Study Of The Main Factors Controlling Mesozoic Hydrocarbon Accumulation And The Regularity Of Hydrocarbon Enrichment In Fuxian Region, Southern Part Of Ordos Basin

Fuxian is an area with relatively low exploration for oil and gas in Yanchang Formation in the southeast part of Ordos Basin. Yanchang Formation in Fuxian region is dominated by lithologic reservoirs which is low in resource abundance, complex in hydrocarbon enrichment regularity and difficult in exploration. It is very significant for the further exploration in this region to study on the main controlling factors of hydrocarbon accumulation and clear the distribution of hydrocarbon rich region on the basis of previous achievement.Most of the known reservoirs are low permeability lithologic reservoirs in Fuxian region. The main oil-bearing series are Chang 6, Chang 8 and Chang2-3 oil-bearings of Yanchang Formation in Triassic. This paper has analyzed the spatial distribution of source rock in the Chang 9, Chang 7 oil-bearings, the microfacies and their characters in the main target oil-bearings, and drew a conclusion that three source-reservoir-cap rock combinations in vertical of Yanchang Formation in this area by starting with the conditions of oil and gas accumulation. Physical properties characteristics and controlling factors of Triassic Yanchang Formation reservoir are studied by depositional facies and diagenesis. The authors have considered that the main depositional microfacies of Yanchang Formation include subaqueous distributary channel, mouth bar, sheet sand and interdistributary bay. Subaqueous distributary channel of delta front is the best reservoir. Among all the diagenesis reservoir experienced, compaction brings physical properties of reservoir down quickly; dissolution bounces porosity to some extent, and cementation leads physical properties of reservoir inferior generally. The carbonate cementation in later diagenesis stage as the main factor is responsible for dropping in porosity and permeability.Hydrocarbon accumulation pattern that refers to shape cross type hydrocarbon accumulation is put forward by the study of typical reservoirs in Fuxian region. The sand body thickness, oil-gas source supply, low amplitude structure and reservoir diagenetic transformed have close relationship with the oil-gas accumulation. Hydrocarbon source rocks provides conditions for hydrocarbon migration and accumulation closely, high tectonic parts with low amplitude is the advantageous site for hydrocarbon enrichment, constructive diagenesis is the important factors for improving porosity and permeability of reservoir. It is important significance for hydrocarbon enrichment. Basis on that, the advantageous area for oil-gas accumulation is evaluated, and the exploration target zone is optimized.