Hydrogeology and Hydrochemical Facies of the San Andres Formation in Eastern New Mexico and the Texas Panhandle

RI0157. Hydrogeology and Hydrochemical Facies of the San Andres Formation in Eastern New Mexico and the Texas Panhandle, by A. R. Dutton and E. D. Orr. 58 p., 13 figs., 3 tables, 3 appendices, 1986. ISSN: 082335X: Print.


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ABSTRACT
Fluid pressure, permeability, rates and patterns of ground-water flow, and chemical and isotopic composition of ground water in carbonate rock in the lower part of the San Andres Formation (Permian) in eastern New Mexico and the Texas Panhandle were studied to characterize the origin and movement of brine within an evaporite-carbonate-shale confining system. Although hydraulic-head data and numerical models suggest that ground water flows downward through the evaporite confining system in the Palo Duro Basin of the Texas Panhandle, evidence derived from study of chemical and isotopic composition of brine from two test wells indicates that post-Permian groundwater movement in the unit 4 carbonate bed of the San Andres Formation has been negligible in the Palo Duro Basin. The conflict between the chemical interpretation and the hydrologic model predictions can be reconciled if (1) the amount of ground-water flow since a significant cross-formation gradient in hydraulic head developed during the Pleistocene has not been enough to flush connate brine from carbonate beds, (2) present ground-water flow is unevenly distributed between fractured and unfractured zones in the evaporite confining system, and (3) brine sampled at test wells differs from other waters in fractured zones not yet sampled.

Hydraulic head of ground water in the San Andres Formation appears to be hydrodynamically controlled by land-surface topography and by production of hydrocarbons and formation water. A ground-water-basin divide inferred from a fold in the potentiometric surface corresponds to the Western Caprock Escarpment and indicates that San Andres ground water below the Southern High Plains is separated from the karstic aquifer in the San Andres Formation in the Pecos Plains. The separation is reflected in a marked difference in hydrochemical facies and salinity. San Andres ground water varies from Ca-HCO₃ and Ca-SO₄ hydrochemical types with salinities of less than 5,000 mg/L in the Pecos Plains of eastern New Mexico to Na-Cl and Ca-C1 brines with salinities of 336,000 to 384,000 mg/L and Na/CI mole ratios of as low as 0.2 beneath the Southern High Plains, east of the ground-water-basin divide. The groundwater-basin divide probably developed during the Pleistocene when the ancestral Pecos River excavated its valley.

Similarity between δD (-15 ‰ to -26 ‰)and δ¹⁸O (+4 ‰ to 6.4 ‰) of San Andres ground water in the Palo Duro Basin and δD and δ¹⁸O of fluid inclusions in halite beds suggests that brine in the carbonate rock could have originated during the Permian as evaporatively concentrated seawater. Dolomitization, ion exchange, clay diagenesis, and loss of dissolved sulfate account for possible modifications of the hypothetical Permian connate brine. However, with a meteoric-water model for brine origin, extensive rock-water reactions, such as ion- and isotope-exchange and incongruent recrystallization of halite, are needed to derive the observed composition. Isotopic exchange between meteoric water and San Andres carbonate rocks cannot account for δ¹⁸O composition of San Andres Formation brine. The reactions needed in a meteoric-water model seem more complex and less documented than simple preservation of a modified-connate, Permian brine.

Keywords: hydrogeology, hydrochemical facies, confining systems, brine, evaporites, drill-stem testing, San Andres Formation, Texas Panhandle, eastern New Mexico, Palo Duro Basin

CONTENTS

ABSTRACT

INTRODUCTION

HYDROGEOLOGIC SETTING

DATA

Hydraulic-Head Data

Chemical Data

RESULTS OF HYDROGEOLOGIC STUDIES

Hydrologic Tests

Ground-Water Flow

Preservation of Permian Formation Water

Vertical Flow from Adjacent Formations

Intrastratal Recharge before Pecos River Valley Incision

RESULTS OF HYDROCHEMICAL STUDIES

DISCUSSION Connate-Brine Explanation

Isotopic Composition

Na/ Cl Ratio

Salinity Patterns

Meteoric-Water Explanation

Isotopic Composition

Na/Cl Ratio

Salinity Patterns

CONCLUSIONS

ACKNOWLEDGMENTS23

REFERENCES

APPENDIX A. Hydrologic Test Data

APPENDIX B. Geostatistical Analysis of Hydraulic Head

APPENDIX C. Chemical Composition of Ground Water in the San Andres Formation

FIGURES

1. Study area, lying between outcrops of Guadalupian rocks in eastern New Mexico and the Texas Panhandle

2. Stratigraphic and lithologic data, San Andres Formation and evaporite confining system

3. Locations of stratigraphic and hydrologic test wells in the Palo Duro Basin

4. Plot of fluid pressure against depth in the San Andres Formation

5. Potentiometric-surface map of the San Andres Formation prepared by hand-contouring hydraulic-head data

6. Plot of fluid pressures in San Andres oil fields prior to and in 1943

7. Trilinear diagram of major ions in San Andres ground water

8. Hydrochemical facies and salinity of ground water in the San Andres Formation

9. Saturation state of San Andres ground water relative to anhydrite and halite

10. Saturation state of San Andres ground water relative to calcite and dolomite

11. Plots of chloride versus sodium and chloride versus sodium+calcium+magnesium in San Andres ground water

12. Isotopic composition of brine from the SWEC Zeeck No. 1 and SWEC J. Friemel No. 1 wells

13. Oxygen isotopic composition of brine as a function of temperature and isotopic composition of dolomite and calcite

TABLES

1. Hydraulic head of San Andres brine in the Palo Duro Basin

2. Chemical and isotopic composition of San Andres brine from test wells

3. Ion content of San Andres brine calculated by meteoric-water model

APPENDIX FIGURES

A1. Geophysical logs and drill-stem-test zones at six SWEC hydrologic test wells

A2. Change in fluid pressure with time and summary of test data during two flow and shut-in periods of drill-stem test 1 at the SWEC G. Friemel No. 1 well

A3. Plots of data and calculated values of permeability from drill-stem test 1 at the SWEC G. Friemel No. 1 well

A4. Change in fluid pressure with time and summary of test data during two flow and shut-in periods of drill-stem test 3 at the SWEC Detten No. 1 well

AS. Plots of data and calculated values of permeability from drill-stem test 3 at the SWEC Detten No. 1 well

A6. Change in fluid pressure with time and summary of test data during two flow and shut-in periods of drill-stem test 5 at the SWEC Zeeck No. 1 well

A7. Plots of data and calculated values of permeability from drill-stem test 5 at the SWEC Zeeck No. 1 well

A8. Schematic drawing of test setup at the SWEC Zeeck No. 1 well during fluid production and four shut-in tests

A9. Plots of data and calculated values of permeability from shut-in tests at the SWEC Zeeck No. 1 well

A10. Change in fluid pressure with time and summary of test data during flow and shut-in periods of drill-stem test 2 at the SWEC Harman No. 1 well

A11. Plots of data and calculated values of permeability from drill-stem test 2 at the SWEC Harman No. 1 well

A12. Change in fluid pressure with time and summary of test data during two flow and shut-in periods of drill-stem test 5 at the SWEC J. Friemel No. 1 well

A13. Plots of data and calculated values of permeability from drill-stem test 5 at the SWEC J. Friemel No. 1 well

A14. Schematic drawing of test setup at the SWEC J. Friemel No. 1 well during fluid production and shut-in tests

A15. Change in fluid pressure with time and summary of test data during flow and shut-in periods at the SWEC J. Friemel No. 1 well

A16. Plots of data and calculated values of permeability from shut-in tests at the SWEC J. Friemel No. 1 well

A17. Plots of data and calculated values of permeability from drill-stem test 5 at the SWEC Holtzclaw No. 1 well

B1. Potentiometric-surface map of the San Andres Formation made by kriging

B2. Variogram of hydraulic-head data and theoretical variogram based on a spherical model

APPENDIX TABLES

A1. Hydrologic test data from SWEC Zeeck No. 1 shut-in and SWEC Holtzclaw No. 1 drill-stem tests

A2. History of fluid production at the SWEC Zeeck No. 1 well

A3. History of fluid production at the SWEC J. Friemel No. 1 well

B1. Geostatistical parameters used to determine the potentiometric surface of the San Andres Formation by kriging




Citation
Dutton, A. R., and Orr, E. D. 1986, Hydrogeology and Hydrochemical Facies of the San Andres Formation in Eastern New Mexico and the Texas Panhandle: The University of Texas at Austin, Bureau of Economic Geology, Report of Investigations No. 157, 58 p.