Wetting weakening of tertiary sandstones—microscopic mechanism

The micromechanism accounting for wetting weakening of tertiary sandstones was studied. It was found that intragranular fracture prevails for all dry sandstones. However, when the sandstone is wet, intergranular fracture occurs for Type B sandstones. Therefore, one sandstone from Type A sandstones, MS1, and another from Type B, TK, were selected to further investigate the nature of the matrix. It was found that (1) for both sandstones, the major mineral components of the matrix are illite and kaolinite except that the MS1 sandstone has more chlorite; (2) leaching of matrix induced an increase of porosity and consequently results in leaching softening; and (3) among the mineral composition, chlorite is easiest to be dissolved and leached out and induces a more significant increase of porosity, which, in turn, results in a more significant leaching softening.