Paper No. 14
Presentation Time: 11:40 AM


BLONDES, Madalyn S., Eastern Energy Resources Science Center, U.S. Geological Survey, 12201 Sunrise Valley Dr, MS 956, Reston, VA 20192 and ENGLE, Mark A., Eastern Energy Resources Science Center, U.S. Geological Survey, MS 956, 12201 Sunrise Valley Dr., Reston, VA 20192,

Compositional data analysis (CoDa) of sedimentary basin brines can help reveal the hydrogeochemical history of hydrocarbon-producing formations. CoDa uses log-ratio transformations to convert compositional data into Euclidean space, a necessary condition for many mathematical models and basic data interpretations. This study demonstrates the novel approach of complementing CoDa with thermodynamic geochemical models for bivariate and multivariate subcompositions for a suite of brines within three producing formations from the Permian Basin, USA. Subcomposition analysis of basin brines using [Na, Cl, H2O] and [Ca, SO4, H2O] with corresponding equilibration models, plotted using isometric log-ratio (ilr) transformations, shows reaction with anhydrite and halite at depth. The [Na, Cl, Br] subcomposition often can discriminate between seawater evaporation and halite dissolution; the sparse Br data suggest both processes occur. Principal component analysis (PCA) of centered log-ratio (clr) data is useful for visualizing combinations of processes that are not readily apparent in the two-solute models. PCA of the Permian Basin brines reveals distinct groups of data, including samples likely affected by water flooding and others influenced by a combination of seawater evaporation or halite dissolution coupled with Ca and Mg ion exchange with Na on clays. These relationships support a hydrogeologic model in which meteoric inflow occurs primarily by vertical transport from overlying units, rather than within unit recharge from the uplifted western portion of the basin.