Feasibility study for the choice of the development system for a massive oil rim of a large offshore field in the North of the Сaspian sea

The oil recovery factor in the development of oil rims remains low compared to conventional oil reservoirs, which is attributed to intensive gas breakthroughs from the gas cap, high gas mobility, bottom water encroachment, and the complexity of controlling displacement processes. In global practice, the development of such assets often leads to increased project costs, since the strategy choice is frequently determined not by geological and physical conditions but by infrastructural or economic factors. New technologies and an integrated approach to development planning make it possible to efficiently exploit these hard-to-recover resources.
This paper presents the rationale for selecting a development strategy for the oil rim of a one field in the Northern Caspian Sea, which is currently at the design stage. The complex geological structure, low effective thickness, and the presence of a gas cap require the implementation of an individual development system involving horizontal wells and reservoir pressure maintenance strategies.
The methodological basis of the study was dynamic simulation using a sector model. Four development strategies were compared: development of the gas cap, oil rim only, sequential and simultaneous production, combined with various pressure maintenance systems. The analysis showed that the highest oil recovery is achieved with the oil rim development strategy that employs a combined reservoir pressure maintenance system: reinjection of 60% of produced gas and water injection. Optimal placement of horizontal wellbores at ¾ of the height from the gas-oil contact was proposed. The obtained results may help reduce the risks of gas and water breakthroughs, improve drainage efficiency, and increase cumulative oil production compared to alternative strategies during field commissioning. The study has practical value for planning the development of hard-to-recover reserves on the shelf.

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