Sandstone Genesis Of Shanxi Formation In Central Daniudi Gas Field And Its Controlling Effect On Oil And Gas Distribution

Combined with the basic knowledge of reservoir,logging geology,sedimentary petrology and previous research results,this paper makes full use of the data of drilling,logging and core observation.In this paper,the sedimentary characteristics,structure and genetic types of sand bodies of Shanxi formation in Daniudi gas field are studied,and on this basis,the controlling effect of different sand bodies on oil and gas distribution is discussed.Through the analysis of the combination of core facies and logging facies,it is concluded that braided river delta plain and braided river deposits are developed in Shanxi formation in the study area.Based on the study of sedimentary microfacies,the genesis of sand bodies under different facies control can be obtained: there are two genetic types of single sand bodies in the study area: braided river delta plain distributary channel single sand body and braided river channel single sand body;According to the accommodation space and sediment supply,the large categories can be subdivided into six categories: high-energy truncated box-shaped distributary channel single sand body,low-energy truncated toothed box-shaped distributary channel single sand body,complete bell-shaped distributary channel single sand body,box-shaped high-energy heart beach single sand body,tooth box-shaped low-energy heart beach single sand body and bell-shaped braided channel single sand body.The genetic types of composite sand bodies in the study area can also be divided into two types: braided river delta plain multi-stage distributary channel superimposed composite sand body and braided river multi-stage channel superimposed composite sand body;It is subdivided into 6 categories: superimposed box distributary channel composite sand body,superimposed bell distributary channel composite sand body,bell + box distributary channel composite sand body and superimposed box braided river channel composite sand body,superimposed bell braided river channel composite sand body and bell + box braided river channel composite sand body.Among them,superimposed box distributary channel composite sand body and bell + box braided river channel composite sand body are the most common in the study area.According to the characteristics of logging facies,it is concluded that the boundary identification marks of composite sand body are as follows: the difference of logging curve shape,the difference of relative elevation,the difference of single sand body thickness and inter-river sediment and so on.Shanxi formation in the study area is a lithologic gas reservoir,and the gas reservoir distribution is more and thin longitudinally.Each small layer of Shan 1 member has thinner gas layer thickness,sporadic distribution and poor gas-bearing property.The gas bearing property of Shan 2 member is better than that of Shan 1 member.The thickness of the gas layer is larger and the horizontal continuity is better.Combined with production data,through the study of the sand body characteristics and oil and gas distribution law of Shanxi formation in the study area,it is considered that the larger the effective thickness of the sand body is,the stronger the ability of oil and gas accumulation is;in the box structure,the gas distribution is uniform,and in the bell structure,the gas is easy to accumulate in the middle and lower part of the sand body.most of the finger-shaped sand bodies are dry layers;the vertical tangential and box-shaped superimposed sand bodies show the best gas,and laterally,the side-cut type is easy to form gas reservoirs.Combined with the characteristics of different genetic types of sand bodies,a comprehensive study of their effects on oil and gas distribution shows that high-energy truncated box distributary channel sand bodies and box-shaped high-energy core beach sand bodies in single sand bodies are most favorable for gas accumulation;in composite genetic sand bodies,superimposed box braided river channel composite sand body and superimposed box distributary channel composite sand body are also favorable locations for natural gas accumulation.