Study On The Effect Of Underground Coal Mining On Safety Of Oil And Gas Pipelines In Different Geological Environments

With the rapid development of China's oil and gas pipeline construction,more and more pipelines pass through existed and planning underground mine resources exploitation area,mostly coal mines.The mined-out area and surface deformation threat the safety of oil and gas pipelines.Different geological environments lead to different deformation and failure characteristics of surface,and then to buried oil and gas pipelines.However,the critical failure criterion of buried oil and gas pipelines in mined-out area in different geological environments is almost a blank.With China-Burma oil and gas pipeline in Guizhou section as the studied area,in order to explore the critical failure criterion,this paper studies the deformation,failure and safety of oil and gas pipelines in mined-out area in different geological environments.Based on the studies,the paper predicts and evaluates the safety of oil and gas pipelines through the five typical mining areas,and compared with numerical simulation results in order to provide basis for relevant norms.Based on engineering examples of oil and gas pipeline in the mined-out area,calculate the deformation and stress of the surface and pipeline with analytical method and numerical method,and contrast with monitoring results.The results show that numerical method results can show more effectually characteristics of pipelines deformation and stress than analytical method,then numerical method is chosen.Through analysis of 20 mines and its geological environment in Guizhou segment of China-Burma oil and gas pipeline,determine the main geological and mining factors effecting pipeline deformation and stress:terrain,ratio between mining depth and mining thickness,coal seam dip angle,fault and multi-seams mining.The geological environment can be divided into two categories and five subgroups.In gentle terrains environments and slope environment,establish ideal model to study the pipeline deformation and stress and the critical failure criterion in mined-out area changing single factors as ratio between mining depth and mining thickness,coal seam dip angle,fault and multi-seams mining-The results show that:in gentle terrains environments,when mining thickness is 4m,critical failure values of ratio between mining depth and mining thickness based on strain failure criterion and stress failure criterion are respectively 70,71,and critical failure values of coal seam dip angle are 55°,48°.In slope environment,critical failure values of ratio between mining depth and mining thickness based on strain failure criterion and stress failure criterion are respectively 72,74.When the surface tendency is consistent with coal seam,critical failure values of coal seam dip angle are 64°,51°.When the surface tendency is contrary to coal seam,critical failure values of coal seam dip angle are 43°,38°.Based on the critical failure criterion above,the paper predicts and evaluates the safety of oil and gas pipelines through the five typical mining areas,and compared with numerical simulation results.The results show that both results of Dishuiyan coal,Tiancheng coal,Jintian coal,Datianba coal are approximately similar,and the same conclusion is obtained that the pipeline is safe.The error of Laowuji coal is large,however the same conclusion is obtained that the pipeline may failure.So,the actual situation is closer to the ideal model,the error is smaller,and more reliant the conclusion is.