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Terms and phrases --- Terminologie --- Langage --- Langue --- Linguistique --- 800 --- Taalwetenschap. Taalkunde. Linguistiek --- #KVHA:Terminologie --- 800 Taalwetenschap. Taalkunde. Linguistiek --- Mots et locutions --- Terminologie (science) --- Vocabulaire

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Nederlands --- Frans

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Dolomitization is the process of altering calcite (CaCO3) into dolomite (CaMg(CO3)2), for this a fluid with a high enough Mg content relative to its Ca content is needed. The oil industry especially is interested in dolomitization since it often results in an increase in porosity, which means that it can provide better oil reservoirs. Several models exist to explain dolomitization. The KU Leuven has developed a new model based on the Latemar platform (northern Italy). In the Latemar platform ferroan dolomite and dolomite is found adjacent to the dikes (ferroan dolomite is dolomite where some of its Mg is replaced by Fe). Based on this a model was developed where seawater first interacted with mafic, igneous dikes, resulting in an increase in the Fe and possibly the Mg content of the seawater. Then this modified seawater flowed into the carbonate (calcite) country rock and induced dolomitization. This thesis explored the same concept by performing geochemical modelling. With geochemical software packages the interaction between the fluid and the rocks was studied. The influence of the seawater and dike composition on the subsequent dolomitization was investigated. One part of this was replacing the Latemar composition, which consists of the rare shoshonite, with the most common magma type on earth: mid-ocean ridge basalt (MORB). The influence of the dike composition was investigated by varying the plagioclase, olivine and clinopyroxene content. The highest dolomitizing potential, defined by the saturation index of dolomite or the Mg/Ca ratio, is obtained at low plagioclase and clinopyroxene contents and a high olivine content. To investigate the influence of the seawater composition, tests were performed with Triassic seawater and with modern seawater. Additionally, the pe, SO4-2, pCO2, HCO3- and Mg+2 contents were varied. These tests showed that the highest dolomitizing potential is obtained at reducing conditions, high HCO3-, high Mg+2, intermediate pCO2 and intermediate to high SO4-2 contents and that the dolomitizing potential of modern seawater is higher than that of Triassic seawater. When compared to the unmodified seawater the fluid resulting from the seawater-MORB dike interaction had a lower dolomitizing potential. This is because the alteration of the dikes acts as a Mg sink, Mg-bearing minerals like chlorite and talc are precipitated. However, calculations showed that there was little difference in the amount of dolomite formed by modified and unmodified seawater. Unlike in the Latemar system, interaction with MORB didn’t result in stabilization of ferroan dolomite, to accomplish this an extra Fe source is needed.