5 Microfabrics Related to Porosity Development, Sedimentary and Diagenetic Processes, and Composition of Unconventional Resource Shale Reservoirs as Determined by Conventional Scanning Electron Microscopy

TLDR: In this paper, the authors describe and illustrate features of shales and mudstones at the nanometer and micrometer scales using standard scanning electron microscopy (SEM) and FEM techniques.

Abstract: This chapter describes and illustrates features of shales and mudstones at the nanometer and micrometer scales using standard scanning electron microscopy (SEM) and field emission scanning electron microscopy (FE-SEM) techniques. Microfabric observations at these scales not only provide insights into sedimentary and postdepositional processes but also offer evidence useful in understanding storage and primary migration patterns in unconventional shales. The images illustrated are suggested as references to guide future shale studies related to shale porosity and permeability. Examples are provided of various shales (Barnett, Woodford, Eagle Ford, Rhinestreet, Fayetteville, and Marcellus). Microfabric and pore features illustrated include clay flakes related to open-network floccules and clay-aligned fabric, plus other features produced by nonclay minerals. Organic matter produced by zooplankton and algae (e.g., coccolithophores, Tasmanites) is described because it may form organic mucus that adheres to and helps aggregate clay flakes. Organic matter is also common within porous fecal pellets. Coccolithophores, sponge spicules, and foraminifera tests contain hollow internal chambers, which provide porosity and probably permeability, even when filled with clay minerals. Conventional SEM provides a rapid and relatively inexpensive way of evaluating pores and microfabrics in shales.