Bill B. Crow
GPS Technology Corp.
Houston
Three relatively new positioning technologies are being used within the oil industry to cut costs and improve profitability. These technologies are the Navstar satellite global positioning system (GPS), digital orthomaps (DOMs), and geographic information systems (GISs).
With these tools, oil company professionals are more accurately positioning their data and making decisions from geometrically correct geographic foundations. Time and money are no longer being wasted attempting to solve location uncertainties.
Three case studies illustrate the improved productivity being achieved.
CORRECT FOUNDATION
One way to build the proper aeographic foundation for a company's geo-scientific data asset is to integrate information from both historical and ongoing operations into a geometrically correct digital base map. This can be achieved today by the combined use of GPS, DOM, and GIS technologies.
The Navstar GPS is a system that is commonly understood within the petroleum industry. It can provide geodetic control points, orthophoto control, and realtime digital GPS fixes for any type of field work, such as seismic surveys or pipeline operations.
Digital orthomaps, as seen in Fig. 1, are less familiar to the oil industry. DOMs are seamless mosaics of digital orthophotographs of the ground that provide a geodetically correct backdrop for use on either a GIS equipped workstation or a light table. TheN" are produced from either high-altitude photographs or satellite images and are used to visually and accurately determine the geographic coordinates of any fixed object on the ground, such as a seismic shot point flag wellhead, or pipeline.
Using differential GPS positioning in the field and plotting one's position on a DOM results in highly accurate location information.
Guessing is eliminated.
While GIS technology has helped users manage ever larger data volumes, GIS systems with geographic foundations built on out-of-date maps have often failed to meet cost, efficiency, and automation expectations. A geometrically accurate foundation for GIS systems has long been needed. The merging of GPS and DOM technologies now provides this foundation and thus promises to improve the accuracy and value of GIS systems. Using seamless DOM images as the geographic foundation, GPS survey and other types of geographically-based data can be fed into and integrated by a computerized GIS. The maps and images output to the enduser are more dependable and accurate.
Specifically focusing on the oil industry, integrating GPS, DOM, and GIS technologies provides the means to optimize three vital functions. These are planning, infield quality control of surveying and operations, and data correction and integration.
PLANNING
Good planning cuts field development costs for acquiring seismic data, setting well locations, and similar operations. It also facilitates improved cost estimates, prior to project initiation. With a DOM, which provides a geodetically correct, photographic base map prior to arriving in the field, one can actually see and precisely determine the areas best suited to a specific project, and those areas that are not.
For example, roads, trails or cleared fields can be selected for seismic vibrator truck activities. Clearings can be chosen over wooded areas when laving out seismic shot hole operations. Land use also can be distinguished on a DOM, which facilitates ownership and permitting activities.
Good planning is further attained by using DOMs as the foundation for integrating various geoscience data for further presurvey analysis. Simply put, when presurvey data analysis is tied to a geodetically correct base, the survey that follows is more accurate. The longhand method for doing this is by directly digitizing data onto a DOM foundation on a light table. Other methods include using GIS work stations with vector-over-raster integration capabilities that can overlay multiple vector data layers over DOMS, or choosing a software package that can directly import DOM data.
IN-FIELD QUALITY CONTROL
Quality control is optimized when every member of a field crew can confidently fix their location on the survey map. Because of the photographic perspective and accuracy provided by DOMS, their use provides each member of a surveying crew a "you are here" mentality (Fig. 2).
Combined use of DOMs and real-time differential GPS ensures that surveying to collect seismic data, or locate wells or pipelines can be done routinely with fewer errors than with conventional methods. Use of handheld GPS receivers enables location errors to be detected and corrected as a project is proceeding. This improves quality control and saves money as it is easier to answer uncertainties while a crew is still in the field.
DOMs also can be used as a communication device for daily operational planning, and between field and office managers for problem solving. A "photomap" or DOM increases everyone's ability to communicate around a common point of reference. Improved communication enhances operational efficiency.
DATA CORRECTION, INTEGRATION
When integrating data of various types from various sources into one project, is it is a challenge to ensure that all are geodetically correct. When using DOMs for the geographic foundation, new seismic data can be correctly tied to historical information and the resulting seismic interpretation can be integrated with well and property information without fear of error. That is, they are each corrected or "fixed" so that integration is possible. As stated before, this is accomplished with digital data by using the vectorover-raster capabilities of GIS hardware and software. For an analog solution, a table digitizer can be used.
When geologists and geophysicists spend less time chasing down location uncertainties, interpretation costs go down. And with fewer location errors, fewer mislocated wells and improperly designed reservoir enhancement programs occur.
ANADARKO BASIN SEISMIC
Recently a geophysicists for Amoco Production Co.'s Midcontinent business unit, Klaas Koster, used combined GPS/DOM technologies to carry out seismic projects from planning through data acquisition and interpretation.
His procedure included roughly designing a survey over a gross area of interest as seen on SPOT satellite images, with about 10 m resolution. Having narrowed down the area of interest in this way, the appropriate DOM images with 2 m resolution were then obtained for more accurate survey planning.
A digital file of the DOM images was ported into a workstation-supported seismic survey design package. Viewing these images on the workstation screen, any physical obstructions (man made or natural) in the survey area were taken into consideration and designed around. Thus avoiding highcost routes, Koster reduced permitting and bulldozing fees.
Because the DOM images are orthorectified, the size and locations of the pixels as viewed on the screen are accurate. That is, by distances in the orthophotograph are true. Thus, once a survey route was determined by Koster, true ground locations could be taken from the DOM image.
Shot point location coordinates were output in a digital file and used in the field by loading them directly into hand-held differential GPS equipment as way points, Only one professional surveyor was required per crew to oversee all the ground work done, as survey crew members were led by the GPS system to the true ground locations chosen. Shot points were fixed with confidence and survey flags were planted almost as fast as the surveying crew could walk. This method varied considerably from traditional surveying operations.
Assigned a 3D seismic project within Oklahoma's Anadarko basin, Koster achieved 10 to 15 ft base map accuracy for planning, using the GPS/DOM methodology outlined. The maps used were more up-to-date than those based on U.S.G.S. quads or old aerial photos.
That is, streams had not changed course and new buildings or roads had not sprung up to cause in-field course changes. This resulted in a 2:1 reduction in seismic permitting costs and a 5:1 improvement in the amount of crowd covered by the field crew per day. Overall, the cost to survey and lay line dropped by 6:1, or from $9,000/sq mile based on a contractor bid using traditional seismic surveying methods, to about $1,500/sq mile using a company crew and the methods cited.
Koster also was pleased with the resulting accuracy of this Anadarko survey. There were very few shot receiver locations in error on the Anadarko project using the new method, said Koster, and of those, most were 1 to 2 ft or less, which is well within current seismic surveying specifications. In this type of work, the inches of accuracy that might be achieved using traditional surveying techniques to lay out a seismic job are not required and are typically too costly. The reliable 2 m DOM base map met all of our requirements at much less cost, emphasized Koster.
All-round error reduction and cost/time savings on the Anadarko basin project were partially due to the improved communications achieved between field crews and office staff, Koster said. Both parties could talk over areas of concern and agree on permitting changes or in-field survey changes while looking at the same up-to-date photo image provided by the DOM base map.
The time from initial survey design to processed data in hand was only about 3-4 months, said Koster, who interpreted the results himself on the same system that was used to plan the survey. The accuracies, functionality, and ease-of-use of the technologies applied helped Koster achieve this quick turnaround.
Koster has been watching the advancement of the GPS/DOM/GIS technologies for several years. One to two years ago, these were difficult to use in combination, he said, due to lack of software capabilities on E&P workstations. With the advancement of vector-overraster capability, this obstacle has eroded. Koster says the strength of these combined technologies is catching on rapidly throughout the industry-within operator and contracting companies alike. Even for independents, Koster believes that if more than an occasional 3D survey is needed, the startup price for these technologies will pay off.
VERIFYING, INTEGRATING A MAJOR'S DATA ASSET
Creating a highly accurate, digital Geographic foundation that can be used throughout the corporation is the task of a recently formed GIS group at a major oil company.
In existence for nearly two years, this group has chosen to build its geographic foundation on 1 m DOMs from newly flown aerial photography. After examining other routes to a geographic foundation, DOMs were chosen in order to achieve data location accuracies of 2 m or better.
Previously, the company had been working, with data containing positional errors ranging from 10 m to 1,000 M, and too much time was spent fixing these location errors. District managers therefore be-an the current GIS effort to create a network of digital base maps whose data were already verified to meet the 2 m standard.
This level of accuracy has been found to be particularly important to the company's production geologists. Creating subsurface maps for production enhancement and infill drilling programs demands extreme positional accuracy. Production geologists continue to be the most frequent users of the map products being - output by GIS. However, geophysicists are currently looking at the 2 m version of the DOM product, and facilities engineers are exploring a more detailed, low altitude (1,5002,000 ft), higher resolution version for facilities management and maintenance.
To create their map product, the GIS group requests an area of interest to be flown at an optimal 1:24,000 scale, which creates images at 1 in. equals 2,000 ft. These images are orthorectifted to ground truth and output into TIFF (pictorial) files as DOMS.
The DOMs are loaded into a workstation-based GIS package, where other survey data are integrated with them.
The DOM map is one of the primary ground truths to which the other data are corrected. All types of survey data are included-township and range boundaries, state and county lines, section and abstract numbers, ownership data, political entities, well spots, lease lines, and more. With all these data being acquired at different times, with differing methods, and by a variety of companies, matching them all to a correct, common base is important, and tedious.
Yet data verification at this step, conducted by specialists as an ongoing assignment, has freed company geologists' and other end users from being sidetracked into the data fixing business. Instead, the digital base map product delivered on line by the GIS group can be confidently imported into other data analysis and mapping packages, improving the geoscientist's resulting interpretation or the landman's resulting decision. A standard of mapping quality is ensured throughout the company.
Because this is a new technology application for the company, it is taking time for end users to spread the word about its potential. Likewise, it will take time for the hardware, software and people investment in this project to pay off. However, a spokesman for the company's GIS group says that feedback from end users is positive, and use of the technology is spreading. The bet is that hi,-h data accuracy will pay off on the bottom line.
ARDMORE BASIN SEISMIC
DOMs played a role in the design of a 3D seismic project in the northwest corner of the Oklahoma Ardmore basin, conducted by Texaco geophysicists Stephen Gardner. The company's intent was not only to achieve a high-quality seismic survey, says Gardner, but also to minimize impact on the area and reduce acquisition costs by minimizing site logistics.
This was not an easy task, as the survey area encompassed 11 sq mi, 840 oil and gas wells (some containing H2S), two gas plants, a spider web of oil and gas supply lines, and many topographic features such as streams. Laving out the traditional orthogonal shotreceiver pattern of a 3D survey around all of these elements while keeping vibrator trucks positioned on existing roads and trails was a challenge.
DOMs provided both the geometric accuracy and up-to-date visual record required to tightly plan this type of seismic survey prior to sending a crew to the field, says Gardner. Using a less accurate planning base would result in many problems arising in the field, which increases permitting fees and suney time. The risk of unintentionally breaking a pipeline in this area also would increase if a less accurate base were used.
Gardner designed this seismic survey by importing DOM digital files into a PC based, design/drafting package with vector-overraster capability. The final layout was then imported into a seismic survey design software package yielding coordinate locations for shot and receiver points.
For this particular job, GPS surveying of shot and receiver stations was not possible as there were too many trees. Traditional field surveying was therefore used to complete the project. However, using DOMs with 2 m resolution for the planning stage alone saved Texaco an estimated $300,000 in acquisition costs.
There were also intangible savings in time and costs avoided. For example, despite the tough logistics of the survey area, no redesign of the survey in the field was required. Gardner say's that using DOMs enabled the survey to be optimally designed the first time. No one needed to be in the field with brush cutters or software to modify the design. Of course, there is still a certain element of "ground truthing" involved, says Gardner, due to the use of a 2 m resolution DOM base instead of 1 m, and due to unavoidable weather changes. However, the 2 m resolution data set was quite adequate for seismic survey design.
In hindsight, Gardner says he could have saved additional time and money on this project by having permitting agents use the DOM base map as well, and may do so in the future. Gardner is also considering using 1 m DOMs for updating ",ell locations. It is through using a new technology, like the DOMS, that new applications arise.
Copyright 1994 Oil & Gas Journal. All Rights Reserved.
Issue date: 11/21/94
