Large-scale gas accumulation mechanisms and reservoir-forming geological effects in sandstones of Central and Western China

Large-scale gas accumulation areas in large oil-gas basins in central and Western China have multiple special accumulation mechanisms and different accumulation effects.Based on the geological theory and method of natural gas reservoir formation,this study examined the regional geological and structural background,formation burial evolution,basic characteristics of gas reservoirs,and fluid geology and geochemistry of typical petroliferous basins.The results show that the geological processes such as structural pumping,mudstone water absorption,water-soluble gas degasification and fluid sequestration caused by uplift and denudation since Himalayan stage all can form large-scale gas accumulation and different geological effects of gas accumulation.For example,the large-scale structural pumping effect and fluid sequestration effect are conducive to the occurrence of regional ultra-high pressure fluid and the formation of large-scale ultra-high pressure gas field;mudstone water absorption effect in the formation with low thickness ratio of sandstone to formation is conducive to the development of regional low-pressure and water free gas reservoir;the water-soluble gas degasification effect in large-scale thick sandstone can not only form large-scale natural gas accumulation;moreover,the degasification of water-soluble gas produced by the lateral migration of formation water will produce regional and regular isotopic fractionation effect of natural gas,that is,the farther the migration distance of water-soluble gas is,the heavier the carbon isotopic composition of methane formed by the accumulation.

Study on preparation and gas sensing property of water-soluble polyaniline/SmBaCuMO_(5+δ)(M=Fe, Co, Ni) for NH_3

Water-soluble polyaniline （PANI）, prepared by chemical-oxide and SmBaCuMO5＋δ（M=Fe, Co, Ni）（SBCM） powders, pre-pared by sol-gel method were analyzed through Fourier transform infrared spectroscopy （FT-IR） spectra, X-ray diffraction （XRD）, transmission electron microscopy （TEM） and energy dispersive spectroscopy （EDS） respectively, so as to investigate the gas sensi-tivities of PANI/SmBaCuFeO5＋δ（SBCF） and its sensitivity to NH3 under room temperature. The results showed that all of SBCM powders were of double-perovskite structure and PANI was successfully obtained. Under the same condition, the gas sensor based on PANI/SmBaCuFeO5＋δ（SBCF） material exhibited higher resistance sensitivity, better selectivity and shorter response-recovery time than others. The resistance sensitivities to NH3 increased with the increasing of atom radius of M in PANI/SBCM.