| Because the shale bonding strength of Sebei gas field is low, the serious phenomenon of sand production from gas wells in the extraction process has appeared. The sand will enter the gathering and transportation pipelines of Sebei gas field with natural gas, and make the pipe fittings suffer from serious problem of erosion. It will affect normal production, cause leakage of pipe wall surface, and even result in relevant safety accidents. To this problem, the erosion properties of different pipe fittings in Sebei gas field were simulated, with considering the ranges of parameters such as entrance velocity, sand diameter and sand mass flow. Targeted erosion-resistance measures from different aspects were proposed and compared. According to the comparison results, the erosion protection effect, erosion failure mechanism, and erosion-resistance property of SiC brittle coating were analyzed when it is applied to the gathering pipe fittings of Sebei gas field. The specific research contents are as follows:(1) In order to establish the mathematical model of simulating erosion property of pipe fittings, the gas phase flow field was calculated by Euler method, and the sand trajectory was tracked by Lagrange method on the basis of gas-solid two phase flow theory. In addition, the gas-solid two phase flow theory and erosion theory of plastic material were combined to finish the establishment of mathematical model.(2) To the erosion problem of pipe fittings in Sebei gas field, the types of pipe fittings were fixed, then the ranges of parameters such as entrance velocity, sand diameter and sand mass flow were also defined. To some gathering pipelines in one exploitation unit, based on the mathematical model above, the maximum erosion rate of pipe fittings in the pipelines was simulated, including elbow, T-shaped tee and ball valve. In addition, the erosion properties of three pipe fittings, including the erosion concentration area and erosion rate, were analyzed by researching the gas phase flow field and sand trajectory in the pipe fittings. The influence rules of pipe fittings structure and working condition on erosion property were also further analyzed. The three kinds of erosion-resistance measures were compared. According to the comparison result, it was concluded that the spraying erosion-resistance coating is the most widely used erosion protection method in the engineering, and it can be applied to pipe fittings of Sebei gas field.(3) In order to optimize the erosion-resistance coating whose erosion protection effect is relatively the best, the characteristics and applicability of three kinds of erosion-resistance coating were compared, including organic material, plastic material and brittle material. By comparison, the brittle erosion-resistance coating was taken as the erosion protection material in pipe fittings of Sebei gas field. In order to evaluate the erosion protection effect of brittle coating, the explicit dynamic model, nonlinear constitutive model for brittle materials, and material failure criteria were combined to establish the mathematical model, which can simulate dynamic process of sand impacting brittle coating.(4) For analyzing the application effect and erosion-resistance property of brittle coating, the relevant parameters of SiC brittle coating and gathering pipe in Sebei gas field were fixed. In addition, the physical model of multi particles impacting coating/pipe partial target plate was established, and the dynamic simulation of the erosion process was then carried out. The erosion protection effect and erosion failure mechanism of SiC brittle coating were analyzed, when it is applied to the gathering pipe fittings of Sebei gas field. And the influence rules of other factors on the erosion-resistance property of brittle coating were also further analyzed by figuring the number of failure units of brittle coating. The research results can provide theoretical basis for the practical application of brittle coating in Sebei gas field. |
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