Central Region Energy Resources Team

Digital Geologic Maps Support
USGS World Energy Assessment

By Thomas S. Ahlbrandt and Christopher J. Schenk

Published in the American Oil & Gas Reporter, Vol. 39, No. 5, May 1996

DENVER­Independent petroleum companies in search of world energy information will find a new digital resource in the World Energy Project (WEP) underway at the U.S. Geological Survey (USGS).

The USGS periodically assesses the undiscovered petroleum resources of the United States and the world. The most recent national assessment was completed in 1995, and the last world assessment was completed in 1994. It is important for the United States to maintain a current, reliable and objective assessment of the world's energy resources because of increased national dependence on foreign petroleum, increasing worldwide energy demand and unprecedented growth of the global population.

The need for an objective assessment is heightened considering the political instability in at least two major petroleum exporting regions: the former Soviet Union and the Middle East. At present, the USGS is undertaking a new assessment of undiscovered, technically recoverable oil and gas resources of the world, which will identify petroleum systems and report all supporting information in a digital format on CD-ROM. An intermediate goal of the World Energy Project is to report initial results for "high priority" provinces and systems. A report will be presented at the World Petroleum Congress to be held in Beijing, China in October, 1997.

Digital Displays

Fig. 1Digital maps are but one product planned for the WEP. Digital displays of all supporting assessment information are also planned. The five year project has been underway for about a year and one of the first products being developed is a series of digital geologic maps of the world. The world assessment is divided into eight regions, based upon U.S. State Department regions, each with a regional coordinator. These regions are illustrated in Figure 1 (63K GIF) and include: Region 1 (former Soviet Union); Region 2 (the Middle East and North Africa); Region 3 (East Asia and Pacific); Region 4 (Europe); Region 5 (North American Free Trade Agreement); Region 6 (Central and South America); Region 7 (Sub-Saharan Africa and Antarctica); and Region 8 (South Asia).

The USGS is designing the digital products so that an exploration company can compare the resource potential of one petroleum system or province against all others, gain an estimate of undiscovered resource potential, or conduct its own economic evaluation based on both discovered and undiscovered resource numbers. This is the same approach that the USGS developed in the 1995 national assessment based upon advice from industry and the Resource Evaluation Committee of the American Association of Petroleum Geologists.

The final products of the 1995 national assessment of the undiscovered, technically recoverable oil and gas resources of the nation, both onshore and beneath state waters, were a series of CD-ROMs. DDS-30 has already been made available and DDS-35 and DDS-36 were to be released this month. These CD-ROMs allow investigators to review the hydrocarbon potential of more than 600 conventional and unconventional plays and download this information into a geographic information system for further investigation.

The CD-ROMs also contain a series of maps which the oil and gas industry had advised the USGS were a critical resource desired by any investigator of oil and gas resources. The maps demonstrate the play outlines, the petroleum production for each play, and other information including a description of the play, a play bibliography, and a series of supporting resource information (such as plots of cumulative discoveries by year versus field size, depth of potential reservoirs, etc.).

The world assessment will contain a series of digitally based geologic maps of the world with overlays defining petroleum province boundaries and oil and gas fields. The USGS has initially focused on preparing a series of geologic maps prepared in a GIS format (Environmental Systems Research Institute Inc.'s Arc/INFO), upon which a series of topical layers can be superimposed. The process of creating geologic bases at large scales (generally 1-to-2.5 million or larger) in a GIS format is a labor intensive but necessary effort in the assessment process in defining petroleum system and provinces.

South America Example

Fig. 2The assessment of oil and gas resources in a region the size of South America requires a suitable digital geologic base map and digital oil and gas data (Figure 2; 95K GIF). The assessment process in Region 5 began by producing a digital geologic map utilizing a published map of South America at a scale of 1-to-5 million in a bipolar oblique projection. The first step is producing a hand drawn mylar overlay of all geologic boundaries on the map. The overlay was then scanned using a large-format scanner, and the data were converted into a vector coverage in Arc/INFO. The source map exhibited 150 categories of geology, which were distilled to roughly 40 categories on the final digital map. These 40 categories will be used world-wide.

Once the geologic map was constructed, the next step was to produce a digital layer of topical data in Arc/Info (also called a coverage) of the South America oil and gas data. Using a commercial database, a coverage of oil and gas fields, and a coverage of oil and gas wells are created. Because Arc/INFO is a relational data base, the oil and gas data for the fields and wells are stored as coverages in a bipolar oblique projection.

The geologic map, the oil and gas field coverage, and the oil and gas well coverages were then used as background for delineating of the geologic provinces in South America as shown on Figure 2. All of South America was divided into provinces, regardless of resource potential. The 2000-meter isobath was used as the offshore limit for geologic provinces. Each province was named and numbered, and this information was entered into the relational data base. The province boundary coverage and the oil and gas field and well coverages were digitally overlain, allowing each field and well to be tagged with its respective province number. In this way, data can be easily retrieved by province.
Fig. 3

The next step in the pre-assessment process is to define petroleum systems within provinces to be assessed. Coverages are being made of the distribution of source rocks, reservoirs, seals, and the location of structures. Maps of the limits of the petroleum systems will be produced, and the oil and gas data are then further digitally tagged to each petroleum system.

The Region 5 map was entirely generated by the USGS. However, cooperative efforts exist with several foreign and domestic groups that separately fund research and assessment efforts. Of particular note is a joint effort with Russian and Ukrainian petroleum institutes such as VINIGNI (Moscow), VINIGRI (St. Petersburg), and UkrGGRI (Kiev) in Region 1. Digital products of these efforts in Russia include a geologic map with mineral deposits and a data base on these deposits, and a petroleum basin map with more than 2,000 oil and gas fields and corresponding database (
Figure 3; 95K GIF). The efforts are funded through the U.S.AID program, with review and possible future participation from industry consortiums.


Assessment Methodology

The assessment process requires adopting of a methodology to provide estimates of the numbers and sizes of fields, as well as total hydrocarbon resources. One methodology under consideration is the GRASP (geological resource assessment program) model. This system is versatile, with the ability to accommodate almost any level of available data ranging from a handful of discovered accumulations to detailed analysis of reservoir-level parameters for as many as 600 discovered accumulations within a given province or petroleum system.

Other methodologies that will also be used include the truncated shifted pareto (TSP) model for sizes and numbers of undiscovered fields, and the Arps-Roberts discovery process model. This latter method will be most useful in those basins and petroleum systems within which numerous fields have been discovered, and for which significant exploratory drilling data exist. A final technique will also be utilized which fits a power-law curve to discovered field data: the so-called fractal, which will be used to calibrate the other techniques.

Petroleum systems will be the basic unit of the assessment, and oil, natural gas and gas liquids will be assessed in the significant petroleum systems. Initial efforts will focus on the potential for undiscovered, conventional accumulations larger than 100 million barrels of oil in place (600 billion cubic feet of natural gas).

Fig. 4An example of an initial test area where the USGS compiling information is the Neuquen Basin in Argentina (Figure 4; 63K GIF). Significant unconventional resources of sufficient size to warrant consideration such as those of the Middle East, Russia and South America will be considered using a separate methodology similar to that used in the U.S. assessment. The project is currently defining provinces within all regions of the world, and focusing on the highest priority petroleum systems, or those having the largest potential resources.

The ultimate goal of the USGS World Energy Project is to provide a new world assessment of future fossil energy supplies (oil, natural gas, gas liquids and eventually coal resources) and provide these products in a digital form. Digital products that are nearing completion are Central and South America, the former Soviet Union, Europe, the Middle East and Mexico. Digital geologic map production efforts have started in all of the regions shown in Figure 1.

Editor's Note: For additional information regarding the World Energy Project, contact Tom Ahlbrandt at the U.S. Geological Survey, Box 25046, Federal Center, Denver, CO 80225-0046; phone 303-236-5776. The authors wish to thank James Schmoker and Robert Zech of the U.S. Geological Survey for their assistance in reviewing this article. The use of specific products, computer systems or software does not constitute a formal endorsement by the USGS.

Author Information
Thomas S. Ahlbrandt is the Project Chief of the World Energy Project and coordinator for Region 2, the Middle East. He received a B.A. and Ph.D. in geology at the University of Wyoming. Ahlbrandt serves on the Executive Committee of the American Association of Petroleum Geologists, and on the U.S. National Committee for the World Petroleum Congress. From 1965 to 1988, he worked for Exxon, USGS, Amoco, Amerada, MRO and Associates, and was a Partner in Petrostrat Consultants. He rejoined the USGS in 1988, and has held various energy positions in Reston, Virginia and in Denver.

Christopher J. Schenk is a research geologist with the U.S. Geological Survey Energy Group in Denver. He received an M.S. in geology from the University of Michigan, and a Ph.D. in geology from the University of Colorado. For the past 17 years, Schenk has focused on reservoir characterization, sequence stratigraphy, and resource assessment in several domestic basins, particularly the U.S. Gulf Coast. He is regional coordinator for the assessment of resources in Central and South America.

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