关键词: 高压气井, 完井管柱, 流固耦合模型, 特征线, 瞬变流

Abstract:

Transient pressure fluctuations in a liquid-filled pipe could induce coupled oscillations of pipe structures, even a structural failure if severe. The present paper elaborated the coupled oscillation process of completion string induced by transient flow of natural gas, and a fluid-solid coupled oscillation four-equation model applicable to completion string in gas wells was derived based on the fluid-solid coupled oscillation model for liquid-filled pipes. The model was numerically solved by the characteristic method and linear interpolation. Taking a transient flow caused instantaneously by opening the valve of a high-pressure gas well as an example, a corresponding software, combined with initial and boundary conditions, was programmed with the MATLAB code, which could calculate and analyze the process in response to coupled oscillations derived from fluid and pipe string. The calculation indicated that the transient flow of natural gas could induce an axial reciprocation of completion string by the Poisson coupling effect, which would aggravate the structural damage of completion string via stress fatigue and rubbing abrasion. This result is, to some extent, of engineering significance in preventing completion string of high-pressure gas wells from pre-failure.

Key words: high-pressure gas well, completion string, fluid-solid coupled model, characteristic line, transient flow