Reservoir Characterization by 3D Modelling of Water Encroachment Using Time Lapse Pulsed Neutron Logs in a Heterogeneous Shalysand Reservoir of Greater Burgan Field

Abstract

AbstractWara reservoir of Greater Burgan field is a heterogeneous shaly sand reservoir deposited in fluvio-deltaic environment. Modeling the changes in hydrocarbon saturation and water encroachment in Wara reservoir has been a great challenge due to a combination of factors like heterogeneity, multiple Oil Water Contacts and multiple Oil Gas Contacts etc. Understanding the water encroachment and monitoring zones of water breakthrough is a key for effective water flooding reservoir management. Pulsed neutron capture (PNC) logs are commonly used for formation evaluation behind casing and to assess time-lapse variations of hydrocarbon saturations. Systematic time-lapse PNC logging can give a detailed description of hydrocarbon saturation changes in response to injection and production operations during water flooding. This paper addresses the workflow that has been utilized to create a 3D static model of Water encroachment using flags that characterize the swept and partially swept zones in the reservoir created from Sigma curves of Time lapse PNC logs along with synthetic sigma curves from the open whole logs acquired at the time of drilling the well. The remaining oil in place volume which was estimated from the sweep model was consistent with the volumetric of the simulation model and with the remaining oil in place calculated from the production data. Volumes of different vintages are created with time lapse PNC logs. The difference between these volumes can be used to understand the complex water encroachment in the reservoir due to multiple oil water contacts and also it can be used as a source to calibrate the 4D seismic data acquisition model. Connected volumes of the swept and partially swept zones computed from the model were utilized to visualize the swept zones.