RESERVOIR CHARACTERISTICS AND CONTROLLING FACTORS OF BRAIDED STEAM DELTA SANDBODIES OF MIDDLE TRIASSIC SERIES IN TUHA BASIN

The braided steam delta sandbody is one of the most important oil bearing system in Tuha basin. In this system, front distributary channel, mouth bar, interdistributary channel, plain braided channel and inter braided channel are main sandbodies in Tuyuke area of Tainan sag in Tuha basin. The reservoir properties are under the control of lithology, sedimentary microface and diagenesis over reservoir development. Reservoir capability of distributary channel sandbody and mouth bar sandbody is better because well development of primary pore and secondary pore. Reservoir capability of sandbody in braided channel and inter channel is worse in this area. The braided steam delta reservoir of middle Triassic can be divided into four types of high porosity and high permeability reservoirs, middle to high porosity and middle permeability reservoirs, middle porosity and low permeability reservoirs, middle low porosity and low permeability reservoirs. Among the four types, the second one is a main type reservoir in this area. The middle sand groups of middle Triassic are the main bed for study.