Waterflood Sweep Pattern Monitoring Using 4D Seismic in Windri Area, Asri Basin, Southeast Sumatra, Indonesia

Abstract

Reservoir characterization in Windri field is complicated by complex lithology and difficulties in predicting changes in fluid distribution. 33-4 Sand body is interpreted as complex compartmentalized channel and part of water flood project associated with distributary channels, mouth bars and delta front shoals. Seismic amplitude mapping at the Base Upper Gita horizon reveals a system of meandering channels. In 2000 and 2004, 4D seismic data set was acquired and processed to take advantage of seismic AVO effects. The base line 1991 seismic data set was reprocessed in parallel. The primary reason for the monitor data set was to observe the reservoir pressure depletion state around a water-flooding project. Detection of 33-4 sandstone reservoir is feasible based on interpretation of AVO P, G, P*G, P(30°) attributes. Fluid replacement model created into three scenarios (oil, water, gas) to predict the hydrocarbon saturation. Integrated time lapse 4D seismic by using map differences in seismic response has been conducted for monitoring pressure decrease and subsequent water flooding sweep patterns. Windri area divided into 6 sweep patterns area to make improved connectivity analysis.AVO attributes using intercept (P), gradient (G), P*G, and P(30°) has been done to determine of 33-4 sand. Feasibility study on AVO analysis has been applied by using fluid replacement model on the well data. A more advanced interpretation of the expanded AVO analysis for 33-4 sand has been done by using simultaneous inversion and 4D time lapse seismic. Practically, this method is used to map differences in seismic response over time attributable to production related processes, especially amplitude response which directly interpreted as replacement of oil by dissolved gas, and also suggest re-pressurizing the reservoir. Reservoir characterization using 4D simultaneous inversion enhances interpretative resolution and reduces uncertainty sand and fluid prediction. Integrated analysis of time lapse 4D seismic has been well implemented for increasing infill and injector success ratio, as well as predominating pressure degradation in Windri field. This comprehensive study is essential for understanding of complex lithology, monitoring pressure decrease and subsequent water flooding sweep patterns in 33-4 sandstones reservoir. Knowing the concept of depositional setting, facies and reservoir behavior to be applied in the waterflood project is crucial to optimize the production.