Tarim Basin, Xinjiang Tahe Oil Field South Of The Middle Ordovician Yijianfang Mound (reef) Beach Reservoir

After finding high industrial oil in yijianfang of Middle Ordovician in S76 in the south of tahe oilfield, the type of beach grain limestone reservoir began to be exploited. Since then a lot of wells has found high industrial oil in the same type of reservoir of yijianfang. This carbonate reservoir is very important to further exploration and exploitation in tahe oilfield.At the present time, there are different opinions about the cause of formation of this reservoir. There are many doubts and no enough evidence about the development of reservoir.In allusion to these problems, we use the views of sequence stratigraphy, the data of outcrop section, drill core and logging, to plot out sequence of single well section. Furthermore we can set up the sequence of strata of yijianfang. Then use diagenies sequences and fluorescence analysis to seek after the mechanism of formation. At last, By researching controlled factors of reservoir and contrasting with pore-reservoir jialingjiang group Triassic System in Sichuan basin, we make evaluation to quality of reservoir. The followings are several points:1. Yijianfang group is devided into one sequence, its high system tracts is devided five parasequence.2. Mechanism of reef and beach facies reservoir in Yijianfang group is that carbonate is soluted when it is deposited. Reservoir is controlled by unconformity that four grade offing drop forms. This is a cause that reservoir is appeared the top or middle of parasequence.3. Yijianfang group has a well foreground of oil exploitation.