Abstract:

 Karst fracture-vug systems of Lower-Middle Ordovician in Tahe oilfield, develop very well, during multi-stage tectonic movement and karstification, from Middle Caledonian to Hercynian. Except for the dissolubility of the rock, karstification mainly depends on the denudation and corrosiveness of karstic water, in course of supply-through flow-drainage. So, predicting the trace of karstic water is an important method. Based on 3D seismic data, applying third generation coherence technique, karst palaeo-drainage systems in the top of Lower-Middle Ordovician can be described, and below overlay area of Upper Ordovician, there are still many palaeodrainage systems, most of which are connected well with palaeo-drainage systems in lost area of Upper Ordovician. According to karst theory in modern times, we divide karstic series of strata, confirm the hydrogeologic condition, and analyse the forming and consuming course of karst palaeo-drainage systems in two stages, which can play an important role on recovering the environment of palaeokarst, dividing the stages of palaeokarst and revealing the rule of palaeokarst.

Key words: palaeo-drainage system, palaeokarst, Ordovician, Tahe oilfield