CLAY MINERAL – GEOLOGY DEFINITION
Mite, sinectite, and chlorite. Smectite is the clay used in drilling mud to increase viscosity and density and to build the filter cake on the sides of the well. Clay minerals, because of their size, decrease the porosity and permeahiliry of a rock and increase irreducible water content. Clay minerals can trade (exchange) cations (positive charges) in their interlayer sites. The amount a particular clay mineral can exchange is called cation exchange capacity. Cations and fresh water can cause some clay minerals to swell (swelling clays) or disperse. This can cause the clay mineral to detach from mineral grains and clog pure throats in sedimentary rocks, reducing or destroying the rock’s permeability in a process called formation damage.
The smectite-type of clay mineral has the greatest cation exchange capacity. Some problems with clay minerals include a) migration of lines (kaoline and fibrous Mite), b) swelling (smectite, vermiculite and mixed layers), and c) HCl acid damage (chlorite and Fe illite).