Proceedings 76th EAGE Conference and Exhibition 2014, 2014
ABSTRACT As part of a study to investigate methods to enhance pore/crack connectivity between the... more ABSTRACT 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
ABSTRACT The Mont Terri rock laboratory (Canton Jura, Switzerland) is an international scientific... more ABSTRACT The Mont Terri rock laboratory (Canton Jura, Switzerland) is an international scientific platform of research on radioactive waste disposal in Opalinus Clay and results provide input for assessing the feasibility and safety of deep geological disposal of radioactive waste in argillaceous formations [1]. A main safety issue is to accurately investigate mass transport rates. To date several methods analyzed bulk permeability and porosity of Opalinus Clay. However, detailed quantitative investigation of microstructure and pore morphology is necessary to understand sealing capacity, coupled flow, capillary processes and associated deformation. To produce high quality cross-sections without microstructural damage that enable investigation of microstructure and porosity down the nm scale a combination of Broad Ion Beam (BIB) milling and SEM imaging has been used [2]. This method allowed direct imaging of the clay fabric and porosity on ca. 1 mm2 areas. The lateral variability of Opalinus Clay is low on the regional scale [1], whereas vertically the Opalinus Clay can be subdivided into six different lithological subfacies [3] based on variable silt layers, sandstone layers and siderite concretions present, where the end-members are the Shaly and Sandy facies. In this contribution microstructures and pore space in Opalinus Clay from the undisturbed Shaly and Sandy facies are studied and compared to disturbed samples from the "Main fault" within the Mont Terri rock laboratory. The Shaly facies in the lower half of the sequence constitutes of dark grey silty calcerous shales and argillaceous marls, whereas the Sandy facies comprises silty to sandy marls with sandstone lenses cemented with carbonate [3]. The qualitative mineralogical composition of all Opalinus Clay facies is similar, whereas the "Main Fault" shows calcite, celestite and pyrite veins. Although the overall microfabric differs per layer and per facies we observe low variability of microstructure and porosity in each individual mineral phase. For example, pores in the clay matrix are distributed following a power law exponent of 2.3 regardless of the facies or cross-section. As a first qualitative result, pore morphology and microfabric varies towards faults, ranging from undisturbed to anastomosing fracture network in damage zones to even brecciated structures in fault cores containing various vein generations. [1] Bossart, P. & Thury, M. (2007) Research in the Mont Terri Rock laboratory: Quo vadis?, physics and chemistry of the Earth, 32, 19-31. [2] Desbois G., Urai J.L. and Kukla P.A. (2009) Morphology of the pore space in claystones - evidence from BIB/FIB ion beam sectioning and cryo-SEM observations. E-Earth, 4 :15-22. [3] NAGRA (2002) Technischer Bericht 02-03, Projekt Opalinuston: Synthese der geowissenschaftlichen Untersuchungsergebnisse, Dezember 2002.
ABSTRACT Opalinus Clay is one of the fine-grained sedimentary formations investigated as a possib... more ABSTRACT 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.
ABSTRACT A combination of Broad-Ion-Beam (BIB) polishing and Scanning Electron Microscopy (SEM) h... more ABSTRACT A combination of Broad-Ion-Beam (BIB) polishing and Scanning Electron Microscopy (SEM) has been used to study qualitatively and quantitatively the microstructure of Opalinus Clay in 2D. High quality 2D cross-sections (ca. 1 mm2), belonging to the Shaly and Sandy facies of Opalinus Clay, were investigated down to the nanometre scale. In addition Mercury Intrusion Porosimetry (MIP) and X-Ray powder Diffraction experiments have been used to extend characterization of the microstructure to the mm–cm scale on bulk volume sample material. Interestingly, both end-member samples of the Opalinus Clay show qualitatively similar mineralogy and pore characteristics as well as a comparable pore size distribution and pore morphology within the different mineral phases and mineral aggregates. Differences between the facies are mainly due to variations in mineral size and mineral amount present in the alternating layers of the different facies. Six different porous mineral phases have been identified and the pores have been subdivided into ten different pore types. Pores visible in the SEM images are most abundant in the clay matrix and these seem to follow a power law distribution with a power law exponent of ca. 2.25 independent of the sample location. Furthermore, all common mineral grains show characteristic porosity, pore shape and pore size distribution in 2D and are proposed to be considered as elementary building blocks for Opalinus Clay. Combined these homogeneous elementary building blocks make up the heterogeneous fabric of the different facies of Opalinus Clay. Based on extrapolation of the power law size distribution in the clay matrix below SEM resolution results in a porosity of 10–25% for clay rich layers (60–90% of clay matrix), whereas sand and carbonate layers show an extrapolated porosity of 6–14%. These extrapolated porosities are in agreement with water-loss and physical porosity measurements performed on bulk material of comparable samples.
Proceedings 76th EAGE Conference and Exhibition 2014, 2014
ABSTRACT As part of a study to investigate methods to enhance pore/crack connectivity between the... more ABSTRACT 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
ABSTRACT The Mont Terri rock laboratory (Canton Jura, Switzerland) is an international scientific... more ABSTRACT The Mont Terri rock laboratory (Canton Jura, Switzerland) is an international scientific platform of research on radioactive waste disposal in Opalinus Clay and results provide input for assessing the feasibility and safety of deep geological disposal of radioactive waste in argillaceous formations [1]. A main safety issue is to accurately investigate mass transport rates. To date several methods analyzed bulk permeability and porosity of Opalinus Clay. However, detailed quantitative investigation of microstructure and pore morphology is necessary to understand sealing capacity, coupled flow, capillary processes and associated deformation. To produce high quality cross-sections without microstructural damage that enable investigation of microstructure and porosity down the nm scale a combination of Broad Ion Beam (BIB) milling and SEM imaging has been used [2]. This method allowed direct imaging of the clay fabric and porosity on ca. 1 mm2 areas. The lateral variability of Opalinus Clay is low on the regional scale [1], whereas vertically the Opalinus Clay can be subdivided into six different lithological subfacies [3] based on variable silt layers, sandstone layers and siderite concretions present, where the end-members are the Shaly and Sandy facies. In this contribution microstructures and pore space in Opalinus Clay from the undisturbed Shaly and Sandy facies are studied and compared to disturbed samples from the "Main fault" within the Mont Terri rock laboratory. The Shaly facies in the lower half of the sequence constitutes of dark grey silty calcerous shales and argillaceous marls, whereas the Sandy facies comprises silty to sandy marls with sandstone lenses cemented with carbonate [3]. The qualitative mineralogical composition of all Opalinus Clay facies is similar, whereas the "Main Fault" shows calcite, celestite and pyrite veins. Although the overall microfabric differs per layer and per facies we observe low variability of microstructure and porosity in each individual mineral phase. For example, pores in the clay matrix are distributed following a power law exponent of 2.3 regardless of the facies or cross-section. As a first qualitative result, pore morphology and microfabric varies towards faults, ranging from undisturbed to anastomosing fracture network in damage zones to even brecciated structures in fault cores containing various vein generations. [1] Bossart, P. & Thury, M. (2007) Research in the Mont Terri Rock laboratory: Quo vadis?, physics and chemistry of the Earth, 32, 19-31. [2] Desbois G., Urai J.L. and Kukla P.A. (2009) Morphology of the pore space in claystones - evidence from BIB/FIB ion beam sectioning and cryo-SEM observations. E-Earth, 4 :15-22. [3] NAGRA (2002) Technischer Bericht 02-03, Projekt Opalinuston: Synthese der geowissenschaftlichen Untersuchungsergebnisse, Dezember 2002.
ABSTRACT Opalinus Clay is one of the fine-grained sedimentary formations investigated as a possib... more ABSTRACT 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.
ABSTRACT A combination of Broad-Ion-Beam (BIB) polishing and Scanning Electron Microscopy (SEM) h... more ABSTRACT A combination of Broad-Ion-Beam (BIB) polishing and Scanning Electron Microscopy (SEM) has been used to study qualitatively and quantitatively the microstructure of Opalinus Clay in 2D. High quality 2D cross-sections (ca. 1 mm2), belonging to the Shaly and Sandy facies of Opalinus Clay, were investigated down to the nanometre scale. In addition Mercury Intrusion Porosimetry (MIP) and X-Ray powder Diffraction experiments have been used to extend characterization of the microstructure to the mm–cm scale on bulk volume sample material. Interestingly, both end-member samples of the Opalinus Clay show qualitatively similar mineralogy and pore characteristics as well as a comparable pore size distribution and pore morphology within the different mineral phases and mineral aggregates. Differences between the facies are mainly due to variations in mineral size and mineral amount present in the alternating layers of the different facies. Six different porous mineral phases have been identified and the pores have been subdivided into ten different pore types. Pores visible in the SEM images are most abundant in the clay matrix and these seem to follow a power law distribution with a power law exponent of ca. 2.25 independent of the sample location. Furthermore, all common mineral grains show characteristic porosity, pore shape and pore size distribution in 2D and are proposed to be considered as elementary building blocks for Opalinus Clay. Combined these homogeneous elementary building blocks make up the heterogeneous fabric of the different facies of Opalinus Clay. Based on extrapolation of the power law size distribution in the clay matrix below SEM resolution results in a porosity of 10–25% for clay rich layers (60–90% of clay matrix), whereas sand and carbonate layers show an extrapolated porosity of 6–14%. These extrapolated porosities are in agreement with water-loss and physical porosity measurements performed on bulk material of comparable samples.
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