| 摘要 |
A method of obtaining rheological data for a waxy fluid in a shut-in pipeline, the method comprising:
(A) creating a model of shrinkage flow in a shut-in pipeline by:
a) (i) determining the length and internal diameter of the pipeline, and (ii) obtaining a topographic relief map of the pipeline that identifies critical waypoints and entering the horizontal and vertical coordinates of these waypoints (relative to a selected low point) as model loci thereby creating a plurality of pipeline sub-sections;
b) calculating the hydrostatic pressure change across each pipeline sub-section;
c) determining the temperature profiles for a plurality of parameters of the waxy fluid over a temperature range typical of the temperatures encountered in the shut-in pipeline wherein the parameters include the density, shear stress, shear strain rate and vapour pressure of the waxy fluid;
d) entering a temperature change into the model for each pipeline subsection for a selected cooling time interval;
e) by reference to the density temperature profile, calculating the mean temperature in each pipeline sub-section, the volume change in each pipeline sub-section, and the resulting shrinkage flow rate in each pipeline sub-section;
f) by reference to the shrinkage flow rate in each pipeline subsection, the mean temperature in each pipeline sub-section, and the shear stress/shear strain rate temperature profile, calculating the wall shear strain rate in each sub-section, the shear viscosity in each sub-section and the pressure difference across each sub-section that is required to maintain shrinkage flow;
g) subtracting the required pressure difference across each sub-section from any existing pressure difference arising from a hydrostatic head and generating a pipeline pressure profile from the resultant pressure differences for the pipeline sub-sections;
h) if the line pressure at any locus fall below the vapour pressure of the waxy fluid at the locus temperature, a void is presumed to form at the locus and the fluid body in
i) the pipeline is divided at that locus; and
j) repeating steps (d) to (h) for a further cooling time interval; and
(B) using the model of shrinkage flow to (i) determine the distribution of any void spaces along the pipeline for the cooling time interval that the pipeline has been shut in; and, (ii) to obtain rheological data for the waxy fluid in each pipeline sub-section for the cooling time interval that the pipeline has been shut-in.
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