Integration of 4D Seismic Data for Water Injection Analysis of Co-mingled Wells

Abstract

Abstract 4D seismic has been utilised on several fields for improved reservoir monitoring and management. This paper describes a specific application of 4D seismic data for the analysis of co-mingled injectors. For optimised pressure support and sweep in water-flood projects, an injector can be completed over several different reservoir units. This, however, can introduce uncertainty on the effective injection into each zone. The reservoir quality encountered at each zone can give an indication of expected injectivity, however, this does not take into account dynamic pressure effects in the reservoir and possible completion issues. In certain cases where injection intervals are changed over time, monitoring the changes in the injectivity index during these different modes of operation can be used to infer relative injectivity potentials. PLT results, when available, can also indicate the split of injection into various zones at a given point in time. In addition, if formation pressure data is acquired after production start-up, this can be used to assess the pressure regimes in different zones. 4D seismic monitoring is the only technique to give an areal view of the reservoir, and injection anomalies from 4D seismic interpretation (3D geobody envelopes) can be used to represent the cumulative injection into a particular zone at the time of the monitor survey. This paper contains illustrations for the comparison of injection split estimates from reservoir quality (logs), well injectivity analysis, production logging, formation pressure testing and 4D seismic monitoring. Consistency between these various data sources reduces uncertainty for important reservoir management and field development decisions (well interventions, infill planning etc.). 4D seismic has proved to be beneficial for the field development and reservoir management of many Angola Block 17 fields and this particular example demonstrates the efficacy of integration of several data sources for effective injection analysis on one such water-flood field.