Comprehensive Analysis Of Tectonics And Stratigraphy In Deep Strata Of Shiwu Fault Depression

After nearly ten years and high-strength exploration in shallow strata of Shiwu depression the favorable tectonic traps become less and less. So the basin needs to enter the stage of subtle reservoir exploration. This paper comprehensively analyses Tectonics and Stratigraphy of the deep strata in Shiwu depression and has drawn the following main conclusion:1. According to comprehensive analysis of regional plates motion and deep structure of the basin, basin filling characters, paleotectonic surfaces, Shiwufault depression has experienced three evolutionary phases. And they are syrift phase, postrift and thermal subsidence phase, structure inversion phase. The phases are identical with tectonic sequence or 1-order sequence of the basin. Further, the syrift phase in J₃-K₁ can be divided three rift episodes, initial rift episode, maximum rift episode, and waning rift episode. And they are identical with 2-order sequence.2. Based on the interpretation of seismic profiles and drilling in detail, the tectonic framework of the deep strata is rebuilt. Shiwu fault depression can be divided into three half-grabens: Shiwu, Yushutai, Shuangchengbao. And they are related with each other through the transfer zones. The important transfer zone locates between the Sangshutai Fault and Huangjin Fault. Because it is not only the most important source region, but led the northern slope basin-ward to uplift and fold forming the bend slope-break and controlling the types and distribution of deposition systems.At the same time, several little-scale half-garbens are recognized in Shiwu halif-garben. These little-scale half-garbens controlled the distribution of the resource rock and inversion structures.3.The intense structures inversion is an important characteristic of Shiwu fault depression. And it led to the absence of Sifangtai and Mingshui formations and the forming of NE, NNE thrusts and dome. Four inversion structure zones are recognized in NW and NE directions. And they are Pijiazi-Maobei-Zhangjiatun, Bawu-Xiaowujiazi-Sijiazi, Gujiazi-Houwujiahu, and Qingjiatun. Further, except the detachment-type fold in depression formation, the inversion structural styles include five types: reviving type forward-expanding type, backward-expanding type, tyrannizing type and truncated type according as the associations of the thrust faults and the early normal faults.4.Combining interpretation of a great deal of seismic profiles and drilling demarcation, key surfaces are recognized in the deep strata of the basin and order of sequence stratigraphic units are discriminated, including one 1-order sequence, three 2-order sequences and five 3-order sequences in the deep strata. And higher-order sequences are recognized in three key wells and two well-well sections. Tracking in the whole 3D project and wells correlation, high-resolution sequence stratigraphic framework is set up.