Not only the fractures can connect the separated cavity to grow the effective reservoir space and improve the permeability of matrix, but also is the main path of petroleum migration.

Thoracic cavity (or chest cavity) : Second largest hollow space of the body, enclosed by the ribs, vertebral column, and breastbone and separated from the abdominal cavity by the diaphragm.

The paths of the corrosive gas can be a hollow cavity formed in the foreign substrate base bar, the hollow cavity and the nitride reacting chamber are separated by the foreign substrates.