A novel DdTS technology based on fiber optics for early leak detection in pipelines

Abstract

Leaks in pipelines transporting oil, gas, or any tluid may cause enormous propern and environmental damage, hence early leak detection and accurate localization are highly desirable. Sensors to detect leaks can be broadly classified into internal and external sensors depending on where they are installed. In general, internal sensors have matured over decades while external sensors based on fiber optics are just beginning to show promise for early and precise leak detection. In this work, a novel technology DdTS (Distributed Differential Temperature Sensor) is developed that can almost instantaneously detect differential temperature in the optical fiber of as little as 0.0005 C with a location accuracy of several meters. The temperature sensitivity is several orders of magnitude higher than other Brillouin or Raman based distributed temperature sensors based on fiber optics in the market. The technology utilizes standard optical fibers installed adjacent to a pipeline and can be retrofitted to a preexisting cable in most cases. In addition to detecting differential temperature, the DdTS technology also uses acoustic signatures to detect leaks, which is effective in cases where the fluid temperature closely matches that of the background soil. The DdTS technology is based on an enhanced version of Coherent Optical Time-Domain Reflectometry (C-OTDR) and can measure not only the quasi-static changes, such as temperature or strain, but also dynamic acoustic signals in the fiber. Experimental results for gas leaks from a simulated buried pipeline are discussed for different vertical and horizontal offsets, gas pressures, leak-hole sizes, and orifice acoustic signals. Experimental data simulating a liquid leak are also discussed. All experiments confirmed the theoretical capabilities of the DdTS sensor.