Laserfiche WebLink
West Elk Mine <br />• with the mining operation. Past drilling shows no evidence of significant discontinuities in the E <br />or B Seams anywhere within the West Elk Mine permit azea. <br />Soft Shales <br />Soft or weak shales in the roof, as discussed here, are local deposits usually related to the <br />presence of rooted or slickensided zones, and to the presence of carbonaceous debris within the <br />shales. Occurrences of these two phenomena aze not predictable but they are usually <br />associated with and aggravated by sandstone channel margins. Slickenside zones and abundant <br />cazbonaceous debris significantly contribute to overall weakening of the roof. In-mine <br />observation during the operation can help delineate these areas so that safe and adequate roof <br />control can be maintained. Areas of weak shale roof were widespread in the F Seam workings <br />and aze also likely in some areas of the E Seam mine, but are less common in the B Seam mine <br />due to the more competent and consistent nature of shales in the B Seam roof. <br />Methane <br />Methane gas as encountered at West Elk Mine is derived from the coals and carbonaceous <br />strata of the local stratigraphic sequence. Recent analysis by Schlumberger Reservoir <br />Technologies (2001, 2002, and 2003) suggests that methane gas in contained in the B Seam. <br />. More importantly, it was also determined that substantial methane gas is contained in the coal <br />seams and strata above the B Seam. The Rollins Sandstone is not considered to contain much, <br />if any, gas. <br />Methane gas is liberated from cleats, faults and fractures during development mining and <br />from the overlying strata that is broken during longwall retreat mining. Geologic structures <br />such as the tectonic fault systems and, to a lesser degree the compactional faults and clastic <br />dikes, serve as conduits for both water and gas -iberation. <br />Exploration drilling throughout the previous 40 years in and around MCC's coal leases has <br />detected minor amounts of gas during drilling. Methane desorbtion testing conducted in 1996 <br />on drill core has determined that, on the average, the B Seam contains 150 scft (standard <br />cubic feet per ton) of methane and the E Seam contains 125 scft or less, depending on the <br />depth of cover. <br />One measure of gas available to the mine environment is total Gas In Place (GIP). The GIP <br />roughly coincides with overburden depth as measured in standard cubic feet of gas per acre <br />(SCF/A). For example, the B Seam GIP under West Flatiron at 2,200 feet of cover is 15,000 to <br />17,000 SCF while the E Seam under 1,000 feet of cover is projected at 5,000 to 7,000 SCF/A. <br />The GIP for the western district of the B Seam mining at West Elk Mine ranged from 0 to <br />12,000 SCF/A at the B South Mains increasing to the east. Existing mine ventilation systems <br />were able to safely dilute the gas and allowed for normal mining practices. Below and on the <br />• flanks of West Flatiron Mesa the GIP increases with the depth of cover. The volume of <br />methane liberated from the overlying strata during longwall mining overwhelmed the mine <br />2.04J9 Revised Nwem6er 1004 PRI G <br />