The overlying strata of the coal bed roof are dominated by sedimentary rocks such as shale, sand stone and limestone, whose physical and mechanic properties differ greatly.
煤层顶板覆岩一般以页岩、砂岩、灰岩等沉积岩为主，其物理力学性质差异很大。
2
The major pay bed is low permeable ultra dense sandstone. Its permeability and pore throat texture are very sensitive to the net pressure of overlying strata.
主要产层为低渗透超致密砂岩，其渗透率和孔喉结构对上覆地层净压力很敏感。
3
The preconditioned fastest descent means in inversion achieves simultaneous in - versions of overlying-bed velocity and refractor depth.