CHARACTERISTICS AND MAIN CONTROLLING FACTORS OF THE FORMATION OF ORDOVICIAN RESERVOIRS IN AREAS COVERED WITH SALT LAYERS IN TAHE OILFIELD

The most important distributional characteristics of Ordovician reservoirs in areas covered with salt layers in Tahe oilfield is well-developed fractures. Vugs, partly filled or unfilled structural fractures with high angles and solution-enlarged fractures are the main types of porosity space in the studied area. Large caves are less developed than the main areas of Tahe Oilfield. Vug-fissure and fissure-vug reservoirs are the main reservoir types. Within this areas, reservoirs in the west part are more developed than that in the east part, and the favorable reservoir belts are mainly extended in north-south direction. Reservoirs developed in the upper part of middle-lower Ordovician are more developed than that in the lower part. Reservoirs developed in Lianglitage formation of upper Ordovician are more developed than that developed in middle-lower Ordovician. The key factors that control the formation and distribution of Ordovician reservoirs in areas covered with salt are tectonic deformation, the karst process occurred in mid-Caledonian orogeny and its sedimentary facies.