Page 196 - Handbook Of Multiphase Flow Assurance

Laboratory verification of chemical performance 193

injection at higher dosage may become uneconomic. The operating expenditure for the
use of production chemistry may add between $0.1 and $2/bbl lifting cost, depending on
the scope and severity of flow assurance and production chemistry issues.

Laboratory verification of chemical performance

Pass/fail criteria for hydrate, wax, asphaltene, scale, corrosion chemicals

Laboratories are used to ensure the chemical performance alone and in a blend with other
chemicals which are planned for injection in a given well or flowline. The criteria for chemical
performance are subjective for each company and laboratory and there is no standard metric
for these. Joint industry projects developed such criteria but their adoption remains gradual.
Some of the chemical performance criteria are suggested below.
Hydrate thermodynamic inhibitor has to completely prevent formation of hydrate solids.
Hydrate kinetic inhibitor has to completely prevent formation of hydrate for at least the
time of residence of fluids in production system at the highest pressure in the system.
Hydrate antiagglomerant chemical has to prevent agglomeration of hydrate and its ad-
hesion to an optical window in a pressurized rocking cell, stirred vessel, flow loop or in a
rotated wheel.
Wax inhibitor has to reduce the mass of wax deposition by at least 50% at the temperature
differential between wax appearance temperature and ambient temperature in the planned
production system at atmospheric pressure in a cold finger, shear cell or flow loop test or at
high pressure (rare shear cell apparatus).
Asphaltene inhibitor has to prevent or reduce the amount of precipitated solids.
Asphaltene dispersant has to prevent adhesion of flocculated asphaltenes on the test cell
walls.
Scale inhibitor has to prevent precipitation of solids by retaining the scale-forming cations
in test solution in a static bottle test as indicated by their residual concentration.
Scale inhibitor has to prevent or reduce deposition of solids in test tubing in a dynamic
loop test as indicated by pressure drop across the loop.
Corrosion inhibitor has to reduce the rate of metal loss so that penetration rate is below 1
mil (0.001 in.) per year. In some cases rates as high as 4 mpy are considered acceptable, de-
pending on the design life of the system.

Lab equipment requirements

Lab equipment should be able to reproduce as closely as possible the pressure and tem-
perature in the production system, and not allow any leaks of test fluids or ambient fluids
across the test apparatus boundary. In some cases it is impractical to use pressurized equip-
ment, then atmospheric pressure is used as in emulsion or some scale or wax tests.

Test procedures
Test procedures for corrosion are documented by NACE.