Geochemical characteristics and genetic analysis of Ordovician medium-light oils from well YQX1 in the northwest of Tahe Oil Field

Medium-light oils were tested in well YQX1 in the Ordovician super heavy oil area in the northwest of Tahe Oil Field. We studied their geochemical characteristics including physical character, group composition, GC-MS of saturated and aromatic hydrocarbons, and made a comparison with the Ordovician super heavy oils in the Yuqi area and the condensate oils in the Yakela area, in order to confirm their genetic types. The medium-light oils from well YQX1 have a high saturate hydrocarbon content, medium aromatic hydrocarbon content, and low non-hydrocarbon and asphaltene contents. The n-alkane series is complete with a single mode. An obvious "UCM" hump appears in chromatogram. The distributions of steranes and terpanes has a good correlation with the super heavy oils of Yuqi area and the condensate oils of Yakela area, which indicates that they have the same source. Maturity parameters such as Ts/(Ts+Tm) and 4-/1-MDBT show that oils from well YQX1 have a high maturity, which is similar to the condensate oils in Yakela and higher than the super heavy oils of the Yuqi area. Combined with terminal accumulation background and tectonic evolution in the northwest of Tahe Oil Field, it is inferred that the oils from well YQX1 mainly came from the north. The high-maturity light oil and gas migrated along the Luntai fault during the Himalayan period, transformed the early heavy oil reservoirs along unconformity from north to south, and finally formed the medium-light oil currently present in the reservoir.