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RI0272. Reservoir Geology, Structural Architecture, and Sequence Stratigraphy of a Growth-Faulted Subbasin: Oligocene Lower Frio

RI0272. Reservoir Geology, Structural Architecture, and Sequence Stratigraphy of a Growth-Faulted Subbasin: Oligocene Lower Frio Formation...

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RI0272

RI0272. Reservoir Geology, Structural Architecture, and Sequence Stratigraphy of a Growth-Faulted Subbasin: Oligocene Lower Frio Formation, Red Fish Bay Area, South Texas Gulf Coast, by Ursula Hammes, R. G. Loucks, L. F. Brown Jr., R. H. Trevino, Patricia Montoya, and R. L. Remington. 28 p., 26 figs., 3 tables, 1 color plate in back pocket, 2007. RI0272, $15.00.

 

ABSTRACT

An integrated study using 3D seismic, wireline logs, and core analyses was conducted to establish new strategies for exploring compartmentalized, lowstand, prograding deltaic systems. The Frio siliciclastics, totaling approximately 11,000 ft, are commercial gas reservoirs in many of the growth-faulted, intraslope subbasins in South Texas. Red Fish Bay field is located in such a growth-faulted subbasin. Some Frio reservoir sandstones in Red Fish Bay field are part of a Frio third-order, lowstand prograding wedge tract. This third-order systems tract is composed of 10 higher-order, lowstand deltaic, and superposed transgressive systems tracts. Many of the reservoirs in the higher-order lowstand deltas and transgressive sandstones are compose of fine-grained, lithic arkoses that have mean porosities of 20 to 25 percent and mean permeability in the tens of millidarcys. Incised rivers contributed large amounts of sediment to the continental slope via shelf-edge, ephemeral, high-frequency lowstand deltas located at notched river mouths. Lowstand depocenters eventually overloaded unconsolidated much-rich, water-saturated sediments. Gravity failure along incipient growth faults, which were present at weaknesses of the slope, displaced highly mobilized muds basinward of the growing lowstand sedimentary wedge. The growth fault, active during lowstand sedimentation, ceased its influence with rising sea level and the shifting of sedimentation shelfward. Regionally, growth faults trend generally northeast-southwest, setting up small subbasins. Associated with the growth faults are numerous subparallel, postdepositional synthetic faults. Some normal faults trend perpendicular to the growth faults, establishing a complex pattern of fault compartmentalization that dissects the prograding-wedge depositional patterns. Pressure-decline analysis demonstrates compartmentalization that is due to (1) laterally discontinuous sandstone bodies and (2) sandstone bodies that have several pressure compartments defined by fault segregation.

Keywords: growth-faulted subbasin, lowstand systems tracts, Red Fish Bay field, reservoir compartmentalization, sequence stratigraphy, South Texas Gulf Coast

TABLE OF CONTENTS

ABSTRACT

INTRODUCTION

REGIONAL SETTING

METHODOLOGY AND DATA

SEQUENCE STRATIGRAPHIC FRAMEWORK

     General Principles and Methodology of Sequence Stratigraphic Interpretations in
     Growth-Faulted Subbasins

     Sequence Stratigraphic Architecture in Growth-Faulted Subbasins and Its Relationship
     to Synsedimentary Tectonics

     Red Fish Bay Subbasin Sequence Stratigraphy

STRUCTURAL ARCHITECTURE

     Tectonic Setting

     Structural Analysis

            Growth Faults

                   Higher-Order Subbasins and Growth Faults

            Normal Faults

RESERVOIR ANALYSIS

    Red Fish Bay Field Production History

            North Area
            South Area

    Reservoir Pressure Performance

            Initial Bottom-Hole Pressure

            Reservoir Compartmentalization

    Production Analysis

             Production Characteristics

                    Reservoir Quality

             Volumetric Estimation

CONCLUSIONS

ACKNOWLEDGMENTS

REFERENCES

Figures

1. Study area along South Texas Gulf Coast

2. General sequence stratigraphic architecture for Texas Gulf coast area

3. S5-benchmark chart of Red Fish Bay area showing composite log and sequence stratigraphy of Red Fish Bay area and southwest-northeast strike cross section

4. Seismic survey outline and detailed top, deep Frio fault map in Red Fish Bay field area

5. Southwest-northeast sequence stratigraphic wireline-log dip section C-C, Red Fish Bay subbasin

6. Northwest-southeast dip structural cross section D-D, with seismic backdrop in southern Red Fish Bay area

7. Growth-faulted subbasins aligning in dip direction along South Texas Gulf Coast

8. Inferred paleogeographic model of Frio lowstand deposition

9. General structural geology of Red Fish Bay area

10. Continuity map within prograding-wedge sequence, exhibiting growth-fault system, with major faults forming west and north boundaries to Red Fish Bay subbasin

11. Composite seismic line, showing three higher-order subbasins within 3rd-order Red Fish Bay subbasin 12. Idealized model of 3rd- and higher-order subbasin development, showing complexity of reservoir development and interplay of sediments and tectonics

13. Dip/strike section showing Red Fish Bay fault influence on structure and sedimentation

14. Alternative models for early development of Red Fish Bay fault structure

15. Red Fish Bay field division into north and south productive areas, showing relationship of well locations to fault patterns

16. Depth structure on top of MFS 3

17. Hydrocarbon phases by region; numbers reflect hydrocarbons produced through July 2006 in Red Fish Bay field

18. Graph showing contrast in condensate dropout

19. Plots for interpreting reservoir drive mechanism

20. Initial bottom-hole pressure versus true vertical depth for productive wells and various sandstone compartments in north area

21. Structure maps on top of zone 35 for parts of north and south areas of Red Fish Bay field, showing reservoir compartmentalization associated with numerous normal faults

22. Examples of cumulative production versus P/Z plots in reservoir zones 35 and 45, displaying convex behavior of decline curve interpreted to indicate compartmentalization

23. Production and pressure history for selected reservoir zones. indicating compartmentalization due to variable decline curves

24. Production characteristics of prograding-wedge reservoirs  

25. Porosity versus permeability for all data from 470 Atlantic No. 4 core

26. Very fine grained lithic arkose with interparticle and moldic pores

Tables

1. Deep Frio input parameters for OGIP and reserve calculations

2. Deep Frio estimates of OGIP and remaining gas reserves organized by productive zones

3. Comparison of reserve calculations by volumetric (Monte Carlo) and material balance method for north area

 

Plate (larger version of figures 3 and 7, in pocket of printed book)