Qianjiang Sag Paleogene Development With The Sedimentary And Tectonic Evolution Of Depositional Systems In Qianjiang Control

Qianjiang depression, a secondary depression in Jianghan basin, containsabundant resources and has produced oil and gas most in the exploration history of thewhole basin. Guided by the methodology of basin analysis, sedimentology and basinmodelling, we start with the development of stratum and partition of structure cell,and then deepen the study of structural and filling evolution, combining severalsubjects. Then we emphasize the discussion about the control on the development anddistribution of the sedimentary system by the syndeposit structure. Through theanalysis of the distribution, character and combination of the fault, we plot out thestructure cells in the depression, expatiate the character of the tectonic framework andtectonic style. The study shows that under the function of the extensional stress field, themargin fault dominated the subsidence of the depression , even the whole basin.Different structure belt have different fault combination and development model ofdepositional system. Different fracture set lead to different pattern of creation ,storageand trap of the oil-gas. The subside history of the stratum segment in typical area from Cretaceous toPaleogene period is studied quantificationally in the thesis. It point out therelationship between fault development and filling evolution. It's concluded that it hadgone through four episodes of crack and subsidence since Paleogene period. As awhole, the subsidence during QianJiang period happened on the largest scale. Thesubside centre of the depression obviously changed in different episode. DuringCretaceous period, the centre is located in the middle and west of the region. Then itmoved to the north (QianBei) and south (Zongkou) in the next episode. In theQianJiang period, QianBei sag had been the upmost subsidence centre of the wholedepression and eventually became the only one. After analyzing the distribution of depositional system and studying themovement of syndeposit fault with the logging and seism information, we realize thatthe syndeposit structure, especially the syndeposit fault, play a leading role all thetime in the sedimentary process. Sedimentary system like river delta, fan delta,shallow lake and deep lake are founded in the region. In the steep slope region,sublacustrine fan and fan delta are easily developed. And river delta usually occur in thegentle slop area, which is regarded as the comparatively high structural position. Inanother word, syndeposit fault in this area provide great condition for the passing andtrap of the oil-gas.