Page 249 - Advanced Mine Ventilation

Reservoir Properties of Coal 14

Seams

Chapter Outline

14.1 Gas Content of Coal 227
14.1.1 The Direct Method of Gas Content Measurement 228
14.1.2 Desorbed Gas 228
14.1.3 Lost Gas 229
14.1.4 Residual Gas 229
14.1.5 Gas Isotherms and Indirect Methods of Gas Content Determination 230
14.2 Coal Matrix Permeability 234
14.2.1 Measurement of Permeability 235
14.2.2 Minifrac Injection Testing 236
14.3 Diffusivity of Methane in Coal 238
14.3.1 The Diffusion Process 239
14.3.2 Determination of Sorption Time 239
14.4 Reservoir Pressure 242
14.4.1 Measurement of Reservoir Pressure 243
14.4.2 The Vertical Pressure, sv 243
14.4.3 Horner’s Plot for Reservoir Pressure Measurement 243
Problems 244
References 245

The most important reservoir properties that dictate not only the gas production and
mine degasification rates but also the correct degasification techniques are
• Gas content of coal and its gas isotherm;
• Coal matrix permeability;
• Diffusivity of coal or sorption time and;
• Reservoir pressures and ground stress.
These subjects have been discussed in great detail in a recently published mono-
graph [1]. A summary is provided here of only those properties that influence the
drainage of methane from coal prior to mining and postmining.

14.1 Gas Content of Coal

The volume of gas contained in coal at standard temperature and pressure (STP)* is
termed the gas content of the coal and is expressed in cubic feet per ton. It is generally
accepted that gas is stored in a monolayer on the microscopic particles of coal that are

Advanced Mine Ventilation. https://doi.org/10.1016/B978-0-08-100457-9.00014-6
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