Isothermal adsorption characteristics of coal reservoir and its gas content prediction in Qinnan-Xiadian block of Qinshui basin

Adsorption capacity of coal is a significant parameter for gas-bearing measurement and development potential of coal reservoir.the content prediction method of coal bed methane (CBM) based on Langmuir equation was established, Adsorption capacity and gas content distribution in coal seam No.3 reservoir in the study area was revealed. It is shown that the main coal type of No.3 coal seam in target area are meagre coal and anthracite coal. The Langmuir volume of air dried coal samples is between 18.15 m³/t and 34.75m³/t, with a mean value of 29.36 m³/t; Langmuir pressure is between 1.47 MPa and 2.71MPa, with a 2.03 MPa mean value. The pressure gradient of coal reservoir is between 0.11MPa/100 m and 1.06 MPa/100 m, with a mean value of 0.49 MPa/100 m. The pressure of coal reservoir increase with burial deepth; and gas saturation of coalbed is under-saturation. According to Langmuir equation, the content prediction method of coal bed methane (CBM) was established, and the gas content in coal seam No.3 reservoir in the study area was predicted. The result show that, the gas content in coal seam No.3 reservoir in the study area is between 2.87 m³/t and 24.63 m³/t, with a mean value of 13.78 m³/t, the gas content increases with burial deepth and it is lower than southern Qinshui Basin. The gas content distribution of coal reservoir is mainly controlled by generating, storing and preserving.