Cyclic Stratigraphy Of S2-S3 Members Of Shahejie Formation In Xiliu Area

Research area is located at Xiliu oilfiled in the north of lixian slope in the middle of jizhong depression of bohai bay basin.Due to the complex formation mechanism and distribution of lithologic reservoir,Xiliu 10 fault block is still of great excavation value.Due to the strong tectonic activities of continental rifted basin,stratigraphic cycles are not well preserved,more elaborate stratigraphic classifications are limited.Therefore,in this paper,we using high-frequency cycles,combining complete core data,log data and previous research in Xiliu area.In order to meet the requirement of research precision in oilfield development stage,the cyclostratigraphy of the 2nd and 3rd member of shahejie formation in Xiliu area are studied.We chose S2-S3 formation as a research section which has obvious climate change and abundant reservoir of oil and gas.By studying basic theories and techniques of cyclic stratigraphy,using natural gamma log curve as proxy index and performing spectral analysis and one-dimensional wavelet transformation on the data.We have determined the main periodic components driven by astronomical orbits.The results show that the 2nd and 3rd member of shahejie formation in Xiliu area are mainly driven by the slope cycle and eccentricity cycle.Among them,identified 40ka slope cycle,95ka short eccentricity cycle and 405ka long eccentricity cycle.Their average cyclic formation thickness was 12.41m,29.38m and 113.25m witch the number of cycles was about 46,19.5 and 4.2.On the whole,95ka short eccentricity cycle are the most widespread.Therefore,according to the 95ka short eccentricity period curve,the 2nd and 3rd member of shahejie formation in Xiliu area was divided into fifth-order sequence with high resolution.The average age of the S2-S3 formation of paleogene shahejie formation in Xiliu area was 1.75Ma,and their average deposition rate is about 0.307m/ka.There is little difference in the average deposition rate of each well and most of them can be stable.Some other strata show unstable contrast due to the denudation and modification in the geological history.