Paluxy Sandstone, East Texas Basin (13)

Comments on Geologic Parameters

13 Rock/Water Reaction:

Kreitler and others (1983) categorized the formation waters of the East Texas basin into two broad groups-shallow formations (Woodbine, Eagle Ford, and Nacatoch) and deeper formations (Glen Rose and Travis Peak). The Paluxy Formation is transitional between these two groups in terms of depth, water chemistry, and rock/water reaction. "The ionic solutes in the deep-basin brines result initially from the dissolution of salt domes by meteoric ground water" (Kreitler and others, 1983, p. 84). Kreitler and others interpreted the Na and Cl in the brines to come from the dissolution of salt domes in the basin throughout geologic time. Therefore, the Na/Cl molar ratio of approximately 1 in the shallower formations "indicates minimal water-rock interactions." Conversely, the brines in the deeper formations have a Na/Cl molar ratio of approximately 0.7. "The increase in calcium... and loss of Na... are attributed to albitization. In this reaction, sodium in solution is exchanged for calcium in the plagioclase" (Kreitler and others, 1983, p. 88). Furthermore, the Paluxy is the first formation in which the higher Ca concentrations are encountered with increasing depth (Kreitler and others, 1983, p. 71). Similarly, Kreitler and others noted an increase in potassium concentration with depth, which they attributed to the dissolution of K-feldspars or the transformation of ("albitization") K-feldspars to albite. Therefore, the waters of the deeper formations, including to some degree the Paluxy, are Na-Ca-Cl type waters that have evolved form Na-Cl waters (Kreitler and others, 1983, p. 67). Immature sandstone composition and high-Ca brine suggest moderate potential for rock/water reaction with injection of CO2.

13 Reference:

Kreitler, C. W., Collins, E. W., Fogg, G. E., Jackson, M., and Seni, S. J., 1983, Hydrogeologic characterization of the saline aquifers, East Texas Basin: implications to nuclear waste storage in East Texas salt domes: The University of Texas at Austin, Bureau of Economic Geology, report prepared for U.S. Department of Energy under contract no. DE-AC97-80ET46617.

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