oa The Geochemical Characterisitics and Origin of Ordovician Ultra-Deep Natural Gas in Shuntuoguole Area, Nw China

All the natural gases in Shuntuoguole area are oil-type gases, in which the gases in SB area are wet gas with kerogen-cracking dominated, whereas the gases in ST, SN, GL, GC areas are dry gas originated from oil-cracking. Both the wet and dry gases in Shuntuoguole area are sourced from Lower Cambrian Yuertusi Formation.

The distribution of two types natural gas is correlated with the present strata temperature and (or) paleo-temperature of Ordovician. The present strata temperature and paleo-temperature of Ordovician in SB area ranged from 150∼160℃, 170∼180℃, unreached the temperature of oil-cracking in large scale. However, the paleo-temperatures of Ordovician in ST, SN, GL and GC areas have exceeded 180℃ and present strata temperatures are high with temperature about 200℃, resulting the paleo-oil reservoir cracking in large scale. Thus, from SB to ST to SN to GL to GC areas, the fluid phase changed from light oil to volatile oil to condensate to dry gas phase gradually.