Pulsed neutron reservoir saturation monitoring logs are being acquired since the early stages of the subject offshore field life to monitor variations of saturation with time in addition to identifying pay zones for well intervention and reactivation operations. This is important given the increasing complexity of reservoir management due to water and miscible gas secondary and tertiary oil recovery schemes adopted by the operator. However, with the introduction of new pulsed neutron technologies and resource limitations, a benchmarking exercise was imperative to confirm data quality and identify any discrepancies in the recorded data.
Two candidate wells were selected based on the maximum Jurassic reservoir units coverage, including a group of lithologies (limestone, dolomitic limestone, anhydrite etc.) and borehole environments (single to multiple casing/tubing, cement and borehole fluids) to establish different correction parameters. The study was conducted with back-to-back logs utilizing current and new pulsed neutron tools from different service providers.
In addition to the comparing the changes of formation capture cross section (SIGMA), borehole salinity, sigma and porosity measurements against the logging environment and changing completion hardware, three-phase fluid interpretation products were compared. The results were validated via well performance and production logging data.
The approach is trying to support the reservoir saturation monitoring end users within the asset units operating in mature carbonate fields to design their time-lapse analysis methodology and to minimize the fluid saturation interpretation uncertainties, and as a result improve confidence in fluid front mapping and infill well planning.