RESERVOIR CHARACTERISTICS AND THEIR CONTROLLING FACTORS OF THE CARBONIFEROUS KARASHAYI FORMATION IN TAHE OILFIELD

The developing degree of reservoirs is the major controlling factor of hydrocarbon accumulation of the Carboniferous Karashayi Formation, an important oil reservoir bed in Tahe oilfield. The physical properties of reservoirs are mainly controlled by sedimentary microfacies and diagenesis. The lithology of branch channel sandbodies of braided river delta and medium-bedded tidal channel sandbodies are mainly medium-coarse-grained sandstone which develops intergranular pore-space and residual intergranular space, and have well accumulation features. The lithology of sandbodies of river mouth bar of braided river delta-front, interchannel, sand flat and sand bar of intertidal zones are mainly silt sandstone and fine-grained sandstone which have worse accumulation properties. In general, sandrocks are low-medium porosity and low-medium permeability reservoirs in this area. The sand-shale segment of the Karashayi Formation can be divided into five sand sets in depth, and the sandbodies of Ⅰ, Ⅱ sand set and Ⅲ sand set have well accumulation properties. The available reservoirs developed in three areas such as 3rd, 4th and 6th block of Tahe oilfield.