Structural genetic types of paleoburied hill in Jizhong depression, Bohai Bay Basin

Buried-hill is an important exploration target in Jizhong depression. Analyzing its geologic structure and disclosing its formation mechanism is key to deepen the understanding of its tectonic evolution and the oil and gas exploration fairways. Based on the high-resolution 2-D and 3-D seismic data, and hundreds of deep exploratory wells across the depression, the paper used the structural analysis method to explore the buried-hill stratigraphic strata, fault system, and tectonic evolution as a whole, and put forward a new scheme for buried-hill genetic classification. It is shown that the buried-hill in Jizhong depression underwent a series of processes such as the sedimentary rock formation before Mesozoic, the compression in Late Jurassic, the multi-phase extension during Cretaceous to Paleogene, and the thermal subsiding and burying during Neogene to Quaternary. According to the tectonic location, the structural deformation feature, and the strength of extension, the buried-hill can be divided into 14 kinds of basic genetic mechanism. Due to the long period of tectonic evolution and the combined influences of the inner- and exo-genetic geological processes, the buried-hill has largely of a composite genetics. In map-view, the different genetic buried-hill zones exhibit regularly. It gives 7 kinds of structural association, such as, the tilted block and high bulge, antithetic fault step, synthetic fault step and high bulge, transverse anticline or relay high and inverted slope, high bulge and extension allochthon block and inverted slope, high high-bi-direction rotation-high bulge; tilted block and metamorphic core complex, etc. Among these, such types of buried-hills as the antithetic tilted block, the high bulge, the fault step, the inverted slope, and the allochthon block have favorable petroliferous potential owing to the matching of the source rocks and the reservoir rocks, the timing for trapping and accumulating. The oil and gas resource is much rich in Jizhong depression. The above genetic classification of buried-hill is helpful for addressing the oil and gas accumulation and distribution.