PAC, short for polyanionic cellulose, is a kind of water-soluble cellulose ether derivative made from natural cellulose by chemical modification, and an important kind of water-soluble cellulose ether. Usually the sodium salt of Polyanionic Cellulose is in application and widely used in petroleum drilling, especially in salt well and offshore oil drilling.
In the shape of white to light yellow powder or particles, Polyanionic Cellulose is tasteless, nontoxic, strong in hygroscopicity, and freely soluble in cold and hot water.
Polyanionic Cellulose polymer has excellent heat-resistant stability, salt tolerance and strong antibacterial activity. The slurry or fluid prepared from the product has better fluid loss reducing capability, rejection capability and higher temperature tolerance. Polyanionic Cellulose is widely used in petroleum drilling, especially in salt well and offshore oil drilling.
Polyanionic Cellulose is more suitable for offshore drilling and the functions of Polyanionic Cellulose in drilling fluid are listed as below.
1). The drilling mud is the suspended matter of solids in the aqueous solution, and the same as other colloidal suspension dispersions, so has a certain life period. Polyanionic Cellulose can keep it stable and then prolong its life period. It has more obvious effects especially in mud suspension dispersions with dissolving salt.
2). The drilling mud with Polyanionic Cellulose can form thin and solid shaft wall as well as filter cake with low permeability, and thus can reduce the hole shrinkage and collapse phenomena resulting from water loss of mud.
3). The mud with the addition of Polyanionic Cellulose is seldom affected by mycete, so it doesn’t need to maintain high pH value or use preservatives. It can still keep stable with corresponding decrease of the usage amount of other chemical agents, or even within a certain range of temperature variation during the drilling process.
4). The mud with Polyanionic Cellulose enables the drilling machine to obtain low initial gel strength, so the mud can discharge air in it easily and discard debris in a mud pit quickly. PAC-HV applies to the mud with smaller proportion and a small usage amount can increase viscosity and reduce fluid loss. A small amount of Polyanionic Cellulose can replace a lot of clay and this kind of mud can reduce the difficulties resulting from encountering CaSO42H20 or CaSO4 salt belt during drilling process. However, PAC-LV applies to the mud with larger proportion, can reduce the fluid loss but have little effect on the viscosity. In use, Polyanionic Cellulose should be dissolved in water to prepare the solution (usually 1/40-1/20) and then add into the mud. Polyanionic Cellulose can also be compounded with other chemical agents to add into the mud.