| The origin of natural gases in central Tarim Basin is very complicated and there has been no definite conclusion in this aspect.
Based on the results of systematic research on their composition and carbon isotopic characteristics, natural gases in central
Tarim Basin are composed mainly of hydrocarbon gas, Ordovician natural gas with the characteristics of crude oil-cracking
gas, and Carboniferous natural gas not only originating from kerogen cracking, but also from oil cracking. There are significant
differences in composition and carbon isotope of natural gases between the eastern and western areas. The causes for the differences
in geochemical characteristics of natural gases are presented as follows: different thermal evolution degrees of organic matter.
Natural gases in the western region may have generated from the Middle-Upper Ordovician source rocks, and natural gases in
the eatern region may be derived from the Cambrian source rocks, which entered into high to over mature stages; the gases
migrated from west to east and caused the different compositional and carbon isotopic characteristics of natural gases; difference
in the strength of thermal sulfate reduction between the eastern and western parts, with the reduction in the eastern part
being stronger than that in the western part. |
