Investigations by the Petroleum Technology Section of the Bureau of Mineral Resources have shown that a substantial residual gas saturation is trapped behind the flood front in gas-producing reservoirs having a strong water-drive; the volume of gas trapped may be as high as 44 per cent of pore space, and lies within the same range as residual oil saturation in a flooded-out oil reservoir.Core samples from gas-productive reservoirs in three Australian sedimentary basins have been subjected to laboratory tests to measure this effect. The tests comprised capillary pressure measurements, water-flooding by dynamic-displacement and imbibition at ambient and elevated temperatures, and repeat gas recovery measurements in core samples exhibiting variations in irreducible water saturation.The results show a loose correlation between porosity and residual gas behind the flood front in these samples. Temperature appears to have little effect on the residual gas saturation. Gas recovery, however, is strongly dependent on the irreducible water saturation established prior to flooding.
Evolution of formation water chemistry and geochemical modelling of the CO2CRC Otway Site residual gas saturation test
