Acting ways and classification of anti-caving additives for drilling fluids

The anti-caving additives are classified into two types and then are classified into 8 sub-types based on their general acting ways. The first type of additives can be used to prevent or slow down transmission of water from well-hole into formations. The second type can bind up mineral particles in formation. The first type includes six sub-types of additives: (1)that can decrease water activity of drilling fluids; (2)that can increase the viscosity of filtering fluid; (3)that can block-up formation pores and fractures; (4)that can reduce the capilary force on water towards formation; (5)that has low hydration energy; (6)that may form compact mud cakes. The second type includes two sub-types: (1)that may link up mineral particles by van der Waals forces; (2)that can adhere mineral particles by chemical bonds. The type of additive that can block-up pores is the essential one for anti-sloughing drilling fluids generally.