Page 180 - Handbook Of Multiphase Flow Assurance

176 5. Flow restrictions and blockages in operations

should be equipped with 2 or 3-in. diameter wax equipment which could adequately mea-
sure the relevant processes.
Gels may be weaker if their cooling rate is non-uniform. Some parts of the gel may break
first, if the crystals making up the network are smaller as caused by the faster cooldown.
Usually, the faster the cooling rate, the smaller are the crystals, the weaker is the gel. This
is observed in laboratories where gel usually breaks at the pipe wall first, where the heat
transfer was the greatest.
In insulated or buried pipes the cooling rate may be more uniform, leading to the uniform
gel strength. Axial center of the pipe may have mechanical deformation of the gel due to its
cooling, and thermal expansion or contraction.
Gels may also be weakened by presence of gas pockets in the pipe.
Typical gelling crudes contain at least 3 wt% wax, as measured by the cold filter method.
Crudes with lower content of normal paraffins are less likely to gel because not enough
solid crystals precipitate on cooling to ambient temperature to form a network. As with any
natural material, a gelling oil may contain less than 3 wt% normal paraffins, but a higher
fraction of isomerized or biodegraded alkanes, which can still solidify into amorphous solids
and cause gelling. Crudes containing more than 5% wax (normal paraffins) may be expected
to have gelling issues.
A correlation between wax content and pour point temperature was presented by Baha
et al. (2018).

Case studies

The following is a MMS record that describes how a wax buildup can contribute to a pro-
cess safety event.
Fire No. 87
Date: 15-Nov-2000 Operator: _____
Area: South Pelto Operation: Production
Remarks: Two operators noticed liquid falling from the still column on the glycol reboiler
and began to shut in the glycol reboiler when they noticed a small fire coming from the
flange on the glycol reboiler stack. The fire was extinguished immediately using a 30-lb fire
extinguisher and a firehose. There were no injuries or pollution. The investigation findings
showed that because of the well's paraffin content, the glycol contactor was contaminated
with condensate and paraffin from the high-pressure separator due to foaming. The paraffin
plugged the ceramic saddles in the still column of the reboiler causing the condensate in the
still column not to drain back into the reboiler. This caused condensate to escape through the
top of the still column onto the stack. The hot flange ignited the condensate.

Reservoir souring

Introduction
Reservoir souring introduces hydrogen sulfide into the produced fluid stream, which af-
fects the corrosion potential of the production system materials and may alter the equilibrium
of some flow assurance solids such as gas hydrates.