Lost Circulation - Additives

Additives

• The most common additive used to control or cease lost circulation is bentonite, in that it inherently will seal small holes or fractures. Bentonite, in higher concentrations, increases viscosity, and therefore slows the fluid flow into the surrounding rock. Although bentonite is the most common additive used, it sometimes is not used at all, depending on the current fluid being used and the current depth of drilling in relation to desired production zones.
• Polymers are also sometimes used to increase the viscosity. Though these are more costly, they are more compatible with several types of fluid systems.
• When it comes to additives which physically plug or seal the losses, there are a great deal of them. Sawdust, flaked cellophane, crushed or ground gypsum are all used.
• Other common, and cheaper additives, that are used are shredded newspaper and cotton seed hulls. Cotton seed hulls are less preferred as they may cause wear to pump swabs and springs. Both of these are generally only used when either fresh or brine water is being used for the drilling fluid.
• When drilling in salt formations, brine water is typically used as it is more difficult to dissolve more of the salt preventing the formation of "washouts". Washouts not only contribute to loss of circulation, but can jeopardize the integrity of the wellbore itself.