NMR Radial Response Function for Thin Bed Interpretation
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Solution Overview
Problem
Interpreting Nuclear Magnetic Resonance (NMR) measurements is challenging due to sensitivity to various factors, including diffusion rates and formation structure, especially for thin bed NMR responses in horizontal or near horizontal wellbores.
Innovation Solution
Acquiring and using a radial response function in conjunction with NMR logging measurements to interpret subterranean formation models, including deploying the NMR tool in a fluid tank to measure NMR responses at multiple fluid levels and computing contribution coefficients from these measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional NMR interpretation methods are used, then measurement process is simple, but interpretation accuracy deteriorates due to sensitivity to diffusion rates, tumbling rates, and formation structure variations
Solution Approach 1:
The patent applies parameter changes by transforming the interpretation approach from direct signal analysis to analysis based on derivative parameters (contribution coefficients). The radial response function and its derivatives are used to characterize the tool's sensitivity distribution, converting a complex multi-parameter problem into a more manageable form that accounts for diffusion and formation structure effects systematically
Solution Approach 2:
The patent introduces the radial response function as an intermediary element between the NMR measurements and the formation properties. This function acts as a transfer function that mediates the relationship between the tool response and the underlying formation characteristics, enabling more accurate interpretation by explicitly accounting for the tool's spatial sensitivity distribution
2Measurement precision
If standard NMR logging is applied, then operational procedure is straightforward, but measurement precision deteriorates for thin bed formations in horizontal wellbores
Solution Approach 1:
The patent applies preliminary action by acquiring the radial response function in advance through a calibration process using a fluid tank with known properties. This pre-acquired response function is then used to interpret actual formation measurements, separating the tool characterization step from the formation evaluation step and enabling improved thin bed detection without complicating the operational workflow
Solution Approach 2:
The patent applies local quality by using the radial response function to characterize the local sensitivity distribution of the NMR tool at different radial positions. The contribution coefficients derived from the radial response function's derivatives provide localized weighting factors that account for the tool's varying sensitivity across different formation zones, particularly improving detection in thin beds
3Measurement precision
If radial response function acquisition is implemented, then interpretation accuracy improves, but measurement time and procedural complexity increase
Solution Approach 1:
The radial response function is acquired in advance during a calibration phase using a fluid tank with known fluid properties. This pre-acquired function is then reused for interpreting actual formation measurements, separating the time-consuming calibration step from the operational logging step. The calibration data serves as a lookup table or reference model that speeds up subsequent interpretation
Solution Approach 2:
The patent uses a simplified proxy system (fluid tank with known properties) to replicate the measurement conditions and acquire the radial response function. This copy of the measurement environment allows characterization of the tool's radial sensitivity without requiring actual formation data, enabling the response function to be determined independently and reused across multiple logging operations
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 improved interpretation of NMR data, particularly for thin bed formations, by accounting for the non-constant radial response of the NMR tool, leading to more accurate formation models and porosity calculations.
Implementation Method 1
Nuclear Magnetic Resonance (NMR) measurements are commonly made while drilling or logging and are commonly used to measure properties of earth formations
Implementation Method 2
The signals measured by NMR logging tools arise from selected nuclei in the probed volume. Since hydrogen nuclei are the most abundant and easily detectable, most NMR logging tools are tuned to detect hydrogen resonance signals
Data Source
AI summary
A method for interpreting nuclear magnetic resonance (NMR) logging measurements includes acquiring NMR logging measurements in a horizontal or near horizontal wellbore. A radial response function for the NMR logging tool is acquired and used in combination with the acquired NMR logging measurements to interpret a subterranean formation model including at least two layers. The radial response function may be estimated by computing contribution coefficients from a first derivative of NMR measurements made at a plurality of fluid levels in a fluid tank.