| Abstract |
Paleo-thermal history, stratigraphy and alteration mineralogy within the Domes field has been of keen interest for the purpose of reservoir monitoring and field expansion. In this paper, we present results of analysis whose objective was to understand temperature changes in Domes area over time. In this study, four wells were analysed. The wells were selected from the eastern and southern sectors of the Domes field. They include OW-914A, OW-916, OW-911A and OW-912B. Rocks encountered in wells OW-914A, OW-916, OW-912B and OW-911A include pyroclastics, rhyolite, basalt, tuff and trachyte. The latter is the most dominant rock type. The wells cut across two intrusives: syenite intrusion and basaltic dyke. However, the depths of the first appearance of alteration minerals in the study wells vary from one well to another. For example, epidote, a high temperature Ca-silicate mineral, was first encountered at 556 m depth in OW-916, 670 m in OW-911A, 732 m in OW-914A and 950 m in OW-912B. Other hydrothermal minerals present include zeolites, quartz, albite, pyrite, Fe-Ti oxides (e.g. titano-magnetite and ilmenite), calcite, chalcedony, prehnite, wairakite, epidote, actinolite, chlorite, and garnet. The highest recorded formation temperature in the four wells is 280 °C, which correlates well with alteration mineral assemblages at various depths. Fluid inclusion in secondary quartz recorded minimum temperature of 160 °C and maximum of 300 °C at 765 m and 1600 m, respectively. These temperatures more or less lie within the same range as alteration mineral and formation temperatures. This is a clear indication that no significant temperature changes have occurred from the time the system was formed, through alteration period to the current time of the Domes field system. |