Volume 34, Issue 3 p. 532-544

The Impact of Ion Exchange Processes on Subsurface Brine Transport as Observed on Piper Diagrams

David A. Cates

David A. Cates

Oklahoma Department of Environmental Quality, Oklahoma City, Oklahoma.

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Robert C. Knox

Robert C. Knox

School of Civil Engineering and Environmental Science, University of Oklahoma, Norman, Oklahoma 73019.

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David A. Sabatini

David A. Sabatini

School of Civil Engineering and Environmental Science, University of Oklahoma, Norman, Oklahoma 73019.

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First published: May 1996
Citations: 9

Abstract

An experimental study was conducted to assess how ion exchange processes, which occur during subsurface transport of oilfield brines, manifest themselves on graphical water quality diagrams. Concentrated brine soil column studies indicated sodium in the brine solution is able to exchange for calcium and magnesium on the soil, thereby retarding transport of sodium relative to the average ground-water velocity and resulting in the development of a “hardness halo” at the leading edge of the brine plume. In this zone, calcium and magnesium concentrations exceed the values for both the brine and the fresh ground water. The hardness halo manifests itself as a characteristic deviation away from the mixing lines on the Piper diagram. Initially, the hardness halo causes concentrations to plot left of the fresh-water end member in the cationic triangle. Chloride domination in oilfield brine causes concentrations to plot in the lower right corner of the anionic triangle almost immediately. After the hardness halo passes through the column, the sampling results show a characteristic pattern of movement parallel to the mixing line in the cation triangle or along the (decreasing) hardness axis of the upper diamond of the Piper diagram. The laboratory results were similar to those exhibited by monitoring well samples taken at a field site involving oilfield brine contamination. The results of this study show the Piper diagram to be potentially useful for early detection of brine contamination episodes.