SHALLOW GAS SAND WITH COAL
Above the obvious sand, there is a shaly sand section. This interval is typical of many so-called "shallow gas sands". In fact, there are more than 40 shaly sands in this well, all of them potentially gas bearing. The moderate GR and moderate resistivity at this depth indicate gas. The SP has a very slight deflection, so this zone is not easy to find on ancient logs when there is no GR log.
The trick is to segregate the coals, which may be coal bed methane prospects, and fresh water sands, which are easily mistaken for gas sands.
Coal is easily detected by the high density porosity, high neutron porosity, and high resistivity values, and should be given zero effective porosity and coloured black on the answer plot.
Fresh water sands are
difficult to distinguish in shaly rocks. Gas bearing
"fairways" are found by trial and error (testing and production).
Integration with hydrodynamics is a useful approach to help define
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