Enhancement of Coal Seam Gas by Nitrogen Injection- a laboratory study

Various sections of the Bulli coal seam in the southern coalfield of Sydney Basis, New South Wales, Australia, have low permeability, and therefore are difficult to drain of its gases. A laboratory study on the effect of N2 injection on sorption and desorption behaviour of various gases stored in the coal matrix is described. Sorption and desorption experiments were carried out on coal samples taken from different mines operating in the Bulli seam, that are known to have difficult to drain sections. Tests were carried out on 54.7 mm diameter coal core samples (length: diameter ratio of one) contained in a specially designed triaxial pressure chamber. The composition of the discharged gases was monitored using an online gas chromatographer. The study found that injected N2 contributes 20% improvement the CO2 recovery at around 40%. Also it was found that the saturation period was an important factor in coal sorption process, the longer the saturation period the greater was the amount of gas stored in the coal.