Drilling fluid additives are essential chemical agents in the drilling process. There are many kinds of additives, and the common kinds are as follows:
1. Dispersant (also known as diluent)
When the clay and cuttings in the drilling fluid reach a certain concentration, the spatial network structure will be formed. When drilling into the salt gypsum layer, the dissolved salt in formation water, especially the high valence cations salt, will aggravate the formation of network structure, which will make the fluidity of the drilling fluid worse. The additive that can break up the network structure, release free water and reduce the viscosity and shear force of the drilling fluid is called the dispersant.
2. Fluid loss control additives
The chemical agent used to reduce the filtration of the drilling fluid into formation and protect the colloidal stability of the drilling fluid is called fluid loss control additives. The material that can reduce the filtration rate of the cement slurry is called cement slurry filtrate reducer. At present, polyacrylamide is the most commonly used filtrate reducer.
3. Weighting agent
When the fluid column pressure of the drilling fluid cannot balance the formation the pressure or well killing is required for blowout, it is necessary to add the weighting agent to the system to increase the proportion of the drilling fluid, so as to achieve the purpose of balancing the formation pressure and preventing blowout accidents.
4. Friction reducer (diluent, dispersant, water reducing agent, turbulence inducing regulator)
Satisfactory results can often be obtained by pumping cement slurry with turbulent flows. Friction reducer can control the fluidity of cement slurry and cause turbulent flows at low pump displacement.
5. Thickening time regulator
Due to the different depth of cementing wells, proper thickening time of the cement slurry is required to meet the needs of the safe operation. Thickening time regulators include coagulants and retarders. Coagulants are additives which can make cement set rapidly. Retarders are additives that can prolong the setting or thickening time of the cement slurry.
6. Specific gravity regulator
According to different formation pressure conditions, the cement slurry with different density is needed. The additives that can change the density of the cement slurry are called gravity regulators, including lightening agents and weighting agents.