Development of Empirical Formation Factors to Estimate Water Quality from Electrical Logs for the Southern Hills Aquifer System of Southeastern Louisiana
Thomas P. Van Biersel
Louisiana Geological Survey – Louisiana State University,
3079 Energy, Coast and Environment Bldg., Baton Rouge, Louisiana 70803
Formation factors have been determined in the past for northwestern, central and southwestern Louisiana. In order to be more accurate in determining the salt and total dissolved solid content of groundwater in southeastern Louisiana, apparent formation factors have been empirically determined for 10 Baton Rouge sub-aquifers of the Southern Hills Aquifer System. Formation factors were determined using the maximum and average (across the length of the screened interval) 64-inch long-normal resistivity amplitude from water wells where both an electrical log and concurrent groundwater chemistry was available. The wells’ electric logs and groundwater sample chemistry (e.g., specific electrical conductance, and chloride and total dissolved solids concentrations) were obtained from the U.S. Geological Survey and Louisiana Department of Transportation and Development files.
The result of the analysis indicates that formation factors generally increase with depth. The 400-, 600- and 800-foot sands exhibit average dimensionless formation factors ranging between 1.7 and 2.7, the 1000-, 1200- and 1500-foot sands between 2.8 and 3.1; and the 1700-, 2000-, 2400- and 2800-foot sands between 3.0 and 3.2. Plots correlating chloride and total dissolved solids concentration with resistivity for all sands indicate relatively good curved relationships between these parameters, with the exception of chloride concentration and resistivity for the 800- (too few data points), 1700- and 2400- foot sands. In the case of the 1700- and 2400-foot sands, there is a negative relationship (e.g., chloride concentration decreases with decreasing resistivity) which indicates that electrical resistivity may not be an accurate tool in estimating chloride concentration in these two sands.
AAPG Search and Discover Article #90069©2007 GCAGS 57th Annual Convention, Corpus Christi, Texas