Geochemical characteristics of H2S-bearing natural gas from Halahatang sag

Key words:  muturity  H₂S  biological sulfate reduction  Halahatang sag

Abstract:

The geochemical characteristics of natural gas such as composition and isotope were studied on the basis of H₂S-bearing gas reservoirs in Halahatang sag, Tarim Basin. And the origin and migration of natural gas were discussed. It is found that H₂S-bearing natural gas in Halahatang sag has a relatively low dry coefficient, which is in the range of 0.45-0.85 and can be classified as wet gas. This most belongs to the oil associated gas with the characteristics of biogas and a relatively low maturity. The decrease of the dry coefficient and maturity from south to north indicates the possible direction of natural gas migration. Sulfur bearing carbonate rock of Middle-Upper Ordovician and the transgressional processes during the deposition provide the material foundation and favorable environment, respectively. The H₂S content has no obvious correlation with the CO_2content and dry coefficient. The values of δ¹³C₁, δ¹³C₂, δ¹³C₃ and δ¹³C₄ decrease with increasing H₂S content. In combination with the biodegradation of the oil, it can be concluded that BSR(bottom simulating reflector) reaction occurs in H₂S-bearing reservoirs in Halahatang sag.