Page 168 - Handbook Of Multiphase Flow Assurance

164 5. Flow restrictions and blockages in operations

The presence of gas decreases the temperature of the produced fluid by J-T cooling due to
gas expansion. Addition of gas lift gas also decreases the temperature of the fluid. The pres-
ence of light hydrocarbons helps solubilize n-paraffins in oil, but the effect of cooling usually
causes more wax deposition with presence of gas.
• Miscellaneous factors
Wax deposit in flexible risers may reduce the potential for adhesion of other solids. Wax is
made of hydrocarbons, so hydrophilic compounds such as gas hydrates may have less possi-
bility of adhesion and plugging in annular flow regime in vertical or near-vertical risers when
some wax deposit is present. However, the wax deposit may trap sand and water and cause
other integrity issues. Wax deposits may be prevented with insulation, mechanical removal,
solvents or active heating.

Prevention techniques
Operations should avoid wax formation and accumulation irreversible by normal oper-
ating procedures. This may be accomplished by keeping oil at temperature above the wax
appearance temperature when system is flowing.
Wax appearance temperature should be used as higher of the measurements from DSC
and CPM or high pressure CPM if available. In case of high content of microcrystalline (bio-
degraded, isoalkane) wax in oil, high pressure DSC WAT should be used instead of high
pressure CPM.
Technologies which could be considered for management of wax and gels in produced
fluids include:
• insulation
• periodic scraping
• wax inhibitor chemical
• pour point depressant chemical
• wax dispersant chemical
• active flowline heating by PIP heating medium circulation
• active flowline heating by wet insulation EH
• active flowline heating by PIP DEH
• active flowline heating by PIP heat tracing
• hot water injection from aquifer if proven in the region
• low rate flow circulation in a shut line to prevent gel from setting

Following remediation technologies could also be considered.
• dry tree wireline scraping
• hot oiling
• wax solvent wash
• coiled tubing to jet out the deposit, especially for a riser
Several techniques are discussed in more detail.
• Wireline scraping
Wireline scraping of wax in well tubing is a commonly used mechanical wax removal
method. Onshore wells use a timer-actuated motor to lower and lift a wireline with a cutter