Page 203 - Handbook Of Multiphase Flow Assurance

200 6. Production chemistry and fluid quality

Chemical characteristics

Chemicals may be formulated in carrier solvents such as methanol, toluene, glycol or wa-
ter. Concentration of active components usually varies from 10% to 40%. Bulk properties of
chemicals such as density, viscosity, vapor pressure and resistance to flashing off of solvent
mainly depend on the properties of the carrier solvent.
Some characteristics of chemicals are available in literature, which may be used for a pre-
liminary hydraulic design of the chemical injection system.
A more robust process is to get the chemical characteristics including density, viscosity
and vapor pressure as function of both temperature and pressure from the potential chemical
suppliers at an early stage of project design, after the scope of potential flow assurance issues
is understood based on appraisal well samples or regional analogs.

Chemical tubing blockage

Vapor pressure of a chemical is an important characteristic because vacuum can occur at
top of chemical injection lines causing flashing off of solvent and deposition of active ingredi-
ent in the chemical tubing, leading to its plugging. Plugged chemical tubing may be remedi-
ated with solvent circulation if there is flow communication through the blockage, or using a
pressure pulsation blockage removal method.
Chemical tubing may also be blocked with flow assurance solids such as hydrates when
pressure in the chemical tubing is less than in the production system. Such difference
in pressures may occur when production is shut in, and chemical is less dense than the
produced fluids. Untreated or undertreated produced fluid may migrate across the check
valve(s) as all valves have some leakage, and form a blockage in the chemical tubing. An
example of a hydrate blockage inside methanol tubing was discussed earlier in Chapter 1.

Dosage selection and optimization

Dosage selection is performed with account to potential loss of chemical effectiveness
when other chemicals are injected, and to project economics. Chemicals performance is tested
at several concentrations both without and with other chemicals, and the lowest concentra-
tion which is sufficiently effective is selected.

Chemical data

• Density of MEG is shown in Fig. 6.3
• Viscosity of MEG is shown in Fig. 6.4
Table 6.1 shows estimated properties of production chemicals at atmospheric pressure and room
temperature. Note that viscosity and density will increase at higher pressure and lower temperature;
data should be obtained from chemical vendors.