Humic acids are organic carboxylic acids of complex molecular structure (aromatic and phenolic). The water solubility of lignite depends on ist humic acid content. Decarboxylation of humic acid groupds by hydrolysis in alkaline muds is a major source of carbonate and bicarbonate anions in water muds.
They can be used as a fluid loss additive in oil base and water base drilling fluids. Humic acids have three types of functions when used in drilling fluids. First of all, they reduce viscosity and gel strengths. Second, they function as thinners, deflocculants, dispersants and as rheological control agents. Third, they also act, as stated above, as fluid loss agents and emulsifiers.
Especially potassium humates are used mainly as a kind of a shale inhibiting agent for freshwater drilling fluids and have a function of viscosity reducer and water-loss reducer.