Abstract:

The Lower Ordovician carbonate reservoir in Tahe Oilfield is a large fracture & cave system formed by supergene karstification. The reservoir pore space of Tahe Oilfield mainly consisted of touchingvugs such as fractures related with karst cavities and pores. The exploration and production of oilfield proved that reservoirs have different connectivity and multipressure system. Based on the characteristics that the carbonate reservoir connected with fracturecavity system, this article analyzed the features different from discrete carbonate reservoir. Approach on the complicated features of the fracture & cave reservoir which are different from sand reservoir, the authors pointed out emphatically that variable dynamic data are very significant for the research on the connectivity of fracture & cave reservoir. By the study on dynamic data the author inferred the “fracture & cave unit” in the karst reservoir, and put forward the research ideas and methods that how to use dynamic data to study on the connectivity of the reservoir. Then the author concluded: (1)in the same fracture & cave system, every well is similar in pressure drop; (2)interwell interference analysis can make sure the connectivity immediately; (3)the changes of development well lead to dynamic changes of other wells in the same flowage unit; (4)connectivity grade can be divided by testing the tracer material in the wells which nearby the tracer injector and making sure how long the wells are affected; and (5) the fluid in different fracture & cave system is variable in composition, density and viscosity. In the end, according to the factual data of Tahe Oilfield, 42 fracture & cave units are recognized, and the author considered that the distribution of the reservoir is in accordance to karst palaeogeomorphology, palaeodrainage pattern and fault zone.

Key words: Tahe Oilfield, carbonate reservoir, karst reservoir, fracture &, cave system, dynamic connectivity, flowage units