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含蜡原油的屈服特性对管道停输再启动起主导性作用。目前,含蜡原油屈服应力大多利用实测的流变曲线,依据某判定条件确定。利用2台同为控制应力型但不同型号的流变仪开展实验,发现在测试的初始阶段,相同剪切加载条件下不同流变仪的实际响应特性(剪切率)不同,流变曲线差别较大;分析含蜡原油在2台流变仪下的屈服响应特性,发现其屈服应力、屈服应变差别较大,即含蜡原油屈服特性与流变仪加载后的实际响应特性密切相关。因此,含蜡原油屈服应力的确定需要考虑流变仪在测试过程中的实际加载条件。基于固体力学中材料强度极限的概念,将含蜡原油黏弹-触变模型中弹性应力的最大值定义为屈服应力。新提出的确定屈服应力的方法能够考虑流变仪在测试过程中的实际加载过程,物理意义也更加明确。
The yield characteristics of waxy crude oil plays a leading role in restarting the pipeline. At present, the yield stress of waxy crude oil mostly uses the measured rheological curve, and is determined according to certain judgment conditions. Two sets of rheometer with the same control stress but different types were used to carry out experiments. It was found that the actual response characteristics (shear rates) of different rheometers under the same shear loading conditions were different at the initial stage of the test, and the rheological curves differed It is found that the yield stress and yield strain of waxy crude oil vary greatly. That is, the yield characteristics of waxy crude oil are closely related to the actual response characteristics of the rheometer after loading. Therefore, the determination of the yield stress of waxy crude oil needs to take into account the actual loading conditions of the rheometer during the test. Based on the concept of material strength limit in solid mechanics, the maximum value of elastic stress in waxy crude oil viscoelastic-thixotropic model is defined as yield stress. The newly proposed method of determining yield stress can take into account the actual loading process of the rheometer during the testing process and the physical meaning is more explicit.