Central Laboratory of Geological Sciences，Research Institute of Petroleum Exploration and Development，PetroChina，Beijing100083
Five types of marine sandbodies were identified in the marine sandy mudstone deposits of the Tierekeawati Formation in northwestern Manjiaer Sag based on detailed analyses of 5 wells including Yangwu 2， Yuenan 2 and Jinan 1， combined with microfacies analyses of single well and interpretation of over 350 km seismic profiles. They are shoreline， inner shelf ridge， inner shelf ditchtrough， storm and tidal channel sandbodies. Ditchtrough sandbodies with transgressive conglomerate and flooding surface at the basal part were developed at the bottom part in Yangwu and Hade areas in the west of the study area which was characterized by normal rhythm. Above it， the inner shelf ridge sandbodies with normal and reverse rhythms and no development of flooding surface. The top part is dominated by shoreline sandbodies with development of paralleling bedding and cross bedding and a reverse rhythm. The storm sandbodies with a strong heterogeneity were developed on the uppermost. In Jinan well area in the east of the study area， inner shelf ridge sandbodies were developed in the lower part， tidal channel sandbodies and tidal deposits were developed in the upper part. The distribution range of sandbodies gradually expanded with the influence of global sea level falling during the Late Ordovician. The marine sandstone reservoir in the Tierekeawati Formation is dominated by secondary pores with a high heterogeneity due to the inhomogeneous cementation， dissolution， and locally developed fissures. Reservoirs are ranked by their properties from good to poor ones as: inner shelf ridge， shoreline， inner shelf ditchtrough， tidal channel and storm sandbodies.
Tarim Basin|Upper Ordovician|Tierekeawati Formation|marine sandbody|reservoir property
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Gao Zhiyong was born in 1974. Now he is an engineer of Research Institute of  Petroleum Exploration and Development，PetroChina and is mainly engaged in researches of sequence stratigraphy and sedimentology. E-mail:gzybox@163.com.