Characteristics Of Fracture Development And Analysis Of Tectonic Stress Field Of Upper Palaeozoic In The Eastern Of Ordos Basin

In low permeability reservoirs,natural fractures not only control the percolation system of low permeability reservoirs,but also control the production of oil and gas in the reservoir,which is an important factor affecting the accumulation of oil and gas.On the basis of collecting and sorting out the previous research results,the description of the outcrop cracks and the indoor test analysis,this paper makes a comprehensive study on the tectonic fractures of the upper Paleozoic in the eastern Ordos Basin by using the theory of petrology,sedimentology and tectonic geology.The main research area of this paper is located in the eastern margin of the Ordos Basin,and its structural location is the Jinxi flexural fold belt.The upper Paleozoic strata in this area are well exposed,and the fractures in the strata are more obvious,which are convenient for statistical analysis.The target layer of the study is Shanxi formation and Shihezi Formation of the upper Paleozoic.The research methods are data collection in the field and indoor statistical analysis.Through the measurement of a large number of joint data and the summary of the macroscopic characteristics of the fractures,the following research results are obtained:(1)the fractures in the strata are dominated by shear fractures that have high angle;(2)according to the direction of the development of the fractures,the fracture systems are divided into three types: NNE direction and NNW direction,NE direction and near EW direction,near SN direction and NE direction,respectively,corresponding to the Indosinian movement,Yanshan movement and Himalayan movement;(3)the degree of fracture development is controlled by lithology,layer thickness,stress field,rock heterogeneity and other factors,and the biggest impact on the fracture is the stress field and lithology;(4)according to the field outcrop observation and previous research results,the regional fracture development model is summed up----there are dense zones and sparse bands in the regional tectonic fractures in the region of the regional stress field,and the two transition occurs gradually.There is a certain regularity in the process of stress transmission,that is,the fracture dense zone is represented near the position of the wave peak or the trough in the transverse wave,and the other zones represent sparse band of fractures between the wave peak and the trough.