| In order to work out the resource potential of conventional oil and tight oil in northern Songliao Basin and guide the exploration direction, based on systematic summarization of petroleum geological conditions such as source rock, reservoir physical properties and so on, oil accumulation patterns and dominant control factors are analyzed. The resources of conventional oil and tight oil are evaluated by both analogy and genesis methods and the distributions of remaining oil resources are studied in order to guide the next exploration direction of oil. Two sets of excellent source rocks of the Qingshankou Formation and Nenjiang Fornation, developing in the Late Cretaceous, spread vastly in the Songliao Basin with large thickness, high organic content and oil-prone kerogen type. The source rock of Qingshankou 1st-2nd Member in the central depression being in mature stage is the primary source rock of both conventional oil and tight oil. Various sand bodies developing in the large-scale lacustrine delta and fluvial facies match well with source rocks and seal beds as reservoirs, forming upper, middle and lower petroleum systems. Tight oil are mainly distributed in Gaotaizi oil layers of the middle petroleum system and in Fuyu oil layers of the lower petroleum system. As to conventional oil reservoirs, there are three accumulation patterns named “accumulation below source”, “accumulation above source”, and“accumulation allochthonous to source”. In contrast, tight oil mainly form in two accumulation patterns named“accumulation in place” and“accumulation above source”. The effective source rocks control the distribution of both conventional oil and tight oil, while the sedimentary facies control the conventional oil reservoir type and the reservoir physical properties control the enrichment of tight oil. Based on fine evaluation of source rocks, the total oil resources are estimated as 102×108 t by basin modeling method. Six calibrating zones for conventional oil and three calibrating zones for tight oil are systematically evaluated, based on which the conventional oil resources are estimated as 88.7×108 t, and the tight oil resources as 12.7×108 t by analogy method. It is suggested that the Putaohua oil layers of Gulong depression, Daqing placanticline, and Sanzhao depression are the primary targets for conventional oil exploration in the near future. The Fuyu oil layers of Daqing placanticline, Sanzhao depression, and Qijia-Gulong depression are the favor targets of tight oil exploration. |
