Abstract:

In order to clarify the tight oil and gas charging periods and their contribution to the formation of the Cretaceous Fuyu oil layer in the Sanzhao sag of the Songliao basin, a comprehensive study was conducted on the micro-oil inclusions and their associated aqueous inclusions in the Fuyu oil layer using methods such as thin section identification, inclusion temperature measurement, and fluorescence spectroscopy. The charging periods and accumulation contribution of oil and gas in this area were discussed in combination with reservoir burial history. The results show that the oil and gas in Fuyu oil layer of Sanzhao sag have the characteristics of multi-stage charging and accumulation, which is generally characterized by two stages of crude oil charging and accumulation. The first stage occurred in the period of 77-74 Ma at the end of Nenjiang Formation, corresponding to the first stage of charging. The second episode occurred during 67-65 Ma at the end of the Mingshui Formation, corresponding to the second, third and fourth episodes. The tight oil filling in the second stage (the end of Mingshui Formation) of Fuyu oil layer in Sanzhao sag contributes  to the current reservoir, with a contribution rate of 83%, and the contribution rate  of  the first stage (the end of Nenjiang Formation) of tight oil filling   is 17%. After comparing the contribution of oil filling in the two periods, it is considered that the crude oil filled in the late Mingshui period contributes greatly to the present reservoir.

Key words:  , fluid inclusions, tight oil and gas, charging periods, accumulation contribution, Fuyu oil layer, Sanzhao sag