Design and Evaluation of a Water-Based Drilling Fluid Formulation Using SiO and Graphene Oxide Nanoparticles for Unconventional Shales

Abstract

Unconventional shale reservoirs have become a key player in the oil and gas industry to cover the world's energy demands. Traditionally, oil-based drilling fluids (OBM) are preferred to drill shale plays due to negligible chemical interactions. Nevertheless, strict environmental regulations have motived the industry to design water-based drilling fluids (WBM) capable to control the shale-water interactions, improving their performance. Still, conventional additives are too large to plug shales’ micro-fractures and nanopores. Thus, nanoparticles due to their unique size, shape, and properties can provide a solution for the WBM. This study focus on the design and evaluation of a customized nanoparticle water-based drilling fluid (NP-WBM) using silica nanoparticles (SiO2-NPs) and graphene nanoplatelets (GNPs). The main objective is to identify the optimal NP concentration to improve the rheological and filtration properties of the NP-WBM and evaluated its inhibition benefit. The NP selection was based on the characteristics of the Woodford shale obtained through x-ray diffraction (XRD), cation exchange capacity (CEC), and scanning electron microscopy (SEM). NPs’ colloidal stability was analyzed in an alkaline environment with zeta-potential measurements. The concentration of NPs was evaluated below 1 wt.%. Laboratory measurements for the NP-WBM included API filtrate test (LTLP) and high-temperature/high-pressure (HTHP) test using a static filter press and rheological analysis with a rotational viscometer. To evaluated the inhibition benefit, the NP-WBM was tested against the Woodford shale by performing immersion and cutting dispersion tests. The results showed zeta-potential values below −30 mV for both nanomaterials, indicating good dispersibility of the NPs within the WBM. Also, significant improvements in the filtration properties were observed when adding 0.5 wt.% of SiO2-NPs with 0.25 wt.% of GNPs to the base fluid with no spurt-loss and minor effects on the rheological parameters. Higher concentrations did not show further improvements; thus the previous combination was selected as the optimal. Chemical interactions tests indicated that the Woodford shale might develop micro-fractures when exposed to water for long periods of time. However, no micro-fractures were observed when the rock was exposed to NPs. Furthermore, the NP-WBM reduced the cutting dispersion by 35.61% compared to the base fluid, showing superior inhibition properties even in high illitic shales that are prone to experience cuttings disintegration. NPs’ stability and benefits at low concentrations, indicates their potential to improve the design of WBM for unconventional shales, reducing the environmental impacts linked to the drilling operations.