1. n. [Formation Evaluation]
The apparent resistivity of the formation water, calculated from log measurements of porosity (phi) and resistivity (Rt) and using the Archie equation with Sw = 1, so that Rwa = phim * Rt. Rwa is a quick-look method of determining if there are hydrocarbons. In a hydrocarbon zone, Rwa will be higher than the actual resistivity of the formation water (Rw), which must be known. A typical rule of thumb is that if Rwa > 3 * Rw, then there are producible hydrocarbons. Rwa is often calculated and output as a quicklook log.
