•It is important to understand how particle sizes in drilling mud are classified and the types of solids that fall into each category. •Particles in drilling mud can range from very small clays, (less than 1/25,400th of an inch), to very large drill cuttings (larger than an inch). •Due to the extremely small particles, sizes are expressed in micron units. •A micron is one-millionth of a meter –(1/1,000,000 or 1 x 10 -6m). –1 in. equals 25,400 microns.
•In a drilling mud, viscosity increases proportionally with the surface area of solids. –The surface area of all solids must be wetted. –As the amount of liquid is reduced due to increased surface area, fluid viscosity increases and performance declines. –Colloidal solids produce most of the viscosity in drilling muds due to this surface area increase. –The volume of colloidal-size solids contained in drilling mud must be controlled for the sake of economy and efficiency. •The picture shows how the same volume of material takes up substantially more surface area
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