Development and Performance Evaluation of a Starch-Based Composite Filter Loss Reducer for Use at 220℃

Drilling fluid additives with both high temperature stability and environment protection ability are the key to “safe, efficient, economic and green” well drilling. A high temperature environmentally friendly starch-based composite filter loss reducer was developed with a water-soluble starch, a fine walnut shell powder and an environmentally friendly acrylic acid resin. The synthesis is completed through inverse emulsion polymerization with the help of a crosslinking agent. This composite filter loss reducer has a maximum thermal decomposition temperature of 286℃, and has fibrous structure of irregular shapes and different sizes. After hot rolling at 220℃, a 4% bentonite base slurry treated with 2% composite filter loss reducer has its API filter loss reduced from 39 mL to 12 mL, and its HTHP filter loss from 172 mL to 52 mL, a rate of filtration reduction of nearly 70%. At elevated temperatures, the composite filter loss reducer shows a low viscosity filter loss control effect. Zeta potential analysis, particle size distribution measurement and SEM observation show that the molecules of the composite filter loss reducer can be adsorbed on the clay particles, thereby enhancing the colloidal stability and optimizing the particle sizing of the bentonite slurry. Meanwhile, the composite filter loss reducer can plug the pores formed in the mud cakes, making the mud cakes thin and tough, and based on these mechanisms, the high temperature filtration rate of the drilling fluid is finally significantly reduced. The results of this study provide a guidance to the research and development of ultra-high temperature environmentally friendly water-based drilling fluids.