Page 199 - Handbook Of Multiphase Flow Assurance

196 6. Production chemistry and fluid quality

Produced water should be discharged overboard, if regional regulations permit. No com-
mingling of produced water with seawater should be allowed on a regular basis because of
compatibility issues and potential for scale deposition.
Topsides process design should include:

• Chemical injection points to deliver required chemicals
• Sampling points to monitor chemical performance and fluid characteristics.
Technologies which could be considered in formulating fluid handling concept of flow
assurance include the following:
• Emulsion breaker chemical
• Defoamer chemical
• Oxygen scavenger chemical
• Reverse demulsifier water clarifier chemical
• Hydrocyclone equipment to separate water
• Vacuum de-aeration equipment
• Filtration equipment for produced water reinjection
• Desulphation membranes equipment for pressure maintenance water injection
• Separator equipment
• Flotation cell equipment

Note that topsides process technologies should be verified by trials as mutually compati-
ble, for example triazine injected for scavenging H 2 S from gas may result in scale deposition,
corrosion inhibitor can adversely affect emulsion separation, etc.
Emulsion breaker and reverse demulsifier chemicals are perhaps the most important
chemical category after the corrosion inhibitor because they ensure quality of the product
stream. When separation is inefficient, it may leave hydrocarbons, both regular organics and
water-soluble organics in water. Disposal of produced water stream with off-specification
residual components in it may lead to either plugging of the produced water reinjection wells
or to sheen on seawater if water is discharged overboard.
In USA, the BOEM regularly monitors the performance of production facilities separation
and issues warnings of non-compliance if they observe it or shut-in the facility. The data on
the incidents of non-compliance (INC) are publicly available and may serve as the lagging
indicator of which operator needs help with their production chemistry operation. Periodic
reviews of chemical effectiveness discussed above may serve as the leading indicator of pro-
duction chemistry performance. The up to date reports of INC for USA operators (BOEM,
2019) are in www.data.boem.gov/Company/INCs/Default.aspx.
The number of both warnings and shut-ins shown in Figs. 6.1 and 6.2 have both been on
a decreasing trend in the past. It may be a coincidence that there is a peak in non- compliance
with water quality specification, which is 29 ppm hydrocarbons in discharged water or
42 ppm momentary excursions, for a 30 day average and daily maximum, respectively, in the
year when petroleum commodity price was low.
The method required to monitor hydrocarbon compounds in produced water is the Federal
EPA Method 1664 (2010). This regulatory compliance method is a weight-based method which
relies on solvent extraction of oil and grease hydrocarbons with hexane followed by solvent
evaporation and weight analysis of the residue.