Leakage detection on multiphase flow pipelines

Leak detection on pipelines has always been an important issue, strengthened lately due to the increasingly concern related to environmental preservation. Still regarding to this subject, an area of extreme importance for the world environmental health is the Amazon Rain Forest. Add the above mentioned two topics to the existence of crude oil production fields in that forest, and it is easy to conclude the importance of avoiding accidents with oil spillages in such a sensitive area. To make things worse, production pipelines do not always behave in a predictable way, presenting most of the times a multiphase flow. Multiphase flow is one of the most difficult situations for leak detection in pipelines, due to several reasons: the existence of two or more different and independent phases, variation of each phase's volume along the pipeline, different fluid velocities for each phase, and sometimes a non-Newtonian associated behavior, due to the formation of an oil-water emulsion. Basically, there are two main groups for leak detection techniques: the models (or CPM, as stated in [API 1130]) which monitor the flow in real time (RTM, RTTM, PPA, etc.) from inside the pipeline (the instrument sensor is actually in physical contact with the fluid), and try to model the flow using a state estimator; and those based on dedicated external sensors (thermal, mass dispersion, etc) along the pipeline. The vast majority of the technologies at the first group is based on volumetric flow rate measurements, which are quite ineffective for multiphase flow. It is also important to mention that the flow pattern in some multiphase pipelines, changes quite random and intensively, from tiny bubbles to a severe slug pattern. This brings unpredictability to those lines, if compared to a regular single-phase line. Consequently, systems based on prediction models tend to be unreliable, inaccurate and not sensitive. The acoustic system is an exception to those two groups of technologies previously mentioned. It has, on one hand, a sensor that really touches the fluid (which would suggest it to be within the first group), but there's no flow model behind it, on the other hand, but an acoustic sign analysis algorithm, acting somewhat like a piece of hardware. The scope of this paper is to present and discuss the adopted solution to monitor and avoid oil spillages from a multiphase pipeline applying an acoustic leak detection system, installed in a pipeline located in the middle of the Amazon Rain Forest in Brazil, managed by PETROBRAS Production & Exploration Department.