Study On Heat Transfer Of Diversion And Diversion Pipes In Jixi District, Xinjiang Oilfield

Crude oil ofJi-7districtin Xinjiang oilfield belongs to heavy oil. The oil was gathered together with pipeline and hot water was mixed at wellhead, then the gathered oil was pulled to joint station with oil truck. Hot water pipe and oil pipe were laid in one ditch and wrapped together with insulation. But there are also some problems in this oil gathering method. One of the problem is high Temperature drop of hot water pipeline, the maximum temperature drop of about1.5km hot water pipeline reached24℃, another problem is that calculation results and the actual results vary greatly, the error is14℃. So the purpose of this paper is to solve these two problems.Based on theory of heat transfer, mathematical models are established in three pipe laying conditions. The first condition is that hot water pipe and oil pipe were wrapped together with insulation. The second condition is that insulation of hot water pipe and oil pipe are set separately. Conformal mapping and temperature superposition theory are used to solve the first model. For the first pipe laying condition, analytical expressions include soil temperature field expression and total heat transfer coefficient expression and axial temperature drop expression are derived. The accuracy of the results is verified. Factors affecting heat transfer between two pipelines are analyzed. For the second condition, expressions of pipeline axial temperature is derived when radiation heat transfer between two pipelines are not considered. Network algorithm methods are used to calculate the radiation heat transfer between two pipelines. A computer program was written in the case of considering radiation heat transfer. The different of heat dissipation and pipeline final temperature were analyzed between two conditions that consider radiation heat transfer between pipelines or not. Temperatures along the pipelines are calculated under two conditions, and results are in contrast to the real data. Factors that affect the heat transfer between pipes were analyzed. Base on the summary of feature about the first condition and the second condition, the third condition that insulation of hot water pipe and oil pipe are set separately was proposed. Calculation method of the heat dissipation and pipeline final temperature of third condition was presented. Applicability of these three conditions on Xinjiang oilfield was analyzed.The results showed that the first model has a maximal absolute error0.58℃. As the insulation layer is thin, the thicker the insulation, the higher the final temperature of pipeline. When the insulation thickness exceeds30mm, increasing the insulation thickness has little effect on final temperature of pipeline. As the insulation layer thickness reach30mm, if increased the distance between the pipes, the temperature along pipeline would reduce in a lesser extent. As pipeline starting temperature improved, final temperature of itself would improved in a large extent, but it has little affect on another pipeline. The final temperature of pipeline has a linear relationship with soil temperature in the depth of pipeline location. When radiation heat transfer is considered in the first laying condition, both total heat dissipation of hot water pipe and heat absorption of oil gathering pipe increase. The ratio of radiation heat transfer and heat dissipation between hot water pipe and air space is9.8%, the value of oil gathering pipe is33%. The result of temperature along pipeline is more accurate when radiation heat transfer is considered. With the increasing of insulation thickness, the final temperatures of pipes improve. But the rate of improved temperature decrease. Final temperatures of hot water pipe and oil gathering pipe will be improved with increasing of hot water starting temperature. Every5℃of hot water starting temperature improved, it’s final temperature increase3.4℃, the value of hot oil pipe is0.7℃because of the increasing heat dissipation along pipeline. For the second pipe laying condition, total heat dissipation is the largest in three conditions, heat dissipation of hot water pipe is less. Heat dissipation of hot water pipe in the first condition is high significantly. For the third condition, both total heat dissipation and heat dissipation of hot water pipe is low. So the third condition should be selected as pipe laying method.