Improving Oil-In-Water Treatment by Optimization of Production Chemicals

The removal of oil droplets from water heavily depends on the ability for these to coalesce into larger drops to overcome size limitation of equipment such as centrifuges, hydrocyclones, gas flotation etc. The composition of PW is a mixture of oily compounds, inorganics from the formation and production chemicals. Chemicals have a significant impact on the stabilization of oil droplets but variations in salinity also plays a role. The repulsion of droplets has detrimental effect on the treatment. In this paper we aim to quantify this in order to develop optimization tools. 

Methods, Procedures, Process: The quantification of droplet coalescence and impact of chemistry is obtained through specially designed microfluidic chips. Droplets are recorded using high speed cameras. Using image analysis coalescence efficiency is quantified. Partitioning of chemicals between water and oil which is affected by both salinity and oil type and measured by capillary electrophoresis. This is analyzed using capillary electrophoresis. Real PW samples and chemicals are obtained from offshore Denmark. Coalescence events are recorded while varying oil type and also diluting the PW to understand which constituents lead to stability of drops and hence potential adverse effects in water treatment. 

Results, Observations, Conclusions: The fundamental Bancroft's rule describes that the component favorable dissolved in one phase will stabilize droplets in this continuous phase. Hence compounds primarily soluble in water stabilize oil droplets in the water treatment system, and can lead to poor water quality-potentially having an adverse effect on sizing of equipment. Accordingly specifically water-in-oil (WiO) emulsion breakers can have a detrimental effect when overdosed, as more is not better. When different water streams are commingled before treatment there might be potential cases where one stream despite its apparent low content of oil-in-water (OiW) can stabilize droplets in another stream. We present data based on microfluidics and analysis of partitioning coefficients using a variety of real PWs and production chemicals from O&G production in the Danish North Sea. This clearly indicates that the main issue is related to water constituents, but that oily polar components have a large impact as well on stability. The qualitative information is linked to quantification using the hydrophilic Lipophilic Deviation theory which can then be used to optimize potential scenarios of synergistic and antagonistic effects of chemicals and PW constituents on water quality. Discussion will also aim understanding mixing rules for quantification in multicomponents mixtures based on surface chemical insight. 

Novel/Additive Information: We apply both novel microfluidics and novel analytical techniques for production chemical partitioning measurements.