Whole Core NMR Scanning
Whole core NMR scanning at Ellington Geological Services provides high axial resolution, enabling detailed analysis of porosity, structure, and fluid variations within the core. This advanced method helps identify zones with superior reservoir quality and permeability that are too thin to be detected by well logging tools.
based on Ecotek high performance NMR sensor
​Parameters of Whole Core NMR Scanner:
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Maximum core OD: 4”
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Minimal TE: up to 0.12 ms
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Axial resolution: ~3” (native), up to 0.25” (with deconvolution)
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Typical throughput: 1 hr for 3 ft core, based on a ~15-20 porosity unit sample and a 2” scanning step
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Operation: inside a chiller room to minimize fluid losses
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Example: Organic Rich Shale Core
Comparison of whole core NMR signal with NMR signal from plugs cut from the same core
NMR T2 distributions obtained from whole core NMR scanning reveal a marked interval at the top of the core with higher concentrations of water in larger pores and residual hydrocarbons in inorganic matrix pores, indicating significantly higher reservoir quality.
Unconventional Core Analysis
Conventional reservoir evaluation relies on the principle that knowing total porosity and water saturation predicts reservoir behavior during production. However, in unconventional reservoirs, diagenetic processes result in varied pore characteristics, necessitating a more complex volumetric model to capture the properties of reservoirs with intricate porosity systems.
Low-field Nuclear Magnetic Relaxometry is the only technique available for core characterization in the lab and downhole measurements sensitive to total fluid volumes and fluid concentrations in different parts of the porosity system. To accurately interpret NMR signals and differentiate fluids in various porosity components, it is essential to develop NMR T2 distribution interpretation schemes tailored to specific unconventional reservoirs.
Example: organic matter hosted porosity formed during reservoir maturation
NMR-focused core analysis provides data that facilitates the creation of T2 distribution interpretation schemes specific to individual unconventional reservoirs. These schemes can be upscaled to NMR logs, enabling the estimation of producible fluid distributions and dynamic reservoir properties.
The main analytical components are listed below.
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Volumetric Core Analysis Workflow​
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Quantifies total porosity, Bulk Volume Oil (BVO), and Bulk Volume Water (BVW) in as-received samples with high accuracy
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Uses differential NMR measurements (before and after fluid extraction) to identify NMR signal components corresponding to extracted fluids
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Pressure Saturation Experiment
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Quantifies total porosity through NMR measurements
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Identifies pores that do not carry fluids in their as-received state
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Estimates the relative producibility of hydrocarbons in different parts of the porosity system (refer to URTeC 4250109 for details)
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Quantifies irreducible Bulk Volume Water (BVW_irr)
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Provides a proxy for sample permeability
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Estimates formation water salinity and resistivity (Rw)
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Estimates liquid permeability and compaction factor for different rock types
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Links advanced volumetrics from other measurements to flow properties
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Complex Reservoir Core Analysis
Flow properties are primarily defined by macroporosity due to the poor interconnectivity of mesopores. Reservoir-specific studies are essential to determine the saturation properties of mesoporosity, which is crucial for assessing the recovery potential of hydrocarbons in the diagenetic part of the porosity system.
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To evaluate reservoirs with mesoporosity, it is important to differentiate total porosity into its meso- and macro-components. This can be achieved through NMR measurements that are differentially sensitive to fluids in various pore types. For rock samples with complex porosity systems, NMR data must be acquired at different Larmor Frequency ranges and echo time values to match the data acquisition parameters of various NMR logging tools. This allows for the development of a relevant scheme to split NMR signals into meso- and macro-porosities.
Typical RCA
Proposed Core Workflow
NMR Logging Tool Response Calibration
For Wireline NMR logging tools, the Larmor Frequency typically ranges between 1 MHz and 2 MHz. For LWD NMR logging tools, the Larmor Frequency is around 0.3 MHz. Consequently, in complex reservoirs, the LWD NMR response is expected to differ significantly from the Wireline NMR response, affecting the processing parameters of downhole NMR measurements used to quantify mesoporosity (Phi_meso) and macroporosity (Phi_macro).
NMR data processing parameters should be derived from lab NMR measurements performed on core samples under conditions close to those of the reservoir.
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At the Ellington lab, we have custom-built instruments designed for such calibration for NMR logging tool response.
Wellsite Pore Pressure Prediction​
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(coming soon)
NMR Core-to-Log Integration​
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(coming soon)