Forecasting the oil temperatures along the proposed China–Russia Crude Oil Pipeline using quasi 3-D transient heat conduction model

The China–Russia Crude Oil Pipeline (CRCOP) faces significant challenges due to differential frost heaving and thaw settlement resulting from significant variations of oil temperatures along the pipeline. Oil temperature distribution along the pipeline during the long-term operation period is a very important factor in pipeline foundation design under future climate warming and various frozen soil conditions. It is important for the assessment and prediction of differential frost heave and thaw settlement of the pipeline foundations soils, forecasting the development of the seasonal and inter-annual frozen and thawed cylinders around the operating pipeline, stress–strain analysis of the pipeline, and mitigation of subsequent frost hazards. A quasi three-dimensional computational model was developed to predict the oil temperature along the pipeline. It was verified by analytic solutions of the minimum oil temperatures along the route provided by the Daqing Oilfield Engineering (DOE) Co. The oil temperatures were predicted and analyzed for two proposed annual oil flow rates of 15 million tons (0.3 mbpd) and 30 million tons (0.6 mbpd) with and without mitigative measures (only pipe insulation was considered here) during the operation period. Also, the inter-annual variations of oil temperature at key typical locations were investigated to understand the impact of climate warming. The results indicated that the maximum oil temperature cools southwards, but the minimum oil temperature warms southwards (with the inlet oil temperatures from − 6 to +10 °C). However, the average annual oil temperature decreases southwards in the northern part of the pipeline, then it starts to slowly increase. The amplitudes of oil temperature change will decrease southwards. Oil temperatures will slightly increase with elapsing time due to the imposed boundary conditions of climate warming. The oil temperatures with a lower flow rate vary more significantly than that with a higher flow rate because the oil temperature with a low flow rate is more affected by the thermal regime of the surrounding soils and the external environments. Insulation around the pipeline tends to reduce the oil temperature variations along the pipeline during pipeline operation period. Therefore, pipe insulation can effectively reduce the development of frozen and thawed cylinders in the permafrost zone. The phase change of water in soils around the pipeline has a distinct influence on the oil temperature during the freeze–thaw transition periods. The oil temperature tends to be equal to the ambient ground temperature around the pipeline with southward distance and with elapsing operation time. The pipeline oil temperature is controlled by the incoming oil temperature and the surrounding ground temperature before the equalization. It would be mainly controlled by the ground temperature around the pipeline afterwards.