Acoustic Reflectometry For Blockages Detection In Pipeline
Authors: Vidal J.L.A. Edson , Silva Luciana , Netto Theodoro , Monteiro Paulo Camara Correia 
Published: June 2014

Flow assurance is an important aspect of offshore, particularly deepwater pipeline design and operation, since one of the critical issues is the eventual initiation and growth of hydrate or paraffin blockages under certain conditions. Ideally, operators would benefit from online information regarding position and extent of an eventual blockage in a pipeline. The aim of this work is to apply acoustic technology to design and make a prototype that can be used in a pipe to efficiently identify and measure blockages. The technique uses a short duration sound pulse that is injected into the pipe. When the acoustic pulse encounters an impedance discontinuity, a portion is reflected back towards the acoustic source and microphones or hydrophones. Analysis of the measured signal reflections can provide valuable data related to location and size of the blockages.

An experimental setup with a pipe of 4?? internal diameter and length of 95m was constructed, and different excitation signals for the impulsive response function measurements were conducted. Microphones and hydrophones measurements were recorded using a fit-for-purpose data acquisition system with sampling rates of up to 1kS/s per channel. The tests were performed in air and water using different sizes of blockages and in different positions in the pipe. In parallel, finite element analyses were performed using the commercial software Abaqus to simulate the same conditions. The experiments were numerically reproduced with good correlation proving the potential of the technique.

Introduction

Hydrate, paraffin wax and incrustation deposition in oil and gas transport pipelines are an important challenge for the development of deepwater environments. These types of deposition always occurs along the inner wall of the pipeline, which reduces the internal diameter and eventually results in the blockage [1,2]. During the service life, pipelines should not fail because such failures could lead to environmental, human, and economic costs. In this context, ?ow assurance is critical for deepwater projects in order to avoid pipeline blockages. Therefore detection and localization of the formation of blockages at its early stage is very important for remedial actions before catastrophic effects occur. In recent years, detection of blockage in pipelines has been an attractive area of research and several methods have been proposed [2,3]. The conventional methods for blockage detection include flow pressure monitoring detection, thermographic, radiographic methods, and others [2-5]. Flow pressure monitoring detection uses quick-acting valve to generate a water hammer and the the reflections produced by any blockage can be recorded. This method has its disadvantages, like the high transient pressure may cause considerable damage to the pipeline. Thermographic and radiographic methods typically require the use of a Remotely Operated Vehicle (ROV) and needs to be near the location and these methods are expensive and time-consuming operations.