Evidence That Old Oil and Gas Fields Influence Chemistry of Overlying Wilcox Aquifer

Douglas Carlson and Marty Horn
Louisiana Geological Survey, Louisiana State University, Baton Rouge, Louisiana

The impact of underlying oil and gas fields on water chemistry within our study area in southern Bossier, southern Caddo, and northern De Soto parishes in northwest Louisiana was revealed by the methane head space concentrations within the Wilcox Aquifer. There is a vast difference of concentrations between the field (Sligo) with highest median head space methane (HSM) concentration (approximately 1000 μg/L) and the field (Bethany-Longstreet) with the lowest median HSM concentration (7μg/L). There are other differences.

The parish concentration differences of HSM lead to determination of the significant differences between HSM concentrations within the Wilcox aquifer above various fields within the study area. Other parameters (barium, bromide, calcium, chloride, chromium, copper, magnesium, manganese, nitrate, nitrite, and potassium) show major differences among the three parishes where average concentrations vary by a factor of 2 among the parishes. Excess concentrations of barium, sodium, and chloride are indicative of upward movement of waters from oil and gas fields into overlying aquifers. Usually the highest concentrations are in Bossier Parish and lowest in De Soto Parish, which is consistent with HSM concentrations. These parameters were then checked to see if fields influence constituent concentrations in the Wilcox Aquifer.

AAPG Search and Discovery Article #90158©2012 GCAGS and GC-SEPM 6nd Annual Convention, Austin, Texas, 21-24 October 2012