Calculation of Resistivity of Irreducible Water for Reserves Estimation

Abstract

A new fluid inclusion technique that allows determination of the resistivity of irreducible water trapped during oil accumulation has been developed. The technique is directly applicable to problems associated with the evaluation of oil accumulations which arise when the salinity and thus the resistivity of present day formation waters differ from those of the irreducible water trapped during oil accumulation. It is possible by measuring the ice melting temperature of samples of formation water trapped during creation of three phase, oil-water-vapour inclusions to calculate a salinity for the irreducible water and thus calculate a resistivity to be used in reserves calculations. Salinities of 71,000 to 85,000 parts per million have been measured on three phase inclusions in oil zone samples from the Papuan Foldbelt. Present day salinities in the Papuan Foldbelt are about 10,000-12,000 parts per million indicating that oil charge occurred before the present day hydrologic system was emplaced. Using salinity data from three phase inclusions results in resistivity values of about 0.05 ohm/m for irreducible water while present day formation waters have a resistivity of about 0.3 ohm/m at formation temperatures of 60[degrees]C. Using the water saturation calculated from three phase fluid inclusion salinity data compared with usingmore » the water saturation from present day formation water results in an estimated 25 % increase in reserves for oil fields studied in the Papuan Foldbelt.« less