1. Introduction
Oil drilling is a complex engineering operation that requires the use of a variety of chemicals to optimize the performance of drilling fluids. Drilling fluids not only lubricate and cool during drilling, but also help carry cuttings, prevent wellbore collapse, and maintain well pressure. Polyanionic cellulose (PAC) is an additive commonly used in drilling fluids and plays an important role in oil drilling with its superior performance.

2. Chemical properties of polyanionic cellulose
Polyanionic cellulose (PAC) is a derivative of cellulose with anionic groups in its molecular structure. PAC can be divided into two categories: low viscosity (LV-PAC) and high viscosity (HV-PAC), based on their viscosity performance in aqueous solution. The anionic properties of PAC enable it to form a stable sol in aqueous solution, which is very important for adjusting the rheological properties of drilling fluids.

3. Role in drilling fluids

3.1 Viscosity adjustment
PAC mainly adjusts the viscosity of drilling fluids by thickening. High-viscosity PAC can significantly increase the viscosity of the drilling fluid, thereby enhancing its ability to carry cuttings. This is essential for keeping the wellbore clean, preventing drill bit blockage, and improving drilling efficiency. Low-viscosity PAC is used in scenarios where the drilling fluid viscosity requirement is low. Its role is to provide a moderate thickening effect to ensure a balance between fluidity and carrying capacity.

3.2 Optimization of rheological properties
The rheological properties of the drilling fluid, that is, its flow and deformation characteristics, are an important factor affecting the stability of the drilling process. PAC can adjust the shear-thinning behavior of the drilling fluid so that it maintains a lower viscosity at high shear rates and a higher viscosity at low shear rates. This rheological property helps reduce frictional resistance under high flow conditions and improves the carrying capacity of the drilling fluid under low flow conditions.

3.3 Water loss control
PAC has excellent filtration control capabilities, which can reduce the penetration of water in the drilling fluid into the formation around the wellbore. This helps maintain the stability of the wellbore and prevent wellbore collapse caused by formation water loss. By forming a thin film, PAC effectively controls the filtration loss of drilling fluid and protects the integrity of the well wall.

4. Application advantages

4.1 Improve drilling efficiency
PAC’s thickening and rheological adjustment effects enable drilling fluid to carry cuttings more effectively, thereby reducing the risk of drill bit blockage and increasing drilling speed. In addition, the use of PAC also reduces friction resistance during drilling, allowing the drill bit to run more smoothly, further improving drilling efficiency.

4.2 Reduce environmental impact
PAC is an environmentally friendly additive with good biodegradability. During oil drilling, the use of PAC can reduce the impact on the environment, especially when dealing with drilling waste and drilling fluid recovery. Compared with other chemical additives, PAC is less harmful to the ecosystem and helps to achieve green drilling.

4.3 Cost-effectiveness
The application of PAC in oil drilling not only improves operational efficiency, but also reduces the amount of drilling fluid and the cost of preparation. The high efficiency and economy of PAC make it one of the preferred additives in drilling fluid optimization. Due to its excellent performance, PAC can reduce the need for other expensive chemicals in the drilling process, thereby reducing overall operating costs.

5. Actual Cases and Applications

5.1 Offshore Drilling
PAC is widely used in the preparation of drilling fluids in offshore drilling operations. For example, in a drilling operation in the North Sea oil field, the use of PAC effectively improved the drilling fluid’s ability to carry cuttings, reduced downtime during drilling, and improved overall drilling efficiency. In addition, PAC’s filtration control performance is excellent in complex marine environments, effectively preventing wellbore collapse.

5.2 High-temperature and High-pressure Drilling
PAC exhibits excellent stability and performance under high-temperature and high-pressure (HPHT) conditions. After an oil company applied PAC in a high-temperature and high-pressure well site in the Middle East, it significantly improved the stability and rheological properties of the drilling fluid, ensured the smooth progress of the drilling process, and reduced the risks and costs caused by drilling fluid failure.

6. Future Outlook
With the continuous advancement of oil drilling technology, the requirements for drilling fluid performance are also getting higher and higher. In the future, polyanionic cellulose will continue to play an important role in the following aspects:

High efficiency and environmental protection: The environmental protection characteristics of PAC will enable it to continue to play a key role in the development of green drilling fluids and promote the development of sustainable drilling technology.
Multifunctional additives: Future research may focus on the development of PAC derivatives with multiple functions, so that it can improve the performance of drilling fluids while providing more specific functions, such as high temperature resistance and salt resistance.
Intelligent control: Through the combination of nanotechnology and intelligent materials, future PACs may have intelligent control performance and can automatically adjust the performance of drilling fluids according to real-time needs during drilling.

As a multifunctional and efficient drilling fluid additive, polyanionic cellulose (PAC) plays a key role in the oil drilling process. By adjusting viscosity, optimizing rheological properties and controlling water loss, PAC effectively improves drilling efficiency, reduces environmental impact, and brings significant economic benefits. With the continuous development of science and technology, the application prospects of PAC will be broader, making greater contributions to the advancement and sustainable development of oil drilling technology.