Jop Klaver

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.

Investigation of microstructures in naturally and experimentally deformed reference clay rocks using innovative methods in scanning electron microscopy

The application of ion-beam milling techniques to clays allows investigation of the porosity at nm resolution using scanning electron microscopy (SEM). Imaging of pores by SEM of surfaces prepared by broad ion beam (BIB) gives both qualitative and quantitative insights into the porosity and mineral fabrics in 2D representative cross-sections. The combination of cryogenic techniques with ion-beam milling preparation (BIB and FIB, focused ion beam) allows the study of pore fluids in preserved clay-rich samples. Characterization of the pore network is achieved, first, using X-ray computed tomography to provide insights into the largest pore bodies only, which are generally not connected at the resolution achieved. Secondly, access to 3D pore connectivity is achieved by FIB-SEM tomography and the results are compared with 2D porosity analysis (BIBSEM) and correlated with bulk porosity measurements (e.g. mercury injection porosimetry, MIP). Effective pore connectivity was investigated with an analog of MIP based on Wood’s metal (WM), which is solid at room temperature and allows microstructural investigation of WM-filled pores with BIB-SEM after injection. Combination of these microstructural investigations at scales of ,1 mm with conventional stressstrain data, and strain localization characterized by strain-fields measurement (DIC – digital image correlation) on the same sample offers a unique opportunity to answer the fundamental questions: (1) when, (2) where, and (3) how the sample was deformed in the laboratory. All the methods above were combined to study the microstructures in naturally and experimentally deformed argillites. Preliminary results are promising and leading toward better understanding of the deformation behavior displayed by argillites in the transition between rocks and soils.

Lessons Learned from Electron Microscopy of Deformed Opalinus Clay

Using a combined approach of ion-beam milling and electron microscopy, we observe, describe and quantify the microstructure of naturally and synthetically deformed Opalinus Clay (OPA) and deduce its microstructural evolution and underlying deformation mechanisms. The investigated samples derive from the so-called Main Fault, a 10 m offset fold-bend thrust fault crossing the Mont Terri Rock Laboratory in the Swiss Jura Mountains. The samples are slightly overconsolidated, experienced a burial depth of 1350 m and a maximum temperature of 55 °C. Most impact on strain is attributed to frictional sliding and rigid body rotation. However, trans-granular fracturing, dissolution-precipitation of calcite, clay particle neoformation and grain deformation by intracrystalline plasticity have a significant contribution to the fabric evolution. The long-term in-situ deformation behavior of OPA is inferred to be more viscous than measured at laboratory conditions.

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.

Multiscale porosity estimates along the pro-and retrograde deformation path: an example from Alpine slates

Estimating the porosity of slates is of great interest for the industries dealing with sub-surface areas such as CO2 sequestration, nuclear waste disposal and shale gas but also for engineering purposes in terms of mechanical stability for underground or surface constructions. In this study, we aim at understanding estimates of the porosity of slates from the Infrahelvetic flysch units (IFUs) in the Glarus Alps (eastern Switzerland). Surface and sub-surface samples were collected along a temperature gradient from 200 to 320 C and therefore give the opportunity to link pore types along this temperature and deformation path. In addition, we indicate which porosity is the effect of surface processes and indicate the contribution of artificially induced porosity. The developed workflow consists of a combination of bulk rock measurements including helium pycnometry (He pycnometry) and mercury intrusion porosimetry (MIP) with image analysis. Image analysis was performed with high-resolution scanning electron microscopy (SEM) on broad ion beam (BIB) prepared cross sections (BIB-SEM). Different vein generations provide evidence of porosity formation at depth, as they present “paleo-porosity”. Towards peak metamorphic conditions (prograde path), porosity reduces to < 1 vol%, indicated by matrix porosity detected by BIB-SEM. During exhumation (retrograde path) porosity increases due to the formation of microfractures interpreted as the effect of unloading (open fractures). At the surface, porosity is further increased due to the formation of macro-fractures (fracture apertures up to 1 mm), which are interpreted as being either due to the effect of weathering processes such as freeze and thaw cycles or artificially induced by sample preparation. Additionally, porosity and pore morphology are strongly dependent on mineralogy, sample homogeneity and strain, which change dynamically in time and space.

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.