Calcium bromide brine effectively restrains clay and shale hydration, swelling and particle migration for the following reasons:
- High‑valence calcium ions replace low‑valence cations on clay surfaces, compress electric double layers, reduce electrostatic repulsion and suppress volume expansion.
- Extremely high salinity and low water activity create osmotic pressure difference, preventing free water from entering clay interlayers.
- Calcium ions embed into clay lattices to form ionic bridging, stabilizing crystal structure and inhibiting layer peeling and particle dispersion.
- Solid‑free brine avoids extra fine solids, preventing pore throat plugging and keeping reservoir pore structure stable.
- High ionic concentration weakens hydration film formation and reduces the inherent hydration activity of shale clay minerals.
