Study On Fiber Optic Monitoring Technology Of Oil Pipeline Deformation Induced By Geohazards

The safe transportation of oil and natural gas is the lifeline of national economic development and people's material life.Most of the oil pipeline projects in China are linear projects of super-long distance.The geographical span of the proj ects is large and the geological and climatic conditions of each geographical unit are complicated.The occurrence of geological disasters along the pipeline poses a severe threat to the safety of long-distance oil pipelines.Therefore,the monitoring of pipeline and geological disasters along the pipeline has always been a key research topic.Traditional pipeline monitoring technology is difficult to achieve long-distance,distributed,systematic,and real-time monitoring at the same time.In view of the characteristics and law of geohazards such as landslides along oil and gas pipelines,indoor pipeline model tests are designed by using the advanced fiber optic monitoring technology developed by the author's research group.The feasibility of the fiber optic monitoring technology and the performance of the sensors are verified.The pipe-soil interaction test is designed,and the law of coupling deformation between pipeline and soil is obtained.The fiber optic monitoring system and disaster analysis method for landslide along the pipeline are established.The fiber optic monitoring system for geohazards along oil and gas pipelines is established in combination with a practical engineering project.The pipeline safety is monitored and evaluated.The results obtained in this paper are summarized as follows:(1)The present research status of the pipeline body and geohazard monitoring technology along the pipeline is summarized.The advantages,disadvantages and applicable conditions of all kinds of monitoring methods are introduced.The types of geohazards along the pipeline and the characteristics of their destruction are summarized.The monitoring elements of pipeline and slope are analyzed.(2)The principle and characteristics of fiber Bragg grating(FBG)and Brillouin optical time domain reflection demodulation(BOTDA/R)are introduced.The fiber optic sensors for slope monitoring and pipeline monitoring are designed and developed.These sensors are:FBG earth pressure box,FBG string,FBG displacement meter,FBG thermometer,FBG stress meter,FBG anchor cable dynamometer,FBG inclination meter,FBG goniometer,0.9mm polyurethane sheathed cable,fixed-point cable,etc.(3)The key technology of optical fiber monitoring of pipeline deformation based on BOTDA and FBG is studied.The model test of PVC pipeline lateral deformation monitoring based on distributed optical fiber is carried out,and the feasibility of the distributed optical fiber in predicting the lateral deformation scale and the deformation direction of the pipeline is verified.(4)The four-point bending test of full-size oil pipeline is carried out.The influence of epoxy powder coating on the performance of the sensor is studied.The performance of the sensor with different encapsulation types is compared.The results show that for the surface strain gauge,in view of welding the gauge to the pipe surface,pipeline coating need to be polished.The FBG single point and FBG patch strain gauges can be directly deployed on the pipe and monitored without polishing.Take the traditional electric resistance strain gauge as a standard,the measurement accuracy of sensors in different encapsulation types is analyzed.It is found that FBG single point sensor and 0.9mm polyurethane sheathed cable perform well,and they are recommended to be used in practical engineering.(5)The model test of deformation monitoring of buried pipeline and soil mass is carried out.The results show that the distributed optical fiber monitoring system can depict the scope and time of landslide occurrence,the strain change of landslide body and its periphery,and the deformation of soil mass.The fiber optic earth pressure gauge can reflect the sliding direction of the slider according to the active and passive earth pressure,while the distributed optical cable and FBG displacement meter can reflect the strain and deflection of the pipe.Thus,these sensors form as a three-dimensional monitoring system and realizing the multi-parameter,comprehensive prediction of pipeline deformation and failure in landslide area,and the law of pipe-soil coupling deformation in the initial stage of landslide development.(6)A set of optical fiber monitoring system for slope stability along the pipeline is designed.In combination with the practical field project,the field construction sequence and monitoring software of the system are introduced.This monitoring system has the functions of monitoring landslide and pipeline deformation,and can realize remote automatic monitoring.The research results are of great significance to the safe operation of China's oil pipeline and the construction of'Belt and Road Initiative'.