Study On Logging Facies Of Lower Ganchaigou Formation In MB12Well Area Of The North Margin Of The Qaidam Basin

Integrating geology and geophysies, the observation and deseription of outcrop anddrilling core, this paper recover its sedimentary facies and logging facies、its space distributionand sedimentary model in Low Xiaganchaigou Formation(E₃^1-1) in MB12, northern margin ofQaidam Basin.Firstly, by using the core observation and thin section, we found the main types ofsandstone reservoir in the Lower Ganchaigou Fomation in MB12of the North Qaidam Basinreservoir are feldspathic-lithic sandstone and lithic-feldspathic sandstone. MB12well area isdeposited in the environment of finegrained、sandy anas-tomosed streams, medium separation,less matrix. And the main cements are calcite cements.Secondly, based on the analysis of cores, grain size, well logging data, the results indicatethat it develops braided deposition. And a detailed description of the sedimentary microfaciescharacteristic of braided deposit is given. Conglomerates, sandstones, mudstones are the mainliteology type, and the percentage of conglomerates is hight. And it is a normal grading changefrom coarse to thin. E₃^1-1-2mainly developed cha-nnel subfacies, and its microfacies areriverbed detainment and channel bar. The E₃^1-1-1and E₃^1-1-3primaryly developed interchannelsubfacies, and the microfacies consisted of flood plain and overbank deposition.Thegranularity of interchannel subfacies is coarse, river channel and channel bar’s well logfocused on box type, while flood plain and mariginal bank was given priority to bell shape.Interchannel lithology had fine granularity and low curve amplitude, and flood poain’s welllog had more straight ones, however, the overbank deposition’s well log mainly preferred tofinger type. Thirdly, the standard lithological electrofacies models of MB12well area havebeen established by factor analysis、discriminatory analysis, and by comparison with core data.Then by applying step-by-step discriminatory analysis, the interprective results of other wellsare good and over73%of the results is right compared with core data.Finally, with the heavy mineral analysis method and mineral maturity index analysismethod, we discuss the source direction of researched area. And combine with logging anddepositional data, we research the sedimentary facies and sedimentary model of researchedarea.