LOCATING BYPASSED OIL THROUGH IN-WELL SURVEILLANCE IN PRUDHOE BAY

摘要

The initial reservoir fluid distribution in the PrudhoeBay Reservoir, Alaska, consisted of relatively planargas-oil and oil-water contacts. These contacts weresoon perturbed by production as well as water and gasreinjection. Understanding the current reservoir fluiddistribution and the movement of fluids in response toreservoir depletion mechanisms is key to optimizingand maximizing recovery.Historically, the focus of much of the successful casedhole surveillance effort in the Gravity Drainage area ofPrudhoe Bay has been directed at tracking themovement of the gas-oil contact and quantifying theremaining oil bypassed by gravity drainage processes.Forward modelling of pulsed neutron tool attributes hasbeen employed to enable gas saturation quantification.Recent introduction of memory Multi-Detector PulsedNeutron technology has enabled the quantification ofbypassed oil in horizontal wells using coiled-tubing.Selective perforation has been used to access undrainedoil.In the Waterflood area of Prudhoe Bay, it is a challengeto use conventional sigma logs to distinguish betweenoil and water due to the relatively low and variableformation and injection water salinity. Consequently,continuous and multiple passes and stationary Carbon-Oxygen logs have been employed to identify bypassedoil.In areas of the field where gas, oil and water columnsexist in a single wellbore, both Carbon-Oxygen andMulti-Detector Pulsed Neutron nuclear attributes arecombined together using a novel three phaseinterpretation technique to quantify oil, gas and watersaturation. The technique has been applied in a numberof Prudhoe Bay wells to enhance understanding of thefluid distribution and to design perforation strategies tomaximize offtake in existing cased hole wells.Case studies of each scenario illustrate the use andintegration of Carbon-Oxygen and Multi-DetectorPulsed Neutron attributes to identify bypassed oil.