When a formation is gas bearing, it is common that gas correction is applied before or during the petrophysical formation evaluation. There are several methods to correct the influence of gas on tool response (" Gas effect"), which were proposed a half-century ago (e.g. Gaymard and Poupon, 1968 and Segesman and Liu, 1971). It has been widely adopted in the petrophysical society today.
However, there was an instance of the gas bearing formation which was not able to be reconciled porosities derived from different tools (e.g. Density, Neutron, and Nuclear magnetic resonance), even though the gas effect being corrected with these methods using appropriate parameters. To examine which porosity was correct, we employed several methods and combination of tools (Density-Nuclear Magnetic Resonance & Dielectric tool), and performed forward modeling studies such as a well log simulator and an invasion profile simulator.
In this paper, we shared our insight on accuracy and limitation of the existing gas correction method.