Donald C. Foley, Tarek Y. Ghazi
Conoco Inc.
Houston
Explorationists are using new technologies like UNIX-based workstations and geographical information systems (GIS) to search ancient events for clues that point to the present location of usable sources of oil and gas-no matter how hidden by time or geological changes they might be.
Conoco Inc.'s Advance Exploration Organization (AEO), based in Houston, is in the business of studying foreign sedimentary basins from a regional perspective to evaluate their potential for petroleum exploration. Recently the company decided to focus some of the AEO's resources on developing a global ranking system for those areas of the world where hydrocarbons might occur.
The group needed a way to rank those areas against each other to see where the company might get the highest rate of return.
To accomplish this directive, AEO obtained software from the University of Texas Arlington that rotates continents or portions of continents through time. Using the software, company geoscientists have created a series of maps, known as a PaleoAtlas, that depicts the geography and selected geological features for different periods in Phanerozoic time.
In addition, the AEO has developed a software package based on ARC/INFO (ESRI Inc., Redlands, Calif.), a commercial GIS platform, to manage, integrate, and analyze those "time-slice" maps. Entitled PaleoAtlas Geographic Evaluation System (Pages), this software also sequences portions of the maps in a montage effect that geoscientists can use to study the geological evolution of petroleum source rocks.
'TIME-SLICE' MAPS
The main purpose of the PaleoAtlas project was to summarize the department's knowledge of paleo-global processes for select geologic periods and to identify where they might be favorable for hydrocarbon generation and preservation.
In July 1989, AEO geoscientists began work on a first-pass compilation of "time-slice" maps (Fig. 1)(173300 bytes). Using inhouse data, published data, and their own expertise they identified 14 time slices in geologic history ranging from 600 million years ago to 14 million years ago. The slices they chose represented the most source rock prone and, consequently, oily ages since the Precambrian period.
The next task was to discover how the land masses were situated during each of the time periods. To accomplish this, scientists used the Paleo-Oceanographic Mapping Project (POMP) software program from UT Arlington.
The program consists of plate boundary files and rotation files with poles of rotation for the plates and angles of rotations throughout time. The program enables users to visualize the movement of continental and oceanic plates based on the pattern of continental drift and then adjust or customize the plate boundaries, poles, and angles of rotation based on the new interpretations.
AEO's version of: POMP, running on a graphical workstation, was used to reconstruct the time-slice maps by relocating the continents to where they would have been 600 million years ago and at other points in time. The result was 14 base maps with reconstructed continental plate boundaries that scientists used to assembly geological features and record their interpretations.
The project was then divided up by assigning a different region to a geoscientist or regional expert. The scientists started with a particular time-slice and studied such items as well logs, published maps, and regional seismic data to discover the nature of the deposits or environment of deposition for that time period and location.
They divided environments of deposition into different types such as deep marine deposits, shallow marine or lake deposits, shallow marine and lacustrine sand, continental deposits, volcanic regions, emergent land and porous carbonates like reefs or carbonate platforms as are found in the Bahamas.
In addition to the environments of deposition, locations of documented source rocks and known hydrocarbon occurrences were recorded on the maps. Major tectonic features like fold axes, thrust faults, strike-slip faults, subduction zones, normal faults, coastline and oceanic spreading centers, and the location of deep sea drilling projects were marked as well.
Geoscientists used a predetermined color scheme to depict types of deposits, patterned lines for tectonic features, and color dots to indicate source rock and hydrocarbon locations. They drew boundaries between each of the environments of deposition and joined the regions together on a single global map. The manager who supervised the generation of the global maps then rectified regional discrepancies.
In the end, the scientists had 14 global maps with reconstructed continents and eight or nine different environments of deposition for each of the basin areas. The maps depicted their best guess of paleo-global distributions of land masses and sedimentary environments throughout Phanerozoic time.
GEOLOGIC HISTORY
Realizing that it was going be a monumental task to maintain the integrity of the maps, AEO's next step was a computer implementation of the PaleoAtlas maps.
An electronic map base would make updating and sharing of the information easier and allow scientists to develop customized maps of selected exploration areas more quickly. It became clear that the PaleoAtlas maps would only be useful for exploration if they could be dynamically changed as new data were received.
After much thought, AEO decided to design in-house software to electronically store, retrieve, and modify maps and attribute data. The project was quite complicated, and the scientists knew they were going to have to develop their own frontier-type tool since there weren't any off-the-shelf packages that could be readily altered to fit their needs.
The resulting software was called Pages, and the software platform selected to implement the program was an ARC/INFO GIS running first on a VMS VAX mainframe and later on a series of UNIX-based SUN workstations.
The scientists needed a versatile system. At the time,
ARC/INFO had a more robust, spatial processing engine available (than other GIS packages) and all the tools necessary for moving polygons and rotating data on a map without losing data integrity (Fig. 2)(265081 bytes).
The initial development of Pages started in January 1991. An outside consultant was hired to build the data input, digitizing, and data editing modules. The result was Pages EDIT, an Arc Macro Language (AML) toolbox for capturing the location and important information about points, lines, and polygons in a spatial database. With the application, programmers can update the electronic maps as new data or information are acquired. They can then transfer or incorporate the data into the original database and from that point on, only the most current datasets are displayed.
AEO technicians performed the actual digitization of the 14 hand-drawn maps into ARC/INFO. It was a lengthy process that varied with the skill of the technicians inputting the data. Digitization of a single map could range from a couple of days to several weeks, depending on the amount of detail. Altogether, it took about a year to completely transfer the maps onto the electronic database.
Another outside consultant used AML to develop a desktop window application for Pages called Pages VIEW. The application, designed to be user-friendly for AEO explorationists, incorporates a menu-based system with point-and-click feature operation. One menu offers a selection of time periods from the 14 time-slice, global maps. After pointing and clicking on a particular time-slice, the appropriate map appears on the screen. The system then prompts the user to select the part of the dataset he or she wants plotted on the global map. The user points with a mouse and clicks on the location to see a particular area in more detail. For example, a scientist can point and click at two corners of an area of the Middle East on the time-slice map and the geology for that time period appears.
Pages VIEW also features a montage builder. With this module, the user can create on-screen montages using different frames of Pages information that have been resized for a particular study. Once the features for a map have been selected and drawn, a second map may be created and placed next to the first image on the screen. The module will allow as many as 14 map view panels to be placed on a single screen, an option that explorationists use to study and compare how local geology has evolved through time.
ADVANCED PAGES
When conducting conventional new regional exploration, the explorers work on base maps comprised of present day culture, showing coastlines and geopolitical boundaries, for example. However, posting paleo-geologic data on a present day base can give a completely distorted idea of the geologic history for a region.
In some areas, like Eastern Europe, the present day picture is a complicated jigsaw puzzle of microplates that have been acccreted over time. Turning the clock back is needed to do a meaningful job of exploration.
Phase one of the project included digitization of the 14 global, time-slice maps and development of the software for viewing and maintaining those maps. There are plans for another phase of Pages to let users compare detailed regional studies for unlimited time periods.
One way programmers think this can be accomplished is by incorporating or annexing with Pages the plate boundary and rotation files derived from POMP (University of Texas). Users would then have the option of selecting present day, geological data such as well locations, and seismic lines, having the data electronically attached to tectonic plates and rotated to age-related coordinates.
From the onset, the Conoco group had this functionality in mind as its vision for the system. The members realized they were going to need a way to partition or intersect the plate boundary polygons with depositional environment, lithology, and present day, surface geological information. In order to accomplish (these operations), they needed the spatial operations and utility of a GIS.
They have a whole host of global databases that they can plot on any time slice. For instance, they have information on many of the known wells that were drilled to a certain level such as the Devonian period. They can ask Pages to extract all of those wells and plot them for a region or on a global scale. With future software developments they will be able to rotate those wells to the way they would have been in the Devonian period. Then they can look at the resulting plots to check their database and see where they have data and where they don't have data.
Other software development plans for Pages will give users the ability to interpolate and extrapolate between the original 14 time-slice maps in order to build basemaps for other time periods. In addition, the attribute database will be expanded to include related graphics such as cross-section images, stratigraphic charts, contour maps, and report text.
In their present forms, Pages and ARC/INFO play important roles in Conoco's new ventures exploration studies. Future software developments will only increase the value of the tools. Using these tools to see how local studies fit into a paleo-global setting will help the company better test and extend old plays and hopefully enable scientists to recognize valuable new opportunities hidden within their data.