A Research On The Relationship Of Oil-gas And The Ancient Structure Evolution In Bachu Area

In the paper, the types and distribution patterns of uncomformity are classified according to explanation on regional geological section and identification of unconformity. Besides, the distribution of eroded thickness in main tectonic movement periods is restored by means of "trend thickness method". Marker bed thickness method is applied to restore the paleostructure framwork in Bachu-Mageti area. The tectonic evolution framework is to be discussed. With the survey into the influence that the paleostructures of different periods, including Caledonian period, Hercynian period and Himalayan, exert on the major exploration target zones in middle lower Cambrian of Bachu-Mageti area, Ordovician, Carbonifrous System, we have got some achievements as follow:1.The main unconformities in eight major tectonic movement period, including T90、T81、T74、T70、T60、T54、T50、T20.By way of trend thickness method, we analysis the trend of eroded thickness of the major tectonic period in Bachu-Megeti area, and the distribution map on the trend of eroded thickness is worked out accordingly. Marker bed thickness method is used to calculate the amount of eroded thickness, together with paleostructure map and analyse the paleostructure characteristics of T74interface in detail.2.The depth of burial of T74in middle Caledonian period ranges from200ms to800ms. The paleozoic topography is shaped with the southwest part higher and the northeast part lower. While in the early Hercynian period, the paleozoic sturcutral shapes is transformed to another form with the southwest part lower and the northeast part higher. In the late Hercynian period, the paleozoic structure continues to develop, expanding its scope and increasing its uplift. The paleozoic structure in middle Xishan period and that of the late Hercynian period are closely successive, and their paleozoic structures are very close to that of contemporary structrual map. 3.The pattern of tectonic evolotuion in Bachu-Megeti area is divided into5stages: the early and intermediate Caledonia period, the later Caledonia period—early Hercynian period, the later Hercynian period, Indo-Chinese—Yanshannian period and Himalayan period. Bashu uplift is a successvie paleo-uplift. The early tectonic framework is altered by many tenctonic movements. The later Hercynian period and later Himalayan period are the major tectonic transformation period.The later period of Early Carboniferous and the later period of Miocene are the key stages in which the tectonic framework is altered.4.Based on analysis of the reservior types and accumulation model, the paper gives more attention to the influence that the three major exploration target zones, including Cambrian, Ordovician and Carboniferous, exert upon the trap, reservoir, preservation and reservoir forming condition in Caledonian period, Hercynian period and Himalayan。The formation of Bachu uplift is farily late. From Caledonian period to the later Hercynian period, the southern part of Bachu uplift is located in upper position and fault area. The southern part of the fault is an effcient way of transferring petroleum. In Himalayan period, Bachu tectonic had changed largely, the north side of trata had uplifted lately, formed from north to south pattern,this period is the most important of accumulation period. And division three favorable zones.