Research On The Blocking Law Of Natural Gas Hydrate In Intermittent Operation Pipeline

In recent years,with the rapid development of economy of our country,the demand for natural gas increases year by year,and the scale of development and utilization of natural gas is getting larger and larger.However,the barrier of gas hydrate flow in the process of pipeline gathering and transportation has become one of the key factors influencing the efficient development of oil and gas resources.During intermittent pipeline transportation,when certain temperature and pressure conditions are reached,natural gas and free water precipitated by gas phase combine to form hydrate particles and deposit on the pipe wall,forming the risk of hydrate blockage and affecting the normal pipeline transportation.Therefore,the formation,deposition and decomposition mechanism of hydrate and the blockage law of hydrate deposition were studied and analyzed in this paper.The main research contents and results are as follows:(1)Investigate the current development status of gas hydrate generation prediction model,compare empirical correlation formula and thermodynamic model with experimental data,and finally select the Chen-Guo model with high accuracy as the hydrate phase balance model of intermittent pipeline.(2)Considering the thermal insulation effect caused by hydrate deposits in the pipeline and the change of gas phase flow parameters,the transient temperature and pressure models of intermittent gas pipelines under different operating conditions were established,and linearization was adopted to speed up the solution process.A transient temperature and pressure model solving program was developed based on python language,and the reliability of the model was verified by comparing with the simulation results of OLGA software.Combined with the phase balance curve of hydrate,the prediction model of hydrate formation region in intermittent gas pipeline was established.(3)Considering the hydrate formation,deposition and decomposition characteristics of the pipeline under different operating conditions,a quantitative prediction model of hydrate deposition and blockage of the intermittent gas pipeline was established by using the prediction model of hydrate formation,deposition and decomposition rate under the gasdominated system,and the accuracy of the model was verified by corresponding experimental data.(4)Considering the hydrate generation area and blockage prediction model of intermittent pipeline comprehensively,the comprehensive model is solved numerically to analyze the blockage law of gas hydrate deposition under different operating conditions of intermittent gas pipeline.The results show that the hydrate deposits along the pipeline present obvious uneven distribution,and the thickness of the hydrate deposits in the pipeline varies greatly under different operating conditions.The decrease of inlet flow and temperature and the increase of outlet pressure can effectively reduce the risk of hydrate plugging.At the same time,based on the blockage of hydrate deposition under the change of different factors,the corresponding optimization of intermittent pipeline transmission parameters and hydrate prevention measures is proposed,which provides a favorable reference for the selection of hydrate blockage prevention methods and process design during the intermittent operation of pipelines.