Amorphous and Crystalline Solids as Artifacts in SEM Images
Minerals can precipitate in samples after coring and after preparation for scanning electron microscope (SEM) imaging. Re-deposition of solids from ion milling also produces artifacts that can be observed in images. Both mineral precipitates and re-deposited solid mixtures can be obvious artifacts, but they can also be subtle and challenging to interpret as features that are not present in the subsurface. The most common mineral precipitates are hydrous calcium sulfate (gypsum or bassanite) and halite. Iron sulfate minerals are also commonly observed. These types of artifacts are illustrated, with examples from ion-milled, mechanically polished, and freshly broken surfaces of various sedimentary rocks. Recognition of these artifacts is important because they can reduce porosity and pore size in SEM images and can affect measurements of rock composition and interpretations of pore fluid chemistry.
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This Memoir covers recent advances in the acquisition and application of high-resolution image data to unconventional reservoirs. The value of integrating multiple techniques is a common theme. Chapters address imaging methods, recognition of artifacts, and case studies that explore nanopore systems within particular depositional settings. The importance of mineralogy, organic matter content, and fabric to reservoir quality issues such as wettability, porosity, and formation damage are addressed. This volume will prove useful to anyone interested in the methods for observing and quantifying the pore systems that control hydrocarbon storage and flow in unconventional reservoirs. Unconventional reservoirs studied include Bakken, Barnett, Bossier, Eagle Ford, Geneseo, Green River, Horn River, Marcellus, Mississippi Lime, Monterey, Niobrara, Wolfcamp, and Woodford formations.