Revealing Absolute Pore Size Distributions in Clay-Rich and Tight Reservoirs by Means of Low-Field Nuclear Magnetic Resonance
Description
Precise evaluation of rock filtration and capacity properties is challenging, particularly in unconventional reservoir formations with high clay content. This data set contains T2 relaxation time distributions of two different Low-Field Nuclear Magnetic resonance (LF-NMR) approaches, standard and modified differential, along with the Mercury Injection Capillary Pressure (MICP) Pore throat size distribution. The modified differential approach employs the subtraction of the dried sample signal from the signal of the 100 % water-saturated sample before taking the Laplace transform, giving a differential distribution devoid of the unwanted signals from rock matrix, closed porosity and clay-bound water. In the proposed PSD conversion workflow based on the percolation theory, a power function relationship between differential LF-NMR transverse relaxation time T2 and MICP pore-throat diameter can be established, enabling the determination of LF-NMR absolute pore size distribution and pseudo capillary pressure (Pc) curves for clay-rich samples.
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Steps to reproduce
To conduct the LF-NMR analysis, core samples in a dried and saturated state were prepared. Dry samples were obtained by vacuum oven drying at 110°C and under the pressure of 0.007 bar for 12 h to remove free and capillary-bound water. Samples in a saturated state were obtained by saturation in demineralized water in vacuum conditions (pressure of 0.007 bar) for 12 h. The LF-NMR measurements were performed using a 2 MHz Magritek Rock Core Analyzer (Magritek, Germany) with a 29 mm probe. Experiments of the T2CPMG (The Carr-Purcell-Meiboom-Gill) sequence were carried out using the following acquisition parameters: repetition time, RT = 2000 ms; echo time, TE = 60 μs; number of scans, NoS = 512; and number of echoes, NoE = 20000. The LF-NMR output data were analyzed using the Prospa software package. 1D distributions of T2 relaxation times for all samples in both dry and saturated states as well as differential T2 distributions were obtained using standard and modified, differential T2 protocols.
Institutions
- Akademia Gorniczo-Hutnicza imienia Stanislawa Staszica w Krakowie