Enhancing the stability of shale in water-based fluid with polyethylene glycol/nanosilica composite grafted with sodium dodecyl sulfate

Shale stabilizers with high-performance properties are necessary when drilling oil and gas wells because unstable shale constantly poses a risk of increased drilling fluid loss and wellbore instability. In this study, a polyethylene glycol/nanosilica composite grafted with sodium dodecyl sulfate (PEG-NS-SDS) was designed and characterized to act as a shale stabilizer, viscosity modifier, and fluid loss control additive. With PEG-NS-SDS, a water-based fluid (WBF) was made to test its ability to prevent shale from swelling. This was carried out with a shale dispersion test and a linear shale swelling inhibition longevity test. The results demonstrated that the particle size distribution of PEG-NS-SDS was 82–410 nm, with a peak maximum, D50, and mean diameter of 270 nm, 195 nm, and 144 nm, respectively. The WBF with 1.5 wt% PEG-NS-SDS showed the best improvement, and it unveiled a 42% reduction in filtrate loss, followed by PEG-NS of 34%, SiO2 NP of 29%, and KCl of 23%. Shale swelling was best inhibited by PEG-NS-SDS over KCl, SiO2 NP, and unmodified PEG-NS. The linear shale A swelling rate of WBF dropped from 72.1 to 31.9% with PEG-NS-SDS, while the swelling rates with KCl, SiO2 NP, and PEG-NS were 35.1%, 49.1%, and 41.5%, respectively. Hot rolling dispersion experiments revealed that PEG-NS-SDS outperformed SiO2 NP, PEG-NS, and KCl. When tested on shale B, PEG-NS-SDS recovered 91.2% of the shale dispersion, while KCl, SiO2, PEG-NS, and the base fluid recovered 89.3%, 83.7%, 87.6%, and 57.6%, respectively. This study showed that PEG-NS-SDS is more effective at preventing shale swelling because of the synergistic effect between the anionic surfactant and PEG-NS. Overall, the study showed that adding PEG-NS-SDS to the base fluid made it easier for the fluid to inhibit shale from swelling. PEG-NS-SDS proved to be a good additive for drilling mud, with a promising improvement in shale swelling control and wellbore stability.