(256e) Characterization of the Effect of Produced Water Composition On Residence Time of Oil-Water Dispersions in Batch Separation Cell*

During the oil production process, the oil/water mixture passes through restrictions, expansions and shearing devices that affect the flow characteristics of dispersions. The oil industry is looking at different ways to characterize oil-water dispersions in order to properly select, size, and predict the performance of downstream equipment such as liquid-liquid separators. One of the parameters that surface facilities engineers need for designing separators is the residence time necessary to completely separate oil/water dispersions. In the literature, there is little work that show and explain the effect of produced water salinity on the oil-water dispersions separation profiles (residence time). For instance, Gomez-Markovich (2006) showed the significant effect of water salinity on the separation profiles of mineral oil and water dispersions. However, Gomez-Markovich (2006) evaluated only one concentration of NaCl in distilled water so the results could not be extended to other concentrations.

Therefore, the main objective of this study is to evaluate the effect of produced water composition on residence time of oil-water dispersions in a batch separation cell. First, solutions of tap water and NaCl are prepared at concentrations from 10000 to 150000 ppm. The separation profile for each oil-water mixture are obtained for 3 water fractions (25%, 50% and 75%) and 3 different choke valve apertures at a constant temperature, cell volume and mixture velocity. Later, three different produced waters, called as A, B and C, are tested utilizing the same experimental protocol. These experiments are carried out in utilizing the Dispersion Characterization Rig (DCR) at the University of Tulsa. It is a state-of-the-art laboratory equipment that can be used to characterize the flow and separation behavior (residence times) of complex oil-water dispersions under controlled conditions. The facility operates under the same principle as the batch separator.

The results show that the residence time to completely separate oil and water dispersion is reduced with the increase of NaCl concentrations. It is also observed that the presence of other ions, as calcium carbonates, may stabilize the dispersion increasing the residence time for the complete separation of oil and water. These experiments indicate the strong relationship between separation process behavior and physicochemical properties of the oil-water interface.

* These activities are supported by Chevron through the TU-CoRE project