Fabric development and the smectite to illite transition in Upper Cretaceous mudstones from the North Sea: an image Analysis Approach
Published:January 01, 2005
R. H. Worden, D. Charpentier, Q. J. Fisher, A. C. Aplin, 2005. "Fabric development and the smectite to illite transition in Upper Cretaceous mudstones from the North Sea: an image Analysis Approach", Understanding the Micro to Macro Behaviour of Rock–Fluid Systems, R. P. Shaw
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In this study, Upper Cretaceous Shetland Group mudstone cuttings from a range of depths in the Northern North Sea, have been studied using X-ray diffraction, mercury porosimetry and electron microscopy. Millimetre to micrometre mudstone textures have been quantified using image analysis of backscattered electron microscope images. Relatively shallow samples (1615 m) have isotropic mudstone fabric (no alignment of clay minerals), are dominated by smectite and have porosity values of approximately 35%. In contrast, more deeply buried samples (3300 m) have developed an anisotropic fabric (distinct alignment of clay minerals), are dominated by illite and have porosity values of approximately 22%. The change in mineralogy is due to smectite replacement by illite, which occurs simultaneously with porosity-loss and fabric development during progressive burial. Image analysis of differentially buried mudstones has proved to be a rapid, flexible and quantitative method for characterizing mudstone textures. The coincidence of mineralogical evolution with textural development and compaction implies that the transformation of smectite to illite occurs by dissolution and precipitation and that chemically facilitated compaction may contribute to porosity loss.
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Understanding the Micro to Macro Behaviour of Rock–Fluid Systems
Understanding how fluids flow through though rocks is very important in a number of fields. Almost all of the world's oil and gas are produced from underground reservoirs. Knowledge of how they got where they are, what keeps them there and how they migrate through the rock is very important in the search for new resources, as well as for maximising the extraction of as much of the contained oil/gas as possible. Similar understanding is important for managing groundwater resources and for predicting how hazardous or radioactive waste or carbon dioxide will behave if stored or disposed of underground. Unravelling the complex behaviour of fluids as they flow through rock is difficult, but important. We cannot see through rock, so we need to predict how and where fluids flow. Understanding the type of rock, its porosity, the character and pattern of fractures within it and how fluids flows through it are important. Some contributors to this volume have been trying to understand real rocks in real situations and others have been working on computer models and laboratory simulations. Put together, these approaches have yielded very useful results, many of which are discussed in this volume.