The Discussion on Height Adjustment of Water Weir Pipe of FPSO Separator in Bohai Sea Area

The FPSO has been operating for many years in an oilfield in Bohai Sea area, but the optimal height of the water weir pipe of the two-stage production separator has not been ascertained. The height of the water weir pipe is often adjusted to make the oil-water interface in the separator too high or too low, resulting in high water content in crude oil at the oil phase outlet or substandard water quality at the water phase outlet. In this paper, the principle of water weir pipe controlling oil-water interface is elaborated, and the relationship between water weir pipe height of two-stage & three-phase separator and oil-water interface height is calculated. Based on the analysis of the factors affecting the oil-water interface of the two-stage three-phase separator, such as the obliquity of FPSO, the effect of chemical agents, the sand accumulation in the separator, the density of oil and water, etc., and combined with the actual production condition of this oilfield, the optimal residence time, the corresponding effective volume and the height of the oil-water interface of the oil and water phases are calculated, which can be used to deduce the optimal height of the water weir pipe. FPSO production operators adjust the height of separator water weir pipe according to the calculation results and verify the accuracy of the calculation results.