M.E. Houben

Microstructural Investigation of the Whitby Mudstone (UK) As an Analog for Posidonia Shale (NL)

As part of a study to investigate methods to enhance pore/crack connectivity between the shale matrix and the induced fractures, we have investigated the matrix microstructure of an exposed analogue of the Jurassic Posidonia shales in the Dutch sub-surface. A combination of Precision-Ion-Polishing and Scanning Electron Microscopy has been used to image the in-situ porosity and mineralogy in shale samples from Whitby (UK), which are an analogue for the Dutch Posidonia shale. First results show a fine-grained mudstone with cm-sub-mm scale stratification. The section at Whitby can be divided into a clay matrix dominated upper half and a coarser grained, calcite-rich, lower half of the section. Commonly occurring minerals are pyrite, calcite (fossils, grains and cement), quartz, mica and dolomite. Organic matter content varies from 0 – 2 % in the calcite dominated layers to 5 – 18% in the clay matrix dominated layers. The most porous phases are the clay matrix and calcite fossils. This microstructural study shows which intervals within Posidonia shale contain the largest porosity and organic matter contents for sweet spot analyses and forms a basis for future research on enhancing connectivity between the pores and induced fractures

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.

Microstructure of the Shaly Facies of Opalinus Clay on the Mm-nm Scale

Opalinus Clay is one of the fine-grained sedimentary formations investigated as a possible geological repository for the long-term storage of radioactive waste. Porosity, pore size, pore shape and connectivity of pores will help to define sealing capacities of a host rock. Here a combination of FIB-SEM, BIB-SEM and µ-CT has been used in order to investigate the nm-mm scale microstructure of the Shaly facies of Opalinus Clay in 2D and 3D. The µ-CT measurements gave a 3D overview of the microstructure of a 2 mm core down to a 2.6 µm voxel size. Which showed cracks, larger bivalve fragments and pyrite nodules embedded in a matrix, which was investigated down to the nm scale (enabling to image the pores) in 2D using the BIB-SEM method. FIB-SEM measurements were afterwards performed on selected areas to investigate the pore shape and connectivity in 3D down to the nm scale.

Porcine epidemic diarrhea virus (PEDV) introduction into a naive Dutch pig population in 2014

Abstract Porcine epidemic diarrhea virus (PEDV) is the highly contagious, causative agent of an economically important acute enteric disease in pigs of all ages. The disease is characterized by diarrhea and dehydration causing mortality and growth retardation. In the last few decades, only classical PEDV was reported sporadically in Europe, but in 2014 outbreaks of PEDV were described in Germany. Phylogenetic analysis showed a very high nucleotide similarity with a variant of PEDV that was isolated in the US in January 2014. The epidemiological situation of PEDV infections in the Netherlands in 2014 was unknown and a seroprevalence study in swine was performed. In total, 838 blood samples from sows from 267 farms and 101 samples from wild boars were collected from May till November 2014 and tested for antibodies against PEDV by ELISA. The apparent herd prevalence of 0.75% suggests that PEDV was not circulating on a large scale in the Netherlands at this time. However, in November 2014 a clinical outbreak of PEDV was diagnosed in a fattener farm by PCR testing. This was the first confirmed PEDV outbreak since the early nineties. Sequence analyses showed that the viruses isolated in 2014 and 2015 in the Netherlands cluster with recently found European G1b strains. This suggests a one event introduction of PEDV G1b strains in Europe in 2014, which made the Netherlands and other European countries endemic for this type of strains since then.

The Effect of Temperature and Pressure on the Rock Mechanical Behaviour of the Whitby Mudstone Formation, UK

We studied the rock mechanical behaviour of the outcropping Whitby Mudstone Formation shales (Toarcian Age) under varying temperature and confining pressure conditions, focusing on strength and elastic moduli. We compared the rock mechanical properties of the Whitby shale to published data of time and depositional equivalent shales from Northern Europe and producing shales from the US. We performed uniaxial and triaxial tests in order to constrain the effect of temperature and pressure on the mechanical behaviour of the shale. We loaded the samples normal to the bedding plane under room humidity conditions. We performed uniaxial tests at room temperature and zero confining pressure, whereas we applied confining pressure in several steps up to 50 MPa and considered temperature values between 20-150°C during triaxial tests. Ultimate strength and elastic moduli are strongly influenced by mineralogy, temperature and pressure. An increase in temperature enhances the deformability, whereby the Young’s Modulus and ultimate strength decreases. With an increase in confining pressure, Young’s Modulus and ultimate strength increases, whereas the Poisson’s ratio decreases.

Matrix to Fracture Flow Inferences from Core Measurements and Structural Fabric (Whitby UK)

The Early Jurassic (Toarcian) Shales in Northern Europe are investigated as possible unconventional sources for gas, where gas in shales is trapped in poorly connected micro pores and is sorbed within particles of organic material and clay minerals in the matrix of the host rock. Having a dual permeable medium consisting of a high permeable fracture network together with a tight shale matrix will improve gas flow rates from matrix to well. The Whitby Mudstone is currently outcropping on the Yorkshire coast hence getting sufficient sample material for permeability experiments is easily available, in combination with mapping of the natural occurring fractures in the cliffs and pavements along the coast this area is an ideal natural analogue to investigate matrix characteristics in combination with the natural fracture network. The studies show that fracture spacing on average is in the order of 10 centimeters and that in combination with a matrix permeability of 1∙10-18 m2 results in gas residue times in the matrix in the order of hours to tens of days depending on the input parameters used.