Evaluating Tight Sandstone Reservoir And Natural Gas Exploration Prospects In Ordos Basin Shanxi Formation

Based on previous researches,and take use of different theories such as Sedimentary geology,Petroleum geology,Reservoir geology,Logging geology and so on,according to the observation of drilling cores,outcrop identification and logging data processing and laboratory analysis and other kinds of geological methods and means and starting from the key wells,This article deeply analyze the depositional system types,characteristics of the sand body distribution,the reservoir rock characteristics,physical properties,pore structure and diagenesis in Ordos Basin Shanxi Formation.On basis of the above research,this paper briefly analyzed the conditions of gas accumulation and exploration prospects in Shanxi Formation and optimized the favorable target area and exploration prospect areas.According to core analysis,outcrops observation and logging curves analysis,it shows that the alluvial fan,braided river,meandering river,delta and shallow lake sedimentary system coexistence in Ordos Basin Shanxi Formation,Overall performance of the deposition pattern,north and south differentiation,the northern delta depositional system scale is larger than the south and it extends far from the north side and smaller from the south,in the southwest and southeast only develope a small delta,from north to south the sand bodies distribute like band,on the whole,the sand body in the North is much thicker than that in the Southern,but extended to the east and west the sand body become thinner or pinch out.Take use of properties,scanning electron microscope,the rock thin section,casting thin sections and mercury porosimetry data,the paper detailed discuss the reservoir rock characteristics,physical characteristic,pore type and pore structure characteristics in Ordos Basin Shanxi Formation.The Ordos Basin Shanxi Formation reservoir rock is mainly quartz sandstone,lithic quartz sandstone and lithic sandstone;the main reservoir space is the intergranular pores,intergranular pores and corrosion particle pores;the reservoirs is a kind of low porosity and low permeability tight sandstone reservoir,the porosity distribution range from 0.5 to 13.8%,average 7.37%,and the permeability distribution in the range 0.002-409×10-3?m2,average permeability is 3x10-3 ?m2;the pore structure is poor,according to the characteristics of the pressure mercury curve and pore structure parameters,the district-pressure mercury curve is divided into the following four types:Class I middle hole-middle throat,class II middle hole-small throat,Class III small hole-small throat,Class IV Small hole-tiny throat;according to the characteristics of clay mineral characteristics as well as the diagenetic stage shows this area has entered a late diagenetic B or C stage.According to these studies,the Shanxi Formation gas accumulation conditions has been analyzed,based on Shanxi specific set of stratigraphic features,combined unconventional natural gas exploration and research progress,as well as the theory of accumulation in recent years,gas accumulation mode of this area has been inducted.Research shows that the area in general as a large continuous accumulation system,the formation of coalbed methane,shale gas,tight sandstone gas,deep basin gas coexistence,and thus naturalgas exploration prospects are very impressive;and on the basis of the above study of composite sand thickness,seam thickness,shale thickness,and depth of change of the Shanxi Formation,preferably three favorable target areas and three favorable prospecting areas.