Abstract: The Ordovician reservoir in Tahe oilfield is a karst fractured-vuggy oil reservoir dominated by large-sized vugs as its reservoir spaces. At present, breakthrough has been made by single well waterflooding process, but it is in experimental stage by multi-well unit waterflooding process for areas with 80% reserves. Based on the numerical simulation and waterflooding practices, the mechanism of the mult-well unit waterflooding process is studied, and an effective pattern in field application is preliminarily summarized in this paper, namely, low water injection and high oil production, injection test to judge connectivity and adjust in time, whole unit gentle water injection and well groups separation management

Key words: Tarim basin, Tahe oilfield, fractured-vuggy reservoir, waterflooding, pattern