The Restored Eroded Thickness And Prototype Basin Of Kongdian Formation And The Fourth Member Of The Shahejie Formation In Dongying Depression

Restored prototype basin is a tough problem for geologists, but it is very important for prospect hydrocarbon. The paper focuses on restoring original thickness, calculating erosion amount, restoring prototype basin and analyzing the structural evolution, restoring the prototype basin of Kongdian formation and the fourth member of the Shahejie formation as well as provides geologic evidence for forecasting and discovering petroleum resource and delineating the benefit targets of prospect for hydrocarbon.It is discovered that the compaction curves of Lijin sag, Minfeng sag, Niuzhuang sag, and Boxing sag are similar and the compaction curves of the north steep slope belt, the south gentle slope belt and the central anticlinal belt are similar during restoring original thickness. In the sag belts, the strata are thicker, and the compaction coefficients are bigger. In the north steep slop belt, the south gentle slope belt and the central anticlinal belt, the strata are thinner, and the compaction coefficients are relative small.A way to restore the eroded thickness of prototype basin is presented under the control of wave analysis method. By means of wave analysis ,the main wavy cycle of 110,25.5and 12.5Ma which reflecting the formation and development of Dongying depression are obtained ,and the range of eroded thickness is limited by 12.5Ma wavy cycle which reflecting the erosion status of each sedimentary interval face, then local status eroded thickness is restored by sedimentary, estimation by porosity date, stratigraphic contrast method and neighboring thickness contrast, last the eroded thickness is obtained by the weighted average of multi-perspective methods. The regions with high erosion thickness are centralized on the edge of depression or near boundary faults. the eroded thickness of Ek2 mostly ranges of 100m to 300m; the eroded thickness of Ek1 mostly ranges of 0 to 300m; the eroded thickness of Es4 is mostly ranges of 0 to 250m.The thickness contour of Ek and Es4 in prototype basin are synthesized form ancient structural analysis of Cenozoic period, the erosion amount, and the original thickness. The results show(1) During Ek2 period, in the north of Dongying depression, the centers of Lijin sag and Mingfeng sag locate the downthrown block of Chennan fault and controlled by Chennan fault with NW strike; in the south of Dongying depression ,Boxing sag begins to form which is controlled by Shicun fault with NW strike and Gaoqing fault with NE strike. The thickest region is the north of Lijin sag. (2) During Ek1 period, because the faults are inherited, the sags are inherited which are controlled by the faults. In the north of Dongying depression, Lijin sag and Minfeng sag are inherited; in the south of Dongying depression, Boxing sag keeps on developing which is controlled by Shicun fault with NW strike and Gaoqing fault with NE strike. The thickest region is the east and north of Lijin sag .(3) During Es4 period, the central anticlinal belt is formed which divided the north depression into two parts, Lijin sag and Minfeng sag in the north, Niuzhuang sag in the south, and Boxing sag is inherited. The thickest region is the center of Lijin sag.