Offshore oil seepage visible from space : a Synthetic Aperture Radar (SAR) based automatic detection, mapping and quantification system

Offshore oil seepage is believed to be the largest source of marine oil, yet very few of their locations and seepage fluxes have been discovered and reported. Natural oil seep sites are important as they serve as potential energy sources and because they are hosts to a very varied marine ecosystem. These seeps can also be associated with gas hydrates and methane emissions and hence, locating natural oil seeps can provide locations where the sources of greenhouse gases could be studied and quantified. A quantification of the amount of crude oil released from natural oil seeps is important as it can be used to set a background against which the excess anthropogenic sources of marine oil can be checked. This will provide an estimate of the 'contamination' of marine waters from anthropogenic sources. Until the onset of remote sensing techniques, field measurements and techniques like hydroacoustic measurements or piston core analysis were used to obtain knowledge about the geological settings of the seeps. The remote sensing techniques either involved manual or semi-automatic image analysis. An automatic algorithm that could quantitatively and qualitatively estimate the locations of oil seeps around the world would reduce the time and costs involved by a considerable margin. Synthetic Aperture Radar (SAR) sensors provide an illumination and weather independent source of ocean images that can be used to detect offshore oil seeps. Oil slicks on the ocean surface dampen the small wind driven waves present on the ocean surface and appear darker against the brighter ocean surface. They can, hence, be detected in SAR image. With the launch of the latest Sentinel-1 satellite aimed at providing free SAR data, an algorithm that detects oil slicks and estimates seep location is very beneficial. The global data coverage and the reduction of processing times for the large amounts of SAR data would be unmatchable. The aim of this thesis was to create such an algorithm that could automatically detect oil slicks in SAR images, map the location of the estimated oil seeps and quantify their seepage fluxes. The thesis consists of three studies that are compiled into one of more manuscripts that are published, accepted for publication or ready for submission. The first study of this thesis involves the creation of the Automatic Seep Location Estimator (ASLE) which detects oil slicks in marine SAR images and estimates offshore oil seepage sites. This, the first fully automatic oil seep location estimation algorithm, has been implemented in the programming language Python and has been tested and validated on ENVISAT images of the Black Sea. The second study reported in this thesis focuses on the optimisation of the created ASLE and comparison of the ASLE with other existing algorithms. It also describes the efficiency of the ASLE with respect to other existing algorithms and the results show that the ASLE can successfully detect seeps of active seepages. The third study aimed to provide the status of the offshore seepage in the southern Gulf of Mexico estimated from the ASLE using SAR images from ENVISAT and RADARSAT-1. The ASLE was used to detect natural oil slicks from SAR images and estimate the locations of feeding seeps. The estimated seep locations and the slicks contributing to these estimations were then analysed to quantify their seepage fluxes and rates. The three case studies illustrate that an automatic offshore seepage detection and estimation system such as the Automatic Seep Location Estimator (ASLE) is very beneficial in order to locate global oil seeps and estimate global seepage fluxes. It provides a technique to detect offshore seeps and their seepage fluxes in a fast and highly efficient manner by using Synthetic Aperture Radar images. This allows global accessibility of offshore oil seepage sites. The availability of large amounts of historic SAR datasets, the presence of 5 active SAR satellites and the latest launch of the European Space Agency satellite Sentinel-1, which provides free data, shows that there is no shortage in the availability of SAR data. The result of the work done in this thesis provides a means to utilise this large SAR dataset for the purpose of offshore oil seepage detection and offshore seepage related geophysical applications. The created system will be an important tool in the future not just to estimate offshore seepage in local seas but in global oceans that are otherwise challenging for field analysis

Remote sensing and GIS-based analysis of hydrocarbon seeps: Detection, mapping, and quantification

The thesis aims to elucidate the transport and fate of hydrocarbon emissions from deep-sea seeps through the water column towards the atmosphere. An array of hydroacoustic, satellite, and optical imaging techniques was employed to detect, map, and quantify such seeps and accompanying oil and gas emissions. The major finding is that gas transport via bubbles is the overwhelming mechanism, to transfer hydrocarbons to the hydrosphere. However, only at seeps that discharge oil and gas (oily gas bubbles) these emissions might reach the sea surface and atmosphere. At other sites gas dissolves in the water column, thus not representing a primary source of atmospheric methane and higher hydrocarbon concentrations. Therefore it is suggested to focus research on oil seeps when aiming to study the potential effect of marine hydrocarbon seeps on the present climate

Hydrocarbon Seepage at Campeche-Sigsbee Salt Province, Southern Gulf of Mexico (Detection, Mapping, and Seafloor Manifestation)

Hydrocarbon seepage is a process during which hydrocarbon fluids are emitted from the seafloor into the water column. This phenomenon has been observed globally from continental margins to the deep abyssal. Hydrocarbon seepage has significant impacts on the marine environment such as (a) influence on sediment composition and dynamics at the seafloor, (b) increasing the habitat heterogeneity on seep biodiversity and (c) contributes to the global carbon cycle. However, the occurrence, distribution, and dynamics of hydrocarbon seepage in the marine environment, especially in the deep ocean remains unclear due to limited investigation. The northern Gulf of Mexico is a well-known prolific petroleum-producing region where numerous gas and oil emissions, associated with salt tectonism, have been observed. The Campeche-Sigsbee salt province in the southern GoM is considered to be an analog to the salt province in the northern GoM, but there has been very little research conducted in this region. Based on the occurrence of natural oil slicks on the sea surface resolved by satellite images, previous studies suggested that there is a widespread distribution of oil seeps in the Campeche-Sigsbee salt province. However, there is still a lack of direct evidence for the presence and the distribution of gas emissions. In addition to gas and oil seepage, Chapopote asphalt volcanism, a novel type of hydrocarbon seepage was first introduced in 2003. Since then, submarine asphalt deposits have attracted considerable research interest. This study aims to have a comprehensive understanding of the hydrocarbon seepage system and dynamics in the southern GoM. The objectives are to investigate the distribution of gas emissions and to understand the controlling factors on the distribution. Furthermore, detailed investigations were carried out at Challenger Knoll and Mictlan Knoll to gain a better understanding of the diverse hydrocarbon seepage system including gas and oil emissions, as well as asphalt deposits. Consequently, the research questions about the fate of the methane bubbles and the quantity of gas bubble released from gas emission site are finally addressed in this study. During research cruise M114 of R/V METEOR, a multidisciplinary approach was conducted, including hydroacoustic surveys, visual seafloor observations, and sampling of gas bubbles. Ship-based multibeam echosounder was used for seafloor bathymetry, backscatter and water column flare mapping in the Campeche-Sigsbee salt province. In addition, multibeam echosounder mounted on Autonomous Underwater Vehicle (AUV) was utilized to obtain high-resolution seafloor bathymetry, backscatter, and water column data at Mictlan Knoll. Remotely Operated Vehicle (ROV) and TV-sled were applied for investigating and documenting seafloor manifestations of hydrocarbon seepage at the seafloor. Gas bubbles were collected by pressure-tight gas bubble samplers operated by ROV at the seafloor of Mictlan Knoll for gas analyses, quantification of gas bubble emissions, and finally gas flux calculation. In summary, gas emissions are found in large numbers in the Campeche-Sigsbee salt province. Their distributions are controlled by the present geological structures. The case study in the Sigsbee Knolls suggests that the edges of flat-top knolls might provide an effective migration pathway for hydrocarbons. As there is no direct evidence for the presence of current oil seepage in the Sigsbee Knolls, we suggested that oil seepage occurs intermittently. Gas, oil seepage and asphalt volcanism are found to occur close together at the Mictlan Knoll, indicating that this diverse hydrocarbon seepage system might be a common phenomenon in the Campeche Knolls. This thesis shows the complex association between the dynamics of diverse hydrocarbon seepage and the geological controls in the southern GoM

Seepage rate of hydrothermally generated petroleum in East African Rift lakes : an example from Lake Tanganyika

Acknowledgements We thank Michael King and CGG | NPA Satellite Mapping for providing us with the GOSD dataset of Tanzania and the permission to publish the SAR images of Cape Kalumba oil seeps. Funding This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.Peer reviewedPostprin

Otkrivanje i mapiranje uljnih mrlja pomoću SAR snimaka na Jadranu

This study provides a new perspective on the hydrocarbon seeps in the Adriatic Sea, supporting both the environmental issues and eventual oil and gas exploration. Remote sensing techniques, particularly synthetic aperture radar (SAR) images are used to detect oil slicks on the sea surface. In such a way two groups of oil slicks have been detected in the Northern and Central Adriatic Sea on the SAR images acquired by the European Sentinel-1A and Sentinel-1B satellites in 2017-2018. Analysis of SAR images together with bathymetry, geological and geophysical data in geographic information system (GIS) have shown that these oil slicks, visible on the sea surface have natural origin, i.e. are seepage phenomena, associated to existing marine hydrocarbon systems. These oil slicks were concentrated over the shallow shelf, and repeatedly or episodically occur in the areas of interest, and are related to local oil-and-gas bearing sediments. Findings of the seeps and seep candidates that passed unnoticed from public attention indicate the effectiveness of the approach used. Finally, it is concluded that the frequent SAR imagery is an excellent tool for monitoring of seepage phenomena, and the results indicate that the use of remote sensing methods can be considered as a good approach to support oil and gas exploration in the Adriatic Basin.Ovaj rad daje novu prespektivu problemu istjecanja ugljikovodika iz podmorja na Jadranu, podržavajući pitanja zaštite morskog okoliša kao i eventualno istraživanje nafte i plina. Tehnike daljinskog otkrivanja, osobito snimci “synthetic aperture” radara (SAR) korištene su za otkrivanje uljnih mrlja na površini mora. Na taj su način na sjevernom i na srednjem Jadranu otkrivene dvije grupe mrlja na SAR snimcima dobivenim od europskih satelita Sentinel-1A i Sentinel-1B u razdoblju 2017-2018. Analiza SAR snimaka uz batimetriju, geološke i geofizičke podatke kroz geografski informacijski sustav (GIS) pokazala je da nađene uljne mrlje, vidljive na površini mora, imaju prirodno porijeklo, t.j. da pripadaju fenomenu podmorskih istjecanja, povezanih s postojećim ležištima ugljikovodika. Ove su uljne mrlje koncentrirane na plitkom šelfu i opetovano ili povremeno se pojavljuju u istraživanom području, a u vezi su sa sedimentima koji sadrže naftu ili plin. Nalaženje takvih izvora ili kandidata za izvore, koji su prošli neopaženi od javnosti, ukazuje na učinkovitost ovog pristupa. Konačno, zaključeno je kako su česti SAR snimci odličan alat za monitoring feno-mena curenja iz podmorja, a rezultati pokazuju kako se korištenje daljinskih metoda može smatrati dobrim pristupom za istraživanje nafte i plina u jadranskom bazenu

Fluid Flow and Sealing Properties Associated with an Active Faults - Kura Basin, Azerbaijan

With the advent of stereoscopic data such as as Landsat and SPOT imagery, these methods have been applied to satellite data and used to successfully obtain quantitative measurements over large areas. On this connection, these methods have assisted considerably in fault analysis considerations and detection hydrocarbon seeps in surface of the Kura basin which are considered main oil and gas bearing region in onshore Azerbaijan. The satellite imagery interpretation drew upon knowledge of structural geology and geomorphology and detected hydrocarbon seeps related to fault and mud volcano geomorphology. The main objectives are to determine the role of faults and mud volcanoes within the geologic structure of the study regions and to guide future oil exploration. Remote sensing to detect hydrocarbon seepage onshore allowed recognition of marginal and sub-marginal low-relief structural prospects and stratigraphic traps that is overlooked by reflection seismic surveys. Remote sensing data and images were integrated in hydrocarbon exploration programs with other exploration data such as seismic surveys, well logs, gravity surveys, and other geologic-geophysical investigations. Analysis of satellite data allowed to determine the geometry of the fault system and around them distributions of hydrocarbon seeps and to predict hydrocarbon potential of the Kura basin

Active microwave remote sensing of earth/land, chapter 2

Geoscience applications of active microwave remote sensing systems are examined. Major application areas for the system include: (1) exploration of petroleum, mineral, and ground water resources, (2) mapping surface and structural features, (3) terrain analysis, both morphometric and genetic, (4) application in civil works, and (5) application in the areas of earthquake prediction and crustal movements. Although the success of radar surveys has not been widely publicized, they have been used as a prime reconnaissance data base for mineral exploration and land-use evaluation in areas where photography cannot be obtained

Oil Seep Detection Using Microwave Remote Sensing at Espírito Santo Basin, Eastern Brazil

Hydrocarbon seepage phenomena can be found in most petroleum provinces located in both coastal and ocean regions. The present work aims to identify, map and quantify oil seep candidates in the maritime portion of the Espírito Santo Sedimentary Basin using Synthetic Aperture Radar imagery from Radarsat-2 and Sentinel-1. The selection of the SAR images was made based on their basin coverage area. Meteorological and oceanographic data, when available, were used to assist interpretation. Later, the presence of structures that may enable fluids to escape (faults, fractures, salt domes, etc.) was verified in 101 seismic lines. After detailed analysis, the obtained data were gathered, aiming to classify the oil seep candidates found according to their probability of happening. There were 3 parameters, subdivided into criteria, used in the ranking score: SAR (distance of vessels, number nearby possible seeps and feature size), Geological (morphotectonic domains) and Seismic (distance from seismic lines, presence of structures and distance from structure). Each criterion received grades ranging from 0.1 to 1.0. The final score is given by the arithmetic mean of the parameters. This allowed the seep candidates to be organized in a ranking. The methodology was successful in identifying 54 promising features in the Espírito Santo basin and northern Campos basin. Half of the seep candidates found, 27 features, obtained a grade higher than 0.7, which strengthens the idea of being oil seeps. As an outcome a map was made in 1:3,500,000 scale with the location of all oil seep candidates mapped in this petroleum province

Massive asphalt deposits, oil seepage, and gas venting support abundant chemosynthetic communities at the Campeche Knolls, southern Gulf of Mexico

Hydrocarbon seepage is a widespread process at the continental margins of the Gulf of Mexico. We used a multidisciplinary approach, including multibeam mapping and visual seafloor observations with different underwater vehicles to study the extent and character of complex hydrocarbon seepage in the Bay of Campeche, southern Gulf of Mexico. Our observations showed that seafloor asphalt deposits previously only known from the Chapopote Knoll also occur at numerous other knolls and ridges in water depths from 1230 to 3150 m. In particular the deeper sites (Chapopopte and Mictlan knolls) were characterized by asphalt deposits accompanied by extrusion of liquid oil in form of whips or sheets, and in some places (Tsanyao Yang, Mictlan, and Chapopote knolls) by gas emission and the presence of gas hydrates in addition. Molecular and stable carbon isotopic compositions of gaseous hydrocarbons suggest their primarily thermogenic origin. Relatively fresh asphalt structures were settled by chemosynthetic communities including bacterial mats and vestimentiferan tube worms, whereas older flows appeared largely inert and devoid of corals and anemones at the deep sites. The gas hydrates at Tsanyao Yang and Mictlan Knolls were covered by a 5-to-10 cm-thick reaction zone composed of authigenic carbonates, detritus, and microbial mats, and were densely colonized by 1–2 m-long tube worms, bivalves, snails, and shrimps. This study increased knowledge on the occurrences and dimensions of asphalt fields and associated gas hydrates at the Campeche Knolls. The extent of all discovered seepage structure areas indicates that emission of complex hydrocarbons is a widespread, thus important feature of the southern Gulf of Mexico