Page 195 - Handbook Of Multiphase Flow Assurance

192 6. Production chemistry and fluid quality

Water should be sampled without leaving un-filled space for air on top of the sampling
bottle. Water should be filled to overflow the bottle and the cap placed on it quickly to limit
exposure to air.
The water sample should be buffered as early as possible to preserve the dissolved ions.
H 2 S or mercury can adsorb to steel container walls. This adsorption would reduce the
quantity of either component in the sample and may give an erroneous measurement indicat-
ing that there is no presence of these compounds in the sample.
Sampling containers where H 2 S or mercury are expected to be present due to regional or
geologic analogs should have special inside liner coating which would prevent adsorption of
either H 2 S or Hg to the container steel wall.
Sampling method recommendations for petroleum fluids are summarized in the API rec-
ommended practice 44 (API, 2003).

Quality: 4Cs of production chemicals

The production chemicals quality may be described with the following characteristics:
• Compatibility
Chemicals should be compatible with each other without a significant loss of
effectiveness, and with the production system materials such as valve elastomeric seals
without degrading or dissolving them.
• Consistency (stability)
Chemical should remain of the same consistency and fluidity over the range of
temperatures and pressures in the production system.
Chemicals should retain their consistency for at least 6 months because chemical injection
may not occur for and extended time while chemical may remain in the injection tubing
at elevated pressure and temperature such as downhole before being injected into the
produced fluid.
Consistency should also remain at reduced pressure such as vacuum. Chemicals are
usually formulated in solvents such as toluene, glycol or methanol. Carrier solvents
may be heavier than the live produced fluid. Hydrostatic pressure of the chemical may
be higher than of the produced fluid at the injection point. In some cases in deepwater
the heavier chemical may fall down the riser portion of the injection tubing and create
vacuum condition. In vacuum, the solvent would flash off or evaporate and leave the
heavier active components which may lead to plugging the chemical tubing.
• Cleanliness
Chemical should be clean and filtered because the presence of even minute quantities of
solids could plug off the chemical injection valve or port.
• Concentration
Chemicals should be effective in fairly low concentrations to remain economic and not
affect the separation process significantly.
Typical dosages of chemicals were shown in Chapter 1. Chemicals are usually injected
in 50–500 ppm concentration (0.005–0.05 wt%). Hydrate control chemicals are used in
much higher concentrations ranging from 10,000 to 400,000 ppm (1 to 40 wt%). Chemical