Water-oil relative permeabilities measured using reservoir fluids and fresh, preserved cores are shown to differ considerably from those obtained routinely using relined fluids and extracted cores. Upon saturating the extracted cores with the reservoir fluids and allowing them to come to equilibrium, in this case for 6 days, the original relative permeability curves were reestablished.
Ordinarily, relative permeabilities are measured using refined fluids and restored-state cores. On occasion, fresh core samples that had been flushed with a refined oil, without any other cleaning or extraction, have been used. To date, no relative permeability measurements have been reported permeability measurements have been reported using reservoir fluids and fresh preserved cores, although a number of published studies have dealt with the influence of core handling and other laboratory experimental factors on results of displacement tests. This is not surprising. Special procedures have to be followed for obtaining, procedures have to be followed for obtaining, preserving, and handling native-state cores; and preserving, and handling native-state cores; and companies are generally reluctant to permit any procedures that may increase the expense or the procedures that may increase the expense or the time required to complete a well. Consequently, suitable cores often are simply not available. Furthermore, only a very few of the petroleum production research laboratories have the facilities production research laboratories have the facilities for measuring interfacial tension, contact angle and relative permeabilities at the elevated temperatures and pressures normally encountered in reservoirs.
The following study provides, for the first time, relative permeability data obtained with fresh, preserved cores and reservoir fluids at reservoir preserved cores and reservoir fluids at reservoir pressure and temperature. Measurements were also pressure and temperature. Measurements were also made routinely with refined fluids and extracted cores to afford comparisons. Advancing and receding contact angles were measured as a function of time with the actual reservoir fluids on a solid surface representative of the reservoir rock to characterize the wetting equilibrium during the tests. Finally, a procedure was devised which, for the extracted procedure was devised which, for the extracted cores, yielded the original set of relative permeability curves. permeability curves.
