Outlining High Gas-Bearing Sub-Panels in Parvadeh I Coal Mine Using Regression and Geostatistical Simulation

High gas volume is the main reason of explosion, rock burst and fatal coal mining disasters. In a coal mining project, it is necessary to model the gas volume at all parts of the target seam. Amoung coal resources of Iran, Parvadeh I has high gas bearing seams with an average of 14 m3/t of gas. C1 coal seam is the main mining target in Parvadeh I and it was explored by 134 core drilling boreholes. Gas study has been carried out for 35 boreholes, in only central and eastern parts of the deposit. Gas volume is not measured at the deep western parts. In this study, fractured zones are identified and their gas data removed from the gas modelling procedure. It is found that gas volume and seam depth are highly correlated and also, two separated populations are evident in the gas vol. – depth cross plot. The first population is related to oxidized shallow, and the second one is interpreted as deep methane bearing zones of the seam. Using the regression kriging method with the seam depth as the auxiliary variable, the gas volume is estimated for the whole mining blocks of the C1 seam. The validity of the estimations is evaluated as 94% by the Jackknife method. In order to avoid the smoothing effect of kriging, the probability of critical gas zones (> 20 m3/t) is modelled by the conditional indicator cosimulation. Results demonstrated that 1.43 million m2 of the C1 seam with the probability of 75%, and 0.38 million m2 with the probability of 100% fell into the critical category. These critical gas zones are located in central, southern and western Parvadeh I. These zones are considered to be the main targets for the future gas drainage studies.