For the offshore oil and gas industry costs of exploration in deep and ultradeep water are immense, and the industry is currently in a state where many operators are limiting exploration activities. In an effort to minimize risks and costs, offshore exploration companies are continually seeking other methods of developing assets that are known producers. It is currently very hard to predict when oil prices will rebound and stabilize; the current market situation increases exploration companies’ need for proven methods of identifying hydrocarbons in offshore basins around the world.

Natural Marine Hydrocarbon Seeps

An overlooked method for hydrocarbon identification is the use of long-term historical space-based radar images and associated analysis methods. These tests enable oil and gas operators/companies to understand natural episodic oil seep patterns over active and unexplored offshore basins. Large numbers of naturally occurring oil seeps are expected in offshore basins and can occur when natural liquid or gaseous hydrocarbons escape to the earth’s surface and atmosphere, normally under low pressure or flow. Seeps are generally found above terrestrial or offshore petroleum accumulation structures.

Large numbers of naturally occurring oil seeps are expected in offshore basins.

When oil is released from the ocean floor, it bubbles through the water column and coalesces on the surface, where the oil is advected by the prevailing mean and surface currents. For example, in California there are hundreds of seeps, and much of the hydrocarbons found during the 19th century were discovered by the observation of seeps on the ocean’s surface. In the Gulf of Mexico, hundreds of seeps result in more than 1 MMbbl/year of oil leaking naturally to the ocean’s surface. Figure 1 illustrates the typical life cycle of naturally occurring oil on the ocean’s surface.

Seeing Oil From Space

Using space-based radar satellites to detect oil on water is a proven technique that has been used for nearly two decades and has multiple applications, including pollution monitoring from all sources (including but not limited to platform/ vessel incidents).

Synthetic aperture radar (SAR) satellites are active sensors that produce energy pulses to illuminate the area under observation. Unlike other passive sensors (such as those on optical satellites), radar sensors are not constrained by lighting conditions and/or cloud cover. SAR satellites also have wide-area capabilities to provide all-weather monitoring for oil on water and metocean support with coverage up to 300,000 sq km (115,831 sq miles) in a single imaging event.

Generally, platforms and ships produce strong radar returns, resulting in bright targets that are easy to identify. Oil slicks cause the ocean surface to appear smooth, reducing the radar return. The ocean surface roughness depends on wind speed and waves, but generally radar returns are brighter than those from oil slicks. Figure 2 shows how a satellite image “sees” oil on water.

Using nonintrusive radar satellite imagery from missions like RADARSAT-2 enables analysts to detect surface seeps and might provide insights into the location of hydrocarbon basins beneath the ocean floor. Satellite coverage is available to locate hydrocarbon systems anywhere in the world. Archived data and seep analysis can leverage more than 20 years of global data coverage. Without the need to deploy any resources offshore, seep analysis is a low-cost risk and impact solution to support lease-block evaluation, and it contributes to exploration companies’ datasets about potential hydrocarbon systems. In addition to performing static analysis from a seeps database, the operator can use historical seep patterns and real-time satellite data to identify areas for geochemical sampling and analysis. Collecting samples from an active seep can provide easy access to evaluate the type of hydrocarbon available at the target location. Employing a satellite- based solution allows exploration companies to have data in hand to help make better decisions about where to invest in higher cost exploration techniques such as piston core campaigns and seismic surveys. The spatial and temporal persistence of the seeps can be used to guide more detailed geophysical surveying.

Some of the key benefits of using satellite-based information that allow the E&P companies to know more and know early are to:

• Cue and target geochemical sampling, seismic studies, piston core drilling programs and seafloor surveys based on seep location and frequency;

• Corroborate seep data to other geological data to reach higher levels of confidence in “telling the data story” early in the exploration decision process; and

• Establish an environmental baseline as evidentiary bases for future work, including production (to help discriminate between naturally occurring oil and oil incidents when producing in an environment with active natural seeps).

Seep Products

Although the seep products might vary from vendor to vendor, seep assessment products most often include summary reports, full-resolution images, wind maps derived from satellites images, oil seep delineations and seep cluster reports.

Seep studies can be catered to the client’s need whether only for a single targeted area or part of a global exploration program with multiple hydrocarbon systems in various exploration phases.

Satellite Use For Oil Spills

Although oil slicks can occur naturally in the form of oil seeps, oil slicks also can be the result of a spill such as the 2010 Macondo incident in the Gulf of Mexico or an accidental discharge from an offshore platform or vessel. When an oil spill occurs, history shows that it is imperative to act quickly to minimize the environmental impact. Using the same tools as for seep analysis, offshore operators can leverage space-based satellites for routine monitoring around their operating areas.

Offshore operations are challenging. Adding tools that require offshore logistical support to monitor accidental discharges is not always cost-effective and introduces even further risks to an already multifaceted operation. Satellite imagery available over the area of interest contains important information and can provide critical data to assist with:

• Situational awareness for security and HSE requirements;

• Metocean and weather support over wide areas; and

• Archiving to support regulatory and legal issues.

Once a satellite image is obtained, it can be analyzed to ascertain the origin of the oil slicks detected. It is possible to discriminate oil that originates from known sources such as offshore drilling platforms or ship bilge-dumping. In both of these cases, the platforms and ships have strong radar returns and can be easily identified. Offshore platforms are stationary, so their location will be constant. The location of ship bilge-dumping is variable, but it is usually characterized by a long linear region of reduced radar backscatter. When known oil slicks have been separated from the unknown oil slicks, the unknown slicks are further discriminated to isolate slicks from slick imposters such as meteorological, oceanographic and coastal processes.

The value of oil slick information is significant, whether for naturally occurring oil seeps or manmade occurrences. If the seeps are naturally occurring, they can be an excellent, low-cost method of determining hydrocarbon presence that are potentially worth exploring further. Alternatively, if slicks are manmade, having satellite imagery available enables the response to be rapid, focused and effective, all the while posing no additional exposure or further damage to the environment.

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