Sedimentary microfacies of the first member of Badaowan Formation in Mahu SAG, Dzungar Basin: Taking well TX1 as an example

Based on the detailed study of the first member of the Jurassic Badaowan Formation in TX1 well in Dzungar basin, it is considered that the first member of the Jurassic Badaowan Formation is mainly composed of polygenetic conglomerate, conglomerate-like sandstone, sandstone, and interbedded coal layers. The first member of the Jurassic Badaowan Formation develops abundant sedimentary structures such as grain sequence beddings, middle to large scale cross beddings, erosion fillings, and plant stem impressions. Well log shows box-type, funnel-type, finger-type and linear in shape. The sedimentary facies gradually retrograded to the margin of the basin in the longitudinal direction, in which the plain subfacies developed from No. 2 to No.5 sand formations dominated by braided distributary channel and interchannel fluvial marsh deposits. The front subfacies developed in No.1 sand formation, which is mainly composed of underwater distributary channels and intertributary bays. The subaqueous distributary channel microfacies in the braided river delta front are the most favorable reservoir facies zones, which are with better porosity and permeability. The microfacies of distributary channel in braided delta plain, are the second-class reservior, whose nomogenity is somewhat bad and the water/oil rate is high.