Application of Starch Microspheres Modified by Alkyl Polyglucoside as Environmental-Friendly Fluid Loss Additive in Water-Based Drilling Fluids

With the continuous improvement of environmental protection requirements in the drilling fluid industry, the research of environmentally friendly additives has been widely discussed. Modified starch is a typical natural material and has been usually used as an environmentally friendly fluid loss additive. However, their high-temperature resistance is poor and limits their application. In this study, a composite fluid loss additive (STA) was prepared by reverse emulsion polymerization using corn starch and alkyl glycoside as raw materials and epichlorohydrin as the cross-linking agent. The molecular structure, thermal stability, and microstructure of STA were characterized, and its filtration properties were systematically evaluated. Results demonstrated that the thermal decomposition temperature of STA was 324 °C and significantly higher than that of corn starch. STA was irregularly spherical in an aqueous solution, and its surface presented a porous structure. Moreover, STA was easily biodegradable with a BOD/CODcr ratio of 19.2%. Filtration tests showed that the temperature resistance of STA could reach 170 °C, and 3% of STA reduced the fluid loss volume of 4% bentonite suspension by 62.71%. In comparison, the filtration performance of STA was better than those of corn starch and commonly used sodium carboxymethyl starch. On one hand, STA had a cross-linked structure and a long paraffin chain, providing strong thermal stability at high temperatures. Besides, the porous structure of STA was beneficial for plugging through shape change and adsorbing water in drilling fluids. On the other hand, STA would interact with clay, increase the viscosity of the bentonite suspension to a certain extent, and improve the colloidal stability. Finally, STA plugged the pores and formed a thin, compact, and relatively hydrophobic filter cake, reducing fluid loss, even at high temperatures. STA can be used as a fluid loss additive with efficient high-temperature resistance and environmental friendliness and also provides new guidance for designing high-performance water-based drilling fluids.