The level of permeability of each cigarette paper was also examined using a PPM1000M paper porosity device (Cerulean, Milton-Keynes, UK) using the vacuum method.
The test results show that the porosity of sandstone decrease with the increasing effective stress at the fixed temperature level, following the law of negative exponent.
试验结果表明，在温度水平一定的条件下，砂岩的孔隙度随有效应力的增加而呈负指数规律减小；
3
The porosity test for sandstone was conducted at various temperature level and various effective stress level.