Log Derived Saturation Functions for Giant Carbonate Reservoirs in the Middle East

Abstract

Fluid saturation distribution at initial reservoir conditions is vital for calculation of original oil in 
place (STOOIP) and reservoir simulation (dynamic models). It is a critical step in model initialization, since the 
subsequent step (quality of history matching) is largely dependent on the initial fluid distribution at time zero. 
In many reservoirs there are limited or no SCAL (drainage capillary pressure) data available and in many 
cases, the available limited SCAL data has poor quality and subjective plug selection. However, log-data (open 
hole logs, OHL) and routine core analysis (porosity and permeability measurements) are usually more available. 
The proposed method combines OHL and routine core analysis (RCA) to derive saturation functions for 
carbonate reservoirs with complex pore structure. 
The proposed method uses a multi-regression technique to relate water saturation to height above FWL and 
rock quality index (RQI) for each reservoir rock type (RRT).
This method already been tested in carbonate reservoirs such as Shuaiba reservoir and Thamama-group 
formations. 
This study used 58 core wells penetrating Thamama reservoir with permeability measurements covering six 
petrophysical groups. The comparison results show a good match between the calculated initial water saturation 
(Swi) from the dynamic model. The STOOIP calculations indicated good agreement (within 3% difference) 
between the dynamic and static models.