Study on Sedimentary Microfacies of Yanchang Formation Chang8 Reservoir in Fanxue District, Northwestern Ordos Basin

The oil sand of Chang8 reservoir of Yanchang formation in Fanxue district,northwestern Ordos basin is taupe fine, fine-grained feldspathic sandstone, grain size probability is curve two-stage form and partial three-part form. Combined with sedimentation in the study area, diagenesis and individual well-phase analysis, it's pointed out that Chang8 reservoir is delta front facies of lake delta depositional system, the provenance of the north or northeast direction from mainly developed underwater distributary channel, river side edge, split between bay microfacies. Logging curve shape is box, bell-shaped and their combination, which reflects the micro underwater distributary channel development, sand bodies were stacked on a series of cycles repeated cross-section, formed flat convex lens on the profile body. In vertical, there is a coarsening-upward sequence, which indicates the scope of the study area sedimentary basin expanded to constitute deltaic sediments.