Monitoring Oil and Gas Pipelines with Small UAV Systems
INTRODUCTION
Pipelines are the safest means for transport of oil and gas. Millions of cubic metres of hydrocarbons are transported daily by pipelines. Globally there are approximately three million km of pipelines (CIA, 2013) valued almost 9,000 million dollars in 2014 (Markets and Markets, 2014). Pipeline networks are of all sizes and lengths and may have above- or below-ground configurations and diametric size up to more than a metre. Despite the safety provided by pipelines, equipment failure may occur with a risk to spill large amounts of oil and gas, damaging the environment through contamination and pollution and affecting ecological health and human security. Typical reasons for failure of equipment are over-age (structures become more prone to corrosion), natural ground movement, accidental hot tap, and third-party interference (CONCAWE, 2015). Minor incidents and failures are more frequent than catastrophic accidents and can also cause important environmental damage and economic losses. According to the Energy Resources Conservation Board, the number of pipeline breaks per 1,000 km year exposure (pipeline lengthxduration) in Alberta (Canada) was
1.5 in 2011 and 2012 (ERCB, 2013). This rate is estimated to be 110-140 per 1,000 km per year in Russia. In Europe, these figures decreased from 1.2 incidents per 1,000 kmxyear in the 1970s to 0.23 incidents per 1,000 kmxyear in 2013 (CONCAWE, 2015) for oil pipelines, and from 0.87 to 0.33 in the period 1970-2013 for gas pipelines (EGIG, 2015). Theft incidents have increased in the last years in both oil and gas pipeline networks (CONCAWE, 2015; EGIG, 2015), becoming one of the most important causes of spillage.
Regardless of their size, placement, or location, the safety and security of pipelines is of paramount importance to stakeholders and to the public. Safety guidelines and regulations for installation and management of pipelines exist worldwide (IPLOC.A, 2003; GL, 2010), commonly including an ‘inspection and maintenance of pipelines integrity plan’. To prevent failures and detect problems on time, a monitoring system providing regular information of the structural state and functional conditions of the pipelines is necessary. Furthermore, monitoring oil and gas pipeline networks involves acquiring knowledge of the impact pipelines produce on the environment over time (i.e. how vegetation and wildlife is affected).
METHODS FOR MONITORING OIL AND GAS PIPELINES
The most widely used methods for monitoring oil and gas transmission pipelines are foot patrols along the pipeline route and aerial surveillance using light aircraft or helicopters. Patrols are carried out at regular intervals throughout the year and regardless of weather conditions. These methods ensure a high level of security but are expensive and with a main disadvantage of detecting failures late, when the output (oil or gas) has been reduced or the environment has already been affected and damaged. Airborne solutions also bring their own difficulties in terms of safety and operation: manned aircraft using pilot and/or operator for detection and identification are forced to fly very close to the terrain; frequently can only detect visible effects (i.e. not gas leak detection); and require expensive aircraft limiting the frequency and duration of flight. Alternative approaches that do not rely on human interventions utilise real-time monitoring systems based on a network of small sensors (e.g. pressure, acoustic, and temperature) designed to measure real-time flow, enabling detection of leakages or to identify changes in the wall thickness through temperature or noise measurements (El-Darymli et al., 2009). These sensors are vulnerable to damage at any point along the network and can produce ambiguous data, providing incomplete or inaccurate information.
Satellite data (e.g. radar, optical) are used operationally to detect oil spills in marine environments (Brekke and Solberg, 2005), where the hydrocarbons’ spectral signature is very distinctive. However, the potential of satellite remote sensing to reach the demands of pipeline monitoring required by pipeline operators has been investigated in numerous research projects (e.g. PRESENSE, PIPEMOD, and GMOSS) without satisfactory conclusions. Progress in high-resolution remote sensing and image processing technology has provided the basis for designing pipeline monitoring systems using remote sensors and context-oriented image processing software (Hausamann et al., 2005; van der Werff et al., 2008).
DETECTION OF LEAKS FROM HYDROCARBON PIPELINES
Hydrocarbon leaks can be identified by trained operators with visual observation (interpreting colour, texture, and pattern) on real-time inspection or analysing a recorded image (still or video). Beyond the visible, other electromagnetic wavelengths are practical to detect hydrocarbon leaking. The thermal infrared (TIR) wavelengths are particularly useful due to the temperature differences between the fluids (i.e. hydrocarbons) and the soil. Draining liquids affect the thermal conductivity of soils, and whilst an oil leak creates a warmer area, gas escapes show colder than the ground substrate. The rationale for detecting hydrocarbon leakages from pipelines using TIR data surveys is based upon thermal differences, either on a single image, where leakage points look remarkably different to the surroundings, or by comparison of images of the same area captured on different days. Detection of small temperature differences is possible with dedicated image analysis techniques, but care should be placed on other factors affecting the soil temperature (e.g. water content). The availability of frequent and regular images increases the sensitivity of the data through the use of averaging techniques, enabling small differences in heat capacity of the soil to be detected, on a day-by-day basis. Leakages can also be identified through a reduction in the vigour of vegetation eventually leading to death (Mishra et al., 2012). Repetitive imagery is needed to identify this change as well as the use of some kind of automated threshold to provide the alert.
Fine spectroscopy of 0.05-0.1 nm spectral resolution has also proven to identify the specific spectral signature of hydrocarbons, as well as the early effects of oil and gas pollution on vegetation. Measurements of solar-induced fluorescence (F) could be used as an early indicator of the health and status of vegetation, although the quantitative estimation of F from the air is complicated by the absorption of the atmosphere en route to the sensor (Meroni et ah, 2009). Currently, laser fluorosen- sors are the most useful and reliable instruments to detect oil on various backgrounds, including water, soil, weeds, ice, and snow. In fact, they are the only reliable sensors to detect oil in the presence of snow and ice, and they do not detect false positives. A different and unequivocal means for the detection of specific gases (e.g. methane) from a certain distance is gas detection, which works in day and night conditions. Despite gas diffusion and dispersion of gas contamination into the atmosphere, particularly in windy conditions, the highest concentration of gas is a reliable indicator of the leakage location (Allen et ah, 2015).
EMERGING OPPORTUNITIES WITH UAV REMOTE SENSING
Progress in remote sensing technology - including sensors and platforms - and data processing software provides new opportunities for the development of spatially precise and comparatively inexpensive monitoring systems to inspect pipelines and identify hydrocarbon leaks. Unmanned aerial vehicles (UAVs) offer an important option with advantages such as improved mission safety, flight repeatability, the potential for reduction in operational costs, and fewer weather-related flying limitations. However, these advantages are dependent upon the type and size of airborne platform, sensor type, mission objectives, and the regulatory requirements imposed. Small UAVs, both fixed-wing and helicopters with rotary wings, are increasingly considered as reliable platforms for capturing data for environmental applications, and a low-cost alternative to larger-scale platforms (e.g. ARC, 2003). With technological developments such as sensor miniaturisation, stabilisation, and navigation systems, small UAVs provide a powerful basis to gather data and produce information that can be tied to in situ ground data and to large-scale satellite imagery, providing a link between multiple spatial scales.
Small UAVs can provide a very flexible means to acquire unique data and information. Currently there is a wide range of commercial UAVs available for the acquisition of low-cost aerial remotely sensed data. The rapid development of microelectronics and microprocessors, battery technology, GPS and navigation systems, together with reduced costs over the last five years have all helped in triggering an unprecedented demand for, and growth in, the use of UAV platforms for many civilian applications (Watts et al., 2012; Colomina and Molina, 2014).
UAVs are now evolving as highly effective tools for tackling the requirements of oil and gas pipeline monitoring, a specific environmental application of the UAV technology. This chapter describes the current use of UAV platforms and sensors, as well as the foreseen potential of small UAV systems for monitoring oil and gas pipelines. The remainder of this chapter will include sections covering the following: (i) an overview of the characteristics of UAVs; (ii) the use of UAVs for oil and gas pipeline monitoring to date with particular attention paid to the strengths and successes, as well as the weaknesses; (iii) considerations and developments in the technology of small-scale aerial platforms and sensors specifically tailored to oil and gas pipeline monitoring applications, including battery, sensor, navigation, software, and platform; and (iv) future prospects for UAV development and application.
UNMANNED AERIAL SYSTEMS (UAS)
A UAV is flown without a pilot on-board and is either remotely and fully controlled from another place (e.g. ground, another aircraft, space) or programmed and fully autonomous (ICAO, 2011). An unmanned aerial vehicle or system comprises the flying platform, the elements necessary to enable and control navigation, including taxiing, take-off and launch, flight and recovery/landing, and the elements to accomplish the mission objectives: sensors and equipment for data acquisition and transfer. A brief description of each of the main elements (platforms, sensors, and auxiliary equipment) now follows: UAVs, also called remotely piloted aircraft systems (RPAS), can be classified under different schemes, using criteria such as flying height and range, size, and weight (frequently referred to as Mean take-off-weight - MTOW). A strict categorisation of UAVs is not however possible because certain characteristics in the various classes overlap (Skrzypietz, 2012). Table 12.1 provides an overview of the types of flying platform as considered by UVS International; a non-profit association dedicated to promote unmanned aerial systems.
