Bottom water coning is a major reason reducing production and recovery factor of single well in reservoirs with bottom water.The Ordovician of the Tahe oilfield has well-developed fractured-vuggy reservoirs with bottom water

which are different from conventional porous reservoirs and fractured reservoirs in many ways.Pores

fractures and vugs coexist and large cavern system dominates the reservoir spaces in this type of reservoirs.Due to spatial diversification of reservoir scale and discontinuous distribution of reservoir space

the fractured-vuggy reservoirs have a water coning mechanism significantly different from that of a regular reservoir with bottom water.Considering its uneven distribution of vugs and strong heterogeneity

we established a conceptual geological model with permeability variation to describe the reservoirs and derived a prediction formula for the bottom water breakthrough by defining permeability variation coefficient and the drainage radius ratio to characterize the development of fractures and vugs.We applied the formula to the calculation of bottom water breakthrough time in the well S48 in Block 4 of the Tahe oilfield.Through the comparison of the results with the actual data

we tried to determine the effectiveness of the formula and analyze the influences of fracture and vug deve-lopment(represented by permeability variation coefficient and drainage radius ratio)

single well production and perforation upon the time of bottom-water breakthrough.