BALANCED HEAT EXCHANGE OF OIL PIPELINE IN PERMAFROST CALCULATION AND THAWING HALO RADIUS DETERMINATION

Abstract

The article presents an analytical solution and formulas that allow carry- ing out practical calculations for determining thawing halo and thermal influence radii around an underground oil pipeline in permafrost. The problem is relevant, since calculations associated with thermal and mechanical interaction of the pipeline and permafrost are important in the design process. Determination of thawing halo radius around the pipeline is necessary in such calculations, since thermophysical state and characteristics of the soil within the thawing halo and the zone of ther- mal influence differ significantly from the characteristics of the frozen soil massif. Therefore, the calculation of heat exchange of the pipeline with the thawing frozen ground can be computed only if the condition of conjugation of the «internal» and «external» heat exchange problems solutions is fulfilled. The problem has been solved as conjugate for the case of isothermal oil transfer with a positive balance temperature exceeding the temperature of the enclosing frozen ground at the depth of the pipeline in undisturbed thermal state. The equivalent thermal conductivity model and the conjugation condi- tion on the pipe boundary in form of the heat balance equation made it possible to obtain a fairly simple solution. The formulas obtained make it possible to calculate the pipeline temperature schedule and determine the thawing halo and thermal influence radii in the enclosing frozen ground without recourse to the numerical methods. The example shows that the thawing halo can be limited, and the pro- gressive thawing of the enclosing soil can be minimized, either with or without pipeline thermal insulation. The use of thermal insulation extends the limit of applicability of the isothermal oil transfer method in permafrost.