CHARACTERISTICS AND MAJOR CONTROLLING FACTORS OF CARBONATES RESERVOIR IN THE MIDDLE ORDOVICIAN YIJIANFANG FORMATION, TUOFUTAI AREA, TAHE OILFIELD

Based on analysis of 30 wells data of logging,well logging,oil production test,geophysical,and rock core and rock thin-section observation,the results show dissolved pores and/or caves,factures are the main reservoir spaces with low matrix porosity in Middle Ordovician Yijianfang Formation,Tuofutai area of Tahe Oilfield.On the plane the reservoir types have the feature of "north-south zoning distribution,east-west heterogeneity".The karst reservoirs mainly formed in middle Caledonian and were controlled by such factors as paleo-geomorphology,faults or fractures,lithology and facies,etc.,showing distinct features of fault-controlled and strata-bound.Thus it is predicted that the areas of favorable reservoir rocks would be developed in the congruent sites of the high position of Caledonian paleo-geomorphology,concentration area of faults or fractures and high energy reef-flat facies,which are mainly distributed in the middle and northern part of Tuofutai area.