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Abstract: Based on water coning and non-Darcy flow theory, a water breakthrough time prediction equation for low-permeability bottom water reservoirs with barrier is derived by material balance principle, which takes the hemispherical radial flow below barrier and plane radial flow above the barrier of water coning into consideration. The calculated water breakthrough time of an oil producer in the sandstone bottom water reservoir in the Ordos Basin by this equation is close to the real water breakthrough time, with a relative error of only 7.85%. In addition, the water breakthrough time of six wells with natural barrier in c3 reservoir, Block hu152, Ordos Basin, were calculated, among which the predicted water breakthrough time of five wells has a less than 10% relative error with the real water breakthrough time. For low-permeability bottom water reservoirs with barrier, the calculated water breakthrough time considering start-up pressure gradient is smaller and more accurate than that without considering start-up pressure gradient. [Copyright &y& Elsevier]