The control of the viscosity of PAC products is controlled according to the application requirements. When PAC is used as a viscosity enhancer or rheology regulator, high-viscosity PAC (product model is usually PAC-HVPAC-R, etc.) is usually required. When PAC is mainly used as a filter loss reducing agent, and when the viscosity of the drilling fluid is not increased or the fluid flow denaturation of the drilling fluid is changed during use, low-viscosity PAC products are usually required. The product model is usually PAC-LVPAC-L

The unique molecular structure of PAC makes it exhibit excellent application properties in fresh water, brine, seawater and saturated brine. It is used as a filter loss reducing agent in drilling fluids. It has the ability to efficiently control water loss, and the mud cake formed is thin and tough.Used as a viscosity enhancer, it can quickly improve the apparent viscosity, plastic viscosity, and dynamic shear force of the drilling fluid, and can well improve and control the rheology of the mud.And these application properties are closely related to the physical and chemical indicators of their products.

1. PAC viscosity and its application in drilling fluid

PAC viscosity is the characteristic of forming a colloidal solution 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.Generally speaking, the higher the degree of polymerization, the higher the viscosity; the viscosity increases with the increase of PAC concentration; the viscosity of the solution decreases with the increase of temperature.For the test of viscosity in the physical and chemical indicators of PAC products, NDJ-79 or Brookfield viscometer is usually used for testing.The control of the viscosity of PAC products is controlled according to the application requirements. When PAC is used as a viscosity enhancer or rheology regulator, high-viscosity PAC (product model is usually PAC-HV PAC-R, etc.) is usually required. When PAC is mainly used as a filter loss reducing agent, and when the viscosity of the drilling fluid is not increased or the fluid flow denaturation of the drilling fluid is changed during use, low-viscosity PAC products (product models are usually PAC-LV, PAC-L) are required.

In practical applications, the flow denaturation of drilling fluid is related to: (1) the ability of drilling fluid to carry drill cutters and clean the borehole; (2) suspension force; (3) the stabilizing effect on the well wall; (4) the optimized design of drilling parameters.Drilling fluid flow denaturation, usually tested by a 6-speed rotary viscometer: 600 rpm, 300 rpm, 200 rpm, 100 rpm, 6 rpm.3-turn reading, calculate the apparent viscosity, plastic viscosity, dynamic shear force, static shear force, etc., reflecting the rheology of PAC in the drilling fluid.Under the same circumstances, the higher the PAC viscosity, the higher the apparent viscosity and plastic viscosity, and the greater the dynamic shear force and static shear force.

In addition, due to the large types of water-based drilling fluids (for example: freshwater drilling fluids, chemically treated drilling fluids, calcium-treated drilling fluids, brine drilling fluids, seawater drilling fluids, etc.), the rheology of PAC in different drilling fluid systems is different. For special drilling fluid systems, the influence of PAC viscosity index alone on the fluid denaturation of drilling fluid may be evaluated, and there may be large deviations.For example: In the seawater drilling fluid system, due to the high salt content, although the product has a higher viscosity, due to the low degree of substitution of the product, the product has low salt resistance, which makes the product have poor viscosity during use, resulting in low apparent viscosity of the drilling fluid, low plastic viscosity, and low dynamic shear force, which in turn makes the drilling fluid have poor ability to carry drill cutters, which may cause stuck drilling in severe cases.

2. PAC substitution degree and substitution uniformity and its application performance in drilling fluid

The degree of substitution of PAC products is usually greater than or equal to 0.9.However, due to the different needs of each manufacturer, the degree of substitution of PAC products is different.In recent years, oil service companies have continuously improved the application performance requirements of PAC products, and the demand for highly replaceable PAC products has shown an increasing trend.

The degree of substitution of PAC and the uniformity of substitution have a large relationship with the salt viscosity ratio, salt resistance, and filtration loss of the product.Under normal circumstances, the higher the degree of substitution of PAC, the better the substitution uniformity, and the better the salt viscosity ratio, salt resistance and filtration loss of the product.

When PAC 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 ions ionized by the salt and the-COH2COO-on the side chain of the PAC molecule.The action of the H2O anionic group reduces (or even eliminates) the isoelectric properties on the side chain of the PAC molecule.Because the PAC molecular chain does not have sufficient electrostatic repulsion, it curls and deform, and part of the hydrogen bond between the molecular chains breaks, destroying the originally formed spatial structure, which is manifested in the decrease of water viscosity.

The salt resistance of PAC is usually measured by the salt-to-viscosity ratio (SVR).When the SVR value is high, PAC exhibits better stability. Under normal circumstances, the higher the product substitution degree and the better the substitution uniformity, the higher the SVR value.

When PAC is used as a filter loss reducing agent, PAC can ionize in the drilling fluid to generate long-chain multivalent anions.The hydroxyl and etheroxy groups on its molecular chain form hydrogen bonds with the oxygen on the surface of the viscous particles or form coordination bonds with the AL3+ on the edge of the broken bond of the clay particles so that PAC can be adsorbed on the clay; and a plurality of sodium carbonate groups thicken the surface of the clay particles through hydration, preventing the clay particles from colliding and coalescing into large particles (glue protection effect), and multiple clay fine particles will be adsorbed on one of the molecular chains of PAC at the same time, forming a mixed mesh structure covering the entire system, thereby improving the coalescence stability of the viscous particles and helping to protect the content of particles in the drilling fluid. , Forming a dense mud cake, reducing the amount of filtration loss.The higher the degree of substitution of PAC products, the higher the content of sodium carbonate, and the better the substitution uniformity, the more uniform the hydration film, which makes the stronger the protective glue effect of PAC in the drilling fluid, so the more obvious the effect of filtration failure.

3. PAC purity and its application performance in drilling fluid

If the drilling fluid system is different, the amount of drilling fluid treatment agent and treatment agent is different, so the amount of PAC in different drilling fluid systems may be different.If the amount of PAC in the drilling fluid is specified, and the drilling fluid is guaranteed to have good rheology and filtration loss reduction, it can be achieved by adjusting the purity.

Under the same conditions, the higher the purity of PAC, the better the product performance.However, when the product performance is good, the purity of the product may not be high.The balance between product performance and purity needs to be determined according to the actual situation.

4. The application performance of PAC antibacterial properties and environmental protection properties in drilling fluids

Under certain conditions, certain microorganisms can cause corruption of PAC, especially by cellulase, amylase, etc., which leads to the fracture of the PAC backbone, the generation of reducing sugars, the degree of polymerization decreases, and the viscosity of the solution decreases.The anti-enzyme ability of PAC mainly depends on the molecular substitution uniformity and degree of substitution. The better the substitution uniformity, the better the anti-enzyme performance of PAC with a high degree of substitution.This is due to the fact that the side chains linked by glucose residues can prevent enzymatic decomposition.

The degree of substitution of PAC is relatively high, so the product has good antibacterial properties, and it will not produce a rancid smell due to fermentation in actual use, so there is no need to add special preservatives, which is conducive to on-site construction.

Because PAC is non-toxic and harmless, it is non-polluting to the environment, and it can decompose under specific microbial conditions, so it is relatively easy to deal with PAC in waste drilling fluid, and it is harmless to the environment after treatment.Therefore, PAC is an excellent environmentally friendly drilling fluid additive.