Geological significances and analysis of gas potential for Jurassic Coal Seam in Ordos Basin

In order to study the gas content distribution features of the Jurassic low rank seam in Ordos Basin and the evaluation significances of the coal bed methan e resources,a mathematical statistics and system theory method was applied to a study on the coal bed methane potential and the composition features,prediction of free g as in the coal and the calculation of the coal bed methane resource volume.The results showed that the coal bed methane potential in Ordos Basin was in middle grade of t he national low rank coal bed methane potential,the desorption gas content was 0.11 ~ 4.33 m3/ t,the lost gas was about 20% of the total gas content,the residual gas wa S less than5% generally,the free gas was 11. 96% ~ 48. 16% of the total gas content,the percentage of the free gas was related to the coal porosity and preservation condit ions. Based on a unit divided from the coal system as the unit of the coal bed methane evaluation,the total volume of the coal bend methane resource calculated with the V olume method was 75 833.62 x 108m3.