USE OF GEOGRAPHIC IN PETROLEUM GEOLOGY INFORMATION SYSTEMS (GIS) By Cengiz Tolga VUR Term Project for Geographic Information Systems in Water Resources Department of Civil Engineering  The University of Texas at Austin December 9th, 1998

  
TABLE OF THE CONTENTS

1. Introduction
2. Background
3. Objectives
4. System Requirements
5. The data
        5.1. Tabular attribute data comprise digital files
        5.2. GIS data comprise digital files
6. Geology and Play Methodology
7. Procedure
        7.1. Obtain GIS and tabular
        7.2. Import GIS digital files to ArcView themes
        7.3. Convert tabular Excel files to .dbf files
        7.4. Join the tables
        7.5. Analyzing attribute data in ArcView environment
            7.5.1. Cumulative oil and gas in place distribution maps
            7.5.2. Porosity distribution map
            7.5.3. Water saturation distribution map
            7.5.4. Reservoir Depth distribution map
8. Conclusion
9. Reference
 
1. Introduction

    Classical petroleum geology applications are basically based on making paper maps to find out geologic features of subject area. Mapping geological atlases are quite difficult and time-consuming work. Recently the data in the atlases are summarized and organized by Geographic Information systems linking map graphics and tabular data in a digital environment.
    The Bureau of Economic Geology (BEG) integrates GIS technology into a wide variety of geologic applications, including petroleum geology, hydrogeology and, environmental geology. My project will focus on petroleum geology subject. The Bureau issuing a digital GIS data set that consists of preliminary aggregated data from the Gas and Oil Atlas Series of the Northern Gulf of Mexico. This data set includes reservoir pool, field, and Play tabular data, as well as GIS files of field and play outlines. This project integrates the GIS and Tabular data together in the Northern Gulf of Mexico data (Figure-1).

Figure-1
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2. Background

    The onshore and offshore of the Gulf of Mexico basin is one of the most productive hydrocarbon basins in the world. The explorations and research are significantly increase on shelf and slope of Gulf of Mexico Basin (Seni and Hentz, 1997). According to Nehring (1991), Gulf of Mexico is such a important basin that has about 9% of liquid hydrocarbon and about 11% gas hydrocarbon known reservoir of the planet.
    The research, preparing Atlas of Northern Gulf of Mexico Gas and Oil Reservoirs, was supported by the Gas Research Institute, the U.S. Department of Energy (Morgantown Energy Technology Center and Bartlesville project Office), and the U.S. Department of the Interior Minerals Management Service. Data were complied and organized by the University of Texas at Austin, Bureau of Economic Geology; the U.S. Department of Interior Minerals Management Service; the Geological Survey of Alabama; and the Louisiana State University Center for Coastal, Energy, and Environment Resources, Basin Research Institute
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3. Objective

    The goal of this term project is to apply Geographic Information Systems (GIS) into petroleum geological applications. The expected results of the project will be basically organized and summarized GIS data and tabular data together in digital environment. So, geological and GIS data will be in same environment to use for other geological applications. Basically the advantages of GIS for petroleum geology are

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4. System Requirements

    The Atlas data files are available for analysis individually or as a group. The files are formatted to run on a PC utilizing Windows 3.1 or higher. The tabular files are formatted in Excel 5.0 and tab-delimited ASCII. The GIS files are formatted in ArcInfo .e00. The user needs a GIS application program to view the GIS files (ArcView 3.0a). GIS data was provided in ArcInfo data exchange format. Tabular files of reservoir-pool data that are associated with the GIS data. They are provided in both Excel and tab-delimited ASCII formats.
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5. The Data

    There are two classes of digital data available for downloading:

  5.1. Tabular attribute data comprise digital files

 5.2. GIS data comprise digital files

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6. Geology and Play methodology

    A play is a group of reservoirs genetically related by depositional origin, structural style or trap type, source rocks, and seals. Plays are determined on the basis of correlation of chronozones, identification of structural and depositional styles, construction of composite type logs of fields, organization of geological data (such as maps and cross sections of type reservoirs), and compilation of geologic and reservoir attribute data on all reservoirs. Retrogradational, aggradational, progradational, and submarine-fan depositional styles are key determinants of plays because they can predict reservoir quality and distribution (Figure-2).

Figure-2

    Structural style determines trapping mechanism. Figure-3 shows schematic cross-section of typical structurally trapped field. Play boundaries enclose fields that contain sandstone-body reservoirs in that play and exclude fields that do not. A play may comprise one or many fields.

Figure-3

    Three are also some other structural traps related to salt domes. Figure-4 shows a North-South cross-section of near Louisiana offshore (Seni and Hentz, 1997).

Figure-4

    Play analysis begins with the correlation of reservoir strata and compilation of reservoir attributes. Initially fields and reservoirs must be correlated within a regional structural-stratigraphic framework. Chronozones provide a temporal framework for grouping reservoirs by age in the Gulf. In the absence of formations, chronozones are typically defined on the basis of biostratigraphic zones. In order to correlate reservoirs within strata of the same age, a Minerals Management Service (MMS)-based chronostratigraphic synthesis of the Gulf was employed according to biostratigraphic zones. Major flooding surfaces and their biostratigraphically rich faunal assemblages are important reference horizons for this chronostratigraphic subdivision (Seni and Hentz, 1997).
    Sixteen chronozones have been identified in the Gulf of Mexico for the Gulf Atlas. From oldest to youngest the chronozones and their abbreviations are:
 

Abbreviation

Chronozone

UU

Jurassic

LK

Lower Cretaceous

OL

Oligocene

LM1

Lower Miocene

LM2

Lower Miocene 2

LM4

Lower Miocene 4

MM4

Middle Miocene 4

MM7

Middle Miocene 7

MM9

Middle Miocene 9

UM1

Upper Miocene 1

UM3

Upper Miocene 3

LP

Lower Pliocene

UP

Upper Pliocene

LPL

Lower Pleistocene

MPL

Middle Pleistocene

UPL

Upper Pleistocene

    See Lower Pliocene plays with State and Federal Fields in ArcView Window: Figure-5 (click to see picture)
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7. Procedure

7.1. Obtain GIS and tabular

    For this project the GIS data and tabular data are available from Bureau of Economic Geology web page. The uncompressed size of that file is 12 Mb.
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7.2. Import GIS digital files to ArcView themes

    IMPORT71 tool is a program that comes with ArcView for Windows and appears as a program item in the ArcView program group, converts an ARC/INFO interchange file created on any coverage or grid. I used IMPORT71 to convert it to add my project and view in ArcView. To run IMPORT71, double-click the IMPORT71 program item in the ArcView program group to display the dialog box.

    See a general view to GIS Data: Figure-6
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7.3. Convert tabular Excel files to .dbf files

    The tabular files are formatted in Excel 5.0 and tab-delimited ASCII. ArcView database support the dBASE files. So, the excel files were saved as in dBASE format (.dbf extension) before joining.
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7.4. Join the tables

    A geographic information system (GIS) provides a better way of viewing and exploring data by linking both graphic and tabular data into an "intelligent" map. By "intelligent" we mean that both the graphic and the table can be queried and can feed back information. For example, by double clicking on a data table, we may be able to locate a field in a graphic illustration. A GIS is also intelligent in that the graphic is generally displayed in real-world coordinates; that is, distances and areas portrayed on the map correspond to real-world locations and distances. If this is your first experience using GIS data, be sure to note that map data (like all types of data) have certain tolerances for accuracy (scale, degree of generalization) or other specific limitations. GIS metadata (data documentation) commonly include how the GIS data were constructed and list any special limitations.
    After adding the themes to view that you want to add data, the excel (dbf) file adds to table. Both ArcView and Excel file should be clicked on the same field. Finally the join tables icon must be click
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7.5. Analyzing attribute data in ArcView environment

    The value of the following attributes can be obtain from the tabular data

    Separate reservoir pool, field, and play data files include the same source data that have been variously grouped, summed, and averaged for the convenience. Pools are aggregations of all sandstone-body reservoirs in a field that occur within the same play, the pool name is the same as the field name. Although records of individual sandstone-body reservoirs are not in this data set, they will be included in the final atlas folios. Because of differences in sources and completeness of data, averaging methods used in this study varied according to source and type of data. Pool values of reservoir attributes have been either summed or weight-averaged, or they have been reported from a dominant reservoir if attributes could not be summed or averaged. If an attribute is a characteristic or a process (that is, a trap or drive mechanism), the dominant characteristic has been listed. Discovery date is the discovery year of the first sandstone-body reservoir discovered.
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    For my project, I analyzed the following attributes,

7.5.1. Cumulative oil and gas in place distribution maps

    All Federal Fields are weighted by reservoir bulk volume of individual sandstone-body reservoirs. If the reservoir contains both oil and gas, then gas is converted to barrels of oil equivalent (5,620 cf gas = 1 bbl oil), and summed with the oil. This averaging emphasizes the attribute values of reservoirs having the most original oil or gas in place. Gas is converted to barrels of oil equivalent (5,620 cf gas = 1 bbl oil) and summed with the oil. Not all pools in a play had enough data for determining original producible in-place gas or oil. However, all pools did have cumulative production statistics.
    With this sense, the following maps were produced with changing the properties of federal and State Fields for chosen pilot area in the project (Figure-7).
    ArcView has an option to show the particular fields with block diagrams.  and Figure-8 shows this view on the pilot area.
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7.5.2. Porosity distribution map

    Porosity is the ratio of the volume of all the interconnected pores to the total volume of a rock unit, expressed as a percentage (Figure-9).

Figure-9

    Only the pores that are connected with other pores (the effective porosity) are capable of accumulating petroleum. With that sense, Figure-10 was produced for the pilot area. The porosity ranges 0% to 36% for State Fields and 10% to 39% for Federal Fields.
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7.5.3. Water saturation distribution map

    Water saturation represents the volume of pore space that is taken up by interstitial water. This water clings to the grains of the rock, making the passageways for oil. Figure-11 shows the distribution map of water saturation for fields in pilot area. Water saturation ranges 0% to 60% for State Fields and 10% to 38% for Federal Fields.
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7.5.4. Reservoir Depth distribution map

    Weighted average of water depth (in feet) of all sandstone-body reservoirs in fields. Figure-12 shows the distribution maps of reservoir depth for fields. The reservoir depth ranges is 1,570 feet to 65,553 feet for State Fields and 1,285 feet to 22,600 feet for Federal Fields. The reservoir depth for State field is higher than federal fields because State fields belong to much more deep pools on the shelf of Gulf of Mexico.
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8. CONCLUSION
 
    Classical petroleum geology applications baded on producing paper maps to reseach geologic interest area. Mapping petroleum geology related maps is quite difficult and time consuming. Resently Geographic Information Systems (GIS) provides a better way of viewing and exploring data by linking both graphic and tabular data into a graphically "intelligent" map with supportive tabular information.
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9. REFERENCES

Bureau of Economic Geology Home page: http://www.utexas.edu/depts/beg/gis.html

Seni S.J. and Hentz, T.F., 1997, Northern Gulf of Mexico Atlas, The university of Texas at Austin, Bureau of Economic Geology, p. 1-5.

Nehring, R., 1991, Oil and Gas Resources, in Salvador, A., ed., The Gulf of Mexico Basin; Boulder, Colorado, Geological Society of America, The Geology of North America, v. J, p. 445-494.

Morris, J., House, R. and McCann-Baker, A., 1985, Practical petroleum Geology, Petroleum Extension Service, Division of Continuing Education, University of Texas at Austin.
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