Study On Physical Properties Of Differentrank Coal Reservoir In The Eastern Margin Of Ordos Basin

Based on the analysis and consolidation of the strata development and tectonic characteristics and the main coal seam distribution in the eastern Ordos Basin,the physical characteristics of the reservoirs such as the pore fissure system and the adsorption are studied.This paper discussed the phasic changes of the pore fissure system caused by coalification and the main factor of adsorption capacity,the influence of the plutonic metamorphism and the magmatic metamorphism on the reservoir physical properties were analyzed.The key coal seam in this study is 4+5# in Shanxi Formation and 8+9# in Taiyuan Formation with a depth of 260-2600 m and a thickness of 1-21 m,the reflectivity of vitrinite were 0.44%-3.2%,from long flame coal to anthracite,all of the coal level were developed.In the macro type of coal,the bright coal and semi-bright coal based,semi-dark coal and dim coal follow;the main organic maceral of coal is vitrinite,and the inertiniteis follow,exinite content is lowest,the content of the vitrinite group showed hight in south and low in north and the content of the inertia group was opposite.Coal and rock industry analysis shows that increased degree of coal metamorphism,moisture and volatile gradually reduced,fixed carbon gradually increased,little change in ash.The physical properties show that the microfractures in the study area are mainly C and D,the porosity of coal reservoir is 2.7-9.4%,the pores are mainly less than 100 nm,means micropores and transition pores,the macropores and mesopores are not developed.BET specific surface area of the study area is 1.782 m2 / g,and the total pore volume of BJH is 0.005 mL · g-1,the average pore diameter was 12.43 nm.the langmuir volume is between 9.11-30.24 m3 / t,langmuir pressure is between 1.84-6.81 MPa.With the coalification second jump,the porosity decreased,in pore structure,the proportion of micropores increased,mesopores and transition pores down,macropores changes little,the microporous volume,the BET specific surface area and the BJH total pore volume decreased gradually.After the second jump,the BET specific surface area and the BJH total pore volume rise slightly,the other parameters change little.After the third jump,the porosity gradually increased,the microporous volume and the BET specific surface area showed an increasing trend,the total pore volume of BJH continued to decrease,and the langmuir volume decreased slightly.Magmatic metamorphism make the coal rank increased,he proportion of micropores increased,mesopores and transition pores down,the microporous volume,the BET specific surface area and the BJH total pore volume dramatic declined,and the langmuir volume increased.The ability of different metamorphic grade of coal reservoir influencing factors on adsorption studies show thatthe pore structure has a certain contribution to the adsorption capacity,which affects the adsorption space of the coal reservoir,but it can not lead to the change of the adsorption capacity of the coal reservoir.The pore shape especially the ink bottle pore is stronger than others.The vitrinite content plays a certain role in the adsorption capacity of the coal reservoirs during the low coal metamorphic grade.In the high metamorphic gradethe fusinite in inertinite' control is stronger.In terms of coal quality,the correlation between the fixed carbon content and the adsorption capacity is strong,and the moisture and volatiles have a certain influence on the adsorption capacity of the coal reservoir due to its take over gas adsorption space.