Abstract:

Reservoirs in the Triassic Baikouquan Formation in Mabei area of northwest margin of Juggar Basin were deve-loped in a fan delta setting, in which the rock types are diversified, the lithologic facies under different sedimentary microfacies played vital role in controlling reservoir properties, and the matching between sedimentary microfacies and lithologic facies was complex.Thus establishing depositional models with matching sedimentary microfacies and lithologic facies is of great significance in studying the main controlling factors of reservoirs and prediction of reservoirs.Based on a combination of analyses of core observation, thin section and log data, with sedimentary background and tectonic settings of the study area, we focused on the configuration relationship between the lithologic facies and sedimentary microfacies and took into consideration the granularity and color of sediments, sedimentary texture and microfacies, and diagenesis.The results shows that 11 main lithologic facies types can be recognized in the study area:superaqueous mudslides conglomerate facies, subaqueous channel conglomerate facies, braided channel coarse-clastic facies, underwater channel coarse-clastic facies, subaqueous debris flow coarse-clastic facies, plain interchannel sandstone-mudstone facies, underwater interchannel sandstone-mudstone facies, underwater channel-end sandstone facies, mouth bar-distal sandbar sandstone facies, frontal fan-delta siltstone facies, and frontal fan-delta mudstone facies.A depositional model with matching sedimentary microfacies and lithologic phase was also established based on lithologic facies characterization, profile analyses of lithological facies and sedimentary facies, as well as sedimentary sequence, depositional texture and sedimentary structure.Then, we studied the planar distribution of the microfacies and lithologic facies in the Triassic Bakouquan Formation.It shows that three members of the Formation contain mainly fan-delta plain and fan-delta front subfacies.The first member developed conglomerate in its fan-delta plain and sandstone in its fan-delta front; the second member grew at its lower part mainly conglomerate in its fan-delta plain and glutenite and sandstone in its fan-delta front; and at its upper part conglomerate with glutenite in fan-delta plain and sand with some coarse-clastic rocks in fan-delta front; and the third member is dominated by coarse-clastic facies followed by conglomerate facies in its fan-delta plain, and it is dominated by sandstone facies followed by coarse-clastic faceis in its fan delta front.

Key words: sedimentary facies, lithologic facies, sedimentary model, Triassic Baikouquan Formation, Mabei Region, Junggar Basin