Investigation of TPEG comb polymer as filtration and rheological additives for high-temperature water-based drilling fluid

During oil and gas drilling, high-temperature and high-salt considerably deteriorate the rheological and filtration properties of drilling fluid. In this study, two novel comb polymers P-TPEG-10 and P-TPEG-24, with different side chain lengths, were synthesised as filtration and rheological additives for drilling fluids under high-temperature and high-salt environments. When 2 wt% isopentenyl polyoxyethylene ether (TPEG) comb polymer was added to bentonite water-based drilling fluid (BT-WBDF), the viscosity and yield point of the drilling fluid were considerably improved, the filtration loss was considerably reduced before and after hot rolling at 220 ℃ and BT-WBDF could resist 15 wt% NaCl or 0.5 wt% CaCl2. P-TPEG-10 has a better viscosity-increasing effect than P-TPEG-24, and P-TPEG-24 has a better filtration control effect than P-TPEG-10. The excellent rheological and filtration control effects are attributed to the spatial network structure formed by the comb polymer and bentonite particles. Strong hydration groups such as sulfonic groups on the main chain and the intercalation of polyethylene glycol (PEG) side chains increases the thickness of the diffusion double electric layer of bentonite particles and inhibit the aggregation of BT particles. BT-WBDF maintains a reasonable particle size distribution, thus forming a thin and dense filter cake, and effectively reducing the filtration volume. It is expected to play an essential role in the filtration and rheological control of high temperature drilling fluid.