Study On Hydrocarbon Accumulation Characteristics Of Ordovician In Slope Zone Of Central

The middle slope zone of Lungu oil field is located in the lower uplift of Lunnan, and the main oil and gas reservoir lies in the stratum of the middle and lower Ordovician Yingshan Formation, which is one of the area with highest degree of prospecting in Tarim Basin. The carbonate reservoir of Ordovician in Lungu oil field has strong anisotropism, and complicated distribution relationship among oil, gas and water. The differentiation of oil, gas and water can be found in part of it while the oil, gas and water are buried quite deeply, and the oil and gas charging can be conducted for several times. This article will take the Ordovician oil deposit in the middle slope zone of Lungu oil field as the main object of study, and will study the features of forming of reservoir in this area by analyzing the group composition of crude oil, biological marker compound of crude oil, inclosure, and biological marker compound of pitch in the reservoir stratum, so as to get the conclusions and understandings below:1、The middle slope zone of Lungu oil field mainly contains three well areas, Lungu7, Lungu2and West Sangnan. The area is located in the uplift of the Lunnan buried hill, where the crack and karst develop quite well. The Ordovician carbonate reservoir mainly contains oil, gas and water. Suffered from strong weathering, the Ordovician reservoir in the middle slope zone of Lungu is mainly middle and lower Ordovician Yingshan formation stratum.2、The rock type in Yingshan formation reservoir of the middle slope zone of Lungu oil field is mostly micrite, and granule limestone ranks the second place. The matrix of the reservoir has low porosity and extra-low permeability. The main reservoir space includes the secondary corrosion holes, seams and karst caves formed through construction and karstification.3、Ordovician hydrocarbon-source rocks in depression of Halakhan pond in the western Lunnan primarily develop in the area of Lunnan, as well as the Cambrian hydrocarbon-source rocks in Caohu depression in the eastern Lunnan. The Ro value of Ordovician hydrocarbon-source rock is now1.2%～1.6%, entering the peak time of oil generation, while that of Cambrian hydrocarbon-source rock is1.6%～2.4%, getting in the stage of gas generation.4. The Ordovician reservoir of Lungu oil field has the same source of oil and gas. It has the features of Cambrian hydrocarbon-source rock and mixed crude oil from the middle and lower Ordovician hydrocarbon-source rock. Moreover, it at least contains three migrations and charging stages of oil and gas. The first oil charging of Lungu7and western Sangnan is relatively earlier, and strong biodegradation has happened then. It has been found through the research on the pitch and inclosure in the reservoir that there exist two-stage inclosure in Lungu7well area, three-stage inclosure in Lungu2well area, and three-stage inclosure in well area of western Sangnan.The amount of oil and gas charging in the later period will determine the crude oil properties. 5. It can be concluded through the judgment by parameters of the biological marker compound that there are twos directions of the oil-gas migration in the middle slope zone of Lungu oil field, that is, charging along north-south direction and east-west direction.