Research On Play Of Lower Paleozoic In The Southern Margin Of Ordos Basin

The Department of marine layer is one of the important development area now and in the future. After the discovery of the gas field in the Ordovician , the natural gas exploitation always has not got new development in . however, the carbonatite is considered as a potetial exploitation area.The study area lying in the south of Ordos Basin (south of north latitude 38%) is boareded with Qingyang and Fuxian county in the north, and with Wei He in the south. In the now structure site, it covers the south of Yishan slope and the south of Weibei I uplift and obduction zone in the western margin). The south edge of Ordos Basin is widely covered by marine facies of Palaeozoic, where the dickness of sedimentation is big, the geological condition of petroleum is advantagous. The menifestation of multi-level oil and gas has been dicovered in inside and residuum of lower paleozoic. The industrial Oil and gas flow have been obtained in the Fugu 4 and 7 well of the Fuxian area. The acquirements of natural gas exploitation discovery in the south of Ordos Basin showes the good exploitation prospect in the study area.Majiagou and Pingliang formation of lower Paleozoic of Ordovician system in the study area is the main source rock ,where the Abundance of organic matter is moderate or better and the organic matter type isⅠ～Ⅱ1. , which is advantageous to form the splitting gas of oil type.nowadays is evolves into the overmature gas phase. So it is able to provide the large scale of natural gas . The crust of weathering reservoir in the study area of lower Paleozoic is the main existence of the natural gas in lower Paleozoic of ords basin. The assemble in in the study area of lower Paleozoic can be divided into four type :Forming pattern of self-generatin gand self-preserving; under-generating and top-preserving; top-generating and under-preserving, hybrid type of generating and preserving. The main migrate mode is homogeneous gas escape. The filtering flow or flashy flow of the natural gas is the main mode. the migration pathway mainly depends on the unconformity (upper and lower Paleozoic unconformity), secondly on the cracks. At the same time, the area uplift in the end of the Early Cretaceous may be the critical period of studying the large-scale migration and accumulation of oil type and coaliferous gas.According to the natural gas reservoir elements and their maching in space and time, pattern of play of the southern edge of natural gas can be divided into three modes:①the mode of play controlled by structural trap②the mode of play controlled by lithology or layer and ancient karst③the mode of play composed of organic mound.