Geochemistry of geopressured geothermal waters from the Texas Gulf Coast

Abstract

Detailed chemical analyses of 48 formation-water samples from 10 oil and gas fields in the Houston--Galveston and Corpus Christi areas, Texas, show that the salinity of water in the geopressured zone ranges from about 15,000 to 75,000 mg/L dissolved solids. The salinity of water in the geopressured zone is higher than that in the normally pressured zone in the Houston--Galveston area but lower than that in the normally pressured zone in the Corpus Christi area. Samples from many gas wells have low salinities tht are not representative of the true salinity of formation water because of dilution by condensed water vapor produced with natural gas. Procedures and equations are given that can be used to identify diluted samples from this and other studies and to estimate their true salinities. These procedures use chemical geothermomenters in conjunction with measured subsurface temperatures, and vapor-pressure data for water at the subsurface conditions in conjunction with gas and water production. The concentrations of H/sub 2/S (< 1 mg/L), silica (< 125 mg/L), and a number of toxic trace metals are low in the geopressured geothermal waters. The relatively high salinity of these waters, however, and the moderatly high concentration of environmentally toxic components (boron, about 50 mg/L, and ammonia, about 15 mg/L, for example) are unfavorable to geothermal development. The chemical data indicate that careful evaluation of the compatibility of the spent geothermal waters and the waters in the formations used for injection will be required to minimize loss of porosity due to precipitation of carbonate and sulfate of Ca, Sr, and Ba.