PEPT Fluid Mobility Imaging in Ultra-Low Permeability Rock
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Solution Overview
Problem
Conventional methods for determining fluid mobility in rock samples, particularly in shale with ultra-low permeability, face challenges due to the need for upscaling and loss of information, as well as limitations in image resolution and processing speed using sinogram data formats, which are not representative of in-situ conditions.
Innovation Solution
The use of time-lapse positron emission particle tracking (PEPT) with radionuclide tags to record gamma-ray emissions from a gas or another gas within the rock sample's pores, allowing for high-resolution imaging of fluid mobility at a rate of more than one image per second, using a PET camera and converting data into list mode for accurate fluid mobility determination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional techniques (NMR, 3D CT scanning, X-ray diffraction, SEM) are used to determine fluid mobility in rock samples, then measurement can be performed on small core plugs, but the fluid mobility determined is not representative of in-situ fluid mobility and requires upscaling which causes loss of information and blurring of spatially continuous extremes
Solution Approach 1:
The patent transitions from measuring small core plugs (1D/2D representation) to imaging entire rock samples (3D representation). By using positron emission particle tracking (PEPT) with radionuclide tags throughout the entire sample volume, the system captures fluid mobility in three dimensions, eliminating the need for upscaling and preserving spatially continuous extremes such as shale barriers and open fractures.
Solution Approach 2:
The patent uses radionuclide tags as discrete markers distributed throughout the fluid phase. These segmented tags allow individual tracking of fluid particles through the rock sample pores, enabling precise measurement of fluid mobility pathways without requiring to represent the entire continuous fluid phase, thus maintaining information about spatial extremes.
2Ease of manufacture
If standard PET imaging stores data in sinogram format, then data acquisition is simplified, but the acquired data results in lower resolution and requires more time to process, producing images every ten minutes
Solution Approach 1:
Instead of following the conventional approach of storing PET data in compressed sinogram format and then reconstructing images, the patent inverts the process by directly reconstructing images from raw list-mode data. This reversal eliminates the information loss inherent in sinogram compression and enables high-resolution imaging with faster processing rates of more than one image per second.
3Adaptability or versatility
If conventional techniques require upscaling from core-plug scale to simulation-grid scale, then fluid mobility can be determined for small samples, but averaging and extrapolation lead to loss of information and blurring of spatially continuous extremes
Solution Approach 1:
The patent applies PEPT imaging to entire rock samples rather than small core plugs, transitioning from a scaled-down representation to a full-scale 3D visualization. This dimensional change eliminates the need for upscaling operations, preserving the spatial connectivity information of extreme permeability values and shale barriers throughout the complete sample volume.
Solution Approach 2:
The patent replaces the mathematical upscaling process (averaging and extrapolation) with direct physical measurement using radionuclide tags. By physically tracking fluid particles through the entire sample with PEPT, the system substitutes computational upscaling with empirical observation, thereby preserving spatially continuous extremes without information loss.
4Measurement precision
If other conventional techniques (grinding, removing water content, injecting He or Hg) are used to determine fluid mobility, then fluid mobility can be measured, but the original geo-mechanical properties of the rock sample are skewed
Solution Approach 1:
The patent introduces radionuclide tags as intermediary markers that attach to fluid molecules without altering the fluid's natural behavior or the rock's geo-mechanical properties. These tags act as passive tracers that enable visualization and measurement of fluid mobility while maintaining the integrity of the original rock-fluid system, avoiding the need to grind, dry, or chemically alter the sample.
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 provides improved accuracy and resolution in determining fluid mobility in rock samples with small-scale pores, enabling better representation of in-situ conditions and reducing uncertainty in permeability estimates, especially in shale formations, by capturing dynamic fluid mobility and enhancing the understanding of fracture connectivity and stimulated reservoir volume.
Implementation Method 1
recording gamma-ray emissions from the tag in a list mode file using a positron emission tomography camera as it traverses with the fluid through the pores in the rock sample
Implementation Method 2
time-lapse positron emission particle tracking (PEPT) with radionuclide tags to record gamma-ray emissions
Data Source
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AI summary
A method for determining fluid mobility in a rock sample using time lapse positron emission particle tracking, which comprises the steps of: selecting a porous rock sample with a permeability less than one micro-darcy; selecting a fluid for the rock sample that is a gas; selecting a tag for the fluid that is the gas or another gas; placing the rock sample in a pressurized container; introducing the fluid and the tag into pores within the rock sample; recording gamma-ray emissions from the tag in a list mode file using a positron emission tomography camera as the tag traverses with the fluid through the pores in the rock sample placed in the pressurized container; converting the gamma-ray emissions into images; and displaying the images.