Applications of Pulsed-Neutron-Capture Logs in Ekofisk Area Fields

Abstract

Summary Phillips Petroleum Co. Norway is engaged in an extensive reservoir-monitoring program in the seven greater Ekofisk area fields. This program includes pressure-transient testing, production log surveys, compaction monitoring, and pulsed-neutron-capture (PNC) log surveys. This paper describes the applications of PNC logging in the six Ekofisk area chalk reservoirs and the analysis techniques associated with those applications. Gas has been injected into the upper portion of the Ekofisk reservoir since 1975, and waterflooding was initiated in 1987. These projects complicate PNC log analysis. Water breakthrough reduces or eliminates the "acid effect, " which can mask any increase in water saturation unless the acid-effect change can be quantified. Gas-saturation changes can introduce systematic error in water-saturation calculations unless taken into account. Phillips Petroleum Co. Norway recognized these complications and developed solutions that can be applied as part of the "standard" analysis techniques. Examples of each application are presented.