The Compatibility Evaluating Of Polyolefin Tubular Product With Media Related To Oil And Gas Production

The polyolefin lined pipes with excellent corrosion resistance are widely used in the gathering and transportation field of Xinjiang oilfield.Especially,polyethylene materials with low cost,excellent performance and good processing quality are easier to get the favor of oilfield users.Polyethylene pipe used.in oil and gas gathering and transportation field in the application process is influenced by the synergistic effects of the temperature of the medium,the internal pressure of the tube,the types and the composition of the conveying medium.The lining material will appear aging phenomenon,the reliability of the pipeline operation is reduced and shorten the service life of the pipe.Scholars at home and abroad have already studied the compatibility of polyolefin materials and the oil and gas media that are in contact with them.The existing research results are mainly aimed at the mechanism of the performance degradation of the pipe in single liquid phase,and it does not involve the compatibility of many kinds of liquid phase mixing in the oilfield gathering process.The operation conditions of pipelines at the gathering site are very complicated,the compatibility experiment data of polyethylene materials are insufficient because,which is not conducive to the compatibility evaluation under the corresponding conditions.Therefore,through the compatibility test of the high density polyethylene dumbbell tensile specimen with the simulated oil and gas field medium containing a variety of liquid phase and gas phase,the compatibility evaluation model of polyolefin lining material is established by a variety of evaluation methods,and the various physical and chemical properties degradation law of the sample under this experimental condition is evaluated.It provides technical support for materials selection of oilfield.The main contents and conclusions are as follows:Four kinds of high density polyethylene（HDPE）samples were simulated in the autoclave at two experiment temperatures 60 and 70℃respectively.The liquid phase in the experimental medium included 0#diesel and 3.5%Sodium Chloride Solution.The total pressure of gas phase is 10MPa,including the CO₂ for simulating acid environment and the N₂ for regulating the total pressure.The experimental time are 240h,480h and 720h respectively.After each experiment time period,the change rate of mass and volume,mechanical properties（tensile property and shore hardness）,thermal properties（vicat softening temperature,dynamic OIT,crystallinity and melt flow rate）,tensile elongation fracture SEM,infrared spectrum,etc.were analyzed.The experimental results show that:in the whole experimental period of two experimental temperatures,the quality change rate,volume change rate and length change rate of the four kinds of samples showed an upward trend,and the change rate under the experimental temperature of 70℃was greater than the change rate of the experimental temperature at 60℃.In the first period,the change rate is about 90%of the change rate in the whole experiment period,and the increase in the last two periods is small.The extraction effect of the additive on the sample is also accompanied by the whole process.The mechanical properties of all the samples after 60℃test are much better than those of 70℃.The yield strength of the specimens are greatly influenced by the temperature.The modulus of elasticity decreases with the crystalline phase and the molecular weight reduced,and the elongation at break doesn’t change much.The crystallinity of samples shows that oil and gas medium can affect the movement of molecular chains,and occupy free volume,which hinders the free end activities of molecular chains.Temperature condition will aggravate the movement of chain ends and accelerate the decomposition of crystalline phases.The vicat softening temperature is affected by the decrease of crystallinity,and it decreases greatly in the first experimental period.The oxidation induction temperature test shows that the antioxidant capacity of the sample is greatly reduced after extraction.The increase of melt mass flow rate represents the decrease of molecular weight and more end groups exposure to oxygen molecules,which is more likely to occur oxidation reaction.FTIR analysis shows that the addition reaction and elimination reaction occur inside the molecular chain.The erosion mode of medium varies with temperature and time.