Characterization And Evaluation Of Shale Reservoir Of Upper Paleozoic In The Northeast Of Ordos Basin

Ordos Basin is rich in oil and gas resources and an important oil and gas bearing basins.Many suits of organic rich shale with great cumulative thickness are widely distributed in upper Paleozoic,which will be an important exploratory development target for shale gas.The distribution,Petrological characteristics,geochemical features,physical property,pore characteristics and gas-bearing properties of upper Paleozoic shale were analyzed and the favorable area of shale reservoir were predicted using the data of Previous studies and laboratory test in northeast of Ordos Basin.Shale,Coal,sandstone and limestone were developed alternatively of Upper Paleozoic in Ordos Basin.Shales of Upper Paleozoic are characterized by thin single sand layer and local area with great cumulative thickness and the organic matters are mostly type ? and ? in the stage of matured to highly matured that is conducive to organic matter into pyrolysis gas.Except at some limited areas effective shale thickness in the formation of Benxi and Taiyuan are thin While the thickness of Shanxi group is larger,more than 30 m.The reservoir pore types are various.There are dissolved pore,organic pore,Clay mineral micro pore and micro crack by the type.There are nano-scaled pore(aperture<1 ?m)with mean pore size of 17.13-67.65nm and average area percent of pore of 5.75 to 9.37,micro-scaled pore(aperture between 1mm to 1?m)with mean pore size of 3.17-5.61?m and average area percent of pore of 10.2 to 19.32 and microcrack with the percentage of 0.36 to 0.72 and an average of 0.53%.The main controlling factors of pores in shale differ in different levels:total organic carbon,the organic matter maturity and illite mixed layer has a promoting effect on the development of nano pores but inhibit by the calcite content;the content of quartz and illite has a promoting effect on the development of shale micron pore,but the carbonate content and burial depth can inhibit shale micron pore;the extent of fracture growth can promote by the content of quartz and total organic carbon and the maturity of organic matter but inhibit by carbonate content.Reservoir classification standard of transitional facies in Ordos Basin was established based on Grey Theory.Type I reservoirs mainly develop micro-scaled microfracture and intergranular pores with high content of organic matter and brittle mineral and large pore size.Type ? reservoirs mainly develop Clay mineral intercrystalline pores and micro-scaled intergranular pores with high content of Clay mineral.Type III reservoirs mainly develop Clay mineral interlayer pores and intracrystalline pores that were relatively small and low permeable.There is not have to form favorable reservoir conditions in the formation of Benxi,but in the area ofShenmu-Fugu of Benxi formation and Shenmu-Suide of Shanxi formation where are respectively developed with favorable area of 4841 Km2 and 9858 Km2,which was predicted by the parameter of comprehensive reservoir evaluation and the distribution of effective shale.