Saturation Height Modelling is a well-established and traditionally used reservoir characterization methodology based on the analysis of capillary pressure data to predict the initial water saturation of a reservoir, a parameter that greatly affects the hydrocarbon in place calculations. The paper points out how the integration of such methodology with the conventional petrophysical analysis can help to build a robust petrophysical model for a more accurate reservoir characterization. The potential of the integrated methodology is analyzed through the application to five case studies of hydrocarbon-bearing reservoirs in clastic sequences where the free water level position was sometimes unknown.
The distribution of fluids in the reservoir depends on several factors, including rock properties and reservoir quality (texture, pore throat size), fluid properties (density, interfacial tension), rock-fluid interaction (wettability) and height above the free water level. The fluid distribution can be predicted using a Saturation Height Model (SHM), which is most effective if calibrated using core data.
The rock and fluid properties and interactions determine the capillary pressure (PC), which in turn governs the access of hydrocarbons to the pore space.
Provided that PC data are available and their representativeness of a reservoir formation is verified, they can be used to construct a saturation height model (SHM) to predict water saturation (SW) at any point in the reservoir if the location of the free water level (FWL) is known. Furthermore, the integration of the conventional petrophysical analysis with SHM enables the petrophysicist:
To validate a water saturation profile from log interpretation;
To highlight a misinterpretation if any anomaly affects the log data;
To verify the consistency between the SW profile from logs (SWCPI) and the height above the free water level (HAFWL) according to the formation properties;
To extrapolate the information on the most likely position of FWL if no formation pressure data are available.
A further benefit of the PC data is that their use can be extended through the SHM to uncored reservoir formations, provided that the analogy of the geological and sedimentological setting between data source and data destination has been proved.
An integrated methodology has been implemented that fixes the required steps of data analysis, elaboration and interpretation to obtain a consistent saturation for hydrocarbon in place estimation.
