Characteristics and controls of Ordovician reef flat reservoirs in the southern Tazhong slope of Tarim basin

Based on a systematic study of the Ordovician carbonate reservoirs using drilling data of Well Zhong 2 in the Southern Tazhong Slope, characteristics and controls of the reservoirs are understood. The Middle and Lower Ordovician sections are composed of carbonate deposits of platform facies; and Upper Ordovician Lianglitage Formation, platform-edge reef flat facies. The reservoir spaces are dominated by fractures as well as dissolution pores and vugs. The petrophysic properties of the reservoirs are controlled with deposition,diagenisis and tectonism. The biohermal reservoirs have petrophysic properties much better than reef flat ones. The Ordovician carbonates have been subjected to two periods of dissolution, improving the petrophysic properties of the reservoirs. Episodes of tectonic events resulted in well-devel-oped fracture-type reservoirs of the Lianglige Formation.