Abstract: The exploration and development of the Ordovician in Tahe Oilfield have been undertaken for more than ten years. In addition to the fine exploration in Tahe Oilfield, exploration is also performed outside of Tahe at present. In recent years, the exploration of the Ordovician carbonate reservoirs in Yubei and Tazhong shows that the reservoir effectiveness evaluation has been becoming more and more important. On the basis of the logging response characteristics and the mutual calibration of the core analysis, imaging logging and conventional logging, the dissolved pore reservoirs, fractured reservoir sand fractured-vuggy reservoirs are further subdivided, and well logging identification and evaluation methods are put forward for the effectiveness evaluation of the Ordovician carbonate reservoirs in Tahe Oilfield. The effectiveness of vuggy reservoirs is evaluated through cross-plotting of natural gamma and apparent formation water resistivity. Additionally, the effectiveness of fractured-vuggy reservoirs is evaluated by using the electric imaging local resistivity method. The practices show that these two methods can better solve the problem of reservoir effectiveness evaluation caused by filling of clay. For the different types of fractured-vuggy reservoirs whose effectiveness is influenced by the strength of fracture development, we studied the relationships between lithology, electrical property, porosity and oil-bearing property and performed mathematical simulation. Based on these studies, we put forward the evaluation model featuring in constant permeability, mutative vuggy porosity and fracture porosity. The application of this model shows that the coincidence rate of the logging interpretation has been improved. It provides evidences for the reservoir effectiveness evaluation, the formulation of completion scheme and the calculation of reserve parameters.

Key words: well logging, vuggy reservoin, fractured-vuggy reservoir, reservoir seepage evaluation, carbonate rock Tahe oilfield