Geological Characterization of Permian Submarine Fan Reservoirs of the Driver Waterflood Unit, Spraberry Trend, Midland

RI0172. Geological Characterization of Permian Submarine Fan Reservoirs of the Driver Waterflood Unit, Spraberry Trend, Midland Basin, Texas, by E. H. Guevara. 44 p., 28 figs., 3 tables, 2 appendices, 1988. ISSN: 0082335X: Print.

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ABSTRACT
More than 350 well logs and core and production data were used to geologically characterize oil reservoirs of the Driver waterflood unit of the Spraberry Trend in the Midland Basin, West Texas, and to assess the relationship between reservoir stratigraphy and oil recovery. Results of this research indicate that to improve oil recovery from the Driver unit, and from the Spraberry Trend in general, selection of completion intervals and strategic infill drilling locations should be determined by both reservoir stratigraphy and natural fractures.

Fifteen log-defined genetic-stratigraphic operational units composed mainly of sandstone and siltstone were delineated in the approximately 1,000-ft- (305-m-) thick, predominantly shale and carbonate Spraberry Formation of Permian (Leonardian) age. Sandstone and siltstone of this lithostratigraphic unit accumulated in submarine fans, forming upward-thickening sequences in the lower (Jo Mill submarine fan system) and upper (Driver and Floyd submarine fan systems) Spraberry. Areas of Spraberry submarine fans having greater net thickness of sandstone and siltstone form NNW- to NNE-trending belts. These sand-rich areas contain the main oil reservoirs of the Driver unit; they consist of low-permeability (less than 1 md), low-porosity (less than 8 percent to approximately 14 percent) sandstones and siltstones capping submarine fans of the lower and upper Spraberry.

Historically, selection of well locations and completion intervals in the Driver unit has been based on the assumption that oil production is largely controlled by natural fractures in homogeneous, laterally extensive, sheet-like reservoirs. However, production data show trends that are generally correlative with axes of maximum sandstone and siltstone in operational units, suggesting that reservoir stratigraphy strongly influences oil production. Complex facies architecture of Spraberry reservoirs produces vertical and horizontal reservoir heterogeneity. Stacking of submarine fans results in multilayered, or stratified, oil accumulations in which reservoir rocks are separated vertically by shales and carbonate mudstones. Oil accumulations are also laterally compartmentalized because the main reservoirs occur in sand-rich belts generally parallel to the basin axis.

The current low recovery efficiency of approximately 10 percent is attributed to reservoir heterogeneity that results in incompletely drained hydrocarbon zones. In performing well recompletions and strategic infill drilling, operators must consider stratigraphic heterogeneity in order to produce oil from untapped or only partly drained reservoir compartments. New well logs and core are necessary for identification and characterization of oil-saturated zones and natural fractures. These reservoir management strategies are also applicable to similar oil reservoirs, such as the Dean Sandstone of the Midland Basin.

Keywords: Driver waterflood unit, Midland Basin, naturally fractured reservoirs, Permian, reservoir heterogeneity, reservoir stratigraphy, Spraberry Formation, Spraberry Trend, submarine fans, Texas


CONTENTS

Abstract

Introduction

Methodology

Paleogeographic Setting

Stratigraphy of the Spraberry Formation

Depositional Systems in the Driver Unit

Facies tract and depositional model

Jo Mill submarine fan system

Driver submarine fan system

Floyd submarine fan system

Sediment Dispersal System

Hydrocarbons in the Spraberry Formation

Influence of natural fractures on oil production

Hydrocarbons in the Driver Unit

Stratigraphic control of oil accumulations

Porosity, permeability, and oil-producing intervals

Stratigraphic heterogeneity of Spraberry reservoirs

Influence of reservoir stratigraphy on oil recovery

Reservoir stratigraphy and waterflood flow paths

Opportunities for additional oil recovery

Acknowledgments

References

Appendix A. Methodology

Appendix B. Development ofthe Spraberry Trend and the Driver unit

Figures

1. The Midland Basin and principal Spraberry oil fields

2. Principal Spraberry waterflood units, central Midland Basin

3. Subsurface control and index of cross sections. Driver unit

4. Stratigraphic subdivisions of the Spraberry Formation. Driver unit

5. Stratigraphic cross section A-A'. northern part of Driver unit

6. Stratigraphic cross section B-B', western part of Driver unit

7. Facies tract, upper Spraberry submarine fans. Driver unit

8. Core from Jo Mill submarine fan system (lower Spraberry), Sun Oil Company Jalonick No. 2 well

9. Net thickness of sandstone and siltstone. operational unit 2L, Driver unit

10. Log facies map, sandstone zone s, operational unit 2L, Driver unit

11. Core from upper Spraberry submarine fans, Sun Oil Company Jalonick No. 1 well

12. Net thickness of sandstone and siltstone, operational unit 5U, Driver unit

13. Log facies map, sandstone zone f, operational unit 5U, Driver unit

14. Net thickness of sandstone and siltstone, operational unit 1 U, Driver unit

15. Log facies map. sandstone zones b-c, operational unit 1U, Driver unit

16. Stratigraphic cross section C-C', constructed from induction and gamma-ray logs, Driver unit

17. Decline curves of wells recompleted in sandstone of operational unit 5U (upper Spraberry), Driver unit

18. Vertical distribution of core porosity, permeability, and fluid saturation, Jo Mill submarine fan (lower Spraberry), Driver unit

19. Vertical distribution of core porosity, permeability, and fluid saturation, Driver unit

20. Areal distribution of well completions by stratigraphic interval, Driver unit

21. Cross section D-D' showing percent sandstone and siltstone in operational units, Spraberry Formation, Driver unit

22. Map of cumulative oil production from January 1961 to February 1985, upper and lower Spraberry. Driver unit

23. Map of oil production in February 1966, upper and lower Spraberry, Driver unit

24. Map of oil production in February 1985, upper and lower Spraberry, Driver unit

25. Water cut in December 1966, upper and lower Spraberry, Driver unit

26. Water cut in February 1985, upper and lower Spraberry, Driver unit

Tables

1. Subdivisions of the Spraberry Formation

2. Characteristics of operational units analyzed in this study

3. Dimensions of channel sandstones in Jo Mill and Floyd submarine fan systems, Driver unit

Appendix Figures

A-1. Net sandstone and siltstone determined from gamma-ray logs, Spraberry Formation, Driver unit

A-2. Principal shapes of gamma-ray logs, Spraberry Formation, Driver unit



Citation
Guevara, E. H., 1988, Geological Characterization of Permian Submarine Fan Reservoirs of the Driver Waterflood Unit, Spraberry Trend, Midland Basin, Texas: The University of Texas at Austin, Bureau of Economic Geology, Report of Investigations No. 172, 44 p.