Slice Selective NMR Testing for Fractured Core Plug Pore Volume
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Solution Overview
Problem
Existing methods are inadequate for accurately determining the in-situ fracture pore volume of fractured core plugs, particularly in vuggy or fractured samples, which is crucial for assessing reservoir potential and optimizing petroleum production.
Innovation Solution
The implementation of local slice selective T2 nuclear magnetic resonance (NMR) testing under in-situ conditions to measure the pore volume of fractures in core plugs, involving initial and in-situ T2 measurements, and comparing the volume of water expelled to verify the accuracy of the fracture pore volume.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If gas or liquid injection method is used to measure pore volume, then the measurement can be performed on general samples, but the measurement accuracy deteriorates for vuggy and fractured samples
Solution Approach 1:
The patent replaces the mechanical injection method with nuclear magnetic resonance (NMR) technology to measure pore volume. NMR uses magnetic fields and radio waves to detect hydrogen nuclei in fluids within pores, providing accurate measurements for vuggy and fractured samples without relying on fluid injection that fails in such complex pore structures.
Solution Approach 2:
The patent changes the measurement parameter from macroscopic fluid volume injection to microscopic NMR signal detection. By measuring the relaxation times (T1 and T2) of hydrogen nuclei in the saturating fluid, the system can accurately determine pore volume and characteristics that are invisible to traditional injection methods.
2Reliability
If traditional pore volume measurement is performed, then the process is simple, but it cannot account for in-situ stress conditions
Solution Approach 1:
The patent integrates multiple functions into a single NMR testing system: it can apply controlled stress conditions, inject saturating fluids, perform NMR imaging to locate fractures, and measure pore volume all within one apparatus. This multi-functional system handles both simple and complex measurements without requiring multiple separate devices.
Solution Approach 2:
The patent uses NMR imaging and T2 distribution analysis as intermediary steps between stress application and pore volume measurement. These intermediaries provide detailed information about fluid distribution and pore characteristics under stress, enabling accurate in-situ measurements that bridge the gap between mechanical testing and porosity determination.
3Measurement precision
If NMR testing is performed on entire core plug, then comprehensive data is obtained, but the fracture-specific pore volume cannot be isolated
Solution Approach 1:
The patent segments the core plug data using NMR imaging to identify fracture locations and orientations. By analyzing T2 distributions at different spatial locations and comparing them to the overall T2 distribution, the system isolates the pore volume contribution from fractures versus the bulk rock matrix, providing fracture-specific measurements.
Solution Approach 2:
The patent applies local quality analysis by examining NMR signals from different regions of the core plug. Fracture zones exhibit distinct T2 relaxation characteristics compared to intact rock, allowing the system to identify and quantify pore volume specifically within fracture regions based on their unique local NMR signatures.
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 method provides an accurate measurement of in-situ fracture pore volume, enabling better reservoir development and optimization of petroleum production by accounting for elevated confining pressure and shear stress conditions.
Implementation Method 1
conducting an initial local slice selective T2 NMR test on a slice of the core plug that corresponds to the location of the fracture to generate initial T2 measurements for the slice
Data Source
AI summary
Provided is a local slice selective T2 nuclear magnetic resonance (NMR) test procedure that includes: (1) identifying a location of a fracture within a core plug; (2) conducting an initial local slice selective T2 NMR test on a slice of the plug that corresponds to the location to generate initial T2 measurements; (3) determining an initial fracture pore volume of the fracture based on the initial T2 measurements; (4) conducting an in-situ local slice selective T2 NMR test on the slice of the plug to generate in-situ T2 measurements and corresponding measures of a volume of fluid expelled from the plug; (5) determining an in-situ fracture pore volume for the fracture based on the in-situ T2 measurements; and (6) comparing the volume of water to a difference between the initial and the in-situ fracture pore volumes to confirm the accuracy of the in-situ pore volume.