250 / 2019-06-30 14:41:49

FIB-SEM Technique to characterize Microscopic PoreStructure of Tight Sandstone Gas Reservoirs: A Case Study of the 2nd Member of Shanxi Formation in Eastern Ordos Basin

FIB-SEM;tight sandstone; nanoscale pore;pore structure

Abstract Focused ion beam scanning electron microscopy (FIB-SEM) is a fine characterization of nanoscale pores, which is mainly used in shale reservoir research and is rarely used in tight sandstone reservoirs. Today, FIB-SEM provides a new idea for the study of microscopic pore structure of tight sandstone. The lithology of the 2nd member of Shanxi Formation in eastern Ordos Basin is an interbedded layer of sandstone and mudstone with coal seams in between. the source and reservoir layers are mutually developed and have great resource potential. The casting thin section and the conventional petrophysical analysis showed that the study area was dominated by lithic quartz sandstone and lithic sandstone,and the main pore types were intercrystalline pores, with porosity ranging from 2.7% to 8.1% and average porosity of 5.3%. The nanoscale pore structure of the tight gas-bearing sandstone in the 2nd member of Shanxi of the study area was characterized by FIB-SEM. It is revealed that the pore radius of the fine sandstone is 4-100nm, the coordination number of pore throat is mainly 2-4, the shape factor is 0.05, the pore are square and triangular, and the connectivity function distribution shows that the critical value of pore and throat radius is 200nm;The pore radius of the siltstone is 3-63 nm, the coordination number of pore throat is mainly 2, the shape factor is 0.05, the pore are square and triangular, and the connectivity function distribution shows that the critical value of pore and throat radius is 50 nm. It is considered that the shape of pore throat of fine sandstone and siltstone is similar, but the pore size and connectivity of fine sandstone are obviously better than siltstone. The gas in the 2nd member of Shanxi of the study area is mainly methane, and the molecular volume is small. The pore structure of the tight sandstone is good and can be a good reservoir. The development prospect is considerable.