IVZ - General Discussion, page-986

"How a company can report high resistivity on the LWD in the Pebbly Arkose then change their interpretation to residual gas is quite concerning. Log results do not usually shift from high resistivity to very low values. "

Generally not...but from what I gather the mineralogy of the Pebbly Arkose is a bit different from the underlying Angwa. The presence of some minerals (eg zeolites) can dick with resistivity readings and in extreme cases prevent calculation of an accurate water saturation. The Pretty Hill Sandstone in South Australia's Ottway Basin is a good example of the latter. The exact mineralogy of the PA would have been deduced from sidewall core petrographic thin section work which would have been done _after_ the initial log interpretation was carried out. This is part of the process of calibration of log data with core data.

Note also that "Arkose" is an old name for what we would now call a felsarenite....a felspathic sandstone. Unless you're running a spectral GR with your LWD/wireline it's often hard to distinguish shaley sands from shales.