Bentonite is a nonmetallic mineral with montmorillonite as its main mineral component, commonly known as "universal soil", and it is generally a dense block, leaf-shaped, fibrous or radial aggregate. Bentonite has strong hygroscopicity and expansibility, which can absorb 8-15 times of its own volume of water, and its volume expansion can reach several times to 30 times. It can be dispersed into gel or suspension in water medium, and this medium solution has certain viscosity, thixotropy and lubricity.

When the above properties can't meet the construction requirements, the related properties of bentonite slurry can be improved by adding polymer additives. Polymer mixed into bentonite suspension can improve its fluidity, permeability and stability. Play the following roles in polymer bentonite suspension:

（1）Viscosity regulation

Bentonite itself will absorb water to form gel or suspension. In this state, bentonite slurry has certain viscosity. Polymer and water molecules in bentonite slurry combine to form a special gel structure, thus increasing viscosity. The characteristics of bentonite added by polymer depend on the interaction between polymer network and fluid medium.

（2）Filtrate reduction

Bentonite additives can be adsorbed on the clay surface to form an adsorption layer, so as to prevent clay particles from flocculating and becoming larger; On the other hand, it can stabilize the fine particles broken up under the action of circulating stirring of bentonite slurry by adsorption, and no longer bind into large particles. In this way, a sufficient proportion of fine particles can be ensured, so that bentonite slurry can form a thin and dense filter cake and reduce the loss of filtrate.

（3）Clay inhibition

Because the bentonite suspension is filled in the gap between the shell and the stratum, when the main stratum contains some clay substances which will be affected by the bentonite slurry, clay suppression must be carried out in the bentonite suspension. The use of polymer prevents clay particles from absorbing water and preventing them from expanding, thus eliminating the threat of annular gap being squeezed. Due to the inevitable long residence time in construction, in order to prevent clay substances in the stratum from absorbing water in bentonite suspension and dissolving too much clay substances in the stratum in bentonite suspension, clay inhibition must be provided in the lubricating suspension in the annular gap.

（4）Dilution

With the continuous improvement of construction requirements, some constructors will ask bentonite manufacturers to provide bentonite with larger consistency. In the actual use process, the fluidity of these bentonites will be relatively reduced, and some polymers will improve the fluidity of suspension while maintaining the original consistency.

（5）Plugging action

In the stratum with big holes or cracks, bentonite will also enter these gaps because of the pressure difference. One of the effective measures to deal with the pressure reduction caused by the inflow of suspension is to add polymer to form a supporting structure in bentonite suspension. The combination of the characteristics of different filling materials (such as size, consistency and strength) can achieve different sealing effects.

（6）lubrication action

The lubrication effect is usually achieved by filling the annular gap with bentonite slurry, using the fluidity and supporting function of bentonite slurry. In some cases, due to the characteristics of bentonite itself, when the lubrication effect is not obvious, some polymer additives can be added to bentonite suspension to achieve better lubrication or antifriction effect.

According to the dosage and use effect of different additives, we will continue to study the use of these polymer additives, and strive to provide customers with a better use scheme of polymer additives to ensure the use quality of bentonite slurry.