SPE Abstract. Introduction

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1 SPE Development and Test of an AUV for Environmental Monitoring and Asset Integrity in Offshore O&G Scenarios: CLEAN SEA Project Melania Buffagni, eni e&p, Francesco Gasparoni, tecnomare, Nora Hveding Bergseth, Eni Norge, Erik Bjornbom, Eni Norge, Patrizia Broccia, eni e&p Copyright 2014, Society of Petroleum Engineers This paper was prepared for presentation at the SPE International Conference on Health, Safety, and Environment held in Long Beach, California, USA, March This paper was selected for presentation by an SPE program committee following review of information contained in an abstract submitted by the author(s). Contents of the paper have not been reviewed by the Society of Petroleum Engineers and are subject to correction by the author(s). The material does not necessarily reflect any position of the Society of Petroleum Engineers, its officers, or members. Electronic reproduction, distribution, or storage of any part of this paper without the written consent of the Society of Petroleum Engineers is prohibited. Permission to reproduce in print is restricted to an abstract of not more than 300 words; illustrations may not be copied. The abstract must contain conspicuous acknowledgment of SPE copyright. Abstract The use of Autonomous Underwater Vehicles (AUV) is an emerging technology in many fields of marine activity (military, scientific, industrial), offering a significant potential in cost savings and extension of the operational capabilities related to the solutions currently adopted in offshore operations. Commercially available AUVs are mainly used by the oil&gas industry for the execution of seabed surveys and they are not routinely applied for carrying out the environmental monitoring and asset integrity around oil&gas offshore infrastructures. Eni e&p and its subsidiary Eni Norge, in cooperation with Tecnomare, have launched the CLEAN SEA project (Continuous Long-term Environmental and Asset integrity monitoring at SEA) with the objective to use a commercially available AUV, properly upgraded with key enabling technologies, for the execution of environmental monitoring and asset integrity in offshore fields where eni operates. This paper will address how to reach this goal. A custom designed mission payload, arranged as modular and interchangeable pods, has been installed at the AUV. These modules, characterised by a set of sensors, are built to perform different offshore monitoring activities according to specific needs: automatic water samples collection; visual inspection (asset, seabed) and hydrocarbon leakage detection; automatic chemical analyses of trace pollutants and acoustic survey of seabed and pipelines / flowlines. This paper will in addition illustrate the possible future extension of the AUV operational capabilities through the integration and field demonstration of key technologies such as underwater docking, wireless underwater communication for mission data downloading and wireless power recharge for increased autonomy. This may enable a permanent operation subsea independently of support from surface. A comprehensive technical overview of the concept will be presented as well as the results of the demonstration tests. Introduction Presently, environmental monitoring and inspection tasks around oil & gas infrastructures are based on periodic surveys (typically on a yearly basis), mainly involving use of supply vessels and underwater equipment (like water/sediment samplers and ROVs) operated by dedicated personnel. Few experiences of use of seabed observatories are known, enabling collection of long-term time series of basic environmental parameters in fixed locations. When moving from traditional (for example conventional platforms in shallow water) to new and more challenging development scenarios (for example subsea production systems in remote, hostile and environmentally sensitive areas), the conventional methods may not be sufficient to ensure a safe and sustainable presence at sea. At the same time, it is widely recognized that underwater technology offers new and interesting opportunities for the development of advanced solutions able to ensure continuous, long-term, automatic execution of monitoring and inspection tasks at sea. In particular, Autonomous Underwater Vehicles (AUV) are an emerging technology in many fields of marine activity (military, scientific, industrial), offering a significant potential in cost savings and extension of the operational capabilities associated to the solutions presently adopted in offshore operations. However, no AUV is presently conceived for the execution of the asset integrity and environmental monitoring tasks required by the oil&gas industry. Technological gaps can be summarized as follows: commercially available AUVs used by the oil&gas industry are basically designed for seabed surveys inspection/intervention AUVs are at prototype or even conceptual development stage; only pipeline surveys have been accomplished by few AUVs suitably equipped no AUV can be configured in field and at the moment it is necessary to use a different tool (dedicated ROV, dedicated AUV etc.) for each different task (monitoring, mapping, surveying) to be accomplished limited autonomy of operation (in the order of twenty hours) does not allow AUV to operate "permanently" at site, independently from surface support. Recognizing these needs and technological gaps, in October 2011 eni e&p division and its subsidiary Eni Norge, in cooperation with

2 2 SPE tecnomare, have launched the project, with the aim of extending the capabilities of the autonomous robot technology, providing a fully operative solution serving the oil&gas industry asset integrity and environmental monitoring requirements. Technical description Clean Sea concept is based on the original and distinctive idea of an autonomous underwater vehicle equipped with a modular interchangeable payload. The system is also characterised by a peculiar hardware and software architecture, where the payload controller is separate from the AUV controller and capable of modifying in real time the mission strategy. Reference missions for Clean Sea system are summarized in Table 1. Table 1 Clean Sea reference monitoring tasks category mission reference cases Environmental monitoring Asset integrity Water column monitoring Benthic habitat monitoring Seabed acoustic survey General oil spill detection Detection and localization of hydrocarbon leakages Visual inspection Environmental survey Environmental survey + collection of water samples for subsequent laboratory analyses Environmental survey + in-situ analysis of trace pollutants Detailed visual survey of benthic communities Seabed survey (geohazards, flora & fauna) Sealine survey Survey of liquid leakages from Subsea Production System (SPS) templates Survey of gas leakages from SPS templates Survey of gas leakage from flowlines SPS (panel, structure) inspection Riser section inspection Flowline / pipeline inspection Figure 1 Clean Sea system Vehicle SAAB Seaeye Sabertooth (derived from the military Double Eagle AUV) has been identified as the most suitable platform for the project. The open-frame, flat-shaped architecture allows volume for the installation of the mission payload and the implementation of the interchangeable payload concept. Being a hybrid AUV/ROV, this vehicle is characterised by the high manoeuvrability required to move in proximity of the structures to be inspected, and by the possibility to hover (essential requisite for some monitoring tasks). Hovering capability is finally an essential prerequisite for possible future applications requiring operation from underwater docking stations ( resident AUV concept ). Sabertooth basic specifications are shown in Table 2

3 SPE Table 2 SAAB Seaeye Sabertooth DH technical specifications Dimensions 3800 mm length x 1350 mm width x 933 mm height (including payload) Weight 1300 kg (including payload) Max speed 4 knots Depth rating 1200 m (optional 3000 m) Battery pack Lithium polymer 20 kwh (30 kwh optional) Endurance (20 kwh) up to m/s up to 12 1 m/s Thrusters 6 x 600 N/thruster Navigation sensors Profiling and obstacle avoidance sonars, Acoustic locator beacon Inertial Navigation System, Doppler Velocity Log, Depth sensor, 3 Cameras, 4 Lamps Communications with ship WiFi, radio link (optional), underwater acoustic modem (optional) Mission payload Mission payload includes all the sensors and devices, even complex, used for the correct accomplishment of the reference missions. Due to the number of parameters to be measured and the different requirements of the tasks to be executed, it is not conceivable to have the entire payload installed on the AUV at the same time. The approach selected to manage this situation is to install on the AUV a set of general purpose sensors (hereafter referred to as standard payload ); arrange into replaceable modules (referred to as e-pods ) the sensors and devices to be used for specific missions. Each module has been designed for the execution of a specific task and is provided with standard interfaces to the AUV. Standard payload The Standard Payload consists of a set of sensors (listed in Table 4) always integrated into the AUV, and intended to monitor the basic environmental parameters provide reference data in support to specialistic monitoring/inspection tasks As shown in Figure 2, large part of the Standard Payload is arranged inside a bay placed in the front of the vehicle; the remaining sensors are placed on the top under a protection cage. Figure 2 (left) Standard Payload arrangement; (right) e-pod arrangement Modular payload Modular payload consists of a set of interchangeable instrumented modules (e-pods), custom designed for the specific application. e-pods are mounted below the AUV, as shown in Figure 2, attached with two metallic clamps. Main technical features are listed in Table 3. Table 3 e-pod technical specifications Shape torpedo-like Dimensions diameter 250 mm, length 2000 mm Weight about Kg in air, neutral or slightly buoyant in water Depth rating 1500 m Battery pack Rechargeable Li-Ion 14.8 VDC, Ah Payload See Table 4 Hardware embedded Linux CPU, Technologic Systems TS-7260 Status Sensors to monitor parameters such as voltage, current, internal temperature and water detection Power regulation and control

4 4 SPE Interfaces Ethernet, power enable Each e-pod is dedicated to one (or more) specific monitoring task(s); list of the e-pods developed in the project is reported in Table 4. Figure 3 (left) e-pod#4, e-pod#2 and e-pod#1 (with upper foams and cover removed); (top right) e-pod general configuration; (bottom right) e-pod#3 mounted on the vehicle Table 4 Clean Sea Payload Payload Task Sensors / instruments Temperature, Conductivity (salinity), Pressure (depth), Turbidity (suspended solids), Fluorescence (chlorophyll), Fluorescence (colored dissolved organic Standard basic environmental parameters matter), Dissolved oxygen, Fluorescence (Policyclic Aromatic Hydrocarbons), Dissolved CH 4, ph, Oxido-Reduction Potential (ORP), Digital stills camera with flash unit, LED lights e-pod # 1 automatic water sample collection for subsequent laboratory analyses Water sampler e-pod # 2 e-pod # 3 e-pod # 4 visual inspection (asset, seabed) and hydrocarbon leakage detection automatic chemical analysis of trace pollutants acoustic survey of seabed and pipelines/flowlines High resolution color video camera, Dissolved CH 4, Passive Acoustic leak detector, Fluorescence (crude oil), Fluorescence (refined fuels) Prototype spectrophotometric analyzer of trace metals (Cr, Cu, Ni, Zn) Side-scan sonar, Echo sounder The concept makes possible future development of new additional pods, dedicated to other tasks and integrating new sensors/analyzers which the technology progress will likely make available in the next years. Mission control A novel approach for the mission management has been implemented, introducing a logical separation between the payload-related functions and the AUV-related ones; this is made possible by an intelligent unit ( Mission Payload Control Unit ) specifically dedicated to payload management (acquisition, storage, pre-processing), independent from the AUV Control System, but able to interact with it for the exchange of navigation data and high level commands, by means of proper client-server Ethernet connections. Using payload measurements and AUV navigation data, transmitted according to a NMEA protocol, Mission Payload Control Unit is capable of modifying in real time the pre-programmed AUV mission strategy, acting either as a trigger (to start specific operations, such as water sampling, switch-on video camera and lights) or to feed more complex operations resulting from any kind of real-time sensor data processing (for instance, generation of navigation commands along the direction of maximum gradient in a measurements map). This behavior has been defined reactive control. A logical scheme of this concept is depicted in Figure 4.

5 SPE Figure 4 Reactive Control logical diagram Field test results Clean Sea tests were carried out in Lake Vattern, Sweden (November 2012, May-July 2013). Additional trials were organised by Eni Norge offshore Hammerfest (Norway) during October The tests were aimed at demonstrating the capability to execute all the reference monitoring tasks, and included the execution of simulated missions well representing, apart the smaller scale and water depth, the complexity of a real scenario. More than 100 missions were carried out, corresponding approx. to 200 hour operation and 350 km run, allowing toverify the reliable operation of all technologies and solutions implemented. Significant examples of results obtained during the tests carried out are presented and discussed in the following paragraphs. Figure 5 Clean Sea System during field tests; (left) Vattern Lake, (right) offshore Hammerfest Example 1) Environmental survey over the water column With this term we refer to direct measurements of physical and chemical parameters over the water column along the area of interest, in support of baseline studies or impact monitoring activities. Clean Sea approach aims to extend (and, in perspective, replace) traditional monitoring activities based on collection of samples and subsequent laboratory analysis, carried out (in terms of frequency, area coverage and parameters of interest) according to the local regulations and company standards. The reference mission consists of a sequence of grids at various quotes, navigating at constant speed and with continuous acquisition of data from all the environmental sensors (sampling rates in the range Hz, depending on sensor). The mission includes the following steps:

6 6 SPE AUV launch Move to the programmed waypoint (first point of the survey grid, first quote) Execute the first grid in N-S direction Repeat grid in the opposite direction (E-W) Move to the second quote Execute the second grid in N-S direction Repeat grid in the opposite direction (E-W) Repeat for other quotes Return home Trajectories are pre-planned and no online modifications foreseen (apart from avoidance of unexpected obstacles revealed by the sonar). A typical environmental survey carried out in Vattern Lake consisted in the execution of 300 x 300 m grids at three different quotes (2, 5 and 10 m water depth), 50 m step and 1 m/s speed. Lake depth in the area was approx 15 m. AUV route is shown in Figure 6. Figure 6 (left) AUV route during environmental survey in Lake Vattern; (right) temperature data In this case the overall distance run by the AUV was 8 km and the mission duration 5 h (representing a scaled down version of a survey in a real scenario); up to nearly measurements were taken for each parameter, with a space resolution of 1 m between consecutive measures. A selection of environmental data collected during the mission are presented in the following graphs. Although significant variations/anomalies were not expected, it is worth noting the quality of the data collected and the high resolution obtained, allowing small but meaningful variations to be appreciated for each parameter along the surveyed area. Figure 7 Selection of data collected during Lake Vattern environmenral survey

7 SPE Example 2) Benthic communities survey Monitoring status of the benthic habitats around oil&gas installations is part of the environmental impact assessment activities and represents task of particular importance in sensitive scenarios. Traditionally carried out by ROVs or towed tools, this task is aimed at providing useful information to determine benthic communities abundance and diversity in the area of interest, and their possible modifications during time. For this purpose, a number of significant sites has to be defined, and periodically visited during a dedicated survey, with detailed photographic/video coverage of the area. For this purpose Clean Sea system uses the Standard Payload only, with the optional addition of E- POD#2 (should video images be required) Typical sequence includes the following steps: AUV launch Move to the programmed waypoint (first point of the first area to be surveyed) Execute the grid Move to the second area to be surveyed Execute the second grid Repeat for all the areas to be surveyed Return home During tests carried out in Vattern Lake, the AUV was programmed to perform three 10x10 m grids centred on the nominal GPS positions of three simulated benthic scenarios, travelling at 1.5 m constant altitude from lake bottom and 0.05 m/s speed; trajectories were pre-planned and pictures taken only during the execution of the grids. Due to the lack of interesting natural features, in the center of each grid an artificial piece of seabed was installed, populated with aquarium accessories. Lake depth in the area was approx 15 m. Figure 8 shows AUV route during a typical mission; colours represents AUV depth, ranging from blue (low depth) to yellow (high depth). Note the not perfect straightness of AUV trajectories during the execution of the grids, due to the combined effect of water current and extremely low speed. An example of images collected during these surveys is shown in Figure 9. Like the environmental data, each photo is referenced to the AUV position and time, making possible the image organisation into a mosaic after download. Also in this type of missions, trajectories are pre-planned and no on-line modifications foreseen. Figure 8 (left) AUV route during benthic communities survey test in Lake Vattern; (right) photo taken during the survey Seabed photographic surveys were repeated in Rypefjord bay (offshore Hammerfest), obtaining images like those shown in Figure 9.

8 8 SPE Figure 9 Examples of images taken during Hammerfest tests Example 3) Water sampling survey With the adoption of e-pod#1, environmental monitoring capabilities of Clean Sea system includes the automatic in-situ collection of discrete water samples; this functionality allows to extend the number and range of parameters detectable in-situ provide ground truth for the real-time measurements taken by the standard payload In fact it is known that not all water properties can be directly measured in-situ, and measurements requiring complex analytical procedures necessitate the collection of water samples for laboratory analysis. This is in particular applicable to trace pollutants. Although other AUVs have already been equipped with a water sampler, the solution implemented in Clean Sea is characterised by specific innovation aspects, which may be summarised as follows: a) being part of the modular architecture of the payload, the vehicle configuration for water sampling task is straightforward and does not require any specific adaptation work b) being integrated into the reactive control capability, water sampling strategy may be activated in different ways Time Position Distance covered Event detection as result of the in-situ observations (e.g. a given parameter exceeding a pre-defined threshold) c) thanks to the vehicle characteristics, samples may be collected in hovering Figure 10 (left) AUV route during a water sampling survey (sampling locations are indicated by the tags); (right) water samples collected Example 4) Hydrocarbon leakage detection and localisation This mission is aimed at a) extending the range of the fixed leakage sensors normally adopted on SPS (e.g. capacitive, acoustic), b) monitor the integrity of long sealines (buried or not) To accomplish these goals, Clean Sea e-pod#2 has been equipped with three different hydrocarbon leak detection methods

9 SPE Fluorescence sensing for oil leakages, based on connercial sensors Chemical sensing for methane leakages, based on commercial sensors Passive acoustics; for this purpose a prototype AUV version of a commercial system (operated by diver, towfish or ROV) has been developed Moreover, for the execution of the tests relevant to hydrocarbon leakages detection and localisation, a plant was developed allowing controlled leakages of gas (methane) or water (simulating an oil leakage). Water leakage plant Methane leakage plant Output pressure Up to 100 bar Up to 5 bar Leakage point diameter 1 mm 0.5 mm Surveys were carried out either with pre-planned trajectories (lines, grids) or under reactive control; in the latter case, an algorithm has been developed to identify the occurrence of an anomaly and guide the vehicle to the source. Tests demonstrated the possibility to detect very small methane leakages (average leak rate used in the tests 1.5 kg/h) providing measurements ranging from the background value (<10 nmol/l) of methane concentration in water, up to thousands nmol/l. As regards the passive acoustic technique, the very low background noise generated by the AUV during navigation ensured better quality data (and consequently better detection capability) than operating the same technique by an average work class ROV. In the following four test cases are presented and discussed. Case a) line survey, gas leakage, 3 bar output pressure In this case the AUV was programmed to run a simple straight trajectory passing over the leakage point. The vehicle navigated at 1.8 m constant distance from seabed, 0.6 m/s speed. Figure 11 shows the leakage (as seen by the vehicle videocamera) and the plot of methane concentration (in µmol/l) vs time (in seconds) measured by e-pod#2 sensor. The anomaly is clarly visible with concentration rising from nmol/l background level up to 1.8 µmol/l in correspondence to the leak point, and decreasing once the vehicle has passed it. Reaction time of the sensor is in the order of tens of seconds; note also the time required to the sensor to return to the background value after the peak has been detected. Figure 11 (left) artificial gas leakage during Lake Vattern tests; (right) methane concentration measured during the line survey Case b) aeral survey, gas leakage, 3 bar output pressure In this case the AUV was programmed to execute a survey over an area around the leakage point, travelling at 0.6 m/s. The survey included three grids at different altitudes (8 m, 4 m, 1.8 m). Figure 12 (left) AUV route and e-pod#2 methane concentration; (right) methane concentrations measured during the aeral survey Plots shown in Figure 12 (right) represent methane concentration (in µmol/l) vs time (in seconds) measured by the two sensors mounted on

10 10 SPE the vehicle (top the high sensitivity sensor, bottom the fast response sensor). Peaks in the plots correspond to vehicle passages in proximity of the gas plume. A clear correlation may be observed between measurements of the two different sensors. Combining navigation data and methane measurements collected, the graph of Figure 12 (left) may be obtained, evidencing two interesting aspects: the AUV deviating from the straight route in proximity of the leakage point; this is due to the fact that the leak is seen as an obstacle by the sonar the effect of the relatively slow methane sensor dynamics on the localization accuracy These aspects, together with environmental conditions (e.g. presence of marine current) and AUV navigation parameters (e.g. speed, altitude ) may affect the localization accuracy and must be carefully taken into account in the implementation of reactive control algorithms. Case c) Water leakage, 50 bar differential pressure This test was carried out verify passive acoustic technique capability to detect liquid leakages. The AUV accomplished the survey following a grid path similar to that of case b). Every passage in proximity of the leak point, a clear acoustic signal has been detected, with a maximum over the leak. Moreover, readings seem to be not affected by the noise generated by the vehicle itself (mainly the thrusters) neither during the navigation nor during the turns. Figure 13 Water leakage seen by e-pod#2 passive acoustic detector The two diagrams of Figure 13 show the passive acoustic detector parameters as a function of time (windows represent a 120 sec period). In the left diagram it is possible to note the AUV noise during a turn (white box) and leak signature (red box). The diagram on the right shows background noise during straight navigation. Case d) Methane leakage, 2 bar differential pressure This test was carried out to explore the minimum detection limit of the passive acoustic detector. The gas leak has small diameter and very low pressure, generating detection conditions well below the threshold specification (1 mm water 10 bar) set as acceptance parameter for the detector. An extensive survey has been carried out with the vehicle following a series of grids centered on the leakage point. Despite the critical leak size and pressure, the system acquired a number of clear leak signals (see Figure 14, left). Moreover, the acoustic signature of the leakages is still well distinguishable from the noise generated by the thrusters during the vehicle turns (Figure 14, right). Figure 14 (left) Gas leakage seen by e-pod#2 passive acoustic detector; (right) vehicle acoustic signature during navigation and steering

11 SPE Example 5) Visual inspection Autonomous Underwater Vehicles feature a great potential in advancing subsea inspections for the oil & gas industry, being capable to provide faster, safer, economical, and more efficient inspections compared to using divers and tethered remotely operated vehicles. Thanks to its peculiar characteristics, Clean Sea system is particularly suited for this type of tasks. The project addressed general visual inspection tasks only (SPS, riser, platform inspection, pipeline surveys, bottom debris surveys), however system evolution to detailed inspection tasks (e.g. with contact) up to light intervention work appears possible. These tests were carried out using a high resolution videocamera integrated in on e-pod#2 and a mock-up of SPS panel (Figure 15, left) deployed in a GPS-known location on the bottom of the lake. An optical modem was adopted to ensure underwater wireless connection between Clean Sea vehicle and surface operator during the execution of the inspection; one unit was instelled on the vehicle (Figure 15, center), while the other was installed on the mock-up (Figure 15, right) and cable connected to the Control Room. Figure 15 (left) SPS panel mock-up; (center) acoustic modem instelled on the AUV; (right) acoustic modem installed on the mock-up With this configuration, possibility to execute tetherless inspections with operator supervision was demonstrated. Three operating modes were implemented a) Manual mode In manual mode, once reached the coverage of the wireless optical link, the vehicle was operated like a ROV. AUV autonomously approached the structure to be inspected on a pre-planned trajectory, stopping in front of it when forward looking sonar detects the foreseen objects at a distance of 3 meters. At this distance, the wireless communication link is established and the control is taken by the operator which proceeds with the inspection of the subsea plant in a way similar to the standard ROV inspection, using video images as a feedback (the optical model used in the tests ensured transmission rates in the order of 5 Mbit/s at 10 m distance). Figure 16 (left) operator console during inspection in manual mode; (center and right) two pictures of the mock-up taken during the inspection (note on the left picture the laser references, giving a known distance baseline of about 65 mm) b) Assisted mode In assisted mode, the inspection is carried out autonomously but with the operator supervision. Once the vehicle has arrived in proximity of the structure (entering under the coverage of the wireless communication link), the operator is required just to drive the vehicle in the initial position. The inspection is then executed automatically under management of the reactive control. Being the video link always available, operator has a visual feedback of the activity and can take control in any moment. c) Autonomous mode In this case there is no link with surface and no communication equipment in required to be installed in the subsea structure. AUV autonomously approaches the structure to be inspected on a pre-planned trajectory, stopping in front of it when forward looking sonar detects the foreseen objects at a distance of 3 meters. Control is then taken by the reactive control which proceeds with the inspection using data coming from the forward looking sonar to move all around the structure. Pictures and videos are taken during the inspection (examples

12 12 SPE shown in Figure 17, and downloaded at the end of the mission. Figure 17 three images collected during AUV autonomous walk-around SPS mock-up; (left) front of the panel (note the optical modem is switched off), (center) mock-up side, (right) rear of the panel Conclusions Tests carried out have provided a clear and impressive demonstration of the potential of Clean Sea technology. Potential benefits of project concept with respect to the present methods include reduced ship time faster response time access to installations that cannot be reached with ships, due to weather conditions and/or ice presence increased verification ability proactive maintenance approach early warning of anomalous conditions or events company reputation Application areas include Environmentally sensitive scenarios and frontier areas (harsh climatic conditions, deep waters, remote, etc.) or wherever required by governments and legislation Areas affected by incidents (like spills, leaks, shipwrecks etc.) Arctic areas, characterized by ice and harsh weather Regions in which it might be challenging to have intervention ships on standby, e.g. in various African countries Large field layouts with many flowlines/risers which need inspection and maintenance Complex SPS systems with frequent intervention intervals (e.g. Subsea Compression Projects) Acknowledgements Clean Sea was carried out in the framework of eni R&D technology plan. Special thanks are due to tecnomare team (Federico Bruni, Massimo Carazzato, Roman Chomicz, Flavio Furlan, Tiberio Grasso, Mauro Favaretto, Michele Filippini) and Eni Norge team (Laura Gallimberti and Arild Jenssen). Finally, authors wish to thank SAAB team for their highly professional support during the integration and field test phase and Marina Locritani (INGV) for the assistance in field test data analysis. References Furuholmen M., Hanssen A., Carter K., Hatlen K., Siesjo J. (2013). Resident autonomous underwater vehicle systems a review of drivers, applications and integration options for the subsea oil and gas market 11 th Offshore Mediterranean Conference, Mar 20-22, 2013 (Ravenna, Italy) Gasparoni F., Favaretto M., Grasso T., Bjornbom E., Broccia P., Buffagni M. (2013). Towards automatic, continuous and long-term asset integrity and environmental monitoring in offshore scenarios: Clean Sea project 11 th Offshore Mediterranean Conference, Mar 20-22, 2013 (Ravenna, Italy) Gasparoni F., Bruni F., Chomicz R., Ciccarelli V., Favaretto M., Filippini M., Furlan F., Grasso T., Hveding Bergseth N., Bjornbom E., Broccia P., Buffagni M. (2013). Development and Test of an AUV for Asset Integrity and Environmental Monitoring in Offshore Oil & Gas Scenarios 23 rd International Ocean and Polar Engineering Conference (ISOPE 2013), June 30-July (Anchorage, Alaska, USA) Husain T., Veitch B., Hawboldt K., Niu H., Adams S., Shanaa J. (2008). Produced water discharge monitoring, paper OTC 19271, presented at 2008 Offshore Technology Conference, May 5-8, 2008 (Houston, Texas, USA) IRIS workshop AUV-based technologies in offshore O&G monitoring, September (Randaberg, Norway) Johansson B., Siesjo J., Furuholmen M. (2011). Seaeye Sabertooth, a hybrid AUV/ROV offshore system, SPE paper , SPE Offshore Europe Oil & Gas Conference and Exhibition, Aberdeen (UK), September 6-8, 2011 Niu H., Adams S., Husain T., Bose N., Lee K. (2007). Applications of Autonomous Underwater Vehicles in Offshore Petroleum Industry Environmental Effects Monitoring, 8th Canadian International Petroleum Conference, Jun 12-14, 2007 (Calgary, Alberta, Canada)