CHARACTERISTICS AND POOL-FORMING CONDITIONS OF THE LOWER ORDOVICIAN RESERVOIRS IN TAHE OILFIELD, THE TARIM BASIN

The integral geological study and petroleum exploration indicated that Tahe oilfield formed on the basis of longdeveloped paleouplift was a large scale one which consisted of karstfracture reservoirs of the Lower Ordovician carbonate rocks. Karst holes, cracks and pores developed in the Lower Ordovician carbonate rock constitute four types of oil and gas reservoirs, including crack type, porecrack type, crackpore type and reef type. Long lasting generation of hydrocarbon, multiphase tectonic movement and multistage karstification resulted in quite different oil characteristics in different part of the oilfield. Petroleum accumulation and pool forming were controlled by the Akekule Uplift, development level of karstfracture in carbonate rocks and distribution of mudstones of the Carboniferous Bachu Formation.