Within the last 10 yrs, faster extraction rates, deeper mining levels, and "complete" mining of several salt dome levels contributed to the increased methane emission hazards, especially those associated with outbursts. The U.S. BoM is actively involved in identifying the parameters governing these hazardous conditions, which may lead to a methane explosion. These parameters are better understood when the ranges of methane contents, emission rates, and the gas pressures are known. Data obtained in Louisiana domal salt mines have shown that variations in methane contents, emission rates, gas flows, and pressures are dependent upon the type of salt encountered. Normal production-grade pure salt was found to have a methane emission rate of less than 0.1 M3/t and methane contents generally less than 0.1 Cm3/100 g. Emission rates from an adjacent anomalous zone ranged from 0.2 to 2.7 M3/t and methane contents as high as 2.6 Cm3/100 g were determined. Extremely low gas flows and lack of pressure buildup were typical during drilling of exploration boreholes in normal salt. Gas flows of 0.33 L/sec and pressures of more than 6.2 Mpa were observed from two boreholes when an anomalous zone was encountered. Localized permeability within this zone was observed by measuring tracer gas migration between two drill holes 7.3 M apart. Methane hazard char. of a localized area within a gulf coast salt mine should consist of the following: (1) methane content deter., (2) Mapping of geo. Features, (3) gas emission surveys, and (4) in situ tests of physical properties related to gas.
Proc. 2nd U.S. Ventilation Symp., Reno, Nevada, Sept. 23-25, 1985, PP. 353-360