Study On Micro-Pore Structure And Seepage Characteristics In He-8 And Shan-2 Sandstone Reservoir In Yanqi-2 Well Block

The He-8 formation and Shan-2 formation are low porosity and low permeability reservoirs,and the further study of reservoir characteristics is of great significance for the further development of gas fields.This paper mainly on the basis of regional geological,core,drilling,logging and other data collection and collation,for small scale formation comparison,identify sedimentary microfacies and sand body distribution characteristics.The characteristics of lithology,physical properties and pore structure of the reservoir were studied by using the methods of rock flakes,castings,scanning electron microscopy,X-ray diffraction and cathode luminescence.The pore and throat distribution characteristics were analyzed by high pressure mercury and constant pressure mercury intrusion techniques.The control effect of different levels of throat on seepage was analyzed.The characteristics of gas-water two-phase seepage and its influencing factors in low permeability sandstone reservoirs were analyzed by using NMR and gas-water seepage experiments.Mainly to obtain the following points:(1)The He-8 formation and Shan-2 formation of the reservoir of research area are delta front deposition.The reservoir sandstone type is mainly lithic quartz sandstone,the content of interstitial material is high,sandstone is given priority to with giant sand-thick coarse sand,followed by medium sand-thick sand,sorting characteristics are good to moderate.Cementing type to quartz secondary increase-pore-based cement,a small amount of porous cementing.Physical properties data show that the Shan-2 formation is better than the He-8 formation.(2)The He-8 formation and Shan-2 formation of the reservoir of research area is now in the middle diagenetic B period,a small part into the late diagenetic stage.The pore types formed during the evolution of the He-8 formation and Shan-2 reservoir are mainly erosive pores,intergranular pores,feldspar dissolved pores,tuffy pores and intergranular pores.The throat type in the study area is mainly flaky,tube-like and point-like.(3)High pressure mercury experiments show that the He-8 formation of the reservoir II have a thicker pore and throat than Shan-2 formation.The classification of pore throat of He-8 formation and Shan-2 formation is similar,they are in the medium-poor level.Crack development of the place of Shan-2 formation have a lower mercury saturation,the site of non-development of cracks have a higher mercury saturation.Comprehensive analysis,the pore throat structure of Shan-2 formation is better than He-8 formation.Experimental analysis of constant pressure mercury showed that,the pore radius distribution range,the peak of Shan-2 formation and He-8 formation is roughly the same,the porosity is also little difference,the throat radius of a certain difference,the Shan-2 formation have a thicker throat radius than He-8 formation,but the pore throat radius ratio is smaller than He-8 formation.It can be seen that permeability is dominated by throat.(4)The experimental study of gas-water infiltration and nuclear magnetic resonance(NMR)the He-8 formation and Shan-2 formation of the reservoir of research area show that He-8 formation have a higher irreducible water saturation than Shan-2 formation,but the movable fluid saturation is lower.Because the physical properties of Shan-2 formation are better than those in He-8 formation,the pore throat is large,the connectivity is good,and the clay mineral content is lower than He-8 formation.