Effect of instantaneous shut-in on well bore integrity and safety of gas wells

The instantaneous shut-in of the gas well produces a transient flow phenomenon. The repeated pressure amplitude and pressure repeated changes will cause the vibration of the tubing and equipment, resulting in damage to tubing and accessory equipment. However, it is difficult to directly adopt the conventional transient flow model due to the particularity environment of the gas well bore. Based on the classical transient flow theory and mechanism of transient flow process in a gas well, a mathematical model explaining the transient flow phenomenon of gas well is established and the method of characteristics is adopted for numerical solution. The calculation results of sample show that, after the wellhead valve is closed instantaneously, the surge pressure is transmitted and gradually attenuates under the influence of frictional resistance, and reaches the balance pressure after a period of time. With the increase of valve closure time, the maximum value of wellhead pressure is reduced, and the time of peak value occurs is also delayed. When the gas well is shut in for a short time, the propagation speed of pressure wave is faster than that in the circumstance of shutting the gas well in a longer time. The transient flow model can accurately reflect the value of surge pressure, the cycle of surge pressure and attenuation law of pressure wave, which has a high reference value for studying the transient process and pressure distribution in the gas well bore. © 2020