Evaluation Of Gas Saturation By NMR

Gas reservoirs of low permeability sandstone is tight, low porosity and high water saturation. Much water may come out with the gas in the development, which reduce seriously the productivity of gas wells. So, it's required very accurate original water saturation and it's mobility, whatever for reserve evaluation and developing program making of the tight sandstone gas reservoirs.How to test the water saturation and it's mobility is key point of this paper. This research uses indoor experiments such as weighing, NMR, centrifugation and gas injection to test the cores of tight sandstone gas reservoir. Analysis the result to find the right approach and get accurate original water saturation, for the final purpose that evaluate the original gas saturation.Get original water saturation and it's distribution by making NMR on sealing coring core. Get the T2 cutoff value by centrifugation and use it to distinguish irreducible water and movable water. Get irreducible water saturation by gas injection and compare the results from different methods for getting the accurate gas saturation.By the centrifugation experiment, conclude that the best centrifugal force for low permeability sandstone is 1.38MPa and the experienced T2 cutoff value is 13.96ms. By the gas injection experiment, conclude that the best coefficient to choose the initial injection pressure isπ1=0.5～0.6, and the best injection volume is 15～25pv.