Abstract:

The structural sedimentary evolution in southern East Chengdao low rise was controlled by both extension and strike-slip effects in the Cenozoic. The fault combination in this area is complex. It is generally believed that the NE and EW faults in the middle-deep stratum belong to contemporaneous and syngenetic faults. In response to this view and the questions it raised, the fracture system is analyzed on the basis of structural geological theory using drilling and seismic data. In the study area, the main types of faults in Cenozoic strata are normal faults and strike-slip normal faults, and there are three types of fault cutting through the blocks of basement-Dongying Formation, Pingyuan-Dongying Formation, and Pingyuan Formation-basement. Taking the regional unconformity between the Dongying and Guantao Formations as a time boundary marker, the existing faults are divided into the early and late fault systems. The early faults, belonging to synsedimentary fault, primarily grew from the basement to the lower part of the Dongying Formation; the late faults mainly cut through the block of the Pingyuan-Dongying Formation reaching the basement, and their evolution was restricted by pre-existing faults. The NE and near-EW faults belong to these two fault systems, respectively, which played a key role in hydrocarbon distribution. The extension caused by the differential elevation and subsidence of the basement formed the NE faults in the early stage, which controlled the trough landform and the sedimentary environment of deep-water gravity flow, and the continuous layered sandy debris flow was developed. The right strike-slip movement of the Tanlu fault initiated the formation of the near-EW en echelon normal faults in the later stage. Fault planes provided not only shielding for developing upward dip direction of reservoirs, but also vertical migration channels for oil-gas due to poor sealing during near-EW compression. Faults and faulting controlled the order of trap distribution and hydrocarbon accumulation. In the E-W direction, fault block traps and oil-water interface increased in proper sequence, and the degree of fullness successively decreased as full, under filled and half filled, etc. Fault system research, putting the geological body in a certain tectonic stress field, analyzes the spatial arrangement and intersectional relationship of fault combination as well as the mechanical mechanism and displacement characteristics of fault, and explores the control effect of space-time evolution on oil and gas distribution. Its research method is applicable in the areas of superimposed tectonics, which has practical significance for oil and gas exploration and development in such areas.

Key words: Chengdao low rise, superposed structure, fault system, tectonic stress, fault sealing, oil and gas migration