Effect of high temperature ageing on TiO2 nanoparticles enhanced drilling fluids: A rheological and filtration study

Design of drilling fluids is critical to the techno-economic success of drilling a petroleum well bore and the present study is a forward step in that direction. Effect of TiO₂ nanoparticles on the thermal stability of drilling fluid properties is evaluated using two different mud systems based on polyanionic cellulose (PAC) and hydroxyethyl cellulose (HEC). Drilling fluids were subjected to high temperature rolling conditions at 110 °C and 30 rpm for 16 hours in order to simulate the wellbore environment using a roller oven. Due to 16 h long hot rolling, the API FL values for DFB (base mud), DFP3 (1.0 w/v% PAC) and DFH3 (1.0 w/v% HEC) increased by ~56%, ~18% and ~46% respectively; whereas in presence of 0.5 w/v% nanoparticles respective figures were ~28%, ~16% and ~25%. In case of DFP3, AV at 25 °C was reduced due to hot rolling by ~34% without nanoparticles and by only ~15% in presence of nanoparticles. For DFH3, the percentage reduction in AV at 25 °C due to ageing was ~24% which decreased to ~16% for DFHN (1.0 w/v% HEC and 0.5 w/v% TiO₂). It was found that nanoparticles imparted resistance to thermal degradation in rheological and filtration characteristics of drilling fluids. Filter cakes were studied using scanning electron microscopy and showed nanoparticles scattered over the surface of filter cakes which were filling the micro and nano sized gaps in the porous structure of mud cake and reducing the filtration rate. This study shows that using TiO₂ nanoparticles along with a conventional fluid loss reducer additive not only enhances the efficacy of that additive but also improves the thermal stability and rheological properties of mud systems.