Pulsed neutron measurements have been used since the early 1960s to measure porosity and sigma through casing. Since the formation sigma response is proportional to the salinity of the formation water, pulsed neutron measurements are used to determine porosity and water saturation behind pipe.
In parts of west Texas and southern California, it is common to use through-casing pulsed neutron measurements for water and CO2 flood monitoring. By comparing time-lapse pulse neutron data, it is possible to determine changes over time in water, gas, and oil saturations.
The concepts and methodologies that allow time lapsed pulsed neutron measurements to be used for water and CO2 flood monitoring can be used to identify bypassed pay in fields that have been under only primary production.
In water and CO2 floods, the base pulsed neutron measurement is compared over time with subsequent pulsed neutron measurements. The changes in the pulsed neutron porosity and sigma measurements are related to changes in oil, gas, and water saturations.
Most producing wells do not have base pulsed neutron measurements. Many of these wells do have porosity and resistivity measurements that were acquired prior to setting casing.
There are many challenges faced when attempting to incorporate various pulsed neutron measurements with the original porosity and resistivity measurements for a consistent evaluation. This paper will present the methodology of incorporating the present day pulsed neutron measurements, with the original porosity and resistivity measurements into a comprehensive petrophysical model. This model will solve simultaneously for the original hydrocarbon in place, along with the current hydrocarbon in place.
This paper will show how the combination of pulsed neutron measurements and original open hole log data, on a multi-well basis, was used to identify bypassed hydrocarbons.
The bypassed pay was used to design a recompletion program and resulted in significant increases in both produced hydrocarbon and proven reserves of hydrocarbon.
Based on the increase of hydrocarbons found by bypassed pay analysis a re-completion program was designed and put into action that resulted in an increase of produced hydrocarbons and proven reserves of hydrocarbons.