The natural gas industry has been under constant pressure to provide public safety and reduce the amount of methane released to the atmosphere as a greenhouse gas (GHG) emission. This involves the entire natural gas supply chain from the wellhead to the burner tip or from upstream, exploration and production to midstream, gathering, storage and transmission to downstream distribution operations.
The industry not only faces continued regulations from the federal Pipeline and Hazardous Materials Safety Administration (PHMSA) and respective state pipeline safety regulatory agencies, but also from federal and state Environmental Protection Agencies (EPA).
The industry has come a long way since the early days of using both portable and mobile flame-ionization (FID) leak detection technology, which used a blend of hydrogen and nitrogen fuel in a detector to walk or drive over natural gas piping networks. These devices required a considerable amount of maintenance along with external bottles of calibration gases.
The key to reducing methane emissions from both above and below ground facilities is regular leak detection inspections, which can be accomplished using fixed gas detection, vehicle-based technologies and portable instrumentation. The industry is seeing the advent of aerial based technologies from satellite, fixed wing aircraft, helicopter and unmanned aerial vehicles (UAV) or drones. We call this the “layered” approach to leak detection where several layers of protection can detect, localize and pinpoint leak locations for repair.
There is not a single technology for leak detection, but a multitude based on the asset location, application and desired result. Most devices detect methane, which is the major component of natural gas and the primary contributor to climate change as a GHG emission. All these technologies’ data can be captured in a software application for federal and state reporting, as well as follow-up repair. Data can involve GPS coordinates of piping networks that were leak surveyed for verification with date and time stamps, leak locations, leak grading, leak quantification and instrument calibration for permanent record keeping. We also know that a mercaptan or sulfide can be added to natural gas as an odorant for the public to detect via their sense of smell for a potential leak indication, but this is primarily used in distribution assets and not common in transmission or gas gathering. The technologies discussed below detect the methane in natural gas and not the added odorant.
Fixed Gas Detectors
Fixed gas detectors based on open path tunable diode laser absorption spectroscopy (TDLAS) technology monitor facilities 24/7 for methane emissions. This technology is typically used at well sites, underground storage, gate stations and high consequence (HCA) pipeline locations. There are several deployed technologies from open-path lasers to point sensors for the continuous monitoring of assets for leak indications. These technologies do not pinpoint exact locations but can give a generalized location for follow-up with portable technology.
Advanced Mobile Leak Detection
Advanced Mobile Leak Detection (AMLD) using open path TDLAS technology for detection of natural gas leakage on gathering, transmission and distribution pipelines. This technology can detect both methane and ethane separately in parts-per-billion (ppb). This allows the operator to differentiate pipeline leaks from natural occurring biogenic, swamp, marsh, decomposition or sewer gas. Vehicles equipped with AMLD can travel much faster and allow more frequent coverage of assets for both public safety and continued reduction of emissions. These systems have very elaborate software packages to analyze detections based on indications, wind direction, GIS location, leak quantification and center the indication for follow-up investigation and pinpointing by “boots on the ground” teams.
Mobile leakage detection using optical infrared controlled interference polarization spectroscopy (CIPS) gas detection with pump drawn sampling for surveying underground gathering, transmission and distribution piping networks, can detect methane in parts-per-million (ppm). This technology can be installed on offroad vehicles for easy access to difficult asset locations. The same technology can be easily removed from the vehicle for portable applications of localizing the leak and doing subsurface bar-hole readings for leak pinpointing and grading with the ability to determine lower explosive limit (LEL) and percent gas readings. It is critical to have a single device to detect ppm, LEL and volume gas percentage all in a quick auto-ranging response for leak centering, leak pinpointing and leak grading. These devices have replaced the earlier FID technology as the primary tool for surface sampling leak surveys for regulatory compliance.
Portable Remote Detectors
Another technology is portable standoff remote TDLAS open path detectors for detecting methane leaks in ppm up to 100 ft away. These are commonly used in natural gas operations wellhead to the burner tip for quick scanning of pipeline assets for leak localization. This innovative tool allows the operator to scan assets when the physical location is approximate, and the venting of the leak could be some distance from the pipeline. It is also extremely useful when assets are in exceedingly difficult to reach areas such as busy highways, bridge crossings or areas surrounded by security fences. The technology uses an eye-safe invisible laser to scan asset locations rapidly and is extremely sensitive to find the smallest leak indications.
Unmanned Aerial Vehicles
Unmanned aerial vehicles (UAVs) or drone applications using downward looking open path TDLAS technology can be used during natural disasters and inaccessible areas with rugged terrain or for rapid inspection. Similar technology also can be deployed on both fixed wing aircraft and helicopters to patrol pipeline right of way (ROW) as instrumented surveys verses just flying pipelines for visible indications.
Natural Gas Detectors (NGD) using non-dispersive infrared (NDIR) technology are designed for indoor residential and commercial application with 24/7 communication back to the utility via automated meter infrastructure (AMI) and designed to give the public both verbal and audible notifications of imminent danger due to a natural gas leak.
This is a quick overview of the common leak detection technologies used today in the natural gas industry to detect, localize and pinpoint natural gas leaks. The layered approach offers several technologies to detect methane not only to provide public safety from a potentially catastrophic event but also to prevent the release of GHG to the atmosphere.