Caustic Soda

Applications

• Primarily used to control alkalinity and pH in aqueous fluids (limits the solubility of calcium and magnesium by precipitating the metal hydroxides, Ca(OH)2 and Mg(OH)2; for the same reason, it cannot be used to increase the pH of divalent metal ion brines)

• Aids the solubilization of products such as lignosulfonates and lignites and activates Bentonite dispersion

Usage

Caustic soda is added as necessary to obtain the required pH and divalent ion concentration. Additions are typically under 1 lb/bbl (2.85 kg/m3 ); however, drilling fluid alkalinity generally falls over time, and additive treatments can rise to total >4 lb/bbl (>11.4 kg/m3). Fatty acids or esters could saponify at high pH; therefore, compatibility with caustic soda solutions must be checked. For safety reasons, caustic soda must never be mixed through the mud hopper; it must be added via a chemical barrel or to a low-volume premix in a slug pit by direct addition through the grating. The premix is then transferred slowly to the active system over the course of one or several circulations.