Experimental quantification of the performance of a horizontal multi-pipe bulk separator of water and oil with crude spiking

Subsea water separation with pipe separators is crucial for ensuring efficient and environmentally responsible extraction of oil and gas from the seabed. In this study, in a process called as crude oil spiking, two concentrations of crude oil (e.g., 185 and 400 ppm) are added to Exxsol D60 to mimic the separation characteristics of real crude oil mixtures in a multi-parallel pipe separator. The pipe separator performance for water-oil bulk separation such as separation efficiency, water cut ratio, the flow pattern at the separator inlet, and the thickness and evolution of the fluid layers in the separator is evaluated and compared to the values when operating with unspiked Exxsol D60. Crude oil spiking significantly reduces the efficiency of the pipe separator and reduces the water cut ratio for oil continuous regimes (low water cuts) up to 49%. Water continuous regimes with water fractions 90% have the highest efficiency values; thus, these are not affected significantly by crude oil spiking. With crude spiking, the flow regime dispersion of oil in water and water in oil (Dw/o + Do/w) occupies more area in the flow pattern map than unspiked Exxsol D60. It was observed through visual inspection that crude oil spiking induces a thicker and more stable emulsion in higher flow rates (e.g., 700 L/min). Therefore, the spiked mixture needs more time to separate. The findings of this study can help in a better understanding of the applicability of pipe separators and the usage of spiked oils to extrapolate experimental results to real field conditions.

Automated summary

Subsea water separation using pipe separators is crucial for efficient and environmentally responsible extraction of oil and gas from the seabed. This study evaluated the performance of a multi-parallel pipe separator for water-oil bulk separation, comparing spiked and unspiked oil mixtures. Crude oil spiking significantly reduced the efficiency of the pipe separator and affected the water cut ratio and flow pattern.