Chevron field crews use satellite imagery like this QuickBird scene in Africa for environmental analysis. (Image courtesy of Corbley Communications)

Chevron has dramatically improved the efficiency of its field mapping activities in advance of upstream development by enabling its map crews to take huge volumes of geospatial data into the field so that GIS feature layers can be created, edited, and enhanced with attributes on the spot. This process, which some refer to as “mobile GIS,” is made possible by a combination of advanced geospatial hardware, digital field mapping tools, and advanced image compression technologies.

Many of the GIS data layers that eventually find their way into Chevron exploration and production sites around the world start off in an Oracle database managed and maintained by the company’s Technical Computing Information Management Group in Houston. This group provides data 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 GIS analyst with Chevron, explained that while verifying the locations of natural and man-made features in the field is important, the collection of attributes describing them is even more critical due to the engineering planning and environmental reporting that occur prior to — and sometimes during — E&P operations.

Planning a pipeline route, for example, must take into account the costs associated with crossing various types of land cover or circumventing sensitive environmental habitats. In addition, many national governments now require detailed reporting of plant species that may be disturbed or populated buildings that may exist near proposed hydrocarbon development projects. Such information must be collected by field crews during the planning phases and then updated periodically during construction and operational stages.

The information is used, Bosley explained “from the very early stages of scoping the project … all the way up to final as-builts for the project.”

Until a few years ago, the recording of feature locations and collection of attribute data had to be performed manually by survey crews. Taking written notes was an especially time-consuming process that required even more time later for conversion into a digital format. Today, however, nearly the entire procedure — acquiring location coordinates and inputting detailed feature descriptions — occurs digitally thanks to the latest geospatial technology.

A combination of tools

Regardless of the upstream development being planned, field work usually begins with a high-resolution satellite image, and Bosley’s group at Chevron prefers to use QuickBird images from DigitalGlobe of Longmont, Colo. The 2-ft (0.6-m) 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 allof the work we do on the ground,” Bosley said. 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. The only option is compression.

Bosley selected the GeoExpress image compression and manipulation software from LizardTech of Seattle because it is capable of shrinking a raster satellite image to 5% of its normal file size without perceptible alteration of pixel values or loss of valuable data content. In addition, this compression package offers a host of image clipping, mosaicking, and re-projecting tools that accelerate data preparation work prior to heading into the field.

In anticipation of a typical field mapping project, Bosley or one of the other Chevron GIS analysts checks the Oracle spatial database to see if imagery is available for the target site. Chevron uses ArcSDE software from ESRI Inc. of Redlands, Calif., as the front end of its spatial database, allowing for easy Web-based search and retrieval of imagery and other relevant GIS data pertaining to a given project area.

Although ArcSDE makes the database accessible worldwide to Chevron personnel via the Internet, Bosley prefers to retrieve the data files before leaving Houston just in case a high-speed connection is not available in the area he will be mapping. These image files usually are archived in the centralized database in a latitude/longitude map projection. He stores as many as nine QuickBird scenes totaling 200 gigabytes on a portable hard drive and carries it with him to the project area.

Once he arrives at the project site, Bosley hooks the external drive to his laptop computer to start manipulating and compressing the images to suit the needs of the field crews. Working inside of the GeoExpress software on the laptop, he selects the desired satellite images and then applies the tools needed to put them into a usable format. Because image manipulation and processing are usually performed simultaneously with compression, Bosley chooses the algorithms to apply and then lets the software go
to work on the files. “The benefit is that you do it all in one process,” he said.

Typically, he will have the software re-project the images into the local coordinate system of the project area. The compression package comes pre-loaded with conversion routines for more than 2,000 worldwide coordinate systems. He also usually has the software fuse the scenes into a seamless mosaic. The mosaicking and re-projecting are accomplished on the fly during the compression process. The output can be saved in a standard file format such as MrSID or JPEG 2000.

Bosley may return to the compression software periodically during the field work to “cookie cut” small image clips from the large mosaic. This is particularly useful when several field technicians are working on the project site. The base map image can be divided up among them as each person covers an assigned portion of the project area. This image “clipping” process is as simple as using the mouse to delineate an image segment of any shape or size onscreen and then having the software cut it from the mosaic.

Taking data to the field

After the compressed images or image chips have been prepared, they are uploaded from the laptop into one or more 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. If the feature is a building, for example, the technician might walk around its 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 field software automatically adds the building footprint to the GIS layer for structures and attaches all of the relevant attributes to that feature. Within minutes, the technician can move on to the next feature, perhaps a marsh, and begin to map its boundaries and describe the make-up of its vegetation. 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 datasets, they are spatially correct with respect to each other,” said 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.”

For 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 Chevron 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.