Implementation of an Acoustic Automatic Leak-Detection Sonar in the Gulf of Mexico
Authors: Carpenter Chris 
Published: January 2017

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper OTC 26270, “A Case Study on the Implementation of an Acoustic Automatic Leak-Detection Sonar (ALDS) in the Gulf of Mexico and Its Application to Current and Future Brazilian Fields,” by G. Brown, S. Fasham, P. Tomlinson, and R. Crook, Sonardyne, prepared for the 2015 Offshore Technology Conference Brasil, Rio de Janeiro, 27–29 October. The paper has not been peer reviewed.

The authors have developed an active acoustic automatic leak-detection sonar (ALDS) designed to detect hydrocarbon leaks (mono- and multiphase oil and gas) at significant ranges, allowing coverage of wide areas from a single sensor. The system’s single subsea sensor offers 360° continuous coverage, providing automatic, robust detection and localization of any leak, followed by an alert within tens of seconds of a leak developing. This paper provides a case study of an experimental program in which the system underwent trials in deep water (2000 m) at the Thunderhorse field in the US Gulf of Mexico (GOM).

Introduction

Most methods for detecting small leaks— for example, passive acoustic detectors that “listen” for the sound of a leak— have very limited range, which makes them suitable for applications such as pipeline surveys but not for wider field coverage. ALDS was developed to address the requirements for a system that can provide leak detection, including the ability to localize the leak, from a single point for a whole drill center. The typical requirements for such a system include

Continuous and automatic detection and localization of oil and gas leaks across a drill center in both cluttered and uncluttered seabed regions with full 360° coverage

Automatic elimination of transient acoustic targets to ensure low false-alarm rates

Alarm on leaks within a few minutes of their initiation

Ensuring that the system is reliable, networkable, compatible with subsea power-distribution requirements, and deployable across the full depth range of producing oil fields (4000 m)

Principles of Operation

The system is an active sonar that transmits ultrasonic pulses or “pings” at 70 kHz into the water and listens for reflections from objects within its field of view. This system is a phased-array processor capable of looking at returns from 360° of azimuth coverage simultaneously.

Hydrocarbons have different acoustic properties from the surrounding seawater, notably a different acoustic impedance, which means that a sound wave encountering the boundary between seawater and hydrocarbon will be partially reflected and therefore “seen” by the sonar head. To determine if a reflection is from leaking hydrocarbons, the sonar map for each ping is compared with a reference map to see if the scene has changed. Data processing is then used to assess any changes from the reference map to see if they match the characteristics of a hydrocarbon leak or those of other objects such as remotely operated vehicles (ROVs), which might be operating within the ALDS field of view.