The relationship between petroleum, exotic cements and reservoir quality in carbonates – A review

Exotic minerals, i.e. those that do not have an obvious source of components within the host rocks, can be major porosity occluding cement and replacement phases in subsurface carbonate reservoirs. Here we present and discuss petrographic and fluid inclusion data from a number of petroleum systems. These have had different geological histories but a common factor is the presence of exotic mineral cements and late stage dissolution. The effect of these cements and late stage dissolution on reservoir quality is also considered.Petroleum filling does not appear to inhibit the precipitation of exotic cements in the way that it appears to inhibit the precipitation of calcite. Burial dolomite and anhydrite are the most important of these volumetrically but they are often accompanied by other late stage cements such as fluorite, kaolin, quartz, barite, celestite, sphalerite and galena, generally in much smaller quantities. In accounting for the concentration of the material contained in these cements compared with the host rocks, stylolitisation is a possible mechanism in some cases, but, in many others, import from sources external to the reservoir is required.