AAPG Geoscience Technology Workshop

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The secondary alteration of the ultra-deep Ordovician light oil to volatile oil reservoir of the North Shuntuoguole, Tarim Basin, NW China


With exploration moving the deep strata in recent years, petroleum exploration breakthrough, such as commercial Jinyue and Yueman oilfield of Petrochina and North Shuntuoguole oilfield of Sinopec, has been achieved in the ultra-deep Ordovician in the Tarim Basin, NW China. The oil in the North Shuntuoguole with depths ranging from 7400~7900m, belongs to light oil reservoir and volatile oil reservoir, which GOR of 200 to 400 m3/m3. The biomarker and carbon isotope of the oil suggested that the oil of the North Shuntuoguole oilfield be the same source with the Tahe, Lunnan, Halahatang, Hadexun oils, excepting the higher maturity. The 4-+3-methyldiamantane concentration of the oils from the North Shuntuoguole oilfield is from 6~17 ppm, showing little cracking. The thiadiamondoid concentration of the oils from the North Shuntuoguole oilfield is from 7~10 ppm, suggesting no TSR occurring. Besides, no evaporative fractionation can be seen from the whole oil chromatogram. Combined with the reservoir static temperature with value of about 150 to 159 ℃, it is suggested that the low formation temperature and low geothermal gradient in the long geological history in the North Shuntuoguole area be the most important controlling factor for the existence of light oil to volatile oil reservoir in the North Shuntuoguole oilfield.