Geology, Structure and Piercement History of South Liberty Salt Dome, Texas, and the Nature of Fluid Flow Around It

By

BANGA, TAT, University of Houston, Houston, TX, CAPUANO, REGINA M.,

and VAN NIEUWENHUISE, DONALD S.

University of Houston, Houston, TX

Detailed log correlation, biostratigraphic data and local seismic data are being used to review the stratigraphic and depositional models of a section of the Houston- Liberty delta during the Cook Mountain - Yegua depositional episodes. A number of structural and stratigraphic cross-sections are compiled to demonstrate the delta progradation with reference to temporal and spatial variables such as sea-level changes, subsidence and sediment supply. An interesting part of this study has been to establish the diapiric history of the South Liberty salt dome, which pierced through the sediments deposited at the junction of fluvial dominated delta and shelf margin slide complex facies during the Eocene time.

Multi-element, d¹⁸O and dD composition of brines collected from non-geopressured oil-bearing horizons of the Frio, Yegua and Cook Mountain Formations along the flanks of the South Liberty Salt Dome have been used to determine fluid sources and flow patterns around the salt dome. The water is a Na-Cl brine with total dissolved solids ranging from 68,000 to 208,000 mg/L. The fluid source as indicated by chemical and isotopic tracers, is brine from the surrounding geopressured sediments mixing with the local meteoric water (deeper samples retaining more geopressured fluid characters). This mixing trend prevails across formations and in some areas it appears to follow a migration pathway. In other areas there appears to be reservoir compartmentalization indicated by large variation in mixing of fluids, and halite and gypsum dissolution within individual fault blocks.

[The Texas Higher Education Coordinating Board Advanced Research Program supported this research.]