NMR Fluid Saturation Estimation in Shale Reservoirs
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Solution Overview
Problem
Nuclear Magnetic Resonance (NMR) well-logging tools face challenges in accurately determining fluid saturation in formations, particularly in shale formations where distinct peak amplitude areas are not present, making it difficult to directly calculate hydrocarbon and water saturation from T1 to T2 ratios.
Innovation Solution
A method using a processor to calculate a mean of amplitude values associated with T1 and T2 relaxation times, estimating hydrocarbon and water saturation by deviating from threshold indicators, and calculating total porosity and oil volume based on these estimates, allowing for hydrocarbon and water volume estimation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If NMR tools are used to measure fluid saturation in shale formations, then measurement capability is provided, but measurement precision deteriorates due to absence of distinct peak amplitude areas
Solution Approach 1:
The patent transforms the NMR data representation by changing from peak amplitude analysis to mean amplitude calculation. By computing the mean of amplitude values across multiple T2 relaxation time bins and comparing it to threshold indicators, the method adapts to shale formations where traditional peak-based analysis fails due to the absence of distinct amplitude peaks in the T1-T2 distribution.
2Ease of manufacture
If traditional peak amplitude analysis is used, then calculation simplicity is maintained, but measurement precision deteriorates in formations without distinct peaks
Solution Approach 1:
The invention changes the computational parameter from identifying peak amplitudes to calculating mean amplitudes across T2 bins. This parameter transformation maintains computational simplicity while improving accuracy in shale formations, as the mean calculation does not require distinct peaks to be present in the data distribution.
Solution Approach 2:
The patent introduces threshold indicators as intermediary reference values that represent hydrocarbon and water saturation characteristics. By comparing the calculated mean amplitude against these threshold indicators, the method provides a simplified yet accurate way to determine fluid saturation without requiring complex peak identification algorithms.
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
Enables accurate estimation of hydrocarbon and water saturation and volumes in subsurface formations, even in complex formations like shale, by processing NMR data and using threshold indicators, improving the accuracy of fluid saturation measurements.
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
Such NMR tools typically 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
AI summary
A method of estimating fluid saturations includes obtaining amplitude values of nuclear magnetic resonance (NMR) data for a material, with each amplitude value being associated with a longitudinal magnetization recovery (T1 relaxation) time and a transverse magnetization decay (T2 relaxation) time. A mean is calculated as a function of the amplitude values and the T1 and T2 relaxation times for the amplitude values. Hydrocarbon saturation of pore space of the material is estimated as a function of the deviation of the mean from a threshold hydrocarbon saturation indicator and a threshold water saturation indicator, using the processor. Water saturation of the pore space of the material is estimated as a function of the deviation of the mean from the threshold hydrocarbon saturation indicator and the threshold water saturation indicator, using the processor.