New method to calculate the formation water resistivity (Rw)

One of the most important parameters needed to calculate hydrocarbon in place from wireline logs is the resistivity of connate water (Rw) in a formation of interest. Connate water or interstitial water is the water, uncontaminated by drilling mud that saturates the porous formation rock. The resistivity of this formation water is an important interpretation parameter since it is required for the calculation of saturations (water and/or hydrocarbon) from the basic resistivity logs. The most accurate method of determining this value is by measuring the resistivity or chemical composition of uncontaminated connate water produced from the formation. In case that the formation does not produce any connate water, e.g., deep basin and tight gas plays, or the produced water is contaminated it is difficult to determine accurate Rw necessary for reliable hydrocarbon-in-place calculation from logs. This paper presents a numerical method to determine connate water resistivity from the true formation resistivity. thod was tested using synthetic and real field data to ensure its ability in determining formation water resistivity.