Polyanionic cellulose (PAC) is a water-soluble polymer commonly used in oilfield drilling operations. It exhibits excellent rheological properties, filtration control, and fluid loss reduction capabilities, making it an essential additive in drilling fluids. In this article, we will discuss the application and dosage of polyanionic cellulose in oilfield drilling.

Application: Polyanionic cellulose is primarily used as a viscosifier and fluid loss control agent in drilling fluids. Its key applications include:

1. Viscosity Control: PAC enhances the viscosity of drilling fluids, improving the suspension and transport of cuttings. It imparts shear-thinning rheology, which means that at high shear rates during circulation, the fluid's viscosity decreases, allowing for efficient pumping. At lower shear rates, such as when the fluid is static, the viscosity increases, preventing cuttings from settling.

2. Filtration Control: PAC forms a thin, impermeable filter cake on the wellbore walls, reducing fluid loss into the formation. This property helps maintain wellbore stability by minimizing differential pressure, preventing wellbore collapse, and mitigating the risk of formation damage.

Dosage: The appropriate dosage of polyanionic cellulose depends on various factors such as well conditions, drilling objectives, and fluid specifications. However, general guidelines for PAC dosage are as follows:

1. Base Fluid Requirements: Before adding PAC, ensure that the base fluid (water or brine solution) meets the required quality standards. The pH level and hardness should be within acceptable limits to avoid any adverse reactions with PAC.

2. Initial PAC Concentration: Typically, the initial PAC concentration ranges from 0.3% to 1.5% by weight of the drilling fluid. The specific concentration depends on the desired rheological properties and fluid loss control requirements.

3. Monitoring and Adjustments: The performance of PAC should be continuously monitored during drilling operations. Rheological measurements, such as viscosity and gel strength, along with fluid loss tests, can help evaluate the effectiveness of PAC. Adjustments in dosage may be required to optimize drilling fluid performance based on real-time well conditions.

Conclusion: Polyanionic cellulose plays a crucial role in oilfield drilling by improving fluid viscosity, controlling filtration, and reducing fluid loss. Its application and dosage need to be carefully determined based on specific drilling requirements and regular monitoring. By utilizing PAC effectively, drilling operations can achieve better hole stability, improved drilling rates, and enhanced overall performance.