Improving Pore Network Imaging & Characterization of Microporous Carbonate Rocks Using Multi-Scale Imaging Techniques

Abstract

Epoxy-pore casting is widely used to characterize geological samples. In this study, we present a robust pore imaging approach that applies Confocal Laser Scanning Microscopy (CLSM) to obtain high resolution 3D images of etched epoxy-pore casts of highly heterogeneous carbonates. In our approach, we have increased the depth of investigation for carbonates 20-fold, from 10 μm reported by (Fredrich, 1999; Shah et al., 2013) to 200 μm. In addition, high resolution 2D images from scanning electron microscopy (SEM) have been correlated with the 3D models from CLSM to develop a multi-scale imaging approach that covers a range of scales, from millimeters in 3D to micrometers in 2D. The developed approach was implemented to identify various pore types, e.g., the inter-crystalline and intra-granular microporosity, and the inter-boundary sheet pores in the limestone and dolomite samples.

Validation of High Pressure Resin Impregnation Technique for High Resolution Confocal Imaging of Geological Samples

“…From the experiments on micromodels, we could optimize the parameters of the process for high-resolution 3D confocal imaging of pore space. We follow the rock characterization procedure presented in (Hassan et al, 2017), where the rock matrix in the fluorescent epoxy pore cast is dissolved using hydrochloric acid to allow relatively large depth of investigation of up to 300 µm. Implementing this approach, we were able to provide high-resolution 3D images of the microporosity present in carbonate samples.…”

“…Then, the sample was degassed under vacuum of 120 mbar for about 10 minutes, followed by pressurized resin impregnation at 65 bar for 36 hours. We followed the procedure described in (Hassan et al, 2017) to image the etched epoxy pore casts of Indiana limestone with confocal microscopy. The samples were etched with dilute acid to dissolve the opaque rock matrix.…”

“…For example, for optical microscopy a dye must be mixed with the resin, while electron microscopy does not require a dye. For confocal laser microscopy, an additional step of etching the rock is required to obtain the 3D rock images (Hassan et al, 2017). In this work, we have critically evaluated and optimized the resin impregnation procedure that generates the high-quality epoxy pore casts for high resolution 3D imaging with CLSM.…”

Background-Free Deep Fluorescent Imaging of a Pore Architecture in Geomaterials Based on Magnetic Upconversion Nanoprobes

“…In LSCM imaging, the vertical depth of the optical section is in excess of 30 μm, and it can even reach ∼150 μm in some quartz sandstones. A bunch of geological materials such as sandstone, carbonates, − mudstones (shales), marble, and even many engineering materials such as polymer membrane, concretes, , and catalysts have been visualized by LSCM. Additionally, many geological applications, including fluid transport in geological materials and brittle failure processes as well as stress-induced damage in rocks, have been studied based on the LSCM imaging data of the pore architecture.…”