Atoka Group (Lower-Middle Pennsylvanian), Northern Fort Worth Basin, Texas:... Digital Download

RI0125D. Atoka Group (Lower-Middle Pennsylvanian), Northern Fort Worth Basin, Texas: Terrigenous Depositional Systems, Diagenesis, and Reservoir Distribution and Quality, by D. M. Thompson. 62 p., 27 figs., 5 tables, 19 plates, 1982. doi.org/10.23867/RI0125D. Downloadable PDF.  To purchase this publication in book format, please order RI0125.


ABSTRACT
The Fort Worth Basin, in North-Central Texas, is a late Paleozoic foreland basin that was downwarped during the Early to Middle Pennsylvanian Period in response to tectonic stresses that also produced the Ouachita Thrust Belt. The Atoka Group was deposited during the initial westward progradation of chert-rich terrigenous clastics derived both from the Ouachita Thrust Belt and locally from the Muenster Arch across the northern part of the basin. At the northern end of the basin, the Atoka Group interfingers with arkosic conglomerates (granite wash) derived from the Red River-Electra Arch. The granite wash is time equivalent but constitutes a separate stratigraphic sequence. The Atoka Group contains three distinct packages of terrigenous deposits: (1) the lower Atoka lithogenetic unit, interpreted to be a fluvially dominated fan-delta system, (2) the upper Atoka "Davis" lithogenetic subunit, interpreted to be a system of coalesced wave-dominated deltas, and (3) the upper Atoka "post-Davis" lithogenetic subunit, interpreted to be a thin, poorly integrated, fluvially dominated fan-delta system.

Atoka Group sandstones are quartz-rich feldspathic (chert) litharenites. The most significant diagenetic events were silica dissolution and cementation. Net porosities of 10 to 15 percent are the result of the preservation of original porosity in between quartz overgrowths and the creation of secondary porosity by chert grain dissolution. Highest porosities occur in channel-fill and coarse-grained fan-delta plain facies.

The Atoka Group has a cumulative production history of more than 160 million barrels (oil plus gas equivalent). Production and reservoir distribution and quality are facies controlled. Most oil and gas fields coincide with the distribution of lower Atoka fan-delta lobe complexes. Minor production is located along the axes of upper Atoka "post-Davis" fan-delta complexes.

Keywords: Atokan, Pennsylvanian, Fort Worth Basin, depositional systems, diagenesis, reservoir quality, Davis subunit, Texas


Contents

ABSTRACT

INTRODUCTION

Setting

Objectives

Methods

TECTONIC SETTING

Regional structural elements

Ouachita Thrust Belt

Red River- Electra and Muenster Arches

Bend Flexure

Local structure

STRATIGRAPHY

Previous work and nomenclature

Operational nomenclature and lithogenetic units

DEPOSITIONAL SYSTEMS

Lower Atoka lithogenetic unit

Sandstone distribution

Limestone distribution

Facies

Interpretive model

Upper Atoka "Davis" lithogenetic subunit

Sandstone distribution

Limestone distribution

Facies

Interpretive model

Upper Atoka "post-Davis" lithogenetic subunit

Sandstone distribution

Limestone distribution

Facies

Interpretive model

PETROLOGY

Composition

Diagenesis

Porosity and permeability

HYDROCARBON PRODUCTION

Historical development

Production characteristics

Volume and distribution

RESERVOIR DISTRIBUTION AND QUALITY

Lower Atoka lithogenetic unit

Upper Atoka “Davis" lithogenetic subunit

Upper Atoka "post- Davis" lithogenetic subunit

CONCLUSIONS

ACKNOWLEDGMENTS

REFERENCES

APPENDICES

(1) Well logs used in cross sections

(2) Fields with a cumulative hydrocarbon production of 100,000 barrels or more (oil plus gas equivalent)

Figures

1. Location of Fort Worth Basin, North-Central Texas

2. Map of study area, showing well control, cross sections, and core locations

3. Ouachita Thrust Belt and associated structural elements

4. Generalized stratigraphy of the Fort Worth Basin, including a classification of the subsurface Atoka Group

5. Type log for the Atoka Group, Fort Worth Basin

6. Core illustrating lithology and sedimentary structures characteristic of fluvially dominated fan-delta facies, Atoka Group, North-Central Texas

7. Lower Atoka facies tract

8. Descriptive log of lower Atoka core, Gulf Oil Company, #2 Button Crowley, Jack County

9. Descriptive log of lower Atoka core, Mitchell Energy Company, #6-4 Deaver, Wise County

10. Distribution of lower Atoka facies

11. Upper Atoka "Davis" facies tract

12. Distribution of upper Atoka "Davis" facies

13. Descriptive log of upper Atoka "post-Davis" core (Shell Oil Company, #1 J. H. Doss, Parker County)

14. Distribution of upper Atoka "post-Davis facies

15. Composition of sandstones interpreted to have been derived from the Ouachita Thrust Belt

16. Composition of sandstones interpreted to have been derived from the Muenster Arch

17. Composition of sandstones interpreted to have been derived from the Ouachita Thrust Belt and the Muenster Arch

18. Diagenetic sequence for Atoka conglomerates and coarse-grained sandstones from terrigenous facies

19. Diagenetic sequence for Atoka fine-grained sandstones and siltstones from terrigenous facies

20. Diagenetic sequence for Atoka sandstones from mixed terrigenous carbonate facies or terrigenous facies that were in proximity to carbonates

21. Photomicrographs of thin sections from Gulf Oil Company #2 Button Crowley core, lower Atoka lithogenetic unit, Jack County, Texas

22. Distribution of lower Atoka hydrocarbon fields

23. Distribution of upper Atoka "Davis" hydrocarbon fields

24. Distribution of upper Atoka "post-Davis" hydrocarbon fields

25. Facies framework of lower Atoka hydrocarbon reservoirs

26. Facies framework of upper Atoka "Davis" hydrocarbon reservoirs

27. Facies framework of upper Atoka "post-Davis" hydrocarbon reservoirs

Tables

1. Classification schemes applied to Lower to Middle Pennsylvanian rocks of Central and North-Central Texas

2. Summary of studies on the Atoka Group and other Lower to Middle Pennsylvanian strata

3. Summary of lower Atoka facies, characteristics, and depositional processes

4. Summary of inferred upper Atoka "Davis" facies

5. Compositional components of sandstones of the Atoka Group

Plates

I. Map of data base, northern Fort Worth Basin, Texas

II. Dip cross section A-A'

III. Dip cross section B-B'

IV. Dip cross section C-C'

V. Dip cross section D-D’

VI. Dip cross section E-E'

VII. Dip cross section F-F'

VIII. Strike cross section 1 -1'

IX. Strike cross section 2-2'

X. Strike cross section 3-3'

XI. Structure map, top of pre-Atoka strata

XII. Isopach map, lower Atoka lithogenetic unit

XIII. Isopach map, upper Atoka lithogenetic unit

XIV. Net-sandstone map, lower Atoka lithogenetic unit

XV. Net-limestone map, lower Atoka lithogenetic unit

XVI. Net-sandstone map, upper Atoka "Davis" lithogenetic subunit

XVII. Net-sandstone map, upper Atoka "post-Davis" lithogenetic subunit

XVIII. Net-limestone map, upper Atoka lithogenetic unit

XIX. Map of volume and distribution of cumulative hydrocarbon production, Atoka Group


Citation
Thompson, D. M., 1982, Atoka Group (Lower-Middle Pennsylvanian), Northern Fort Worth Basin, Texas: Terrigenous Depositional Systems, Diagenesis, and Reservoir Distribution and Quality: The University of Texas at Austin, Bureau of Economic Geology, Report of Investigations No. 125, 62 p.