"We [were] looking at imagery for planning purposes related to seismic survey activities, pipeline routing and facilities planning," relates George. "With seismic surveys and well planning, for instance, we like to have a better understanding of what we’re getting into before we actually get there to mitigate the costs associated with certain hazards."

The most daunting hazards in the Ghadames Basin are the giant sand dunes that tower 120 or more feet into the air, creating an undulating landscape that slowly shifts with the winds. According to George, recent satellite imagery was needed to find flat sites where drilling pads could be positioned, hydrocarbon processing facilities could be built and access roads could be carved into the sand.

Spatial Energy saw SPOTMaps as the ideal solution for the oil field applications. SPOTMaps are regional mosaics created from recent 2.5-meter resolution images acquired by the SPOT 5 satellite. Spot Image has mosaicked the images into seamless and color-balanced data sets available off the shelf for many parts of the world. With pricing by the square kilometer, a user is able to purchase an entire country or regional mosaic, or select the size and shape of any area of interest within a mosaic.

According to Pope, the immediate availability, cost and spatial resolution were the primary factors that led Pioneer to give the new SPOT products a try. Spatial Energy ordered the necessary SPOTMaps data from Spot Image in Chantilly, Va., and delivered them to Pioneer in August 2008.

"Since our area was so large, we knew that SPOTMaps, at 2.5-meter resolution, would give us the resolution we needed to do our planning," agrees George. "We could definitely see our facilities that were already in place, as well as some of the road and pipelines networks that had already been built over the years."

Putting Imagery to Work
After receiving the SPOTMaps data file, Pioneer loaded it onto the company’s Web mapping service for access by personnel in London, Tunisia and the United States. The first order of business was to use the imagery to create an accurate map of existing infrastructure in the basin. Until then, Pioneer only had engineering sketches and Global Positioning System (GPS) locations of the well pads and processing facilities. Technicians in Dallas overlaid the sketches on the images to construct the infrastructure feature layer, ensuring that each building and drill site had been precisely located and accurately depicted. A layer of pipelines was generated the same way.

"We finally had our first compiled map of infrastructure in southern Tunisia," relates George.

Once existing facilities had been mapped, a common use of the imagery was to select routes for laying pipelines between newly drilled wells and the hydrocarbon processing plants. Technicians examined the images for what they call the paths of least resistance, which usually means limited elevation change and absence of natural hazards that could result in future pipeline damage. Because every linear foot of laid pipe adds to development costs, they rely on the imagery to find the shortest route around tall dunes, seasonal streambeds and drainage washouts.
 

Pioneer also expects to use SPOTMaps extensively in planning seismic surveys in Tunisia. As the locations for seismic lines are selected, technicians can review the imagery to determine the best route for the heavy seismic trucks to reach the target. Because the trucks often get stuck in the sand, the technicians can plan in advance where bulldozers will be needed to clear a path for the trucks that follow.

"Clearing these paths is expensive," says George. "The imagery gives us an idea of estimates on additional costs and time."

This planning allows Pioneer to more accurately budget each seismic survey. In addition, such actions can potentially avoid time-consuming delays caused by vehicles getting stranded in the sand.

DEMs for Seismic Surveys
The sand dunes in Tunisia also have caused problems in exploration activities. Specifically, seismic surveys in areas covered by thick layers of unconsolidated overburden, such as sand dunes, often yield inaccurate results. This problem is caused by seismic velocities varying as they pass through the sand layer. In addition, most seismic processing algorithms assume a linear relationship exists between the vibration source and receivers, but in Tunisia there are sometimes huge elevation gaps between those points due to the extreme undulations in the sandy terrain.

"Historically, you use whatever data you have," says George. "But recent seismic publications suggest that using DEMs, along with remote sensing data, may help build an accurate 3-D geologic model as an input to better static corrections of seismic data."

Pioneer field crews typically collect regional up-hole data and x, y and z coordinates at each source and receiver point in the seismic survey using GPS devices, but acquiring a more detailed elevation grid with ground-based GPS over such an expansive area would take years. And, as is the case with aerial photography, collecting DEMs with airborne resources is out of the question in Tunisia. So in 2009, Spatial Energy recommended SPOT DEMs, an inexpensive yet accurate alternative to aircraft or field surveys.

SPOT DEMs are digital elevation models produced by automatically correlating stereo pairs acquired by the High-Resolution Stereo-scopy (HRS) instrument aboard the SPOT 5 satellite. Spot Image already has captured and archived HRS data for two-thirds of Earth’s surface, including Tunisia, which means DEM products can be
delivered quickly for many parts of the world. Each DEM has 20-meter post spacing, 15-meter horizontal accuracy and 10-meter vertical accuracy. In addition, the DEM is produced without using ground control points.

In early 2009, Pioneer received the first SPOT DEM products for Tunisia to integrate into the seismic processing workflow. If the project proceeds as planned, Pioneer expects the DEMs will enhance the accuracy of the seismic processing in two ways:

1. The DEM will fill in differences in elevation values between the vibration source and receiver points, which traditionally have been interpolated.

2. The DEM will allow Pioneer to build a more precise geologic model from the surface of a dune down to the bed rock, so velocity variations through the sand layer can be modeled and accounted for more accurately during seismic processing.

"The introduction of these DEMs could significantly improve the quality of our seismic processing in Tunisia," relates George. "Depending on the results we achieve, high-accuracy satellite-derived DEMs may become standard data inputs in our seismic processing workflow."
 

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