DYNAMICS OF PULSED SIGNALS IN A PIPELINE FILLED WITH A METHANE–VAPOR–DROPLET MIXTURE AND AFFECTED BY GAS–HYDRATE DEPOSITS

A study is made of the evolution of pulsed pressure perturbations in a pipeline fi lled with a gas–droplet medium, which represents "moist" methane at a below-dewpoint temperature, and having a portion in the form of an extended channel constriction. For this process, the authors have adopted a theoretical model of propagation of acoustic waves in the longwave range in the gas–droplet medium. The problem of propagation and refl ection of pulsed pressure perturbations in a horizontal pipeline having a portion of constriction because of hydrate deposits is solved by the method of fast Fourier transformation. Results of dispersion analysis of acoustic equations in a vapor–gas–droplet system are presented. Based on them, for real values of the parameters of pipelines, and also of the parameters of vapor–gas–droplet systems in them, the authors have obtained dependences of the phase velocity and the attenuation coeffi cient on the frequency of perturbation of an acoustic wave and the volume content of a suspended phase (water droplets). Also, an analysis has been made of the manifestation of viscosity and heat conduction in the wall pipeline layer saturated with water droplets. For the coeffi cients of refl ection and transmission of acoustic signals at the sites of constriction of the pipeline because of hydrate deposits, use has been made of the existing formulas. Results of numerical calculations have been presented, which illustrate the evolution of pulsed signals of varying duration and show the infl uence of the thickness of a gas–hydrate layer on the interior pipeline wall. It has been shown that growth in the thickness of the hydrate deposits on the wall and increase in the duration of the pulsed signal cause the amplitude of the returned signals (echo) to grow.
A study is made of the evolution of pulsed pressure perturbations in a pipeline fi lled with a gas–droplet medium, which represents "moist" methane at a below-dewpoint temperature, and having a portion in the form of an extended channel constriction. For this process, the authors have adopted a theoretical model of propagation of acoustic waves in the longwave range in the gas–droplet medium. The problem of propagation and refl ection of pulsed pressure perturbations in a horizontal pipeline having a portion of constriction because of hydrate deposits is solved by the method of fast Fourier transformation. Results of dispersion analysis of acoustic equations in a vapor–gas–droplet system are presented. Based on them, for real values of the parameters of pipelines, and also of the parameters of vapor–gas–droplet systems in them, the authors have obtained dependences of the phase velocity and the attenuation coeffi cient on the frequency of perturbation of an acoustic wave and the volume content of a suspended phase (water droplets). Also, an analysis has been made of the manifestation of viscosity and heat conduction in the wall pipeline layer saturated with water droplets. For the coeffi cients of refl ection and transmission of acoustic signals at the sites of constriction of the pipeline because of hydrate deposits, use has been made of the existing formulas. Results of numerical calculations have been presented, which illustrate the evolution of pulsed signals of varying duration and show the infl uence of the thickness of a gas–hydrate layer on the interior pipeline wall. It has been shown that growth in the thickness of the hydrate deposits on the wall and increase in the duration of the pulsed signal cause the amplitude of the returned signals (echo) to grow.
Author:  V. Sh. Shagapov, É. V. Galiakbarova, and Z. R. Khakimova
Keywords:  gas–droplet medium, hydrate plug, pressure pulse
Page:  678-685