Triassic sedimentary microfacies in the second and third well fields in the Lunnan Oil Field,Tarim Basin

The Triassic strata occur as the main oil reservoirs in the Tarim Basin.The planar and spatial distribution of sedimentary microfacies in individual oil reservoirs of reservoir sandstones is explored on the basis of the analysis of cores and well logs,in combination with the petroleum exploration in recent years.The Triassic sandstones in the Lunnan Oil Field are composed of gravelly medium-to coarse-grained sandstones with coarser grain sizes,indicating typical gravity flow deposits,and fluvial-and lacustrine-dominated clastic deposits.The source rocks are developed in the deep lake and bathyal lake,shallow lake and delta subfacies,and typical of the gravity flow deposits by suspension transport.Three types of sandstones have been recognized,including braided distributary channel microfacies,distributary channel flank microfacies and interdistributary way microfacies sandstones.The Middle and Upper Triassic coarse-grained clastic rocks,mudstone and siltstone are assigned to the bathyal lake,shallow lake and littoral deposits in the fan-delta plain,fan-delta front and prodelta subfacies from the base upwards.