Hydrologic-Hydrochemical Characterization of Texas Gulf Coast Saline Formations Used for Deep-Well Injection of Chemical Wastes: Project Summary

Abstract

This research program was conducted to investigate fluid migration potential, direction, and velocities in the regional hydrologic environment of the Texas Gulf Coast Tertiary formations in the context of deep-well injection of hazardous chemical wastes. The study has focused on the Frio Formation due to its status as the target of a very large waste injection volume and the availability of a large database of formation pressures and water chemistry in the Frio.

Pressure data gathered from drillstem tests and bottomhole pressure measurements in onshore oil and gas wells were used to evaluate pressure regimes. Pressure-depth profiles and potentiometric surfaces were constructed from the pressure data, revealing the existence of three hydrologic regimes: a shallow fresh to moderately saline water section in the upper 3-4 thousand feet, an underlying 4-5 thousand feet thick essentially saline hydrostatic section, and a deeper overpressured section with moderate to high salinities. The complexity of the hydrologic environment is enhanced by extensive depressurization in the 4,000 to 8,000 ft depth interval, presumably resulting from the estimated production of over 10 billion barrels of oil equivalent and associated brines from this interval alone in the past 50 years. Hydrologic analysis indicates that the transition to geopressured sediments in some areas of the Gulf Coast is encountered as shallow as 6,000 feet.

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