Preservative Conditions Of Shale Gas From Wufeng Formation To Longmaxi Formation In Northeast Of Chongqing

This thesis takes shale of the Upper Ordovician Wufeng formation-the Lower Silurian Longmaxi formation in northeast Chongqing as the research object to analyze the preservation conditions.Previous studies have made some progress in the research area,which has a good base of shale gas.But it is affected by multiple tectonic activities,many folds and cracks developed in the study area.Therefore,the preservation conditions of shale gas in studied area can mostly be analyzed from the characteristics of caprock,sealing,sealing and hydrogeological conditions.The fault sealing property is studied by the carbon and oxygen isotopes of veins.The results show that the fluid is mainly derived from the carbonate rocks,which has the characteristics of external fluid mixing that related to the infiltration of atmospheric precipitation.According to the composition and homogenization temperature of fluid inclusions,the Dabashan tectonic zone is the main channel of gas emission.Chengkou fault experienced high thermal evolution andthe degree of thermal evolution was gradually reduced in its south direction.Also the ancient meteoric water infiltration depth is calculated.Between the Chengkou fault and Pingba fault,the infiltration depth is 2400 m.Between the Pingba fault and Jimingsi fault,the infiltration depth is 1800~2000m.In the south of Jimingsi fault,the infiltration depth is 1200~1600m.Comprehensive analysis showed that the area south of Pingba was poor affected by the tectonic movement,that with good sealing condition.By analyzing the cover type and thickness,lithology,roof and floor to determine the caprock sealing property.The results show that the studied area has developed three set covers,including the Silurian,Permian,Triassic.The fractures between the Jimingsi fault-Pingba fault are developed,where the stratum is high and steep.The overlying strata has basically poor preservation condition.The faults between Jimingsi fault and Shashi fault are less developed.In this area,the upper cover is mainly Permian-Triassic strata and the burial depth is between 2800~4000m,generally less than 4500 m.In this paper,the source of deuterium and oxygen isotope of groundwater is analyzed,and the hydrogeological sealing condition is analyzed by the characteristic coefficient of groundwater.The results show that the groundwater in the studied area is derived from meteoric water,and the mineralization degree of groundwater is high and the metamorphic coefficient is low.The calculated circulation depth of the hot spring water temperature is 500~710m,which indicates that the formation of the 710 m below is in a relatively good alternating block zone with relatively closed hydrogeological conditions.According to the comprehensive analysis of the northeast area of Chongqing,selected the Wufeng formation-Longmaxi formation's favorable region.The zone north of Jimingsi fault has a poor preservation.Meanwhile the zone between Jimingsi fault and Shashi fault that in the coverage of Triassic is considered as the favorable area.We can furtherly select three areas in good preservation near Yanshui,Ningchang,Badong as the favorable area with the area about 218km~2,132km~2,89km~2.