| Some of China’s oil fields have entered the late stage of development,and low-temperature transportation technology has been tested and applied,but the corrosion of metal pipelines is relatively serious due to the high water cut.FRP pipes are widely used in oilfield for gathering and transportation of crude oil due to their excellent anti-corrosion properties.Therefore,it is important to study on low-temperature transportation of crude oil with high water cut using FRP pipes to further expand the scope of application of low-temperature transportation technology.The interfacial characteristics experiment was conducted by optical contact angle meter to investigate the influencing factors of the three-phase contact angle.The contact angle of crude oil on the solid surface decreased with the increase of temperature and increased with the increase of wax content in aqueous phase.The contact angle of crude oil on FRP surface was larger than that on stainless steel surface.And the interfacial tension of crude oil in aqueous phase decreased with the increase of temperature.According to the results of experiments,the adhesion effect of crude oil was analyzed.Compared to the stainless steel surface,the adhesion work of crude oil on the FRP surface was lower.The cohesion work between crude oil increased with decreasing temperature,which was the main reason that affecting the thickness of the adhesion layer on the pipe wall.The adhesion experiments of crude oil with high water cut were conducted using the stirred experimental apparatus,and the influencing factors of crude oil adhesion law were analyzed.The adhesion temperature decreased with the increase of water cut and shear rate,and increased with the increase of wax content when the comprehensive water cut was in the range of 70%～90%.The adhesion temperature was independent of the pipe material,and the properties of pipe only affected the quality of crude oil adhering to the wall of pipe.A discriminant formula of adhesion temperature for crude oil with high water cut of FRP pipe was proposed according to the results of indoor experiments,and the error of calculation results was within 2 °C.Experiments on the heat transfer characteristics of different pipes with high water cut crude oil were carried out using an indoor flow loop device to investigate the variation of pressure and heat transfer performance of FRP and stainless steel pipes in the low-temperature transportation.During the cooling process,the pressure drop in the test section of FRP pipe was slightly lower than that in the test section of stainless steel pipe.Considering the influence of the adhesion layer and the thermal conductivity of the pipe,the thermal insulation performance of FRP pipe was better when the transportation temperature was higher than the adhesion temperature.And hence,it was believe that FRP pipeline was more suitable for the low-temperature gathering and transportation.The FRP gathering pipelines were selected for cooling transportation tests in field to verify the reliability of the adhesion experiment for crude oil with high water cut.After the cooling transportation in field,the inlet temperature of 1#～3# crude oil single well gathering line was reduced by 7℃,15℃ and 6℃ respectively,and all of which were reduced to the vicinity of adhesion temperature.The FRP gathering pipelines with high water cut can transport safely and stably when transportation temperature is located at adhesion temperature and above. |
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