Summary
In the case of altering the pressure/volume/temperature properties of oil,
change of the aggregate state of oil is one of the main issues in oil
processing. When oil lifts to the surface, the most advantageous energy state
of high-weight components becomes the state in which a portion of the molecules
becomes solid. Phase-behavior diagrams could be plotted using a typical
compositional simulator, but even if one knows the phase behavior, one still
will not be able to understand the wax deposition in the tubing or pipeline and
will not forecast this process performance.
As some authors have mentioned, the resin and asphaltene concentrations in
the oil affect the wax-deposition velocity. Because of the high complexity of
the crystallization mechanism, the high-weight molecules are not taken into
consideration in a phase-behavior simulator. Thus, with the intent of
qualitatively characterizing the oil tendency to the aggregate, the oil from
different reservoirs has been compared.
Because of the temperature gradient between rock (permafrost) and oil, there
is a probability of wax deposition in the tubing. The deposition-growth model
makes different diffusion assumptions. The equilibrium model and the
film-mass-transfer model (as well as solidification and separation) have been
applied. Using these models, the wax-growth velocity and tubing-drift diameter
have been forecast.
As a result of the harsh northern environment, there is a serious risk of
oil solidification in the surface pipeline in the case of a pump stopping. On
the basis of the laboratory measurements and with the help of a stepwise
approximation, the oil-viscosity dependence on temperature has been derived. By
solving the heat-transfer equation (between oil in the pipeline and the
environment) and using nodal analysis, the maximum safety time in case of an
accident in the pipeline has been determined.
© 2012. Society of Petroleum Engineers
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History
- Original manuscript received:
15 March 2012
- Meeting paper published:
20 February 2012
- Manuscript approved:
20 April 2012
- Published online:
7 November 2012
- Version of record:
13 November 2012
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