Seawater mixing with formation water

Figure 8 Distribution of Cl and Br in formation waters from the central Mississippi Salt Dome Basin relative to the evaporation line for seawater (SW, A-B) and mixing lines between Norphlet water (Norph. W) and meteoric (MW) and sea (SW) waters. Line E-F gives the trend when the mixture of meteoric and Norphlet waters dissolves halite with 70 ppm Br. Line C-D gives the trend where 50% of the Cl concentration in the mixture of meteoric and Norphlet waters is from dissolution of halite. Note that the samples from Coastal Texas and Louisiana (dashed field) plot in a different field (source Kharaka and Thordsen, 1992).

To illustrate the matrix damage problem in the reservoir and scale formation in production wells an application using the numerical code is presented. In this example, sulfate scaling occurs by mixing of injected water (seawater rich in sulfate and poor in Ca", Sr" and Ba ) with a connate water rich in Sr and Ba" cations. From this mixing strontium sulfate salt (SrSOj) and barite (BaS04) precipitations are expected. This kind of scaling is typical from the North Sea (Osborne et al., 1994) and also common in Campos Basin, Brazil (Silva et al., 2001). 

The Michigan Basin brines very low pH helps to explain their ability to leach and react with other rocks, as is indicated by their high contents of strontium, barium and other metals, although much of the Sr and Ba probably came from the reaction with calcite. Geothermal water also probably mixed with some of the formations, as indicated by the variable presence of iodine, boron, lithium, cesium, rubidium and other rare metals. With most of the brines, the calcium concentration is somewhat higher than its magnesium equivalent in seawater end liquor from a potash deposit, and the potassium a little lower. Wilson and Long (1993) speculated that this occurred by the conversion of the clays kaolinite and smectite to illite ... 

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