Study and Application of a Non-Bromide, Environmentally Friendly, High-Temperature Resistant, and High-Density Solid-Free Completion Fluid

Abstract

Global oil and gas exploration has expanded to deep wells (>4500 m), ultra-deep wells, and complex environments (e.g., HPHT and permafrost). Such conditions impose stringent requirements on completion fluids: wide-temperature stability (-30 to 220°C), high density (≥1.70 g/cm3), and environmental friendliness. Traditional bromide and chloride fluids have inherent drawbacks like strong corrosivity (>0.2 mm/a on 13Cr steel), scaling risks, and high toxicity (LC5₀ < 500 mg/L), making them unsuitable for green development. To address these challenges, a novel bromide-free solid-free completion fluid (NONCORCLEA COMPL®) was developed using a synergistic design of organic acid salts, chelating agents, imidazoline inhibitors, and surfactants. A comprehensive evaluation system covered thermal stability, compatibility, corrosion resistance, inhibition, reservoir protection, and toxicity. Results show the fluid exhibits a wide temperature range of -30°C to 220°C and adjustable density of 1.6 to 1.82 g/cm3. The corrosion rate on Super 13Cr steel is 0.004276 mm/a (far below the 0.076 mm/a industry standard) with negligible pitting. The system demonstrates ≥89% clay anti-swelling rate, ≥96% cuttings recovery, and ≥88% core permeability recovery. Environmental tests show plant LC5₀ > 2000mg/L and animal LC5₀ 1000mg/L, complying with green standards. Field applications in Well ST-7 (170°C) and Well TT-1 (210°C) in the Sichuan Basin demonstrated stable wellbore conditions and excellent compatibility with on-site fluids. Oil production efficiency increased by 20.3% compared to water-based fluids. This fluid provides an efficient, environmentally friendly solution for deep and complex wells.