Research On Deposition And Reservoir Characteristics Of Shahezi Formation In Zhaozhou Block In North Xujiaweizi Depression

This research follows the theory of sequence stratigraphy, started through lithology data, using logging method to assist, taking well seismic combination as the principal thing. On the basis of these Shahezi formation in South Xujiaweizi depression was divided into 4 third-order sequence as SQ1 to SQ4 from bottom to the top. By the means of core observation, grain size analysis, logging facies analysis, seismic reflection characteristics analysis, the marks of sedimentary facies in South Xujiaweizi depression was summarized. Combining single well facies analysis and the control of sequence stratigraphic framework, the types of sedimentary facies in study area mainly includes fan delta, braided river delta and lake facies. Fan delta mainly develops in the west steep slope controlling by West Xujiaweizi fault and braided river delta mainly develops in the east gentle slope belt.Through the statistical analysis of reservoir physical property,thin slice,scanning electron microscopy and mercury injection experiment data of Shahezi formation in study area,this paper considers that the reservoir of Shahezi formation is tight sandstone reservoir,its lithology is mainly lithic feldspar sandstone and feldspathic lithic sandstone,pore-type calcareous cement and clay is its main fillings,the type of reservoir space is characterized by rare primary pores、many secondary pores visible cracks and occasionally intergranular holes。Its main controlling factors can be summarized as follows:deposition is the main controlling factor,compaction is the dominant factor,cementation makes the reservoir more compact,corrosion add pores,and cracks improve the permeability well. Compaction and cementation damage the reservoir physical property by decreasing the pore space and filling the throat,corrosion has constructive effect to reservoir physical property,tectonic activity improve the permeability of reservoir by creating microcrack. The fan delta front subfacies in west is the most favorable reservoir development area,braided river delta front subfacies in east takes second place. Since the minor measured property data in study area,log fitting were used. Combined with the comprehensive interpretation, property data of gas reservoir and empty reservoir was counted respectively in study area. Comparing with gas bearing layer and dry layer through gas testing method and frequency distribution function method, the lower limits of parameters of effective reservoir can be determined :the limit of its porosity is 3.5% and the limit of its permeability is 0.053 mD.