In mature fields, optimization of CO2 flood and tertiary oil recovery demand accurate and consistent formation evaluation in producing wells. The complex well history—including near-wellbore (NWB) stimulation and recompletion for flood injection—often poses challenges to interpretation. Conventional water saturation (Sw) from resistivity based saturation modeling is of large uncertainty because of reservoir heterogeneity: variable M, N, and Rw parameters. Often, openhole (OH) logs might not even be available.

To address these challenges, a new multidetector pulsed-neutron tool (MDPNT) has been designed to enhance radial measurement sensitivity. In this paper, case histories are examined to illustrate a consistent workflow for deriving calibrated cased-hole (CH) porosity from capture gamma ratios and gas saturation from gas saturation gate (SATG) response of the MDPNT. The SATG curve computed as the ratio between inelastic counts and slow capture counts from a single gamma detector has reduced lithology and water salinity dependences compared to traditional saturation analysis using a PNT.

CH MDPNT accurately identify CO2 breakthrough and monitor CO2 saturation changes. Time lapse use of MDPNT and log interpretation guides conformance work design to improve aerial and vertical sweep efficiency in the field.

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