In petroleum drilling, the apparent viscosity of polyanionic cellulose (PAC)
I. Sand - carrying function
1. Preventing cuttings from settling
- During the drilling process, a large amount of cuttings are produced as the drill bit breaks the rock. Poly - anionic cellulose with an appropriate apparent viscosity can increase the viscosity of the drilling fluid, enabling the cuttings to be suspended in the drilling fluid, just like glue can stick to small particles. A higher apparent viscosity helps to overcome the gravitational settling of cuttings, ensuring that the cuttings are carried to the surface along with the circulation of the drilling fluid and preventing the cuttings from accumulating in the wellbore.
2. Keeping the wellbore clean** - If the apparent viscosity is insufficient, cuttings are likely to settle in the wellbore, which may cause serious accidents such as pipe sticking. By adjusting the amount of polyanionic cellulose to control the apparent viscosity, cuttings can be effectively carried out of the wellbore, keeping the wellbore clean and ensuring the smooth progress of drilling operations.
II. Wellbore stability
1. Forming filter cakes
- The apparent viscosity of polyanionic cellulose is crucial for forming a good filter cake. When the drilling fluid permeates into the wellbore wall under pressure, the drilling fluid with a certain apparent viscosity can form a thin and dense filter cake on the wellbore wall. This filter cake can prevent the drilling fluid from further permeating into the formation in large quantities, reducing the risk of formation hydration expansion and collapse.
2. Supporting the wellbore
- An appropriate apparent viscosity enables the drilling fluid to exert a certain pressure on the wellbore wall, playing a role in supporting the wellbore. Especially in some formations prone to collapse, sufficient apparent viscosity helps prevent the wellbore from collapsing and protects the integrity of the wellbore.
III. Controlling fluid loss
1. Reducing fluid loss
- A higher apparent viscosity will reduce the filtration rate of the drilling fluid. Poly - anionic cellulose increases the internal friction of the drilling fluid, making it difficult for the liquid in the drilling fluid to permeate into the formation through the wellbore wall. This helps to reduce the loss of the drilling fluid, improve the utilization rate of the drilling fluid, and reduce drilling costs. 2. Protecting the reservoir
- When drilling through oil and gas reservoirs, it is particularly important to control fluid loss. An appropriate apparent viscosity can prevent the solid particles and chemicals in the drilling fluid from excessively invading the reservoir, avoiding damage to the reservoir's permeability and other properties, thereby protecting the production capacity of the reservoir.
IV. Improving drilling efficiency
1. Improving hydraulic performance
- An appropriate apparent viscosity helps to optimize the hydraulic performance of the drilling fluid. It can affect the flow state of the drilling fluid in the wellbore, for example, reducing the degree of turbulence and improving the laminar flow stability. This is beneficial for cooling and cleaning the drill bit, prolonging the service life of the drill bit, and increasing the drilling speed.
2. Enhancing power transmission** - In the drilling fluid circulation system, the apparent viscosity affects power transmission. An appropriate viscosity can ensure that the drilling fluid effectively transmits the power of the surface equipment to the drill bit at the bottom of the well, enabling the drill bit to break the rock better and improving drilling efficiency.
