Structural Styles of the Wilcox and Frio Growth-Fault Trends in Texas: Constraints on Geopressured Reservoirs

RI0154. Structural Styles of the Wilcox and Frio Growth-Fault Trends in Texas: Constraints on Geopressured Reservoirs, by T. E. Ewing. 86 p., 61 figs., 2 tables, 1986. ISSN: 0082335X: Print.


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ABSTRACT
The wide variability in structural styles within the growth-faulted, geopressured trends of the Texas Gulf Coast is illustrated by detailed structural maps of selected areas of the Wilcox and Frio growth-fault trends and quantified by statistical analysis of fault compartment geometries. Structural variability is a key determinant of the size of geopressured aquifers in the deep subsurface.

Two major structural styles exist in the Wilcox trend. (1) In southeast and Central Texas, the trend consists of continuous, closely spaced faults that have little associated rollover despite moderate expansion of section; the fault plane flattens little with depth. Where the trend crosses the Houston Diapir Province, growth faults are localized by preexisting salt pillows; however, the salt diapirs pierced the growth-faulted horizons after the main phase of faulting, so that salt-related movement deforms the growth faults. (2) By contrast, in South Texas a narrow band of growth faults having high expansion and moderate rollover lies above and downdip of a ridge of deformed, overpressured shale but updip of a deep basin formed by withdrawal of overpressured shale. Large antithetic faults are associated with this band of faults.

Frio fault systems generally display greater rollover and wider spacing than do Wilcox fault systems; however, the Frio trend displays distinctive features in each study area. At Sarita in South Texas, shale mobilization produced shale ridges, one of which localized a low-angle growth fault. Shale mobilization at Corpus Christi produced a series of large growth faults, shale-cored domal anticlines, and shale-withdrawal basins, which become younger to the east. At Blessing, major growth faults show little progradation seaward. A major early-formed growth-fault system was deformed by later salt tectonism at Pleasant Bayou. At Port Arthur, low-displacement, long-lived faults formed on a sand-poor shelf margin contemporaneously with broad salt uplifts and basins. Most of the Frio growth faults, however, have a similar geometry, showing substantial rollover, expansion of section, and a moderate flattening of the fault zone with depth, possibly related to a deep decollement surface. Shale ridges are common but not ubiquitous. The local variability in style is related to the magnitude of Frio sedimentation and progradation and to the presence of thick salt or shale.

Data on the sizes and shapes of fault compartments in the Texas Gulf Coast growth-fault trends confirm substantial differences between the two fault systems. Frio compartments generally show less elongation and higher absolute curvature than do Wilcox compartments. The compartment areas in both trends are distributed exponentially (small compartments outnumber large ones). There are more very large compartments than the best-fit exponential model predicts, however. The observed distribution of fault compartment curvature is consistent with a simple trapezoidal model of their geometry.

Finding and developing a large geopressured aquifer require recognition of a favorable combination of sand-body geometry, reservoir quality, and fault compartment size and shape. In the Wilcox trend, reservoirs are predominantly dip-oriented sandstones of high-constructive deltaic origin. This geometry, together with the close spacing of faults and the characteristically low permeabilities, limits the size of geopressured reservoirs. The largest reservoirs in the Wilcox trend may be in areas between major fault trends or in salt- or shale-withdrawal basins. In the Frio trend, widely spaced faults and higher permeabilities are more favorable to reservoir development. Blocks showing dip reversal and salt- and shale-withdrawal basins were all found in the trend and are likely to contain large geopressured aquifers. Reservoir quality is the primary limitation.

Keywords: Gulf Coastal Plain, Texas, Tertiary, structural geology, clastic sediments, geopressure, faulting, salt tectonics, seismic surveys, geothermal energy

CONTENTS

ABSTRACT

INTRODUCTION

WILCOX GROWTH-FAULT SYSTEM

Katy study area

Stratigraphy

Structural development

Structural constraints on the occurrence of geopressured reservoirs

Fostoria dip section

Stratigraphy 4

Structural development

Structural constraints on the occurrence of geopressured reservoirs

Zapata study area

Stratigraphy

Structural development

Structural constraints on the occurrence of geopressured reservoirs

Discussion

FRIO GROWTH-FAULT SYSTEM

Corpus Christi study area

Stratigraphy

Structural development

Structural constraints on the occurrence of geopressured reservoirs

Sarita dip section

Stratigraphy

Structural development

Structural constraints on the occurrence of geopressured reservoirs

Port Arthur study area

Stratigraphy

Structural development

Structural constraints on the occurrence of geopressured reservoirs

Discussion

Comparison of structural styles of the five Frio study areas

Structural constraints on the occurrence of geopressured reservoirs

REGIONAL FAULT COMPARTMENT GEOMETRIES OF THE WILCOX AND FRIO TRENDS

Introduction

Methods

Discussion

Distributions

Models

Significance of analysis

CONCLUSIONS.

ACKNOWLEDGMENTS

REFERENCES

 

Figures

1. Growth-fault trends of the Texas part of the Gulf Coast Tertiary Basin; stratigraphic column

2. Location map showing study areas in the Wilcox growth-fault trend, Texas Gulf Coast, and their relation to the Rockdale and Rosita delta systems

3. Location map of Katy study area

4. Structure section A-A', Austin and Fort Bend Counties

5. Isopach map of upper and middle Wilcox strata, Katy study area

6. Schematic palinspastic sections across San Felipe area showing sequence of structural development

7. Structure map contoured on top of Wilcox strata, Katy study area

8. Isopach map of Vicksburg and Jackson strata, Katy study area

9. Structure section C-C' across San Felipe dome, Austin, Waller, and Fort Bend Counties

10. Structure map contoured on top of Vicksburg Formation, Katy study area

11. Map of Fostoria area, Liberty and Montgomery Counties, showing approximate locations of dip section and oil and gas production

12. Structural cross section of the Fostoria area

13. True-depth interpreted section of Fostoria area

14. Location map of Zapata study area

15. True-depth sections of Zapata study area

16. Structure map contoured on top of Wilcox strata, Zapata study area

17. Dip cross sections of Fandango field, restored to its appearance in middle and late Wilcox time

18. Structure map contoured on base of Yegua Formation, Zapata study area

19. Map of depositional systems of the Frio Formation showing locations of Frio geopressured trend study areas

20. Location map of sections and wells used, Corpus Christi study area

21. Stratigraphic diagram of Frio and related units, Corpus Christi study area, showing electric log correlation markers used in this study

22. Plot of interval velocity versus depth as determined from velocity surveys of four wells in the Corpus Christi study area

23. Structure map contoured on CC-1 (top of Frio) showing large oil-bearing structures

24. Structure map contoured on CC-4 (approximately Nonion struma)

25. Structure map contoured on CC-9 (approximately Textularia mississippiensis)

26. Structure map contoured on CC-11 (approximately Anomalina bilateralis)

27. Isopach map of the CC-1 to CC-4 interval (upper Frio)

28. Isopach map of the CC-4 to CC-9 interval (middle Frio)

29. Isopach map of the CC-9 to CC-11 interval (lower Frio)

30. Interpreted seismic section, Nueces County

31. Interpreted seismic section, Corpus Christi Bay, Nueces County

32. Structure section across a shale diapir, San Patricio County

33. Structure section along structural strike from Mobil-David dome to Bohemian Colony dome

34. True-depth sections A-A', southern Nueces County; B-B', northeastern Nueces County; and C-C', San Patricio County

35. Plot of distribution of fault-well intersections with depth, Corpus Christi study area

36. Structure map contoured on S5 horizon, Sarita prospect area

37. Structural dip section H–H', Sarita prospect

38. Structural dip section constructed near the seismic line

39. Seismic reflector facies interpretation of seismic line

40. Interpreted seismic section, Sarita dip line

41. True-depth structure section constructed from seismic line and well data

42. Palinspastic reconstructions (neglecting compaction) of western part of seismic line across Sarita prospect area

43. Location map of Port Arthur area showing well control, general locations of seismic lines, and locations of salt domes

44. Map showing regional distribution of sandstone-bearing lower Hackberry channels in Hackberry Embayment west of Acadia Parish, Louisiana

45. Interpreted dip- and strike-oriented seismic lines, Sabine Lake

46. Stratigraphic diagram of Frio and related strata, Jefferson County study area

47. Structure section C-C' near Port Arthur field and Spindletop dome

48. Plot of interval velocity versus depth for two velocity surveys and velocity analyses from seismic data

49. Isopach map of A3–Vicksburg interval, Port Arthur area

50. Isopach map of A3–A4 interval, Port Arthur area

51. Structure map contoured on A4 horizon, Port Arthur area

52. lsopach map of A1–A3 interval, Port Arthur area

53. Isolith map of Heterostegina limestone (middle Anahuac)

54. Structure map contoured on A2·horizon, Port Arthur area

55. Map of study area, Texas Gulf Coast, with numbers of closed compartments found per Tobin grid . . . . 56. Map of well density, Texas Gulf Coast, in wells per 620 mi² (1,000 km²)

57. Diagram showing measurements performed on a typical Gulf Coast fault compartment

58. Histograms of size and shape parameters of the Wilcox trend

59. Histograms of size and shape parameters of the Frio trend

60. Plot of cumulative percentage of areas accounted for by blocks of less than a given area, Wilcox and Frio trends

61. Parallelogram and trapezoid models of fault compartments

 

Tables

1. Summary by sector of mean, 10th, 50th, and 90th percentiles for size and shape parameters, fault compartments of the Texas Gulf Coast

2. Cross-fault angles and validity tests for the parallelogram and trapezoid models as applied to Wilcox and Frio fault compartments



Citation
Ewing, T. E., 1986, Structural Styles of the Wilcox and Frio Growth-Fault Trends in Texas: Constraints on Geopressured Reservoirs: The University of Texas at Austin, Bureau of Economic Geology, Report of Investigations No. 154, 86 p.