Techniques for analyzing the geological properties of rocks

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Mineral composition and internal structure are essential information for evaluating the properties of reservoir and source rocks. At present, Japan Organization for Metals and Energy Security (JOGMEC) uses two types of scanning electron macroscopes, namely, scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) and focused ion beam scanning electron microscope (FIB-SEM), along with a quantitative evaluation of minerals by scanning electron microscope (QEMSCAN) that can map the minerals on the surface of a rock. Using these tools, JOGMEC can acquire information on mineral composition (volume ratio) and distribution and analyze the microscopic pore structure of a rock.
The distribution of pore diameter is also an important parameter to evaluate rock properties; therefore, JOGMEC uses nuclear magnetic resonance (NMR) to measure the distributions of different pore diameters within rock samples.
These techniques can be applied to conduct accurate lithological evaluations with respect to carbon capture and storage (CCS) and oil/gas development; these methods can also be used to analyze the interactions/reactions between CO2 and minerals and assess the behavior of CO2 fluids in reservoirs (by conducting fluid simulations in microscopic structures).

Main technical elements

Focused ion beam scanning electron microscope (FIB-SEM)

FIB-SEM is capable of capturing a series of two-dimensional (2D) SEM images, while shaving surfaces of a sample by FIB (Figure 1). The model can also be used to acquire three-dimensional (3D) images (by restructuring 2D images).

Figure 1 FIB-SEM scanning electron microscope

SEM-EDS with QEMSCAN (SEM-EDS with Quantitative Evaluation of Minerals by Scanning electron microscopy)

JOGMEC uses a combined SEM-EDS and QEMSCAN tool (Figure 2). QEMSCAN can observe SEM images and acquire a chemical component of a sample surface using EDS; it can also automatically identify a mineral by reflecting the density and chemical component information through reflected electrons that are detected during SEM imaging. Notably, the model can be used to acquire an image of the mineral distribution across a sample surface (mineral mapping analysis).

Figure 2 SEM-EDS with QEMSCAN

Nuclear magnetic resonance (NMR)

JOGMEC uses NMR to analyze reservoir characteristics (Figure 3). Specifically, it measures an attenuation time (T2) of the resonance signals caused by the unilateral magnetic fields of hydrogen atoms. Note that T2 distribution can be used to analyze the porosity and permeability of a rock sample and assess the distribution of pore diameters (the smaller the pore diameter, the earlier the T2 attenuation.

Figure 3 NMR core analyzer

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Japan Organization for Metals and Energy Security
(JCN 4010405009573)

Toranomon Twin Building 2-10-1 Toranomon, Minato-ku, Tokyo 105-0001, JAPAN
Tel : +81-3-6758-8000