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The degree of substitution of PAC products is usually ≥ 0.9. However, due to the different needs of each manufacturer, the degree of substitution of PAC products varies.
The degree of PAC substitution and substitution uniformity are closely related to the product's salt-to-viscosity ratio, salt resistance, and filtration loss. Generally, the higher the PAC substitution degree, the better the substitution uniformity, and the product's salt-to-viscosity ratio, salt resistance, and salt resistance. Better performance and filtration.
When polyanionic cellulose is dissolved in a strong electrolyte inorganic salt solution, the viscosity of the solution will decrease, resulting in the so-called salt effect.
The positive ion ionized by the salt interacts with the -COH2COO-.H2O anion group on the side chain of the PAC molecule, reducing (or even eliminating) the homoelectricity on the side chain of the PAC molecule.
Due to insufficient electrostatic repulsion, the PAC molecular chain is curled and deformed, and part of the hydrogen bonds between the molecular chains are broken, which destroys the originally formed spatial structure, and specifically shows the reduction of water viscosity.
The salt resistance of PAC is usually measured by the salt-to-viscosity ratio (SVR). When the SVR value is higher, the polyanionic cellulose package shows better stability. Generally, the higher the degree of substitution of the product, the better the substitution uniformity. The SVR value is high.
When PAC is used as a fluid loss control agent, PAC can be ionized in drilling fluid to generate long-chain polyvalent anions.
The hydroxyl and ether oxygen groups on its molecular chain can form a hydrogen bond with the oxygen on the surface of the viscosity particle or form a coordination bond with the AL3+ on the edge of the broken bond of the clay particle, so that PAC can be adsorbed on the clay;
And multiple sodium carboxylate groups thicken the hydration film on the surface of the clay particles through hydration, preventing the clay particles from agglomerating into large particles due to collision (gel protection).
In addition, a plurality of fine clay particles will be simultaneously adsorbed on a molecular chain of polyanionic cellulose to form a mixed network structure covering the entire system, thereby improving the coalescence stability of the viscosity particles and helping to protect the particles in the drilling fluid. content, forming a dense mud cake and reducing filtration loss.
The higher the degree of substitution of the PAC product, the higher the content of sodium carboxylate, the better the substitution uniformity, the more uniform the hydration membrane, which makes the PAC in the drilling fluid produce stronger glue protection effect, so the effect of filtration reduction is more obvious.
The dosage of drilling fluid treatment agent and treatment agent is different for different drilling fluid systems, so the dosage of PAC may be different in different drilling fluid systems.
If the amount of polyanionic cellulose encapsulated in the drilling fluid is specified, and the drilling fluid is guaranteed to have good rheology and fluid loss reduction, it can be achieved by adjusting the purity.
Under the same conditions, if the purity of PAC is higher, the performance of the product will be better, but PAC with good product performance does not necessarily have high product purity, and the balance between product performance and purity needs to be determined according to the actual situation.
Under certain conditions, certain microorganisms will cause PAC to spoil, especially by the action of cellulase, peak amylase, etc., resulting in the scission of the main chain of PAC, the generation of reducing sugar, the decrease of the degree of polymerization, and the decrease of the viscosity of the solution.
The anti-enzyme ability of PAC mainly depends on the substitution uniformity and substitution degree of the molecule. The PAC with high substitution degree has better anti-enzyme performance, which is because the side chain linked by glucose residues can prevent the enzyme from decomposing.
The degree of substitution of PAC is relatively high, so the product has good antibacterial properties. In actual use, polyanionic cellulose will not produce rancid odor due to fermentation, so no special preservatives are added, which is conducive to on-site construction.
Because PAC is non-toxic and harmless, it has no pollution to the environment, and it can be decomposed under specific microbial conditions, so it is relatively easy to treat PAC in waste drilling fluid, and it is harmless to the environment after treatment, so PAC is an excellent environmental friendly drilling fluid additive.
