Abstract
Conventional drilling fluids experience the problems of a low cleanup efficiency and oily drilled cutting disposal. To resolve these problems, a type of pH-responsive drilling fluid with a temperature resistance of up to 150°C resistance a density of 1.5 g/cm3 was prepared using mixed emulsifiers. Stable reversion from a water-in-oil (W/O) emulsion to an oil-in-water (O/W) and vice versa was realized. The results of light backscattering and sag stability suggested that the W/O and O/W emulsion-based drilling fluids showed excellent resistance to coalescence or sedimentation. There was no demulsification or barite sedimentation during emulsion reversion. W/O and O/W emulsions exhibited small droplet sizes and uniform distributions. The properties of the W/O and O/W emulsion-based drilling fluids were similar even after hot rolling at 150°C for 16 h. The reversible drilling fluid showed excellent resistance to contamination by saline water and drilled cuttings. The residual W/O emulsion-based drilling fluid was cleaned with acids at a high efficiency. The oil content of the drill cuttings generated by the W/O emulsion-based drilling fluid was reduced using simple acids. The improved reversion stability with high temperature and density resistance makes it possible for applicable reversible drilling fluid in deep or ultra-deep wells required by different geological formation.
Highlights
Conventional oil-based drilling fluids typically have high emulsion stability and strong oil-wetting properties, which render contact drilling pipes, formation, and drill cuttings oil-wet (Nooripoor and Hashemi, 2020)
There is no creaming or sedimentation. These results show that the reversible drilling fluids with a density of 1.5 g/cm3 achieve stable emulsion reversion even after hot rolling at 150°C for 16 h
The filtration loss for both W/O emulsion and O/W emulsion are less than 10 ml, which meets the American Petroleum Institute (API) standard. These results show that the properties of the reversible drilling fluid can be adjusted to maintain stability in wellbores even exposed to gypsum formation
Summary
Conventional oil-based drilling fluids typically have high emulsion stability and strong oil-wetting properties, which render contact drilling pipes, formation, and drill cuttings oil-wet (Nooripoor and Hashemi, 2020). Previous studies have proposed several methods to solve the follow-up problems associated with conventional oil-based drilling fluids, e.g., oil-based drilling fluid filter-cake removal (Bageri et al, 2019; Bageri et al, 2020), hole cleaning (Boyou et al, 2019; Guo et al, 2020), and waste oily drilled cutting processing (Sharma et al, 2020). These methods are expensive and complex, and
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