Dolomitization of Ekofisk Oil Field reservoir chalk by injected seawater

Seawater that is being injected into the fractured chalk reservoir of the Ekofisk Oil Field is reacting with it at 131 degrees C and 28-34 MPa and being produced again, after some months, from a few wells. Changes in its composition, modeled with SOLMINEQ.88, show that very slow dolomitization is occurring in the reservoir and the precipitated dolomite is very disordered. Also, brine chemistry shows that the very sparse indigenous dolomite in the Ekofisk reservoir chalk is partially ordered. Our observations provide direct evidence of dolomitization of CaCO3 rocks by seawater, such as is inferred to occur within the endo-upwellings of atolls.