Completion fluids are specialized fluids used during the final stages of well construction to prepare the well for production. They are designed to minimize formation damage, maintain wellbore stability, and ensure efficient hydrocarbon flow. Below is a detailed breakdown based on the search results:
1. Definition and Purpose
Completion fluids are typically brines (e.g., chlorides, bromides, and formates) but can also include other nondamaging fluids with proper density and flow characteristics. Their primary functions include:
- Wellbore stability: Preventing collapse or fluid influx.
- Formation protection: Reducing permeability damage.
- Corrosion inhibition: Protecting downhole equipment.
- Pressure control: Balancing formation pressure to avoid kicks or losses.
2. Types and Compositions
- Water-based completion fluids: Commonly used due to cost-effectiveness and environmental considerations. For example, a 210°C ultra-high-temperature water-based system was developed for buried hill reservoirs, containing seawater, NaCl (25%), cleanup surfactant (STIMFC-1), and high-temperature corrosion inhibitor (COROHIB-1).
- Brine-based fluids: Include chlorides (NaCl, CaCl₂), bromides (NaBr, CaBr₂), and formates (KCOOH, NaCOOH).
- Oil-based and synthetic fluids: Used in sensitive formations but less common due to environmental concerns.
3. Key Performance Metrics
An effective completion fluid should meet the following criteria:
- Thermal stability (e.g., stable at 210°C for deep reservoirs).
- Low interfacial/surface tension (e.g., 31 mN/m surface tension, 7.7 mN/m interfacial tension) to reduce water-blocking effects.
- Corrosion resistance (e.g., corrosion rate < 0.012 mm/a).
- High permeability recovery (>85% to minimize formation damage).
4. Applications in Different Reservoirs
- High-temperature reservoirs (e.g., Bozhong buried hill): Require thermally stable fluids with corrosion inhibitors.
- Low-permeability gas wells (e.g., Sulige field): Need solids control to prevent pore clogging.
- Offshore wells: May use integrated drilling-completion fluids to simplify operations.
5. Innovations and Trends
- Temporary plugging technology: Used in Yaha Oilfield to enhance reservoir protection.
- Solids distribution control: Critical in water-based fluids to prevent formation damage.
- Environmentally friendly formulations: Increasing focus on biodegradable additives.
For further details, you can refer to the original studies on ultra-high-temperature completion fluids 1or integrated drilling-completion systems.
