Modified Starch as a Filter Controller in Water-Based Drilling Fluids.

Herein, the effectiveness of an itaconic acid (IA) graft copolymer on native corn starch (NCS) as a filter control agent in fresh water-based drilling fluids (WBDFs) was evaluated. The copolymer (S-g-IA_APS) was synthesized by conventional radical dispersion polymerization using the redox initiation system (NH4)2S2O8/NaHSO3. The modification of the starches was verified by volumetry, Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). Then, three WBDFs were formulated in which only the added polymer (NCS, S-g-IA_APS, and a commercial starch (CPS)) was varied to control the fluid losses. The physico-chemical, rheological, and filtering properties of the formulated systems were evaluated in terms of density (ρ), pH, plastic viscosity (µp), apparent viscosity (µa), yield point (Yp), gel strength (Rg), and filtrated volume (VAPI). In order to evaluate the resistance to temperature and contaminants of the WBDFs, they were subjected to high pressure and high temperature filtering (VHPHT). The filter control agents were also subjected to aging and contamination with cement and salt. The S-g-IA_APS addition improved the filtering behavior at a high pressure and temperature by 38%.