Modelling effective diffusion for accurate NMR pore size analysis in nano- and microporous rocks

Description

This database contains the complete dataset supporting the study titled "Modelling effective diffusion for accurate NMR pore size analysis in nano- and microporous rocks". It includes raw and processed data acquired from three complementary petrophysical methods: Low-Field Nuclear Magnetic Resonance (LF-NMR), Mercury Intrusion Capillary Porosimetry (MICP), and Low-Temperature Nitrogen Adsorption (LTNA), as well as Magnetic Susceptibility (MS) data. The data were collected from a diverse set of 9 tight siliciclastic rock samples: sandstones, heteroliths and mudstones. In addition to standard measurement files, the dataset includes a numerical simulation tool for modelling the pore-size-dependent effective diffusion coefficient, D(d). By using this dataset, researchers can reproduce the data analysis presented in the associated article, test their own T2-PSD conversion models, and simulate the impact of restricted diffusion on T2 relaxation in tight porous media. The data can be interpreted as follows: MICP and LTNA data serve as a reference for the Pore Size Distribution. These two methods can be combined to create a comprehensive reference PSD across a wide range of pore sizes (from nano- to micrometres). LF-NMR T2 relaxation data provides an alternative, non-destructive method for estimating PSD after T2-Pore Size transformation. MS data can be used to calculate the magnitude of internal magnetic gradients' influence over a given PSD range. The included effective diffusion simulation file allows users to model the relationship between the diffusion coefficient (D) and pore diameter (d). This is crucial for accurately converting T2 relaxation times into pore sizes, especially in systems where diffusion is restricted. Parameters such as time echo (TE), magnetic susceptibility, and porosity can be changed to fit the model to your data.

Steps to reproduce

Sample Preparation: Nine cylindrical core plug samples (diameter 2.2–2.5 cm, length 2–5 cm) were cut from Miocene-age siliciclastic formations in southeastern Poland. For each sample, one plug was used for LF-NMR analysis, while the second was crushed for complementary MICP, LTNA, and magnetic susceptibility measurements. Drying: Samples were dried at 110 °C for 24 hours (LF-NMR) or 105 °C (MICP), and 200 °C (LTNA) under vacuum for 12 hours. Saturation (LF-NMR): 100% saturation with kerosene was achieved by applying vacuum conditions at 0.007 bar for 12 hours. LF-NMR T2 Acquisition: Instrument: Magritek Rock Core Analyzer (2 MHz). Pulse sequence: CPMG (Carr–Purcell–Meiboom–Gill). Parameters: Echo time (TE): 60 µs; Number of echoes (NoE): 50 000; Number of scans (NoS): 512; Residual time (RT): 5000 ms Processing: Inverse Laplace Transform (ILT) with smoothing factor α = 1; Differential T₂ distributions were obtained by subtracting dry-state signal (rock matrix, bound fluids) from saturated-state signal prior to ILT Mercury Intrusion Capillary Porosimetry (MICP): Instrument: Micromeritics AutoPore IV 9520 Measurement range: 0.003 – 414 MPa (equivalent pore diameters ~500 µm to 3–4 nm) Processing: Pore diameter calculated using Washburn’s equation with γHg = 0.485 N/m and θ = 130°; Permeability estimated using Katz-Thomson model Low-Temperature Nitrogen Adsorption (LTNA): Instrument: Anton Paar NOVA 800 Adsorbate: N₂ at −196 °C Measurement range: Relative pressure (P/P₀) from ~10⁻³ to 0.99 Processing: Specific surface area determined using the BET method; Mesopore distribution (2–50 nm) obtained via NLDFT (Kaomi 2.0 software) Magnetic Susceptibility Measurements: Instrument: Bartington MS2 susceptibility meter (Bartington Instruments Ltd.) Sensor: Laboratory probe with an induction coil coupled to a thermally stable oscillator Measurement principle: The presence of magnetically susceptible material shifts the oscillator frequency due to local changes in magnetic permeability. This frequency shift is automatically calibrated and converted to volume magnetic susceptibility (χSample).

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