Clay: Geologic formations, carbon management, and industry

Abstract

The term clay is used interchangeably for the particles and the minerals, the latter commonly referred to as clay minerals to distinguish them from the clay particle size. Clay sediments are typically deposited in quiet-water environments, settling out as fine-grained mud, which may then be buried and lithified into shale. The quiet-water depositional environments are favorable for deposition of organic material as well, which over geologic time, may result in the shale becoming a source rock for petroleum and natural gas. Hydrocarbons have traditionally been produced from porous and permeable reservoir rock, where they had migrated from source rock and become concentrated in geologic traps. The recent development of “unconventional resources” like shale gas and tight oil has allowed hydrocarbons to be produced directly from the source rock. Conventional natural gas and oil reservoirs that have been depleted of hydrocarbons provide a viable option for secure carbon storage because there is a known trap and seal. CO2 can potentially be used for enhanced recovery of the hydrocarbons and for pressure management in shale, to minimize the loss of permeability that comes from increased net stress during drawdown. As a side note, natural clay-rich geomaterials can be used in agriculture, industrial processes, and for clay liners in chemical and radioactive waste disposal sites. The purpose of addressing geomaterials here is to give the readers an idea of the enormous breadth of each subject and point them toward other resources for additional information.