Research For The Lower Palaeozoic Carbonatite Reservoir Characteristics In The South Of Ordos Basin

Ordos Basin is the second largest basin and one of the largest resource bases in China. In the recent years, exploration in Ordos Basin is facing more and more complicated objects, therefore at the time to strengthen the theory research, exploration will further focus on the new areas and new stratum. The new areas in western and southern mainly refer to the basin with low level of exploration, whereas the new stratum aims at the weathering crust of Ordovician of the Lower Palaeozoic group and the one below, etc..Based on the basic geological conditions and the parameters, including the core, the cast, physical properties, sedimentary facies, diagenesis, reservoir thickness, pore types and structure characteristics, single-well gas testing and productivity, this study combines the actual situation of the Lower Palaeozoic group in the research region, and takes gradual steps by different levels to carry out the research of the characteristics of carbonate reservoir of the Lower Palaeozoic group in the southern margin of Ordos Basin. The main research results obtained are as follows:The exploration potential of Cambrian of the Lower Palaeozoic group in the southern margin of Ordos Basin is relatively low, and only Zhangxia and Snashan groups have certain reservoir, whereas its value has not been confirmed. Exploration potential of Ordovician is significantly better than that of Cambrian, the weathering crust of Ordovician and biogenic reef as major.Weathering crust of Ordovician in southern basin in the different areas, erosion and filling are quite different. If Mawu 1 is open shell, the solution cave is the best developed. Formation and evolution of weathering crust reservoir of Ordovician is closely related to the role of fassil karst, and the fassil karst is the major controlling factor of the reservoir. In addition, different karst periods have an important effect on formation and distribution characteristics of the reservoir. Sedimetary facies and weathering crust reservoir have certain matching relationship. If dolostone containing gypsum that is distributed in large scale is consistent with the open shell , it helps for dissolution occurred and strengthening, therefore best for formation of the reservoir.Biogenic reef of Ordovician belongs to the Pingliang group of middle Ordovician,and the Beiguoshan group of the upper Ordovician in horizon, erosion and filling role is developed relatively, then not all cave holes saved, most are filled in parts, only some large caves can be seen, and the formation of these caves may be related to Caledonian movement. Besides, the seam acted by the pressure solution is common. If these reefs are located Caledon ancient weathering crust, the solution caves are very developed.According to the characteristics of the property, establishing the evaluation standard and determining the research area is the low porosity and low permeability dense weathering crust reservoir, making a comprehensive evaluation on the Lower Palaeozoic group in research area through sedimentary facies of the reservoir, petrological characteristics, paleogeomorphology unit reservoir characteristics and reservoir distribution characteristics, and then predicting the favourable exploration areas.