(75h) The Influence of Nanocomposite Pour Point Depressant on Wax Deposition of Waxy Oil

The Influence of Nanocomposite Pour Point Depressant on Wax
Deposition of Waxy Oil

ABSTRACT: line-height:200%;font-family:" times new roman>

With
the advancement of deep-water oil and gas energy strategy, the flow assurance
problem of various solid depositions in pipelines is becoming more severe as
the heavy hydrocarbons produced from the offshore fields accompanied with
sharply variable temperature of outflow environment. The nanocomposite pour
point depressant (NPPD), which is developed by blending of nanocompostie and
polymers, has been introduced to improve the fluidity of waxy oil and aroused
tremendous attention. The modification effect of NPPD on the rheological of
waxy oil and its interaction mechanism are widely investigated, however, the
influence of NPPD on wax deposition process is not further discussed.

In
this work, a new NPPD was synthesized based on the melt blending of organically
modified nano-montmorillonite and ethylene/vinyl acetate copolymers. The high
temperature gas chromatography (HTGC), cold finger and flow loop were chosen to
investigate the variation of line-height:150%;font-family:" times new roman>carbon number
distribution font-family:" times new roman> and thickness of the wax deposition
layer before and after NPPD modification. The crystal morphology and rheological
behavior of undoped/doped waxy oil were characterized by polarizing microscope
(POM) and rheometer. Based on the macro and micro results, the interaction
mechanisms between NPPD and wax molecules were discussed systematically, which
provided a better understanding of the effect of NPPD on wax deposition of waxy
oil.

As
is shown in Figure 1(A), for undoped system, with the increase of deposition
time, the heavy component wax content (carbon number>=C31) of sediment progressively
increases and the peak of chromatogram moves to higher carbon number. After addition
of NPPD (50 mg/kg), this trend is enhanced obviously (Figure 1(B)), where the
content of heavy component wax is almost twice larger than undoped system. Comparing
the absolute mass of individual carbon number components, it is found that the
deposits of doped waxy oil tend to have more high carbon number components (>=C33)
than undoped waxy oil deposits (Figure 1(C)). The results of macroscopic
rheology further inferred that the decrease of the bulk viscosity after NPPD
modification facilitates the diffusion and deposition of wax molecules (Fick law),
which is benefit to the deposition of higher wax fraction (>=C33). Furthermore, the
loop experiments of undoped/doped waxy oil under laminar flow and turbulent
flow indicates that the wax deposition thickness is decreased after addition of
NPPD. However, it is noticed that the deposit thickness-time curves are
almost overlapping at range of 100 to 200 mg/kg NPPD in the turbulent
flow state (Figure 1D). The observation results from POM exhibit that wax
crystal morphology of waxy oil is sensitive to the dosage of NPPD, which varies
from 0.025mm (0 mg/kg) to 0.012mm (200 mg/kg). A plausible explanation for
these results is that the introduction of NPPD which provides a nucleation
template for wax crystal and modifies the morphology of crystal morphology,
resulting in weaken of three-dimension network of wax crystals and decrease the
deposition thickness layer. These conclusions provide a comprehensive theory
analysis for the application of NPPD and the technology of flow assurance in
waxy oil pipelines.

12.0pt;font-family:" times new roman>Figure 1.  The
carbon number proportion of undoped waxy oil in cold finger experiment (A); the
carbon number proportion of doped waxy oil (50 mg/kg NPPD) in cold finger experiment (B); the absolute wax content of
deposition layer in cold finger (C); the thickness of deposition layer in flow
loop under turbulent (D).

Keywords:
font-family:" times new roman>Flow assurance; Wax deposition; Waxy
oil; NPPD