Page 64 - Handbook Of Multiphase Flow Assurance

Fluid characterization 59

phases. This alters the rate of processes such as corrosion or formation of hydrate, deposition
of wax or asphaltene.
One should keep in mind that predicted stability of a solid phase does not guarantee solid
formation at exactly the predicted condition because nucleation kinetics may be delayed, and
formation of a solid does not always lead to a deposition and a blockage.
At the same time, if a phase is not stable, it does not mean that it could not form in real
operations. The software predictions and laboratory measurements can provide a warning
for a specific set of conditions and fluid compositions. However, operations in the field can
show that reality is more complex because not all factors and phase transitions were taken
into account by a software or a lab such as reaction kinetics, solids nucleation and metasta-
bility, and the influence of one solid phase on another. As an example of such influence, in a
system where scale is not stable, a hydrate formation can remove some water from a system.
Hydrate consumes pure water and leaves salt in the remaining water. If a nearly saturated
brine is present and the hydrate forms, it will cause water to become supersaturated with
salt, leading to scale precipitation and deposition. Similarly, injection of methanol to inhibit
hydrate into a produced fluid, which included a brine nearly saturated with NaCl, had led
to a change is salt solubility and an unexpected halite scale blockage in a North Sea pipeline.
Additional laboratory studies

Additional laboratory studies which may accompany a PVT report may include:
Oil pour point temperature
Oil HTGC or high-temperature gas chromatogram to resolve amounts of wax-forming
components
Oil emulsion stability study
Oil TAN total acid number and TBN total base number analysis
Oil SARA or saturates, aromatics, resins, asphaltenes content analysis
Oil foaming study

Wax appearance temperature measurement in CPM or cross-polarized microscope or
DSC differential scanning calorimeter at stock tank conditions
Wax appearance temperature measurement at pressurized conditions with reservoir fluid
with either DSC or CPM
Wax deposition study in a bench-scale mini-loop or a filter-plug apparatus
Wax deposition study in a pilot-scale loop
Wax deposition study in a cold finger apparatus with effect of chemical inhibitors
Wax deposition study in a pressure cell
Wax content from a cold solvent filtration study

Wax dissolution study with dispersant chemicals or solvents
Wax melting study for hot-oiling process

Waxy gel strength test in a small diameter tube
Asphaltene titration study for stock tank oil
Asphaltene isothermal depressurization for live reservoir fluid under pressure