Although the application of nanoparticles in drilling fluid has been reported under static test by our research group, understanding inhibition formation of damage by filtration volume reduction in porous media under dynamic conditions is still a crucial issue. In this research, synthesised silica nanoparticles modified with acid treatment (Si11A) evaluated in previous results in the bentonite-free water-based drilling fluid (BFWBM) in static tests were analysed in the coreflooding test under dynamic and reservoir conditions. Si11A nanoparticles were evaluated by permeability return tests under reservoir conditions overburden, pore, and overbalance pressures, and temperatures of 3000 psi, 1700 psi, 1200 psi, and 87 °C, respectively. Coreflooding test with a concentration of 0.1 wt% Si11A nanoparticles based on our previous work showed a reduction in the filtration volume by 77%, decreasing the formation damage by 51% compared to the drilling fluid without nanoparticles. Also, the oil recovery obtained with the best design fluid using the Si11A nanoparticles was 10% higher than the baseline. Additionally, the effluents of crude oil obtained from permeability return test were evaluated at reservoir temperature using a rotational rheometer at shear rates varying between 1 and 100 s −1 , obtaining a reduction of the viscosity up to 28% during nine pore volume injected using the BFWBM with S11A nanoparticles. The role of the nanoparticles in the drilling fluid is the rapid deposition in the mudcake to enhance the properties, the subsequent filtration volume reduction, and the enhancement of the petrophysics properties may be described by dynamic filtration curves, effective oil permeability and relative permeability curves.

The study aims to evaluate the effect of size and surface acidity of synthesised silica (SiO 2 ) nanoparticles in a bentonite-free water-based drilling fluid (BFWBM) to minimise its impact on formation damage by filtration volume control and mudcake thickness reduction. Nanoparticles were synthesised through the sol-gel method, and the surfaces were modified through the incipient impregnation technique using acidic and basic treatments. The nanoparticles were characterised by dynamic light scattering (DLS), Fourier transforms infrared spectroscopy (FTIR) and zeta potential measurements. Drilling fluid properties in the presence and absence of nanoparticles were evaluated through the analysis of pH, density, solid content, rheology, and static filtration tests at high pressure and temperature. Drilling fluids were described as shearthinning fluids under the rheological model of Herschel-Bulkley. The smallest nanoparticles (Si11) contributed to the highest filtration and mudcake thickness reduction. Hence, these were modified to obtain a different surface charge. Silica nanoparticles modified with the acidic treatment (Si11A) in drilling fluids showed the highest reduction of the filtration volume and mud cake thickness with values of −22% and −65%, respectively. Also, the filtration volume appeared to be a function of the zeta potential of nanoparticles that were investigated, for the highest zeta potential value, SiA −48.66 mV @ pH 10, the filtration volume is lower. SiO 2 nanoparticles in a BFWBM reduce the filtration volume due to their nanometric size occupying empty spaces in the mudcake and promoting the repulsive forces avoiding the flocculation of the drilling fluid thanks to the anionic surface charge. This study provides a wider landscape about

This study aims to understand the interactions among SiO 2 nanoparticles (NPs) and the main chemical constituents of bentonite-free water-based mud, including CaCO 3 and xanthan gum. To this end, both theoretical and experimental protocols are developed coupling molecular dynamics simulations with filtration and rheological property measurements of mud systems having different NP contents. The resultant filter cakes are inspected to capture the role of interactions among the deposited components. Static filtration tests at high pressure−temperature are carried out on a standard filter paper as well as an in-house prepared sandstone disk. The filtrate volume and filter cake thickness and permeability were reduced by 56, 36, and 72%, respectively, at an optimum NP content of 0.1 wt %. Using the sandstone disk, the mud with the optimum NP content showed a 72 and 59% reduction in spurt loss and total filtrate volume, respectively. Scanning electron microscopy images showed that the NPs improved the morphology of the filter cake. The higher NP−sandstone interaction was successfully described by molecular dynamics simulations, which showed the highest interaction between sandstone and NPs followed by CaCO 3 and then the system xanthan gum and water polymer solution. Moreover, the theoretical analysis showed that SiO 2 NPs reduced the repulsion energy among the CaCO 3 surfaces, promoting a tighter filter cake and subsequently less mud filtrate, as evident experimentally.

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