Joyce Schmatz

Nanoscale imaging of pore‐scale fluid‐fluid‐solid contacts in sandstone

Direct observations of oil-water-rock contacts are key for improving our understanding of multiphase flow phenomena in mixed-wet reservoir rocks. In this study we imaged pore-scale fluid-fluid-solid contacts in sandstone with nanometer resolution using cryogenic broad ion-beam polishing in combination with scanning electron microscopy and phase identification by energy-dispersive X-ray analysis. We observed, as expected, the nonwetting oil phase separated from quartz surfaces by a thin brine film, but also direct contacts between oil and rock at asperities and clay aggregates, which act as pinning points and cause discontinuous motion of the oil-water-solid contact line. For the rare classical configuration of a three-phase contact the microscopic contact angle has been determined by serial sectioning. Our results call for improvements in models of multiphase pore-scale flow in digital rocks.

Using BIB-SEM Imaging for Permeability Prediction in Heterogeneous Shales

Organic-rich shale samples from a lacustrine sedimentary sequence of the Newark Basin (New Jersey, USA) are investigated by combining Broad Ion Beam polishing with Scanning Electron Microscopy (BIB-SEM). We model permeability from this 2D data and compare our results with measured petrophysical properties. Three samples with total organic carbon (TOC) contents ranging from 0.7% to 2.9% and permeabilities ranging from 4 to 160 nD are selected. Pore space is imaged at high resolution (at 20,000x magnification) and segmented from representative BIB-SEM maps. Modeled permeabilities, derived using the capillary tube model (CTM) on segmented pores, range from 2.3 nD to 310 nD and are relatively close to measured intrinsic permeabilities. SEM-visible porosities range from 0.1% to 1.8% increasing with TOC, in agreement with our measurements. The CTM predicts permeability correctly within one order of magnitude. The results of this work demonstrate the potential of 2D BIB-SEM for calculating transport properties of heterogeneous shales.

Porosity and Pore Connectivity in Immature and Artificially Matured Source Rock Using BIB-SEM, WMI and MIP

Porosity and pore connectivity in organic-rich shales change with thermal maturity. To document such effects, an immature source rock sample was artificially matured under controlled pressure conditions. Afterwards, its pore structure was compared to the one of an untreated sister sample. Pore space and pore connectivity were investigated by Broad Ion Beam (BIB) polishing and Scanning Electron Microscopy (SEM), Mercury Intrusion Porosimetry (MIP) and Wood’s Metal Injection (WMI) followed by BIB-SEM. The SEM images of both samples show cracks indicating enhanced porosity. The organic matter of the matured sample exhibits porosity, however, the portion of identifiable organic matter is drastically lower than in the untreated sample. MIP indicates an increase of macro- and meso-porosity for the matured sample, which is consistent with the BIB-SEM observations. WMI at comparable pressures as MIP also reveals clear differences between the two samples: the untreated sample shows a complex heterogeneous intrusion of the Wood’s Metal (WM), filling the matrix for several hundreds of micrometers at various locations while other large parts of the matrix remain unfilled. In contrast, in the matured sample WM was identified throughout the entire sample demonstrating good connectivity.

Fault Gouge Evolution in Layered Sand-Clay Sequences - First Results of Water-Saturated Sandbox Experiments

We present first results of model experiments aimed at better understanding of clay smear processes in layered sand-clay sequences. The apparatus is a version of the conventional 2D sandbox with transparant glass windows, modified to operate under water.

Standardized Automated Multiscale Imaging Technologies to Quantify Microstructure and Petrophysical Properties in a Range of Rock Types

Rocks are heterogeneous at all scales in composition, microstructure and petrophysical properties. Starting from representative sampling and quantifying microstructure together with measurement of rock properties in the laboratory, we show that it is necessary to treat different rock types in specially tailored workflows. Our multiscale imaging technology combines the advantages of a novel virtual polarizing microscopy (ViP) with high-resolution scanning electron microscopy on broad-ion-beam sputtered sample surfaces (BIB-SEM). Automated image registration and segmentation allows a fast and reliable analysis of the microstructural features as well as the assessment of petrophysical properties. This unique combination of methods allows a comprehensive analysis of various rock types including identification of diagenetic features and the quantification of pore size distribution and effective porosity from the cm to nm- scale as shown for different carbonates and tight siliciclastic rocks. Results were used to develop new porosity models that can be used for upscaling and permeability assessment in digital rock models.

Overview of Integrated Microstructural Studies to Better Understand Mechanical and Fluid Flow Properties of Fine Grained

A comprehensive understanding of mechanical and fluid flow properties in fine-grained geo-materials like shales requires imaging the microstructure at a range of scales as the microstructures are small and the samples are heterogeneous. Broad Ion Beam (BIB) milling followed by Scanning Electron Microscopy (SEM) imaging provides access to these microstructures at nanometre resolution and large cross sections of up to several mm². Applying BIB-SEM on naturally and experimentally deformed or Wood’s Metal injected samples enables to resolve the related deformation processes and to image the pore connectivity, respectively. The pore fluid distribution, however, can be resolved by integrating BIB-SEM with cryogenic techniques. Examples of such integrated studies indicate calcite in shear fractures in Opalinus Clay and high connectivity in a fine-grained Boom Clay sample.