Deeply buried claystones, salts, and anhydrite have capillary displacement pressures great enough to exceed the buoyancy pressure from any reasonable oil column height (hundreds to thousands of feet). Conversely, [[silty mudrock]]s, shallow-buried claystones, and [[argillaceous siltstone]]s have displacement pressures low enough to allow leakage even where the petroleum column has not filled to the structural spill point. | Deeply buried claystones, salts, and anhydrite have capillary displacement pressures great enough to exceed the buoyancy pressure from any reasonable oil column height (hundreds to thousands of feet). Conversely, [[silty mudrock]]s, shallow-buried claystones, and [[argillaceous siltstone]]s have displacement pressures low enough to allow leakage even where the petroleum column has not filled to the structural spill point. |