Paper: Clay Technology And Well Stimulation

Pores in sedimentary rocks may be lined or filled with a variety of different clay minerals. These clays can greatly reduce permeability, increase acid or fresh-water sensitivity, totally alter the electric log response, and increase irreducible water saturations. The composition of the clays is of great importance in reservoir management. Different clays have different compositions. und thus will react differently to various drilling and completion fluids. As a result, fluids should be designed for the specific variety of clay present in the pores. Four families of clay minerals exist, and each causes different reservoir problems: (I) kaolinite is primarily responsible for the migration-of-fines problem associated with many reservoirs, (2) smectite can be extremely sensitive to fresh water, (3) illite increases pore tortuosity, and (4) chlorite is very acid sensitive. If well stimulations are designed without a knowledge of the type of clay minerals present in the pores, rapid production declines may occur after treatment. In some instances, the damage is permanent. In other instances, a new, properly designed acid job may result in dramatic increases in flow. Therefore, in designing a mud system, a frac job, or even a Waterflood project, it is vital to know what sort of clays occur in the pores of the reservoir rock.