Saline brines in South Texas are now known to exhibit wide ranges in salinity, ionic and isotopic composition. Some formation waters are hypothesized to form in shale-rich sections as water is released by the transformation of smectite to illite, and acetic acid is generated from kerogen. Very saline brines are clearly derived from underlying formations. In one growth fault zone it its hypothesized that elevated geothermal gradients are due to a vertical flux of brine from deeper in the basin. Some brines bear evidence of interaction with basement rocks which underly the Mesozoic-Cenozoic sequence. This project seeks to test these various hypotheses by carefully and systematically characterizing the major element, and isotopic composition of brines from producing oil and gas fields in a 14-county wide area. Spatial variability and relation to structure are critical variables interpreting the ultimate origin of the formation waters, and their role in effecting diagenesis. Brine sampling has proceeded beyond the "reconnaissance" stage in this area (Morton and Land, 1987), and now should be restricted to manageably small areas known to exhibit significant problems which can be addressed by future "saturation" sampling. This project will have significant bearing in our understanding of ore genesis, burial diagenesis, fluid behavior, petroleum generation and sedimentary geochemistry in a region close to DOSECC deep-drilling operations.
