Compositional Systematics of Deep, Low Salinity Formation Waters in the Upper Wilcox of Southeastern Texas
Overpressured Eocene Wilcox sandstones in the Newton County, Texas Sabine Tram field contain water with salinities ranging from 14 to 28 g/L. The solutes appear to fall loosely into three groups. Na, Ca, and Mg follow systematics previously known globally for saline formation waters whereby their concentrations are controlled by fluid-mineral equilibrium. Cl, Br, I, and B are conservatively diluted constituents of some saline endmember that is not solely connate marine. Potassium does not follow any known basinal systematic, and the formation water is supersaturated with respect to SiO2 by an order of magnitude. Meteoric water is not a probable source of fresh water in the production interval. Diluting water is suspected to be produced by illitization, but could in fact be any water low in dissolved constituents. Mass balance calculations indicate that mixing water of marine salinity with shale dehydration water could produce waters with salinities in the range of values seen at Sabine Tram. Isotopic compositions indicate a diagenetic or saline endmember that is depleted in deuterium and enriched in 18O.
It is apparent that multiple contributing sources and reactions are progressing simultaneously in the study area. The possibility is proposed here that residence times are likely short, and the concentrations of the solutes represent multiple, sometimes spatially localized, reactions in progress. A downdip, higher temperature source may possibly be contributing constituents to the system. The data set for Sabine Tram provides an extension of knowledge regarding sedimentary basinal chemical systematics, and characterization of one possible endmember in the Gulf of Mexico sedimentary suite of formation water compositions.
Advisor:Jeffrey Hanor; Bob Gambrell; Lui Chan
School:Louisiana State University in Shreveport
School Location:USA - Louisiana
Source Type:Master's Thesis
Keywords:geology and geophysics
Date of Publication:04/10/2003