Azimuthal NMR Well-Logging Sensor Array Design
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Solution Overview
Problem
Downhole NMR tools face challenges in acquiring accurate and high-resolution borehole information, particularly in harsh drilling environments, due to limitations in signal-to-noise ratio and the need for precise characterization of reservoir fluids and rock properties.
Innovation Solution
An NMR apparatus with an array of sensors having different directional sensitivities is used to acquire and combine signals, potentially enhancing the signal-to-noise ratio by combining signals before pre-amplification and utilizing phased array antennas to improve data quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single NMR sensor is used, then the device complexity is low, but the signal-to-noise ratio and measurement precision are insufficient
Solution Approach 1:
The NMR measurement system is segmented into multiple independent sensors (at least two, preferably three or more) arranged in a specific geometric configuration. Each sensor independently measures NMR signals from the formation, allowing the system to overcome the limitations of a single sensor by combining multiple measurements to improve signal-to-noise ratio while maintaining manageable complexity through modular sensor design
Solution Approach 2:
Multiple NMR sensor signals are merged and processed together to achieve improved measurement precision. The sensors are positioned to measure signals from different spatial locations or orientations, and their combined data provides a more accurate representation of formation properties, effectively merging individual measurements into a superior composite measurement
2Measurement precision
If multiple sensors with different directional sensitivities are used, then borehole image resolution is improved, but the device complexity increases
Solution Approach 1:
Different sensors in the array are assigned different directional sensitivities or measurement orientations tailored to their specific positions. This local differentiation allows each sensor to optimize its measurement capability for its particular spatial location, thereby improving overall borehole image resolution while the systematic arrangement keeps the complexity manageable through predictable geometric patterns
3Measurement precision
If signals are combined before pre-amplification, then signal-to-noise ratio improves, but the device complexity increases
Solution Approach 1:
Signal combination is performed as a preliminary action before the pre-amplification stage. The sensor signals are summed or processed together in advance, allowing the subsequent pre-amplifier to work with a stronger, cleaner signal. This timing of the combination operation optimizes the signal-to-noise ratio improvement while the integration into the existing signal chain minimizes additional complexity
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 the generation of high-resolution borehole images and improved characterization of formation porosity, permeability, and fluid properties, enhancing the accuracy of reservoir evaluation and fluid property estimation.
Implementation Method 1
Nuclear Magnetic Resonance (NMR) tools used for well-logging or downhole fluid characterization measure the response of nuclear spins in formation fluids to applied magnetic fields
Implementation Method 2
Downhole NMR tools typically have a permanent magnet that produces a static magnetic field at a desired test location
Implementation Method 3
The static magnetic field produces a magnetization in the fluid. The magnetization is aligned along the direction of the static field
Implementation Method 4
A transmitter antenna produces a time-dependent radio frequency magnetic field
Implementation Method 5
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 field
Implementation Method 6
This causes the magnetization vector to precess around the static field at the Larmor frequency
Data Source
AI summary
An NMR apparatus disposed in a wellbore and having an array of two or more NMR sensors located at substantially the same axial position on the NMR apparatus and having different directional sensitivities is used to acquire an NMR signal from at least two of the two or more NMR sensors. The NMR signals are combined to obtain borehole information. The borehole information may include an azimuthal image of the formation surrounding the borehole. The azimuthal image may be a formation porosity image, a formation bound fluid image, a T2 distribution image, a T2 log mean image, a formation permeability image, or a formation fluid viscosity image. If two or more pre-amplifiers and receiver circuitry are also provided, the NMR signals may be combined prior to passing through the pre-amplifiers and receiver circuitry to improve the signal to noise ratio of the total signal from the desired sample space.