Multi scale quantitative evaluation of water resistance capacity of Fengfeng formation in Baode Coal Mine

In order to evalute the water resisting property of the Fengfeng formation of Baode coal mine in Hedong Coalfield,the methods of thin section identification,micro CT scanning and field water pressure test were used.The characteristics of lithology,pore structure and permeability of the Fengfeng formation are revealed from micro macro multi scale.The research shows that the lithology of Fengfeng formation has obvious difference in vertical direction.The lithology of the upper strata mainly consists of argillaceous limestone and silty limestone,with grain structure,mainly consisting of argillaceous calcite and part of argillaceous structure.The clayey lens is distributed in layers.The lithology of the lower strata mainly consists of silty dolomite.Most of the intergranular pores and solution pores are filled by argillaceous calcite and argillaceous matrix.The rock is obviously compacted,cemented and recrystallized.The porosity of Fengfeng formation is about 2.42%-3.18%,in which 96.35%-96.74% of pore radius is between 2-8 μm,78.9%-87.6% of throat radius is between 0.6-1.5 μm,and the distribution of pore and throat radius is centralized and single,which is characterized by low porosity.The water pressure per unit length of the whole section of Fengfeng formation is 0.43-1.16 L/(m·min),the average water pressure is 0.95 L/(m·min),and the permeability rate is 0-2 L/(m·MPa·min).The water pressure value gradually increases with the depth.The water pressure value at the top of Fengfeng formation is the smallest,and the water pressure value at the depth of 96.4 m entering Fengfeng formation is the largest,with slight fluctuation,but the overall trend is relatively stable.The permeability coefficient calculated by the horslev formula is 10-3-10-4 m/d,showing the characteristics of weak permeability.The Fengfeng formation can be regarded as aquiclude.