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Use of Geographic Information Systems in Hydrocarbon Resource Assessment and Opportunity Analysis
Kenneth C. Hood
Bernard C. South
F. Dennis Walton
Otha D. Baldwin
William A. BurroughsExxon Exploration Company (now part of ExxonMobil)
Houston, Texas, U.S.A.
Analysis of undiscovered resource potential is a critical aspect of the petroleum exploration business. The probable number and size of undiscovered oil and gas fields, coupled with economic considerations, forms the basis for determining which areas are most favorable for exploration. Geographic information systems (GIS) provide an excellent tool for analyzing remaining exploration potential and comparing the results among areas. To be effective, the method used must be applicable to settings in which the amount of information available varies widely.
One of the best ways to assess undiscovered potential is in the context of the overall hydrocarbon system. The hydrocarbon systems approach considers the overall history of hydrocarbons, from generation and migration out of primary source intervals to entrapment and retention at reservoir levels. Each hydrocarbon system can be subdivided into one or more exploration plays or families of fields and prospects having similar geologic controls. Geologic maps are constructed for each play element (e.g., source, migration, reservoir, trap/seal) within a hydrocarbon system. Some elements, such as reservoir and seal, must be analyzed separately for each stratigraphic interval. Other elements may be the same for multiple intervals (i.e., several reservoir levels may depend on the distribution and maturity of a single source). In many cases, play element maps may be constructed by combining information from several geologic maps. As an example, a trap adequacy map may be derived from the combination of maps representing structural style and top-seal distribution.
Individual play element maps can be spatially joined to create a play summary map. The play summary map, which encapsulates the best understanding of the geologic controls on hydrocarbon distribution, can be calibrated to
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historical data (fields and dry structures) to quantify spatial variation in geologic risk. Locations of undrilled prospects can be spatially joined to the play summary map to provide an estimate of the geologic risk for each prospect that is attributable to the regional geology. Counts of known prospects, coupled with an estimate of the number of prospects inferred to exist in unmapped or data-limited areas, can be melded with the geologic risk to estimate the number of future fields. The risked mean volume of undiscovered hydrocarbons for each exploration play can be calculated by multiplying the risked number of future fields times the average size of future fields. Because much of the input into this overall process is based on geologic maps, the assessment results can be kept current as the maps are updated.
Although an understanding of the undiscovered resource potential is a critical piece of an exploration evaluation, it is but one component of opportunity portfolio management. Many areas provide a wide variety of other opportunity types, including discovered undeveloped and enhanced-recovery possibilities. Incorporation of all opportunity types into a GIS provides a highly effective planning tool because the results can be partitioned both spatially and by opportunity type to answer a variety of business questions. For example, undiscovered potential located beneath producing fields (deeper pool objectives) might have a different strategic or business value than undiscovered potential in untested structures. Additionally, assessment results for multiple stratigraphic intervals can be combined to identify areas containing stacked pay potential. A GIS-based analysis tool can be invaluable when attempting to develop a strategic acreage position through acquisition or trade.
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