Influence of pressure and solvency on the separation of water-in-crude-oil emulsions from the North Sea

The effect of pressure on the stability of emulsions has been studied for a recombined crude oil from the North Sea. The experiments have been conducted in a combined high pressure and temperature rig at Statoil R&D Centre. Through addition of the solvent toluene, the composition of the crude has been altered. This addition results in a decreased stability of the emulsions at the corresponding pressures, which has also been confirmed by bottle tests at 1 bar and ambient temperatures. The crude oil has been recombined with separator gas giving a bubble point of 11 bars (100 °C). Experiments show a significant increase in separation efficiency, as the separation pressure is lowered from the bubble point and downward. The experiments conducted at lower separation pressures all show a degassing, which creates a flotation effect where the rising gas bubbles transport surface active material away from the water–oil interface, resulting in less stable emulsions. The formation of a foam in the separator verifies this proposed mechanism.