Geochemical Studies Of Petroleum Accumulation Of Hade 4 Oil Field

Hade 4 oil field is located in the Hadexun structural zone in the north of the Manjia'er depression, the Tarim Basin. Since the Hade 4 oil field was found in 1998, this area has become the important district for black oil exploration, Geochemical studies on petroleum migration and accumulation of Hade 4 oil field is significant to the forming theory of marine crude oil and oil / gas exploration in Tarim cratonic basin.Applying qualitative and quantitative analysis (such as GC, GC/MS, GC/MS/MS), similarity and heterogeneity of reservoir fluid chemical composition in horizontal distribution are described according to the detailed analysis on crude oil chemical composition. Comparing with marine oils in the adjacent areas, all crude oils in Hade 4 oil field (except for HD401 well) have following peculiarity: very similar in the composition of light hydrocarbon fraction, and the distribution of of phytane-series isoprenoid alkanes, high concentration in steranes, terpanes and their aromatized compounds, as well as rearranged steranes; low concentration of gammacerane, 24-norcholestanes and 24-rearranged steranes, and low C2g regular steranes (C2g/(C27+C28+C29)<20%); 3-methyl steranes and 27-norcholestane predominated, respectively; very low concentration of dinosterane and 4-methyl steroid. The oil-oil and oil- source correlation indicated that chemical composition of crude oils in Hade 4 oil field was very resemble to adjacent oil fields surrounding the Halahatang depression, including Tahe oil field, well XiangS, Lunnanl and Lunnanll. Those oils are originated from middle & upper Ordovician source rocks according to the age-specific biomarker assembly.In the other hand, chemical composition of crude oil in Cm oil pool in Hade 4 oil field also exhibited heterogeneity in horizontal distribution, the concentration of aromatic steroids, terpanes and steranes generally increases from north to south. Obviously, this distribution character is related to the petroleum migration, charge process and filling direction.Analysis of nitrogen-containing compounds (NCs) in crude oils in Hadexun and surrounding areas indicated that the relative composition distribution, concentrations and ratios of " shielded " type and "exposed" type NCs were coincidently varied. Geochemical parameters based on NCs are effective tools to indicate petroleum migration direction and distance according to correlation analysis of 13 migrating parameters. The distribution of migrating parameters in Hade 4 Cm oil pool suggested the crude oils charged from north to south. Furthermore, from north to south migration and filling trend also exist in the large scale, from well Xiang3 and Tahe oil field surrounding the Halahatang depression to Hade oil field, the migrating parameters show an increasing trend from north to south.The crude oil composition of well Hade 401 is obviously unusual, which differs from crude oils in Hade 4 oil field in the physical properties of crude oil, the distribution of normal alkane, the concentration of sterane and terpane, relative concentration of different structural steroid and maturity parameters of aromatics fraction etc. Correlation of age-specific biomarkers suggested oilsin well Hade 401 originated from lower Ordovician and Cambrian source rocks. Obviously, crude oils of well Hade 401 were charged in early phase, and petroleum derived from middle & upper Ordovician source rocks was charged from north to south in the later phase. The later emplacing process of hydrocarbon fluids from north to south induced oils from lower Ordovician and Cambrian source rocks located in the most southern area. The filling direction of and unusual distribution of crude oil in well Hade 401 predict that effective areas occurred with Hade-type crude oil should be in the north of well Hade 401.In conclusions, petroleum in Hade 4 oil fields was accumulated in very later phase (Pliocene Kuche formation depositing period (N2k)) according to timing of trap forming, hydrocarbon generation and expulsion period, homogenization tem...