Enhancement of rheological properties of water-based drilling fluids using modified nanosilica for deep-sea drilling

Abstract
In the context of deep-sea oil and gas drilling, drilling fluids undergo substantial rheological changes due to the extreme temperature gradient experienced, which ranges from subsea low temperatures to deep-sea high temperatures. This results in complex variation patterns, significantly impacting the safety and efficiency of oil and gas exploration. Consequently, a rheology modifier was developed through the surface modification of nanosilica with a phosphate modifier (TMP). The retooled nanosilica was subjected to a battery of tests, including Fourier infrared spectroscopy, thermogravimetric analysis, and particle size measurements. A host of experiments were carried out to evaluate the effect of tweaking the rheological attributes of the altered nanosilica. A set of deep-sea drilling fluid formulations that exhibited optimal rheological properties were identified and evaluated for their fundamental performance. The findings indicated that the particle size distribution of the modified silica nanoparticles was within the range of 43–164 nm. After hot rolling at 180 °C/16 h, the thermal degradation rate of plastic viscosity (PV) decreased from 55.9% to 6%, and that of yield point (YP) was mitigated from 66.7% to 28%. Furthermore, within the temperature range of 4–90 °C, the thermal variation rates of PV and YP were significantly reduced from 33.3% to 11.1% and from 17.6% to 0%, respectively. Based on these findings, an optimized deep-sea water-based drilling fluid system was developed using the modified nanosilica as a key regulator. This optimized formulation exhibits excellent stability, with PV and YP variation rates of 30.4% and 36.8% across the wide interval of 30–180 °C. The system maintains favorable rheological and filtration properties even after hot rolling at 190 °C/16 h which can satisfy the basic technical requirements of the deep-sea drilling fluids for deep-sea wells.