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Searching with Satellites (Oilfield Technology Article)

WorldDEM image: Wipena Pound, Australia

WorldDEM image: Wipena Pound, Australia

Around the world, decades of successful oil and gas exploration has left geologists and seismic engineers with an increasingly difficult task – to discover and evaluate well-hidden geological features that have the potential to hold recoverable hydrocarbon resources.

This article discusses how the latest satellite technology and derived products and services are being applied to increase efficiency and reduce risk. These specialist data sets, are being continually developed, evaluated and combined with other tools to help the industry identify new opportunities where oil and gas can be extracted safely and cost-effectively.

Licensed to search

When a country announces an oil and gas exploration licensing round, suitable baseline information, such as geological data, infrastructure or terrain information may not be available. Increasingly, explorers are using fast developing satellite technology to support operational activities. Traditional earth science disciplines used by upstream companies, including geology, geophysics and geochemical sampling, are being augmented with earth orbiting satellites, which support geological interpretation, seismic planning, engineering applications, offshore oil seep detection and asset monitoring for any location in the world.

The increased appetite for exploring less accessible locations means oil and gas explorers are also turning their attention to a host of previously undeveloped frontier areas. From offshore Croatia, the Irish Atlantic and Canada’s East Coast through to the Torres Basin and Southeast Asia, governments around the world are looking to promote their territories to attract investment.

Advances in satellite technology and image analysis are supporting this shift through the development of radar and optical sensors with resolutions of less than 1 m and the capability of frequent revisit rates. In addition, the latest generation of satellites are equipped with sensors capable of obtaining the data required for producing three dimensional models of the ground’s surface, known as ‘Digital Elevation Models’ (DEM). Searching for oil and gas reserves onshore and offshore is greatly enhanced by the use of this satellite data. Onshore, structure and stratigraphy of the surface geology can be assessed using optical and radar imagery, while assessing offshore potential, radar sensors can be used to identify natural oil seeps by identifying slicks on waterbodies, be it on oceans or lakes.

Onshore search

Having an up-to-date satellite based overview of an area of interest provides a wealth of information on the distribution and extent of human activity in the region. This land cover information can be fed into the planning process to minimise disruption to local communities. Environmental and safety concerns can be also mitigated by identifying environmentally sensitive locations and existing access routes that can then be used to support logistical operations and ground survey planning.

Using satellite imagery for onshore geological mapping is an established technique used across the sector, particularly for remote, inhospitable areas. Initial data collection includes understanding structural issues such as bedding dip and orientation, fault identification and classification, which together with spectral and textural information allows the assessment of surface stratigraphy.

Follow up work often involves gathering higher resolution data over specific areas from satellite constellations, including optical satellites such as SPOT6 (1.5m resolution) and Pléiades (0.5m resolution).

Understanding the Earth’s surface

When analysing terrain features for geological interpretation or seismic planning, accurate terrain height information such as Digital Elevation Models and 3D representations of the target landscape are critical.

DEM are created using advanced processing of satellite imagery. There are two distinct types of elevation models: Digital Terrain Models (DTM) and Digital Surface Models (DSM). A DSM is an elevation model which contains objects on the ground’s surface, whereas a DTM typically has been edited to remove objects such as vegetation and infrastructure – leaving it clear for pipeline companies to accurately plan routes.

Satellite imagery and interpretation suppliers offer a range of DEM products, based on client’s detail and accuracy requirements, which are either proprietary or available ‘off-the-shelf’. Airbus Defence and Space’ ‘WorldDEM’ is one of these datasets. WorldDEM is an edited DSM with hydrological consistency including the flattening of water bodies, consistent flow of rivers and editing of shorelines. A distinguishing feature of this dataset is its standardised, orthorectified pole-to-pole coverage of the earth’s surface.

Using elevation data assists hydrocarbon explorers to develop an understanding of the surface characteristics of an area contributing to informed decisions on whether to bid for specific licence blocks. When opportunities are identified, companies can use this data to prioritise which areas should be the focus of its exploration efforts and where further data gathering from geologists and seismic teams is required.

Looking at high resolution elevation models, Airbus Defence and Space’s Elevation1 proprietary DEM (with a 1m posting), is among the most accurate satellite-based elevation models currently available. Elevation1 is aimed at providing high-resolution elevation information, where accuracy and resolution is critical such as in engineering projects focused on facility or detailed pipeline planning.

Using satellite imagery, near-shore bathymetric information can be obtained in water depths up to around 30m in areas with clear water. This bathymetric information can be used for a range of applications in the coastal transition zone, an environment which is often lacking suitable water depth information. Application areas include the assessment of an area or block identified as a possible exploration target in shallow waters, or where pipelines and other infrastructure are being planned, for example offshore in West Africa. In addition, near-shore bathymetric mapping offers a fast, cost-effective way of gathering data for use in future surveys or to optimise grid alignment for  seismic studies, as well as to risk-rank ‘go’ or ‘no-go’ areas prior to expensive seismic acquisition.

Offshore hydrocarbon potential

Geologists seeking indicators of a deeply buried working petroleum system within a basin often look for evidence of surface oil slicks. Radar satellite imagery is an established method for identifying these offshore surface oil slicks, with the technology based on the dampening effect oil has on the sea surface wave amplitude, which directly influences the backscatter returned to the satellite radar sensor. In effect, the influence the oil is having on wave conditions is being assessed, rather than direct observation of the oil itself.

By collating information on oil, geographic information system (GIS) databases have been developed, which include slick source points, slick vectors, and confidence levels. Airbus Defence and Space’s Global Seeps product is a non-exclusive database of offshore potential oil seepage slicks, constructed from over 19,000 satellite scenes and 60 million sq. km of data. It holds more than 22,000 potential identified and interpreted slicks. Each slick is characterised and ranked according to the probability of it being sourced from natural seepage or man-made pollution. The interpretation process is undertaken manually by an experienced team of analysts. Ultimately, this valuable seep data is then integrated and compared to other geological or geophysical data such as seismic to assist in developing an understanding of the hydrocarbon system of a region and potential target areas and therefore allowing more informed decisions.

Image analysis & archives

Satellite imaging companies are continuously adding images to their archives to ensure the data they are providing is as up-to-date as possible. In order to extract the maximum value from this satellite imagery, satellite operators typically have teams of in-house specialists able to process and analyse the imagery to further support oil and gas exploration and production companies together with related service companies.

Associated application areas include:

  • Environmental studies: Baseline assessment of environmental conditions including previous exploration activities and pollution before a new exploration project starts.
  • Geological assessment: Interpretation of structural features and stratigraphy for optimising seismic and fieldwork planning.
  • Infrastructure and land-cover interpretation: Mapping of access roads, other infrastructure and land-cover types.
  • Security and monitoring: Archive data gives a snapshot of the situation on the ground at any given time, this can be reviewed alongside images obtained at a later date to identify change or to continually monitor assets remotely.

Prospecting offshore Canada

When Canada-based energy corporation Nalcor started prospecting off Newfoundland and Labrador, as well as areas off Greenland’s southwest coast, the company used the Global Seeps database, augmented with seismic data, to better understand future exploration potential across a vast, largely unexplored area.

The collected data helped in the targeted seismic acquisition process and improved chances of finding hydrocarbons and evidence of active petroleum systems. The collected data helped in the targeted seismic acquisition process and improved chances of finding hydrocarbons and evidence of active petroleum systems.

Nalcor’s oil and gas division is a partner in three offshore developments in the region – the Hebron oil field, the White Rose Growth Project and the Hibernia Southern Extension.

A wide range of satellite data was weather-screened to ensure its suitability for oil slick during the Nalcor project. Suitable satellite scenes were analysed by technical image analysts, to identify oil seeps and slicks. Each slick was characterised and ranked according to the probability of it being sourced from natural seepage or man-made pollution. Distinguishing between slick and pollution enhanced Nalcor’s understanding of the region, allowing the company to demonstrate there is a positive correlation between some slick locations and subsurface hydrocarbon migration.

Essential tool

Satellite imaging is now an integral part of a hydrocarbon explorer’s toolbox, offering consistent interpretation of surface geology and terrain characteristics onshore, together with giving an insight into the presence of working hydrocarbon systems offshore. Combining such imagery and derived information with other supporting geoscience datasets such as 2D or 3D seismic data is providing improved efficiency in the exploration workflow, assisting in the discovery of oil and gas resources in remote and often hard to access locations. The application of satellite produced data and intelligence is only set to increase, with the current price of oil driving efficiency and the need for effective risk-ranking of exploration opportunities.

Read this article in Oilfield Technology

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