Not only before exploration and production projects, but on an ongoing basis after pipeline production has begun, oil and gas companies need to continue to create and maintain reliable maps showing natural and man-made features and updates to existing facilities.

Technologies converging in the mapping space, such as global positioning systems, portable geospatial hardware, and image compression, are making field mapping considerably easier, and big companies such as Chevron and Enbridge are taking advantage of the benefits.

Satellite Imagery Ideal for Base Maps

Chevron’s Technical Computing Information Management Group in Houston maintains an Oracle database that supports the wide variety of mapping projects that precede construction of pipelines, drill sites, gas plants, access roads and housing.

Nearly every project requires an exhaustive collection of surface data so that accurate analyses can be made of hydrology, hydrography, vegetative cover, soils, lithology and environmental conditions. Cultural features such as roads, buildings and houses must also be mapped with details relating to their size, condition and construction type. Richard Bosley, a Chevron GIS analyst, says that the information gathered by Chevron’s field crews is used “from the very early stage of scoping the project…all the way up to final as-builts.”

Until a few years ago, the recording of feature locations and collection of attribute data had to be performed manually by Chevron’s survey crews taking written notes. And the construction and maintenance crews of another company, Enbridge Inc., navigated its entire pipeline territory using paper maps. “This was a slow and frustrating process,” says Jason De Leon, a field designer in Enbridge's Pampa office outside of Amarillo. “Often our field people were given coordinates for their destinations, but were not able to find those coordinates on the paper map. Also, the maps made by the Texas Department of Transportation did not necessarily show all the roads that we have up here. Crews spent a lot of time driving around in circles. You’d get instructions like, ‘Go to the windmill that’s losing one of its blades and turn right, then turn left when you see three cows.’”

Today, both companies do nearly all field mapping and navigation digitally.

Field work usually begins with a high-resolution satellite image. Bosley’s group at Chevron uses QuickBird images from DigitalGlobe of Longmont, Colo. Bosley stores as many as nine QuickBird scenes totaling 200 gigabytes on a portable hard drive and carries it with him to the project area. The 0.6-meter spatial resolution of these digital images makes them ideal base maps compared to vector line maps because surface features and land cover types as small as a manhole cover can readily be identified.

“Imagery is the backdrop for all of the work we do on the ground,” says Bosley.

Making Big Images Work in the Field

But the downside to using the high-resolution images in the field is their enormous file size – about 20 gigabytes each. And multiple images are typically required to map an average project area. Even with an added memory card, a top-of-the-line portable mobile GIS device can’t handle files that large.

Bosley selected the GeoExpress image compression and manipulation software from LizardTech of Seattle because it is capable of shrinking a raster satellite image to five percent of its raw file size without perceptible alteration of pixel values or loss of valuable data content. In addition, GeoExpress offers image clipping, mosaicking and reprojecting tools that accelerate data preparation work prior to heading into the field.

In the field, Bosley hooks the external drive to his laptop computer and uses the GeoExpress software to manipulate and compress the images to suit the needs of the field crews. He usually has the software fuse the scenes into a seamless mosaic, which is accomplished on the fly during the compression process. The output can be saved in a standard file format such as MrSID or JPEG 2000. “The benefit is that you do it all in one process,” he said.

Bosley also uses the software to ‘cookie cut’ small image clips from the large mosaic for members of the crew to use in their assigned portion of the project area.

Building a GIS on the Spot

After the compressed images or image chips have been prepared, they are uploaded from the laptop into Trimble GeoExplorer handheld mobile GIS devices. These rugged field computers have integrated GPS receivers and run ESRI’s ArcPad field mapping software. This application allows Bosley to pre-program a variety of pull-down menus so that attributes relating to ground features can be entered by pointing and clicking on the display screen.

As field technicians view the compressed satellite image onscreen at full resolution, they identify the features they need to map. For example, the technician might walk around a building’s perimeter to collect the precise coordinates of its footprint. Then he or she would access the ‘feature’ menu for structures and enter queries relating to its height, construction type and use. The building’s footprint is automatically added to the GIS layer for structures with all of the relevant attributes attached.

As the GIS is being built on the spot, these layers are compiled by the field software and are automatically rectified with the satellite base map.

“When we start overlaying the different data sets, they are spatially correct with respect to each other,” says Bosley. “If you have trees next to a road, you can measure on the map the correct distance from the edge of the road to a tree.”

Reprojecting Compressed Imagery

One hindrance to using compressed satellite imagery in the field, as De Leon discovered, is that the field mapping software cannot reproject compressed image files.

Based in Houston, Enbridge U.S. is a wholly-owned subsidiary of Canada's Calgary-based Enbridge Inc. It operates pipelines in the Midwest, Mid-Continent and Gulf Coast regions of the United States, and operates natural gas midstream businesses, including gathering, transmission, processing, treating and marketing subsidiaries.

The Enbridge Houston office has a large repository of color and infrared aerial photography purchased from the U.S. Department of Agriculture’s National Agriculture Imagery Program (NAIP). The company also uses one- to three-meter-resolution satellite imagery from the Texas Natural Resources Information System (www.tnris.org), which includes black-and-white, color and infrared.

Reprojection means translating the coordinates and other georeferencing information accompanying the image from one coordinate reference system (a.k.a. spatial reference system) to another. Reprojection is necessary because the vectors are created in their local map projection, State Plane NAD 83 Texas North Feet, which won’t align with the WGS 84 coordinate system that nearly all of the aerial photography is delivered in.

Reprojecting the imagery ensures that the vectors and imagery overlay properly for accurate editing, according to De Leon, whose office spent weeks looking at the various solutions available for working with compressed imagery and only received positive feedback on LizardTech’s GeoExpress.

Benefits of the New Geospatial Technologies

"By reprojecting this imagery with GeoExpress, we've saved literally tens of thousands of dollars over what it would have cost to have each county separately reprojected by a contractor, says De Leon, adding that for cropping and color balancing, using the software also costs Enbridge a fraction of what it would cost to outsource those jobs.

But for both Enbridge and Chevron, the ultimate advantage of using these advanced geospatial technologies is the enhanced productivity of the field crews. They collect a greater volume of information faster than they previously could taking written notes and surveying transits. The end result is that field crews can build a highly accurate GIS for a project site practically from scratch – and sometimes in a matter of days – without leaving the field and maintenance and construction crews can navigate more efficiently. As De Leon says, “Having all the image and map data they need for a job in the palm of their hand saves field operators, measurement technicians, and engineers hours and hours on the road."

*The author wishes to thank Kevin Corbley of Corbley Communications for contributing to the content of this article.