Subtle Reservoir Formation Condition And Distribution In Qikeshu Area Of Lishu Rift

Lishu rift located in the southeast uplift of the Songliao basin which is a graben basin controlled by Sangshutai arc fault in the west since early Cretaceous. The paper focuses on subtle reservoir formation conditions and distribution on the Qikeshu area in the eastern slope of Lishu rift.Based on high-resolution sequence stratigraphy, sedimentary facies, sedimentary characteristics of the source system and tectonic evolution stages in Lishu rift, the paper researches Yingcheng and Shahezi groups on Qikeshu area.Based on the research in the Lishu rift, using high-resolution sequence stratigraphy, drilling cores, well logs and high-resolution seismic response characteristics, sequence- interfaces of Yingcheng and Shahezi groups are identified and high-resolution sequence stratigraphic framework including three third sequences is built in Qikeshu area. Qikeshu area is a slope depositional background which is controlled by Xiaokuan and Qinjiatun fault. Overall, the thickness of the sequences in north and south are thinner than in center, as well as they are thicker in west than in east because the layers in eastern edge are seriously denuded.According to lithology, shale color, sedimentary structure and fossils characteristics, it was divided into eight types of core microfacies; fan delta, braid delta, nearshore subaqueous fan and lake facies are found according to a variety of sedimentary marks. The main source direction of Qikeshu area is from eastern. Sedimentary facies distribution of each sequence cycle are completed combined with statistical law lithology and seismic facies.Reservoir facies are mainly fan-delta, braided river delta, shallow lake sand. Rock type is mainly fine sandstone, medium sandstone, coarse sandstone content is extremely low. According to core descriptions, oil and gas mainly exsit in the sandstone, coarse sandstone, and siltstone and argillaceous siltstone have no oil and gas shows.According to the seismic interpretation, sequence stratigraphy, sedimentary facies research, trap types are divided into nine categories in Qikeshu area. Based on the the basic elements of formation of subtle traps, identified six kinds of subtle trap which Sand lens trap and sandstone updip pinch out trap are main traps.Comprehensive analysis of sequences, sedimentary facies, reservoir, petroleum geology and structure, 16 subtle traps were predicted, in which six in sequence SQ4, six in sequence SQ5, four in sequence SQ6.