Reservoir characteristics (geometry, porosity and permeability) of hydrothermal dolomite (HTD) bodies: Ramales platform case study

Hydrothermal dolomite (HTD) bodies are known as high-quality hydrocarbon reservoirs; however few studies focus on the geometry and distribution of reservoir characteristics. Across the platform to basin transition of the Ramales Platform, fault-controlled HTD bodies are present. Three kinds of bodies can be distinguished based on their morphology, i.e. elongated HTD corridors, a massive HTD body (Pozalagua body) and a HTD cemented breccia body. The difference in size and shape of the HTD bodies can be attributed to differences in local structural setting. For the Pozalagua body an additional sedimentological control is invoked to explain the difference in HTD geometry. A (geo)-statistical investigation of the reservoir characteristics in the Pozalagua body revealed that the HTD types (defined based on their texture) show spatial clustering controlled by the orientation of faults, joints and the platform edge. Porosity and permeability values are distributed in clusters of high and low values; however they are not significantly different for the three HTD types. Two dolomitisation phases (i.e. ferroan and non-ferroan) can be observed in all HTD bodies. In general the HTD resulting from the second non-ferroan dolomitisation phase have lower porosity values. No difference in permeability is found for the ferroan and non-ferroan dolomites.