Investigation on propagation characteristics of the pressure wave in gas flow through pipes and its application in gas drilling

• We develop a model estimating pressure wave propagation characteristics in gas pipes.
• Experiments are conducted to validate the proposed analytical model.
• The effects of operating parameters on pressure wave propagation are analyzed.
• We propose an early detection method of unexpected gas influxes in gas drilling.

This paper aimed to investigate propagation characteristics of the pressure wave in gas flow through pipes and the potential application of the pressure wave propagation theory in the early detection of gas influxes due to encountering gas-bearing fractures in gas drilling. In this work, a simpler and reliable analytical model characterizing the propagation and attenuation of the pressure wave in gas flow through pipes with the effects of wall shear stress and viscous dissipation was proposed by performing the perturbation method, and the model was validated against experimental results. A parametric study was also performed, and the results indicate that the static pressure, angular frequency, gas mass flow rate and temperature have obvious influences on the propagation characteristics. In general, the factors above have more serious effects on the attenuation factor than the wave speed. Lower angular frequency, gas flow rate, temperature and higher static pressure tend to reduce the attenuation of the pressure wave traveling in the pipes. Based on observed characteristics of the pressure wave, a rapid and reliable technique was proposed for the early detection of the unexpected gas influxes induced by encountering gas-bearing fractures in gas drilling. The concern about the proposed detection method stems from the fact that the speed of the pressure wave propagating in drill strings is much higher than that of the produced gas travels in the annulus. Field test results indicate that the technique has a shorter detection time than traditional methods.