Publications

The Sembakung Field, located in North Kalimantan within the Tarakan Basin, has been producing oil since 1977. Characterized by complex fault compartments and a predominantly solution gas drive mechanism, the field has experienced a production decline over time. To mitigate this decline and extend field life, a waterflood pilot project was initiated in February 2019 in the south segment of the field. Initially, formation water was injected at a rate below 400 BWIPD. To improve water quality and enhance injection efficiency, a water treatment plant was added and brought on-stream in April 2023, allowing the injection rate to be optimized to 1,800 BWIPD. The pilot employed a direct line drive pattern covering 1,232 MSTB of pore volume, with one injector and two producers. While early results showed an incremental oil recovery of 10.51% within 1.5 years after WTP On-stream, premature water breakthrough was observed in early 2024, significantly increasing the Water-Oil Ratio (WOR) and reducing production efficiency.

To assess and optimize the pilot's performance, a comprehensive surveillance and analysis workflow was implemented, utilizing diagnostic tools such as Water Oil Ratio (WOR) vs. Cumulative Production, Oil cut vs Cumulative Production, Y-Plot, X-Plot, CVRR/IVRR monitoring, and decline curve analysis. These techniques provided insights into reservoir connectivity, water encroachment dynamics, and displacement efficiency. The findings indicated that high-permeability pathways contributed to rapid water breakthrough, negatively impacting oil recovery.

In response, a re-adjustment of the injection rate was implemented, leading to an incremental oil gain of 28.77 Mbbls and a more controlled production decline. This optimization also delayed water breakthrough, as observed through shifts in WOR and oil cut trends. The study emphasizes the importance of adaptive reservoir management, demonstrating that targeted injection control and continuous surveillance are essential for optimizing sweep efficiency and mitigating water encroachment challenges. The insights gained from this study provide valuable guidance for improving secondary recovery efforts in mature reservoirs with complex geological settings.