Analysis On The Problem Of Hydro-acoustic Detection Method Of Submarine Pipeline

Because of the complexity and particularity of the ocean environment, the safety of subsea oil and gas pipeline itself suffers great challenge in process of offshore oil and gas transport, especially after exposing, even suspending, it will be failure easily. in order to gain the occurrence state of the pipeline, to determine its depth, length of exposure, the span height and other information during submarine pipeline inspection, many with high frequency sub-bottom profiler and side scan sonar and other acoustic detection equipment is always first choice.After the arrangement of the pipeline routing survey data then, it is realized that under the interference of seabed topology, working environment conditions and the multiplicity of sonar detection data of, often lead to pipeline state misjudgment, as the buried status of pipeline discrimination when use sub-bottom profiler, also there are difficulties in determining suspension section height and length when analysis the sonar data.According to the above problems, this paper use forward modeling of geophysical detection method and analysis the typical submarine pipeline acoustic data, generate accurate synthetic seismogram of the "pipeline and seabed pits" coexistence of submarine slope and pit geological model, and compare to actual detection image, results show that the detection data of the special terrain does not reflect the true state of pipeline, and combined with the evolution trend of seafloor topography and geomorphology, to analysis geological factors affecting the state of pipeline.The main achievements of this paper are as follows:(1) When the submarine pipeline is located at slope, pit and such inclined formation, migration of sub-bottom profiler detection of reflection interface in the image often confuse interface of pipeline-top and seabed position, lead to artifacts of suspended span of the pipeline is buried below seabed; migration of the sub-bottom profiler detection data by Kirchhoff integral migration method is an effective method, which can restore the seabed terrain and eliminate interpretation pitfalls.(2) To detect underwater pipeline at the slope with side scan sonar, pipeline acoustic shadow in shallow water side is significantly narrower than the deep side, leads to the pipeline span height is compressed at shallow water side while amplified at the deep side, cause interference judgment of span height, based on geometry of sonar detect to correct spanning height with the method of numerical deduction. When detect pipe in the trench with Side scan sonar, due to recognition of overlapping of trench slope and tube-trench feature, the actual pipeline state is difficult to obtain, it is advised to use the beam control of multi beam and accurate measuring equipment to detect pipeline state if the adjustment of sonar beam incident angles fails.(3) The pipe fulcrum position gradually moving towards two ends because of the soil strength decreases at the tube cross supports, and the soil buried in the pipe across a range of endpoint does not change magnificently in short term, so that the actual position is difficult to obtain through the side scan sonar, the span length displayed as in sonar image is shorter than the actual length. The span length obtained with sonar directly used for safety assessment of submarine pipeline may exist risk.(4) In the complex ocean environment in estuarine and coastal area, state of submarine pipeline is mainly controlled by the topography long term evolution trend in routing area and short-term seasonal adjustment. Such as the active sand wave migration, seabed dynamic change caused by seasonal storm erosion, non-uniform erosion caused by the seabed sediment difference, mass movement and so on destruct seabed stability and the safety of the pipeline operation.It is suggested to take corresponding measures in collecting data in field and post processing stage to identify the authenticity of the data and avoid detection image multi solution problem with traditional acoustic detection equipment when detect submarine pipelines, not only can improve the accuracy of interpretation in the state of pipeline for engineers, and obviously reduce the workload and operation cost in field.