2Productivity
If fast logging speeds are used, then the productivity is improved, but incomplete pre-polarization and T2 relaxation time compression occur, leading to measurement inaccuracies
Solution Approach 1:
By segmenting the antenna functions and placing the receive antenna within the excited region, the system can maintain accurate measurements even at fast logging speeds. The stationary receive antenna continuously samples the excited region, ensuring complete pre-polarization and eliminating T2 compression effects regardless of instrument velocity.
Solution Approach 2:
The transmit antenna establishes a stable excited region in advance before the receive antenna begins measurement. This preliminary action of creating a well-defined excited region allows the receive antenna to remain stationary and continuously sample fully polarized spins, enabling fast logging without compromising measurement accuracy.
3Ease of operation
If the receiver antenna moves with the instrument during measurement, then the ease of operation is improved, but the T2 speed effect occurs causing loss of transverse magnetization and signal amplitude reduction
Solution Approach 1:
The antenna system is segmented into mobile transmit antenna and stationary receive antenna. The receive antenna is decoupled from instrument motion and remains fixed within the excited region, eliminating the T2 speed effect. This segmentation allows the receiver to maintain stable signal amplitude while the rest of the instrument moves at operational speeds.
Solution Approach 2:
The receive antenna is positioned in a different operational dimension - it is stationary relative to the excited region while the instrument moves. This dimensional separation allows the receiver to maintain a constant position within the magnetic field gradient, preventing loss of transverse magnetization and ensuring reliable signal amplitude regardless of instrument velocity.
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 NMR logging at speeds comparable to other formation evaluation tools, reducing inaccuracies in porosity and fluid characterization, and enhances the efficiency of data acquisition.
Implementation Method 1
A transmitter antenna produces a time-dependent radio frequency magnetic field that is perpendicular to the direction of the static field. The radio frequency magnetic field produces a torque on the magnetization vector that causes it to rotate about the axis of the applied radio frequency magnetic field.
Implementation Method 2
Many NMR tools have a permanent magnet that produces a static magnetic field at a desired test location (e.g., where the fluid is located). The static magnetic field produces an equilibrium magnetization in the fluid that is aligned with a magnetization vector along the direction of the static magnetic field.
Implementation Method 3
nuclear magnetic resonance (NMR) to measure the response of nuclear spins in formation fluids to applied magnetic fields
Data Source
Figure 1A
Figure 1B
Figure 2A~2B
AI summary
The present disclosure relates to a method that includes generating a first pulse at a first position along a geological formation with a plurality of antennae, wherein the first pulse comprises a Carr-Purcell-Meiboom-Gill (CPMG) sequence, and wherein each antenna of the plurality of antennae is configured to generate NMR data via transmitting and receiving pulses into the geological formation.