A Quantitative Study on the Gravel Orientation of Typical Sedimentary Microfacies in Baikouquan Formation, Mahu Sag, Junggar Basin

Key words: 
• gravel orientation /
• quantitative characterization /
• sedimentary microfacies /
• Baikouquan Formation /
• Mahu sag

Abstract: Gravel orientation can be used to judge the environment of coarse grain deposits. On the basis of the analysis and measurement of the gravel image from the core image, using the parameters a and σ to study the 152 types typical conglomerate lithofacies and four typical sedimentary microfacies of characterization of gravel orientation in the Baikouquan Formation sandstone in the Mahu sag. The parameter a is the maximum value of the sum of the radius of the gravitational axis of any adjacent three small fans, parameter σ is the degree of deviation of the small fan radius. It is found that the larger the a and σ is, the better the orientation of the gravel is; There are some differences in the orientation of different lithofacies and sedimentary microfacies in the Baikouquan Formation in the Mahu area; the orientation of lithofacies with the cross-bedding, the parallel bedding and the small conglomerate attribute is better, the orientation parameter is relatively large. The orientation characteristics show that vertical rotation of the braid channel, the underwater distributary channel and mouth bar are apparent, but the debris flow microfacies's is vague. The size of the orientation parameters exist a difference in four typical sedimentary microfacies, the orientation is poorly followed by debris flow microfacies (σ has a maximum value of 6.61, a minimum of 3.00, and an average of 4.03; a has a maximum value of 52.94%, a minimum of 22.95%, and an average of 41.41%), braided channel (σ has a maximum value of 8.91, a minimum of 3.11, and an average of 5.31; a has a maximum value of 65.79%, a minimum of 25.93%, and an average of 32.87%), underwater distributary channel (σ has a maximum value of 7.22, a minimum of 2.96, and an average of 5.11, a has a maximum value of 55.71%, a minimum of 25.93%, and an average of 32.87%), mouth bar (σ has a maximum value of 10.34, a minimum of 3.65, and an average of 5.54, a has a maximum value of 83.02%, a minimum of 32.35%, and an average of 44.42%). We can use these differences to determine different sedimentary microfacies.