Research On The Caprock Sealing Ability And Comprehensive Evaluation Of Mud Cap Rock In Damoguaihe Group Of Bei'er Depression

Through the research of well log and formation etc. data,from the up to bottom,develop five suites of mud cap rock in Damoguaihe group of Bei'er depression,with the cyclic sequence being the upper ,the middle ,the lower sequence of the second member of Damoguaihe group and the upper,the lower sequence of the first member of Damoguaihe group.On profile,the mudstone thickness of cap rock in the first member of Damoguaihe group is larger than the one of the second member of Damoguaihe group,besides more developed in the lower part of the depression.By means of determining the functional relationship among the acoustic travel time ,mudstone displacement pressure and fluid pressure of mudstone porosity,the study of the mustone caprock capillary seal and overpressured sealing ability with lots of acoustic travel time shows that:the mudstone cap rock of the lower cyclic sequence of the first member of Damoguaihe group is more larger in thickness,wide ranging in distribution range,high value in displacement pressure,more developed in overpressured,which can become better areal caprock..On the basis of the study of caprock macroscopic development and microscopic closed feature,selecting five parameters,that is diagenetic evolution stage ,thickness of mustone, thickness ratio of mudstone and stratum,overpressured value, displacement pressure and damage degree of caprock by fault, make a comprehensive evaluation to caprock sealing ability of Damoguaihe group in Bei'er depression with method of weighted mean. The result show that the evaluation order of caprock of Damoguaihe group in Bei'er depression is mainly middle,and the evaluation order is bad and good in local area, just odd distribution of the goog caprock .The study of caprock and spatial distribution of hydrocarbon show that the oil and gas sealed by Damoguaihe group caprock in Bei'er depression is mainly distributed below mudstone cover of the lower part of cyclic sequence of the first member of Damoguaihe group.In southwest of Huhenuoren tectonic belt,Huoduomoer structural belt,the southwest part of Aonaohaiwacao,distributed much more oil and gas. From the comprehensive evaluation class,we can see that the cover of middle or above comprehensive evaluation class is benefical to hydrocarbon accumulation.From the time match relationship between caprock and source rock ,we can see that the cover sealing ability of Damoguaihe group is mainly formed in early and middle stage of the second and the third member of Yiming group ,later stage of the second member of Damoguaihe group,early stage of the first member of Yimin group,earlier than the expulsion stage——last stage of deposition of Yimin group,which indicate it is effective to seal oil and gas,and beneficial to oil and gas accumulation.