Brief Introduction to the Application of Polyanionic Cellulose (PAC) in Water-based Drilling Fluids

Brief Introduction to the Application of Polyanionic Cellulose (PAC) in Water-based Drilling Fluids

PAC's unique molecular structure enables it to show excellent application performance in fresh water, salt water, sea water and saturated salt water. It can be used as a fluid loss control agent in drilling fluids with efficient water loss control ability, and the formed mud cake is thin and tough.


As a tackifier, it can rapidly increase the apparent viscosity, plastic viscosity and dynamic shear force of drilling fluid, and can well improve and control the rheology of mud. These application properties are closely related to the physical and chemical indicators of their products.


Ⅰ. Polyanionic cellulose viscosity and its application in drilling fluids


The viscosity of PAC is the characteristic exhibited by the colloidal solution formed after dissolving in water. The rheological behavior of PAC solution has an important influence on its application. The viscosity of PAC has a certain relationship with the degree of polymerization, solution concentration and temperature.


In general, the higher the degree of polymerization, the higher the viscosity; the viscosity increases with the increase of PAC concentration; the solution viscosity increases with the increase of temperature. decline. The viscosity test in the physical and chemical indicators of PAC products is usually tested by NDJ-79 or Brookfield viscometer.


The viscosity of PAC products is controlled according to the application requirements, when polyanionic cellulosepackagingHigh viscosity PAC is usually required when used as a tackifier or rheology modifier (the product model is usually PAC-HV  PAC-R, etc.).


When PAC is mainly used as a fluid loss control agent and does not increase the viscosity of drilling fluid or change the rheology of drilling fluid during use, it needs to be low Viscosity PAC products (product models are usually PAC-LV, PAC-L).


Ⅱ. The effects of polyanionic cellulose on the rheological properties of drilling fluids in practical applications


(1) The ability of drilling fluid to carry cuttings and clean the wellbore;


(2) Suspension force;


(3) Stabilization of borehole wall;


(4) Optimal design of drilling parameters. Drilling fluid rheology is usually tested with a 6-speed rotational viscometer: 600 rpm, 300 rpm, 200 rpm, 100 rpm, 6 rpm, and 3 rpm readings.


Calculate the apparent viscosity, plastic viscosity, dynamic shear force, static shear force, etc., reflecting the polyanionic cellulose in drilling Rheology in liquid. In the same case, the higher the viscosity of PAC, the higher the apparent viscosity and plastic viscosity, and the greater the dynamic shear force and static shear force.


In addition, due to the wide variety of water-based drilling fluids (eg: freshwater drilling fluids, chemically treated drilling fluids, calcium-treated drilling fluids, brine drilling fluids, seawater drilling fluids, etc.) drilling fluid, etc.), so the rheology of PAC in different drilling fluid systems is different.


For a special drilling fluid system, there may be large deviations in evaluating the influence on the rheology of the drilling fluid solely from the PAC viscosity index.


For example, in the seawater drilling fluid system, due to the high salt content, although the product has a higher viscosity, the product has low salt resistance due to the low degree of product substitution.


The polyanionic cellulose has poor viscosity increasing effect during use, resulting in low apparent viscosity, low plastic viscosity, and low dynamic shear force of the drilling fluid, which in turn makes the drilling fluid poor in carrying drill cuttings, which may lead to sticking in severe cases.