Summary
Paraffin deposition is a very complex phenomenon. Whenever paraffinic oil
comes in contact with a cold pipe wall, that is below the wax appearance
temperature (WAT) of the oil, solid paraffin crystals can precipitate and
deposit on the pipe surface. This may significantly reduce or even block the
area open to flow.
Most oil fields produce water along with the oil, and the deposition process
is not well understood for oil/water flow conditions. Very few studies have
been conducted to investigate the effect of water on the deposition
process.
The objective of this study is to investigate paraffin deposition under
different oil/water conditions. The tests were conducted using a cold-finger
device and a crude oil from the Gulf of Mexico. Emulsions were created with
both fresh water and brine. A simple oil/water wax-deposition model was
developed by modifying the current University of Tulsa single-phase deposition
model for solubility and physical properties of the mixture as a function of
water content.
Introduction
Transportation of paraffinic oil in an environment that is below its WAT or
cloud point can result in deposition of solid wax particles on the pipe wall.
The deposit will decrease the area of the pipe open to flow or block it
completely. It is essential to have a better understanding of the
paraffin-precipitation and deposition processes, since problems related to
deposition of paraffin during production and transportation of crude oil can
cause significant financial losses through prevention and remediation costs,
which increase as oil production moves into deeper water.
Most oil fields produce water along with the oil. The paraffin-deposition
process is not well understood for oil/water-flow conditions. Very few studies
have been conducted to investigate the effect of fresh water or brine on the
deposition process. This is because of the higher complexity of the problem
with the addition of the water phase and the difficulty in obtaining consistent
results with oil/water mixtures. Hsu et. al. (1994) conducted
high-pressure-flow-loop experiments with waxy crude oils to study the effect of
water on paraffin deposition under turbulent-flow conditions. The results
showed that wax deposition was significantly reduced with the addition of
water. Cole and Jessen (1960) conducted a series of laboratory experiments in
laminar conditions using a deposition cell consisting of a cold plate through
which the oil/water solution could flow and where the paraffin deposition would
occur. The study included the effect of wettability characteristics of the pipe
wall on paraffin deposition. The wettability of the deposition surface was
altered through the use of various substances. The results showed that, with
the presence of water, paraffin deposition on the more-water-wet surface was
significantly reduced, while no difference in deposition was found for the
oil-wet surfaces.
In this study, paraffin deposition for oil/water-mixtures conditions was
investigated using a cold-finger device and a crude oil from the Gulf of
Mexico. Oil/water paraffin-deposition tests have been conducted with both fresh
water and brine for various temperature gradients, deposition periods, and
emulsion characteristics. Single-phase tests have also been conducted to serve
as a baseline for the oil/water tests.
The TUWAX single-phase paraffin-deposition model has been modified to
accommodate the oil/water mixtures. Oil and water phase are assumed to be well
mixed, with no free water or free oil.
© 2008. Society of Petroleum Engineers
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History
- Original manuscript received:
16 May 2006
- Meeting paper published:
1 May 2006
- Revised manuscript received:
9 May 2007
- Manuscript approved:
1 June 2007
- Version of record:
20 February 2008
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