Page 38 - March 2020 - WT Site

The Baleen system is impressive when comparing inlet and outlet system must be selected to remove the type of emulsions or
samples of the flow back water. The laboratory method used, upsets which occur in the process.
EPA 1664A, has a minimum reporting limit of 5 mg/l. The
Baleen system removed from 300 mg/l to non-detectable with Additionally, Organic Acids (water solube oils) are polar molecules
the bi-modal membrane technology. present in most produced water that are highly soluble in water.
WSO concentrations are usually stable after gravity separators
Dispersed, Dissolved and Water Soluble because they are not removed.

Water treatment systems are often judged on their ability to Oil in Water Measurement
remove oil. To understand the technology and performance of
a system, it is good to know how oil is measured and what the The common practice for analyzing a water sample is to add a
data generated means. With no clear definition of oil, the method specific volume of a solvent (10:1 ratio) and a strong acid. Next,
used to analyze a water sample will define oil for that process and the sample bottle is vigorously shaken for 2 minutes and then
method. the solvent is analyzed for oil concentration after it has settled.
The acid addition causes the polar hydrocarbons (including water
There are many terms used in the discussion of oil that can soluble organics) to be readily extracted by the solvent. Some
have different meanings. Oil is often described as dissolved, procedures then pass the extracted solvent through a silica gel so
dispersed, emulsified, free, total, etc. In the oil and gas industry, that only the non-polar hydrocarbons remain in the solvent.
oil is relatively easy to define in a generic sense. Oil is the mixed
hydrocarbon produced in the wells. However, oil can range from In other methods, a specific sized filter is used to remove all large
extremely light natural gas condensates up to heavy crude oil, particles and droplets to understand the particle size distribution
sometimes referred to as bitumen. Gravity separators, adsorbant of the oil and solids.
media and membranes as well as analytical methods will behave
differently when different oils are present. The choice of solvent is important to the results. Solvents will
have different extraction efficiencies for different hydrocarbons.
In simple terms, there are two conditions for oil in water, The choice of solvent can have a significant effect on the presence
dissolved and free. Dissolved oils are molecularly incorporated of waxes and asphaltenes in the final analysis.
and uniformly mixed in the water. Free oil is entirely in droplet
form throughout the water mixture. However, in practice, oil Many of the polishing filter systems describe the ability to reduce
may be considered to be dissolved because the oil droplets are oil concentration to below 1 ppm, and remove BTEX and other
sufficiently small enough that separation does not occur without light hydrocarbons. A common analysis method is the EPA 1664A
additional treatment. method. This method is used for reporting oil concentrations
in discharged waters to the local government environmental
Emulsions by definition are any mixture of oil and water. Often agencies in many parts of the world.
oil which cannot easily be removed by the water treatment
technology is referred to as an emulsion. In primary separation In simple terms, the EPA 1664A method uses hexane to extract
vessels, an emulsion can be water with 1–5 per cent oil present. a water sample, separates the hexane and allows the hexane to
However, after gravity based produced water system, high oil
concentration upsets in the 50–150 ppm range are often referred
to as emulsions because they cannot be separated.

The makeup of the oil can affect the emulsions. Natural gas
condensates tend to have high BTEX concentrations, which have
high solubility. With their low gravity, gas condensates separate
quickly in gravity separators. Heavy bitumen doesn’t have gravity
separate well, but has low solubility. The tertiary water treatment

40 Water Today - The Magazine March 2020