Poly Anionic Cellulose (PAC) is a water-soluble cellulose derivative widely used in offshore drilling due to its exceptional properties that enhance the performance of drilling fluids. Derived from natural cellulose through chemical modification, PAC is typically used in its sodium salt form and is particularly valuable in challenging environments like offshore oil and gas operations, including salt wells and deepwater drilling.

In offshore drilling, PAC serves multiple critical functions in water-based drilling fluids:

1. Fluid Loss Control: PAC reduces filtration loss by forming a thin, low-permeability filter cake on the wellbore wall. This minimizes the invasion of drilling fluid into the formation, protecting the reservoir and maintaining wellbore stability—crucial in offshore settings where formation damage can significantly impact productivity.
2. Viscosity Enhancement: Available in high-viscosity (PAC-HV) and low-viscosity (PAC-LV) grades, PAC increases the thickness of drilling mud, improving the suspension and transport of drill cuttings to the surface. PAC-HV is particularly effective in low-density muds, boosting viscosity while reducing fluid loss, whereas PAC-LV controls filtration without significantly altering viscosity in heavier muds.
3. Salt and Temperature Resistance: Offshore drilling often involves high-salinity conditions (e.g., seawater or saturated brine) and elevated temperatures. PAC’s anionic structure provides excellent salt tolerance and thermal stability, maintaining drilling fluid performance up to 150°C, making it ideal for deepwater and high-temperature wells.
4. Stabilization and Rheology Control: PAC stabilizes drilling mud, extending its lifespan even in saline environments. It enhances rheology, lubricates solids, and reduces the risk of stuck pipe incidents by improving wellhole cleaning and wall cake characteristics.
5. Environmental Advantage: Being biodegradable and derived from natural cellulose, PAC aligns with the environmental requirements of offshore drilling, especially in sensitive marine ecosystems, offering a greener alternative to synthetic polymers.

In practical applications, PAC is dissolved in water (typically at a 1/40 to 1/20 ratio) and added to the mud system, often in combination with other agents. Its ability to form a protective mud film, resist bacterial degradation (eliminating the need for high pH or preservatives), and perform reliably across a wide pH range further enhances its suitability for offshore operations.