NiO nanoparticles for enhanced thermal stability and filtration control in HPHT water-based drilling fluids

Abstract

High-pressure high-temperature (HPHT) wells present significant challenges for conventional water-based drilling fluids (WBDFs), including thermal degradation of additives, excessive fluid loss into formations, rheological instability, poor cuttings suspension, and weak, permeable filter cakes. These limitations result in increased non-productive time (NPT), wellbore instability, elevated equivalent circulating density (ECD), and higher operational risks in deep and ultra-deep hydrocarbon reservoirs. This study systematically investigates the application of nickel oxide (NiO) nanoparticles as a functional additive to enhance thermal stability, rheological properties, and filtration control of bentonite-based WBDFs under HPHT conditions. NiO nanoparticles with an average size of 10–20 nm were dispersed in 7 wt% bentonite suspensions at concentrations ranging from 0 to 1.0 wt%. Rheological behavior was evaluated across 25–125 °C using a rotational rheometer and fitted to the Herschel–Bulkley model. High-temperature high-pressure (HTHP) filtration tests were conducted at 150 °C and 500 psi differential pressure. Filter cake microstructure was thoroughly characterized using scanning electron microscopy (SEM). Experimental results demonstrate a clear concentration-dependent performance. At the optimal concentration of 0.2 wt% NiO, the fluid exhibited significantly improved yield stress and gel strength while maintaining desirable shear-thinning behavior and avoiding excessive viscosity buildup that could impair pumpability. This formulation markedly reduced HTHP fluid loss and produced a denser, more uniform, and lower-permeability filter cake compared to the base fluid. SEM micrographs revealed that NiO nanoparticles promote effective nano-bridging between bentonite platelets, resulting in enhanced particle packing density and reduced porosity. In contrast, higher concentrations (e.g., 0.5 wt%) led to noticeable aggregation, creating micro-channels and reducing filtration efficiency. Compared to widely studied nanoparticles such as SiO₂ and TiO₂, NiO provides a superior balance between thermal stability, filtration control, and rheological performance. This work highlights the promising potential of NiO nanoparticles for the development of next-generation, cost-effective, and environmentally acceptable HPHT water-based drilling fluids, contributing to improved drilling efficiency, wellbore stability, and reduced non-productive time in challenging ultra-deep reservoirs.