The efficiency of methane released from a coal bed depends on various physical and structural factors of the coal bed. Methane is a gas that is absorbed on the internal surface of coal. The amount of gas that can be produced from a given coal bed depends on various factors such as seam thickness, lateral continuity and the rank of the coal; moderate to high permeability that is controlled by the amount of fracturing of cleats; depths of burial and other barriers, such as impermeable layers, or structures as faults and folds that keep the gas trapped within the coal seam.
Key words: rank of coal, cleats, depth of burial, faults and folds
[...] Table 1 Input data for Simulation Properties Coal seam Thickness, ft Depth of Coal Seam, ft Fracture Permeability, md Porosity Reservoir Temperature, C Reservoir Pressure, psia Fracture Water Saturation Langmuir Volume scft Langmuir Pressure psia Sorption Time, days Bottom hole Pressure, psia Values Production data of the simulated quadrant were multiplied by four in order to obtain data for the whole 160 acre area. In-situ methane was assumed to be 60% and 80%. Results Figure 3 shows the production rate (in standard cubic feet per day) with Time(in days) of production for a methane saturation of 60% and 80%. [...]
[...] Bituminous and Sub-Bituminous coals have been mineable till a depth of around 450m (Thalcher, Orissa). The seam thickness is not more than 7-8m in most mines in India whereas this simulation had a data input of approximately 20m. As methane production is directly related to carbon dioxide sequestration due to its preferential sorption by coal sequestration characteristics of coal also need to be studied. Moisture saturation of the bed up to the extent of critical moisture affects sequestration capability gravely due fracture occupancy by moisture. [...]
[...] Flow of gas and water occurs in cleats or fractures (also called secondary porosity systems) and is governed by Darcy Flow. The cleat system is assumed to be continuous and provides flow paths to producing wells. Gas is stored in the primary porosity system (the coal matrix) and flows due to diffusion from discontinuous matrix blocks into the fracture system(Figure 1). Fig Warren and Root idealization of a fractured media In the USA where most of the CBM (Coal Bed Methane) operations are placed three areas of well spacing are used - 40 acre acre and 160 acre For the purpose of this study a 160 acre well spacing was assumed. [...]
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