REMOTE SENSING/GIS/CAD: Assessing
Field Remediation Economics with Integrated Data Analysis
Two companies team to develop a thematic imaging and spatial analysis technique for exploration and field purchase purposes.
By Jim Walsh

Purchasing an existing production operation has always required a detailed examination of field economics. The primary concern focuses on whether future production will cover the cost of buying the concession, upgrading older facilities and, in many cases, applying expensive enhanced recovery techniques to spike production.
      In recent years, however, environmental considerations have dramatically complicated the economic calculations related to field purchases. Besides taking into account field operating expenses, potential buyers must also add into the equation the cost of assessing and remediating any existing environmental contamination at the site. The buyer is wise to ensure that clean-up liability is established before proceeding with the transaction.
      Today, much exploration and field purchases occur internationally where pre-existing environmental damage is large, but liability laws are inconsistent. This situation places the potential buyer in jeopardy. Even when responsibility does not transfer, the purchaser still must document the degree of existing contamination to avoid taking the blame for it in the future. In countries where liability laws are less clear, the purchaser needs to quantify potential remediation costs that it may incur and take those expenses into account when weighing the field's operating costs against its output.
      In a best case scenario, the purchaser can identify the extent of pollution up front and insist the seller pay for the cleanup or include compensation in the purchase negotiations. Advance knowledge of field conditions also enables the purchaser to protect itself from future liability for past contamination.
      "A potential purchaser of a petroleum production operation needs a very accurate and defensible technology to identify contamination, quantify its extent, and put a dollar value on its clean-up," said Clark Hull, international environmental manager for Occidental Oil & Gas Corp. (Oxy) in Bakersfield, Calif.
      Over the past five years, Oxy has worked closely with Walsh Environmental Scientists & Engineers Inc. of Boulder, Colo., to develop a thematic imaging and spatial analysis technique that accomplishes those objectives. The process quantifies hydrocarbon contamination of soil and ground water at oil fields and can be applied in virtually any terrain conditions.
      The technique has been built around the TNTmips image processing software developed by MicroImages of Lincoln, Neb., and integrates a variety of satellite images, aerial photography, field database information, and GIS analysis routines.
      In 1994, Walsh employed this technique at the request of Oxy in a South American oil field where the oil company was planning to place a privatization bid. The results revealed unexpectedly high levels of contamination that would have adversely affected the economics of the field's operations, which was considered in the decision not to operate the property.

First Full-Scale Application
In the summer of 1994, Oxy was invited to submit a bid on a large producing block being privatized in South America. The block had been under government production for more than 30 years. In this particular country, the purchaser would assume environmental liability for existing conditions unless other arrangements were negotiated.
      Walsh and Oxy field crews made cursory inspections of the site on the ground. They identified considerable petroleum contamination in the soil around at least 22 major facilities - tank batteries, well pads, manifolds, and processing plants. The crew also noted that many pipes and wellheads were in poor condition with noticeable leakage.
      Oil contamination was readily visible to the naked eye, staining the hard-packed, dry soil dark brown or black. The crew also identified several drainages running though the site, leading them to believe that ground water may also have been contaminated.
      "The entire block covered 165 square kilometers, which would have taken too long to map on foot," said Beth Behl, GIS/remote sensing laboratory manager at Walsh Environmental. "We decided to map contamination around the facilities by air, shooting 35mm still photographs and High-8 color video."
      Oxy obtained the services of a military helicopter and pilot. One problem had to be solved immediately - the helicopter was not rigged for aerial photography. It did, however, have a machine gun mount which Walsh technicians converted into a 48-inch boom for the two cameras. (For continuing projects in other areas, Oxy utilizes a helicopter with a belly camera mount capability.)
      Prior to flying the block, the field crew placed 7'x 9' blue tarps next to major facilities in the field. Facility identification numbers were painted on the tarps so the photographs could be easily georeferenced to field maps. The known dimensions of the tarps would also enable the image processing technicians to calibrate the scale of the photos and video.
     Real-life field projects always teach new lessons. Several tarps had to be replaced because they were taken during the night by local goat farmers who used them to fortify their huts.
     Actual photography took two days, with the pilots requiring several practice runs to perfect lining the 48-inch camera boom up with desired targets. The aerial work was flown at 200 meters above ground level and was conducted in several passes over and around the production facilities.

Processing the Imagery
Walsh acquired the photos and video to calculate the areal extent of contamination on the surface of the ground. The 35mm negatives and video were taken back to Boulder for processing and analysis.
      "As soon as we saw the pictures, we confirmed what we had already suspected about the contamination," said Behl. "It wasn't limited to areas around the facilities. The whole area was a mess due to leaky pipes and lateral seepage."
      Walsh immediately placed an order for a SPOT panchromatic satellite image of the entire block. In the meantime, the image processing laboratory technicians began analyzing the photos and video.
      Commercially available TNTmips image processing software was chosen for the analysis because of its ability to integrate raster and vector data, along with CAD files and other database files in a single processing environment where intelligible information can be extracted. All of these different types of data were eventually required in the project.
      The 35mm photos were loaded into the image processing system as raster files on CD, while the necessary video frames were grabbed and imported using a Targa board. Originally, the technicians expected to perform primary feature mapping with the video, filling in with 35mm where needed. However, just the opposite was done due to the high quality of the photos. A total of 22 photos and video frames were used to cover the major facilities.
      "We used the 'Feature Map Process' in the TNTmips software to run supervised classifications on the photos and draw vector outlines around areas of contamination," explained Fred Groth, a Walsh remote sensing specialist. "In some cases, mesquite vegetation had similar spectral signatures as oil patches, but these were easily discerned by visual inspection on screen."
      The SPOT image of the entire block arrived and was loaded directly into the system. Minor enhancing was applied to highlight the stained soil. Oxy provided a CAD file showing the locations of all wells and production facilities in the field. This file was overlaid on the SPOT image in the system to facilitate feature mapping.
      The technicians used training sets extracted from the photos to run supervised classifications on the satellite image. As with the photos, vegetation was sometimes included in the same spectral classes as oil stains, but visual clarification on-screen was difficult because the 10-meter satellite image was coarser than the air photos.
      "In those cases, we referred to the CAD overlay to determine whether a feature was an oil stain or vegetation," said Groth. "If the uncertain feature was located near any field facility or pipeline, it was assumed to be contaminated soil." Walsh used a statistical software package to verify the accuracy of the SPOT vector map against the 35mm feature maps. The correlation was 90 percent. This finalized vector map enabled Walsh to calculate that contaminated surface area at the block was 494,000 square meters.

Field Checking Soil and Water
Two weeks later, Walsh and Oxy crews were back in the field equipped with vector maps of contaminated areas. The crews used these to decide where backhoe trenches should be excavated and soil samples taken. Due to concerns over ground water pollution, trenching focused in the natural drainages.
      Soil analysis revealed that total extractable petroleum hydrocarbons in contaminated soils ranged from 110 to 150,000 milligrams per kilogram (mg/kg) with an average of 50,000 mg/kg. In many areas the soil was saturated at least to 2.5 meters below the surface. Ground water samples confirmed the presence of hydrocarbons in some locations.
      Walsh calculated that in the vicinity of 16 major facilities where soil samples were taken, 230,000 cubic meters of soil was contaminated. Based on the total surface area pollution determined from the photos and satellite image, the scientists extrapolated cubic volume of soil contamination for the entire block.
      The technicians turned their finding over to Oxy environmental scientists so they could convert the contamination information into cleanup cost estimates. Oxy received a written report as well as a copy of the GIS database compiled in TNTmips.
      Walsh combined the field sample data with the feature map images in the image processing system to make the results more easily understandable. Soil and water sampling tables were attached directly to the overlaid image/photo/CAD map in the system. This enabled Oxy personnel to view the raster and vector maps of the field and click on a soil sampling site to pull up exact contamination figures for that site.

Economics Didn't Add Up
Based on the total volume of soil contamination, Oxy officials calculated the cost to remediate the site. They weighed those costs against the production potential and concluded the investment was not economically justified.
      "The contract was not constructed in such a way that we could have avoided paying for the cleanup ourselves," said Hull.
      Although the property was not purchased, Oxy deemed the project a complete success because it served as the testing ground to fine tune the analysis technique which it has since used in several other fields. Oxy has successfully applied it at production sites in desert, rainforest and temperate regions of South America, Asia and the Middle East.
      Hull is quick to point out that the utility of image processing and spatial analysis techniques for environmental assessment is not limited to due-diligence in preparation for field acquisition. Oxy has integrated different aspects of these technologies into virtually every step of its exploration and production processes at old and new fields, along seismic lines, in pipeline corridors, and even at staff housing sites.

About the Author:
Jim Walsh is president of Walsh Environmental Scientists and Engineers Inc. in Boulder, Colo. He may be reached at 303- 443-3282 or by e-mail at [email protected]

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