Bentonite is added to water based muds to increase the viscosity and gel strength, suspend solids and increase the carrying capacity of the mud. Bentonite forms a filter cake and, if properly dispersed, is the main agent for reducing water loss.
Bentonite will yield in fresh water (less than 50 g/l salt) but not in salty water. Hence if bentonite is to be used in salty water, it must be prehydrated in fresh water. Before adding bentonite to the water (or any other chemical), test the water for salinity and hardness. As a guide, use soda ash at 1 lb/10.0 bbls water every one ppm total hardness, then add caustic to obtain the required pH. Note that in salt saturated muds, even prehydrated bentonite may have limited use as osmotic forces will dehydrate the bentonite again.
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