| Based on the comprehensive research on well drilling, core, well log and seismic data, stratigraphic division and demarcation on well-drilling-logging has been made, seismic sequence of Lower Cretaceous has been explained as well, stratigraphic profile framework, sedimentary facies and its distribution of Lower Cretaceous have been finally established according to drilling - seismic - logging as one of the sequence division and correlation.On the basis of rock stratigraphic units classification, seismic horizon demarcation and logging characteristics identification, all wells drilled into the Lower Cretaceous will be brought into stratigraphic correlation framework and detailed stratigraphic correlation. The top and bottom section of the interface and internal group boundaries of the Lower Cretaceous has been re-determined of and recognized for the distribution of the strata and the divison of stratigraphic sequences. Based on the litho-electric characteristics and the results of seismic demarcation from Bacun Formation to Shangshui Formation of Lower Cretaceous in research areas, top and bottom interfaces separately were in contact with overlying and underlying strata by dip unconformability, which composed of a complete second-grade sequence. There is no obvious unconformity between the interval Shangshui Formation and the Upper Yongfeng Formation and the Lower Yongfeng and Bacun Formations. According to detailed division and description of sequences, system tracts and surfaces of Lower Cretaceous, one second-grade sequence and seven third-grade sequences are recognized and sequence stratigraphic characteristics of Yongfeng Formation are mainly studied as well. Sedimentary system and the growth and division of sedimentary facies of the sequence stratigraphic frameworks of the lower and upper of Yongfeng Formation as important targets are set up for the first time.On the basis of rock core, thin section and log data in the Tanzhuang-Shenqiu depression, the lithology of Lower Cretaceous mainly consists of fine-grained sandstone, siltstone and mudstone and contains a lot of volcanic debris. The composition and structural maturity of sandstone are in the low-middle, which belongs to shallow-water delta and lake sedimentation and constitutes two huge sedimentary sequences vertically. Three sedimentary facies also developed, including normal delta, braided river delta and lacustrine facies (shallow lake). 8 subfacies and 25 microfacies were divided such as meandering delta plain and front, prodelta and braid river delta plain and front, prodelta subfacies, shore-shallow lacustrine, half deep lake and so on.The spatio-temporal distribution and evolution of sedimentary facies of Lower Cretaceous were mainly controlled by provenance supply. Research result shows that the sedimentary provenance mainly came from the south, while in the early-middle stage, it came from the north and in the late stage it began to weaken. Half-deep or deep lake deposited during the early and middle stage in the basin, while tn the mid-late stage, shallow lake mainly developed. Sedimentary facies and sub-facies in the plane migrated from south to north, distributed from east to west. Deposition and subsidence center is south-southwest and tended to north from the early to late stages.Lower Cretaceoust in Tanzhuang depression was characterized by 18 structurte traps of nose-shaped, fault block and fault anticline structure, and 37 layer traps, which covers 363.8 km~2. In Shenqiu depression, 4 structure traps and 12 layer traps have been recognized, which covers 71.19 km~2. Shuangloutian nose structure zone and eastern faults zone are favorable zones for petroleum exploration and development by comprehensive evaluation in Tanzhuang dedpression. |
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