Continuity and Internal Properties of Gulf Coast Sandstones and Their Implications for Geopressured Fluid Production

RI0132. Continuity and Internal Properties of Gulf Coast Sandstones and Their Implications for Geopressured Fluid Production, by R. A. Morton, T. E. Ewing, and Noel Tyler. 70 p., 42 figs., 7 tables, 1983. ISSN: 0082335X: Print.

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ABSTRACT
Continuity of sandstone reservoirs is controlled by various factors, including faults, sand-body geometry, and the distribution of framework grains, matrices, and interstices within the sand body. Except for faults, these factors are largely inherited from the depositional environment and modified during sandstone compaction and cementation. Regional and local continuity of Gulf Coast sandstone reservoirs depends on a four-level depositional and structural hierarchy: (1) genetically related sandstones commonly associated with a single depositional system, (2) areally extensive fault blocks, (3)individual sandstones within a fault block, and (4) isolated reservoirs within a fault-bounded

Published and unpublished data on Tertiary and late Quaternary Gulf Coast sandstones of fluvial, deltaic, barrier-strandplain, and submarine channel and fan origins suggest that volumes of sand systems (first hierarchical level) are about 10¹¹ to 10¹³ ft³, whereas volumes of individual sand bodies are about 10⁹ to 10¹¹ ft³. The continuity and productive limits of ancient sandstones are substantially reduced by faults and internal heterogeneities, which further subdivide sand bodies into individual compartments. In the Wilcox Group and Frio Formation trends of Texas, fault blocks (second hierarchical level) vary greatly in size, most being between 0.3 and 52 mi²); however, the distribution of fault blocks is strongly skewed toward small areas (<I0 mi²). Volumes of individual reservoirs (fourth hierarchical level) determined from engineering production data range from 50 percent less to 200 percent more than volumes estimated by geologic mapping. In general, mapped volumes are less than production volumes for reservoirs in which faults are nonsealing and are greater than production volumes for reservoirs in which laterally continuous shale breaks cause reductions in permeability.

Gross variations in the pore properties (porosity and permeability) of a reservoir can be predicted by examining its internal stratification and its sandstone facies if original sedimentological properties are not masked by diagenetic alterations. Six patterns are recognized that describe, in general, the vertical variations in pore properties within a sand body at a well site. Core analyses show (1) upward increases, (2) upward decreases, (3) central increases, (4) central decreases, (5) uniformly low values, and (6) irregular changes in porosity and permeability with depth. Within these trends, porosity and permeability are generally highest in large-scale crossbedded intervals and lowest in contorted, bioturbated intervals and intervals of small-scale ripple cross-laminations.

Sandstone facies models and the regional structural fabric of the Gulf Coast Basin both suggest that large and relatively continuous reservoirs should be found where barrier-strandplain and delta-front sandstones parallel regional faults. These conditions should optimize the yield and rate of fluid production from geopressured geothermal aquifers and maximize the efficiency of primary and enhanced recovery of conventional hydrocarbons. Thick fluvial-channel deposits trending roughly normal to regional faults are laterally less continuous than barrier and delta-front sandstones, but they may also be significant targets for exploration and production of unconventional and conventional energy resources.


Keywords: Texas, Gulf Coastal Plain, Tertiary, sediments, structure contour maps, stratigraphic maps, reservoir properties, sand bodies, geothermal energy

CONTENTS

ABSTRACT

INTRODUCTION

Quantification of inhomogeneities

STRUCTURAL AND STRATIGRAPHIC LIMITS OF SANDSTONE RESERVOIRS

Sand-body and reservoir hierarchy

Possible external contributions

CHARACTERISTICS AND DIMENSIONS OF GULF COAST SANDSTONES

Limitations of data

Late Quaternary sediments

Fluvial sandstones

Mississippi River

Rio Grande

Brazos River

Deltaic sandstones

Mississippi delta

Rio Grande delta

Brazos delta

Barrier and strandplain sandstones

Padre Island

Galveston Island

Grand Isle

South Padre Island

Ingleside strandplain

Shelf and slope sandstones

Tertiary sediments.

Fluvial sandstones.

Deltaic sandstones

Barrier and strandplain sandstones.

Shelf and slope sandstones

Sediments in other basins

FAULT-COMPARTMENT AREAS

COMPARISON OF PRODUCTION AND GEOLOGIC ESTIMATES OF AQUIFER FLUID VOLUME

Calculation of aquifer fluid volume from production data

South Cook field

Stratigraphy of producing sands

Structure of the South Cook area

Reservoir volume of the B sand

Reservoir volume of the C sand.

Summary

Yorktown and South Yorktown fields

Stratigraphy of the Migura sand.

Structure of the Yorktown area

Reservoir volume of Yorktown field

Reservoir volume of South Yorktown field

Summary

Christmas field

Stratigraphy of the Migura sand.

Structure of the Christmas area

Reservoir volume of Christmas field

Southeast Pettus field

Stratigraphy of the First Massive sand

Structure of the Pettus area

Reservoir volume of the First Massive sand

South Braslau field

Stratigraphy of the First Tom Lyne sand

Structure of the South Braslau area

Reservoir volume of South Braslau field

South Peach Point field

Stratigraphy of the Frio A sand

Structure of the Peach Point area

Reservoir volume of South Peach Point field

Mobil-David L field

Stratigraphy of the Anderson sand

Structure of the Mobil-David area

Reservoir volume of the Anderson sand

Comparisons and conclusions

GEOLOGIC SETTING AND RESERVOIR CHARACTERISTICS, WELLS OF OPPORTUNITY

Riddle No. 2 Saldana well

Stratigraphy of the First Hinnant sand

Reservoir volume of the First Hinnant sand

Ross (Coastal States) No. 1 Pauline Kraft well

Structure of the Mobil-David area

Reservoir volume of the Anderson sand

Lear No. 1 Koelemay well

Stratigraphy of the Leger sand

Structure of the Leger sand

Reservoir volume of the Leger sand

Conclusions, well-of-opportunity study

INTERNAL PROPERTIES OF SANDSTONES.

Porosity and permeability of modern sands

Detailed investigation of vertical changes in porosity and permeability

Variations in grain size and primary sedimentary structures

Bioturbation and texture

Induration

Porosity and permeability as a function of depositional environment

Facies control on reservoir continuity

Vertical patterns of pore properties

Pore properties and stratification

Frequency and arrangement of flow barriers

IMPLICATIONS FOR GEOPRESSURED FLUID PRODUCTION

ACKNOWLEDGMENTS

REFERENCES

APPENDIX A: Metric conversion factors

FIGURES

1. Locations of sand bodies listed in table 1

2. Stratigraphic section of late Quaternary Rio Grande deltas near South Padre Island

3. Distributions of subaerial environments and subsurface sediment types in the recently formed Brazos delta

4. Histograms of fault-compartment

5. Locations of hydrocarbon and geothermal trends, geothermal test wells, and Texas Gulf Coast areas studied in this report

6. Calculations for estimating aquifer volume

7. Net·sand map, B and C sands, South Cook field

8. Structure and net-sand map, Yorktown area

9. Stratigraphic section of lower Wilcox Group sands, Yorktown area

10. Structure sections, Yorktown area

11. Structure and net-sand map, Christmas area

12. Stratigraphic section of lower Wilcox Group sands, Christmas area

13. Structure and net-sand map, Pettus area

14. Stratigraphic section of upper Wilcox Group sands, Pettus area

15. Structure and net-sand map, Braslau area

16. Stratigraphic section of upper Wilcox Group sands, Braslau area

17. Structure and net-sand map, Peach Point area

18. Stratigraphic section of sub-Nodosaria blanpiedi sands of the Frio Formation, Peach Point area

19. Structure section, Peach Point area

20. Structure and net-sand map, Mobil-David area

21. Stratigraphic section of lower Frio Formation sands, Mobil-David area

22. Comparison of production and geologic estimates of aquifer volume

23. Structure and net-sand map, Riddle No. 2 Saldana area

24. Porosity and permeability variations and spontaneous potential of three reservoirs tested by the well of-opportunity program

25. Stratigraphic section of First Hinnant sand, Riddle No. 2 Saldana and Northeast Thompsonville areas

26. Stratigraphic section through Riddle No. 2 Saldana well of uppermost Wilcox Group sands

27. Structure section through Ross (Coastal States) No. 1 Pauline Kraft well, Mobil-David area

28. Structure and net-sand map, Lear No. 1 Koelemay area

29. Stratigraphic section of Yegua Formation sands, Lear No. 1 Koelemay area

30. Location of the General Crude Oil-Department of Energy Pleasant Bayou Nos. 1 and 2 geopressured geothermal test wells and structure at the TS marker

31. Explanation of symbols in figures 32 through 35

32. Detailed core description, pore properties, and interpretation of the upper part of the Frio T3 correlation unit

33. Detailed core description, pore properties, and interpretation of the geopressured geothermal production interval (Andrau, or C, sand)

34. Detailed core description, pore properties, and interpretation of the upper part of the Frio F correlation interval (TS unit).

35. Detailed core description, pore properties, and interpretation of the lower part of the Frio F correlation interval (TS unit)

36. Large-scale cross-stratification in permeable, porous sandstone interpreted as a bed-load distributary-channel deposit; intermediate- to small-scale crossbedded sandstone of the geopressured geothermal production interval; and ripple-laminated sandstone overlain by horizontally bedded sandstone with thin mud drapes

37. Interlaminated very fine grained sandstone and siltstone interpreted as shallow marine storm-related sequences; highly bioturbated sandstone

38. Net-sand map of the sub-TS Andrau sand (the geopressured geothermal production interval)

39. Fence diagram showing the continuity of depositional units in the geopressured geothermal production interval

40. Lobate net-sand pattern of the T3 correlation interval

41. Cross sections through the T3 correlation interval

42. Generalized patterns of vertical changes in pore properties within a sand body

TABLES

1. Approximate dimensions of late Quaternary Gulf Coast sand bodies

2. Approximate dimensions of Tertiary Gulf Coast sand bodies

3. Approximate dimensions of non-Gulf Coast sand bodies

4. Areas of fault compartments in Wilcox geopressured fairways

5. Areas of fault compartments in Frio geopressured fairways

6. Volume estimates of geopressured gas reservoirs, Texas Gulf Coast

7. Reservoir area and volume of Texas Gulf Coast wells of opportunity


Citation
Morton, R. A., Ewing, T. E., and Tyler, Noel, 1983, Continuity and Internal Properties of Gulf Coast Sandstones and Their Implications for Geopressured Fluid Production: The University of Texas at Austin, Bureau of Economic Geology, Report of Investigations No. 132, 70 p.