PolyDADMAC is a cationic polymer with a number of N+ perssad in its molecular structure, and the N+ perssad can exchange with the low valence cation in the clay lattice, which makes clay particles not easy to be hydrated, expand, and be transported, so it is a good organic anti-swelling agent for clay. At the same time, the compound of PolyDADMAC with inorganic clay anti-swelling agents will make them complementary to each other and play a synergistic effect.
There are special properties on the clay surface: first, the clay surface is negatively charged, and the exchangeable cation can dissociate and diffuse in water to form a diffused double layer; The second is surface hydroxylation. The inherent hydroxyl group on the clay surface and the oxygen atoms on the clay surface interact with water to produce hydroxyl functional groups. Therefore, clay minerals are easy to expand, disperse, and be transported when exposed to water, thus blocking the throat of the stratum pore structure and reducing the permeability of the formation. PolyDADMAC clay anti-swelling agent has obvious characteristics of preventing clay minerals from hydration expansion and dispersive transport, and its action mechanism is as follows:
On the one hand, PolyDADMAC can adsorb on the surface of clay particles and form a layer of organic cationic polymer protective film through the action of molecules, which can not only neutralize the positive charge on the surface of clay particles, reduce the intergranular repulsion of clay particles but also separate clay particles from water molecules, thus inhibiting the hydration expansion of clay particles.
On the other hand, the chain of the organic cationic polymer is relatively long, and a large number of positive charges on the chain can absorb several clay particles at the same time, so it limits the hydration, dispersion, and transport of clay particles, and plays a role in stabilizing the clay and particles.
In addition, the adsorption of organic cationic polymer and clay particles is multi-point adsorption with strong adsorption capacity, which can effectively inhibit the hydration expansion and dispersion of clay. While it is not easy for other cations to exchange organic cationic polymer from clay particles.