An extensive laboratory study to determine initial water saturation as well as remaining oil in water flooded regions has been initiated using porous plate measurements at reservoir temperature and net overburden pressure conditions using stock tank oil and simulation formation water as the displacing fluids. The results of Primary Drainage, Spontaneous Imbibition and Forced Imbibition experiments are presented in this work which capture the capillary pressure (Pc) behavior and the electrical resistivity (Sw-RI) changes all the way down to Swi for drainage and Sor for imbibition. The impact of both drainage and imbibition laboratory results for the well and for the reservoir is also considered.
The initial water saturation was estimated using the RI-Sw curves in drainage. Very low saturation was reached covering the range of saturation of interest in the field. The saturation exponents ‘n’ appear to be around 2 for the reservoir rock types (RRT) containing most of the STOOIP while the tighter RRT's show lower values. Capillary pressure and Resistivity Index data when grouped according to geological lithofacies confirm the distinct RRT characteristics.
The remaining oil saturation was estimated using the RI-Sw curves in the imbibition mode. Interesting capillary pressure behavior has been observed in the spontaneous imbibition cycle which can directly be linked to the pore throat size distribution curves obtained from mercury injection data on corresponding sample ends.
Forced imbibition curves were established using five capillary pressure steps with a maximum value of 5 bar (72.5 psi). Little hysterises in the Resistivity Index has been noticed in the drainage/imbibition cycle which tends to increase the saturation exponent "n" above 2 Obtained Sor values have shown little variations among all samples except for the tightest RRT's which show higher values.
Grouping of the capillary pressure, water saturation and resistivity index results together with the basic petrophysical data including poroperm, NMR, CT scans, mercury injection and thin-section images confirm the efficiency and consistency of the collected data.
The value of the well defined laboratory data and its integration to logs is presented. Despite intermediate to oil wet conditions, ‘n’ values are lower than the default value of 2 in the drainage cycle and much lower than that expected for oil wet conditions. The laboratory measurements reduced the uncertainties in the oil in place estimations and allowed a realistic evaluation of the water flooding performance.
