Abstract:

Based on the research of sequence stratigraphy, sedimentary systems distribution, petroleum accumulation models and  lithostratigraphic traps, great exploration breakthrough of the lithostratigraphic reservoir has been achieved in the slope zone of Jizhong Depression. Here, a case study has been made in the Lixian slope of Raoyang sag. “Fourstep” method including sequence division of single well, sequence correlation of connecting well, identification of seismic sequence and construction of sequence models was applied to study the characteristics of sequence stratigraphy. In Lixian Slope, the result suggested that its sequence stratigraphy framework of paleogene was incomplete, compared with Jizhong Depression. Its lower secondorder sequence and six thirdorder sequences, from SQ1 to SQ6, were not developed well. But the other two secondorder sequences, the upper and middle sequences as well as its seven thirdorder sequences, from SQ7 to SQ13, were developed completely. Accordingly, there is an incomplete vertical sequence evolvement and filling series from faultsubsidence to depression. Two thirdorder sequence, SQ9 and SQ10 consisting good sourcereservoirseal assemblages and possessing a good oilbearing properties, become the main exploration target zone. Two different sedimentary systems including braided delta and shallowshore lacustrine were classified in SQ9 and SQ10. Moreover, subaerial and subaqueous distributary channel sandbodies of braided delta plain and front as well as beachbar sandbodies of shallowshore lacustrine, developed in TST and HST, formed the main favourable reservoir. According to the relationship between the favorable reservoirfacies belt and palaeogeomorphology, as well as the characteristics of lithostratigraphic traps and source conditions, different petroleum accumulation models of lithostratigraphic reservoirs, such as stratigraphic overlap reservoir around of buried hills, sandbodies updip and pinchout reservoir in the “platformslop” area, and lenticular reservoir around of lowamplitude nosing structures were established respectively. After drilling, more than a hundred million tons of oil reserves were discovered in the middle and north part of Lixian Slope.

Key words: Jizhong Depression, slope zone, sequence stratigraphy, lithostratigraphic trap, exploration results