Study on Filter Loss Reducer for High Density Clay-free Saturated Saltwater Drilling Fluids

Clays used in high density saturated drilling fluids for drilling gypsum, salt formations and formations with high-pressure brines have some drawbacks, such as formation damage by the invasion of clay particles, and progressive gelling of the drilling fluids caused by uncontrollable viscosity uprising at elevated temperatures and overuse of sulfonates. Progressive gelling of drilling fluids with clays usually cannot be controlled by rheological optimization. To resolve this problem, a filter loss reducer, BH-HSF, for high density clay-free saturated drilling fluids has recently been developed through synthesis of modified starch and other polymers. BH-HSF is able to develop an "interpenetrating polymer network" in water solution, and performs well at 150℃ and Ca²⁺/Mg²⁺ concentration of 4,000 mg/L. High density clay-free saturated saltwater drilling fluids treated with BH-HSF have API filtration rate of less than 4.0 mL. They have good capacity for suspending weighting materials, and no weighting materials settlement has ever occurred after long period of standing. Deterioration of the rheology of BH-HSF treated drilling fluids can be controlled by rheological optimization. BHHSF has properties that are equivalent to HT-Starch (a well-known drilling starch with advanced performance) and is well compatible with other drilling fluid additives.