Comb‐shaped copolymer as filtrate loss reducer for water‐based drilling fluid

ABSTRACT A new comb‐shaped copolymer was synthesized by free radical copolymerization of 2‐acrylamide‐2‐methyl propane sulfonic acid, acrylamide, N‐ vinyl‐2‐pyrrolidone, and allyl polyoxyethylene ether (APEG) monomers. The copolymer was evaluated as a filtrate loss reducer in water‐based drilling fluid at 180 °C environment, and found to work well without causing high viscosity effect. Composition of the copolymer was determined by Fourier transform infrared spectroscopy (FTIR), proton nuclear magnetic resonance spectroscopy, and gel permeation chromatography. FTIR, X‐ray diffraction,, and environmental scanning electron microscopy characterizations were used to probe the filtrate loss mechanism of the comb‐shaped copolymer. Thermogravimetry and differential scanning calorimetry results showed that thermal degradation of the copolymer is not obvious before 293.6 °C. The copolymer is found to be superior to its commercially available counterparts for controlling filtrate loss volume and maintaining a steady viscosity after 180 °C aging. Higher content of APEG in the copolymer helps maintain rheological properties of the drilling fluid after aging and reduces filtrate loss volume. The morphology of the copolymer in aqueous solution displays a comb‐shaped 3D structure and shows clear adsorption onto clay particles. The working mechanism for copolymer is that anchoring groups bind the copolymer onto clay particles through different binding mechanisms, while colloidal suspension stability is achieved by steric hindrance and electrostatic repulsion, as well as through PEG segment intercalation into clay lamellae. The copolymer is able to cover and seal the micro‐holes in the mud cake even at high temperature to reduce permeability. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135 , 45989.