Joyce Schmatz,Jop Klaver, Mingze Jiang,Moritz Süß,Janos L. Urai

Structural Geology, Geomechanics and Tectonics,

RWTH Aachen University

Lochnerstraße 4-20, 52056 Aachen, Germany

MaP - Microstructure and Pores

RWTH Aachen University Spin-Off Project @ map@emr.rwth-aachen.de

URL www.ged.rwth-aachen.de, www.m-a-p.expert

Desbois, G., Urai, J.L., Hemes, S., Brassinnes, S., De Craen, M., Sillen, X., 2014. Nanometer-scale pore fluid distribution and drying damage

in preserved clay cores from Belgian clay formations inferred by BIB-cryo-SEM. Engineering Geology 179, 117-131.

Desbois, G., Urai, J.L., Kukla, P.A., Konstanty, J., Baerle, C., 2011. High-resolution 3D fabric and porosity model in a tight gas sandstone res-

ervoir: A new approach to investigate microstructures from mm- to nm-scale... . Journal of Petroleum Science and Engineering 78, 243-257.

Desbois, G., Urai, J.L., Pérez-Willard, F., Radi, Z., Offern, S., Burkart, I., Kukla, P.A., Wollenberg, U., 2013. Argon broad ion beam tomography

in a cryogenic scanning electron microscope: a novel tool for the investigation of representative ... . Journal of Microscopy 249, 215-235.

Hemes, S., Desbois, G., Urai, J.L., De Craen, M., Honty, M., 2013. Variations in the morphology of porosity in the Boom Clay Formation: in-

sights from 2D high resolution BIB-SEM imaging and Mercury injection Porosimetry. Netherlands Journal of Geosciences 92, 275-300.

Hemes, S., Desbois, G., Urai, J.L., Schröppel, B., Schwarz, J.-O., 2015. Multi-scale characterization of porosity in Boom Clay (HADES-level,

Mol, Belgium) using a combination of X-ray μ-CT, 2D BIB-SEM and FIB-SEM tomography. Microporous and Mesoporous Materials 208, 1-20.

Houben, M.E., Desbois, G., Urai, J.L., 2013. Pore morphology and distribution in the Shaly facies of Opalinus Clay (Mont Terri, Switzerland):

Insights from representative 2D BIB–SEM investigations on mm to nm scale. Applied clay science 71, 82-97.

Klaver, J., Desbois, G., Littke, R., Urai, J.L., 2015a. BIB-SEM characterization of pore space morphology and distribution in postmature to

overmature samples from the Haynesville and Bossier Shales. Marine and Petroleum Geology 59, 451-466.

Klaver, J., Desbois, G., Urai, J.L., Littke, R., 2012. BIB-SEM study of the pore space morphology in early mature Posidonia Shale from the Hils

area, Germany. Int. J. Coal Geol. 103, 12-25.

Klaver, J., Hemes, S., Houben, M., Desbois, G., Radi, Z., Urai, J.L., 2015b. The connectivity of pore space in mudstones: insights from high-

pressure Wood‘s metal injection, BIB-SEM imaging, and mercury intrusion porosimetry. Geofluids 15(4) 577-591.

Norbisrath, J.H., Eberli, G.P., Laurich, B., Desbois, G., Weger, R.J., Urai, J., 2015. Electrical and Fluid Flow Properties of Carbonate Micropo-

rosity Types from Multiscale Digital Image Analysis and Mercury Injection. AAPG Bulletin.

Schmatz, J., Urai, J.L., Berg, S., Ott, H., 2015. Nano-scale imaging of pore-scale fluid-fluid-solid contacts in sandstone. Geophysical Research

letters, 2015GL063354.

BIB-SEM, Cryo-BIB-SEM and Wood’s Metal Injection to image and ana-lyse pore morphology, pore connectivity, and fluid distribution in seals and reservoirs

Fig. 2 Image showing example of BIB-polished limestone sample imaged in the SEM. The large (up to 4 mm2) cross-section allows investigation of dual porosity from mm- to nm-scale.

Pore geometries and associated mi-neral phases and fluids are important properties in fine-grained rocks such as a range of cap rocks (e.g., chalks, mudstones and shales, Figs. 1&2) and also reservoir rocks such as gas shales, tight gas sandstone and car-bonates. Imaging of the pore space using Broad Ion Beam (BIB) milling and Scanning Electron Microscopy (SEM) allows accurate quantification of the pore space from millimeter to nanometer scale resolution on a relatively large area in these kind of rocks, as shown over the past few years in numerous applied studies (Desbois et al., 2011; Hemes et al., 2015; Houben et al., 2013; Klaver et al., 2015a; Norbisrath et al., 2015).

Introduction

From the mm2 size Argon-ion polis-hed sample area we can obtain the mineral porosity by combining image data from SE, BSE and EDX detectors using dedicated image segmentati-on algorithms to automate the pro-cess of porosity analysis based on SEM-Image data from the cm- down to the pixel size (Jiang et al. 2015, Fig. 3). Our workflow allows accura-te segmentation of pores and deter-mination of phase porosity. Based on the porosity segmentation, pore statistics and physical properties of the materials, such as pore size dis-tribution and permeability, can be inferred. It was found that the visible pore size distribution in fine-grained rocks follow a power-law behaviour from the µm- down to the nm-range (Hemes et al., 2013; Houben et al., 2013; Klaver et al., 2012).

Fig. 1 Broken vs. BIB-polished surface in mudstone: The BIB removes surface material by ar-gon ion beam milling to create a smooth, planar and damage free surface.

BIB-SEM

Literature

Affiliations

Combining BIB-SEM with Wood’s Metal Injection (WMI) enables to vi-sualize the preferred transport pa-thways and to determine the cont-rolling pore throat diameter and to infer the sealing capacity. The WMI experiments followed by BIB-SEM illustrated the significant effect of fractures on transport pathways and the low connectivity of the clay-rich matrix in mudstones (Klaver et al., 2015b, Figs. 4&5).

WMI-BIB-SEM

Fig. 3 Combining BIB polishing with SEM imaging enables topography-, phase-, and chemi-cal-mapping using Secondary Electrons (SE), Backscattered Electrons (BSE) and Energy Dis-persive X-ray Spectroscopy (EDS; Fig. 2). The large BIB cross-section allows Gigapixel imaging at nano-scale resolution of the microstructure followed by image processing to resolve the visible porosity. By overlaying the pore segmentation on the BSE and EDS mineral maps we can calculate the mineral phase and organic-matter porosity. These findings can be com-pared with bulk measurements like X-Ray powder Diffraction (XRD) and Mercury Intrusion porosimetry (MIP).

EDX-mapping for phase identifica-tion. 3D-reconstruction of capillary contact angles is done using serial sectioning with a distance of 1 µm. Our results call for improvements in models of multiphase pore-scale flow in digital rocks. Further anticipa-ted applications of the method are i. a. the investigation of pore-level me-chanisms of EOR or aging proces-ses; the investigation of oil-sands, gas-hydrates, and other sensitive or wet materials; or the investigation of in-situ fluid distribution reservoir- sandstones and carbonates.

Cryo-BIB-SEMBIB-SEM under cryogenic conditions allows direct study of the oil-water-mineral system in hydrocarbon-be-aring reservoirs, at resolutions of 10 nm. We quenched a range of muds-tones (Desbois et al., 2014; Desbois et al., 2013) and also sandstone re-servoir samples equilibrated with oil and brine (Schmatz et al., 2015), to li-quid nitrogen temperature and sub-sequently sectioned them using BIB-cutting under cryogenic conditions (Figs. 6 & 7). The flat cross-sections with dimensions of 4 mm2 allow cryo-SEM imaging of oil-brine-mine-ral interfaces, with high-resolution

Fig. 4 Pressure vessel showing the injection set-up and typical pressure steps used to inject rocks samples with the WM.

Fig. 5 Overview BSE image of a WM injected Boom Clay. The sample is almost completely filled except for some cracks and locally smaller (<100 nm) pores (left inset). Pores of about 10 nm can be filled and imaged using this method (right inset). Image modiefied from Klaver et.al. 2015.

Fig. 6 BSE image showing large pore, which is almost entirely filled with kaolinite. Kaoli-nite porosity is mainly filled with brine with a few enclosed oil droplets. Arrows point to mineral-oil pinning points. (Modified from Schmatz et al., 2015).

1 μm1 μm

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Fig. 7 cryo-BIB-SEM on water-filled Kaolinite paste: (a) High resolution image of a satura-ted clay sheets (b) Same image location as (b) but after sublimation of the water phase. Images were scanned without coating at 1.5kV using the SE2 detector. Images with cour-tesy of G. Desbois.