Many Permian Basin fields are considered "mature", with some of these fields almost depleted and/or undergoing water or CO2: flooding. Operators are being faced with decisions to P&A or to recomplete in other zones, often with inadequate data. Unfortunately, many of these wells were logged before modem porosity logs were available. In other wells, for various reasons, the entire well was not logged.

The integration of modem pulsed neutron technologies1  can. however, provide the operator with reservoir parameters from inside casing. For porosity, pulsed neutron systems can make a thermal neutron ratio porosity' (RPHI) similar in response to the compensated neutron. Pulse neutron systems can also be used to make a new type of porosity (IPHI) derived from gamma rays created by inelastic scattering of fast neutrons. IPHI is similar in response to an open hole density and can be crossplotted with RPHI to help identify lithology changes and differentiate tight zones from gas. The crossplotted porosity also helps compensate for lithology and gas effects, and to some extent for some variations in near wellbore environment. The crossplotted porosity can then be used with sigma and/or CATO2  to determine water saturation.

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