Structal Evolution Of The Clino Northeast To Central Palaeohigh And Gas Accumution In Ordos Basin

Structural evolution is the resurgence of geological events in geological body. A geological body can or not turn to be reservoir, not only being decided by the sedimentary characters, but also by its evolution in geological history and the personalities of all events. So, it is the composite effect of all phenomena. From this view, the study on possibility of gas-bearing of beds in late fifth phase of majiagou formation is much more scientific and dynamic.The research is based on the fore studies about this theme, and based on the analysis about 300 drills' data. And in this paper, all the convenient conditions to gas accumulation in Ordovician, the spreading form and the characters of reservoir beds have been involved.Through the study, some conclusions have been drawed. Firstly, the structural evolution of central palaeohigh has been divided into three stages: uplift stage, development stage and extinction stage. Secondly, the geological characters of majiagou formation had been mainly controlled by central palaeohigh, in sediment period, its lithofacies and lithologies having been effected, during weathering age, the intensity and character of weathering influenced in different areas. Thirdly, the area in uplift had been weathered strongly, so had some regions of clino where there were erosion valleys or furrows. The form and the evolution of reservoir was dominated by the weathering, and the gas accumulation was dominated by the reservoir in different areas. Majiagou formation was good reservoir in clino and turned to be capping bed in depression. At last, the main trap manifested by the structure evolution in the area is not structural trap, but lithological trap, ancient landform trap and combination trap.