This Analogue Spotlight is the Nagylengyel Field in Hungary. This global oil and gas analogue provides a fascinating case study on the effectiveness of CO₂ injection in unusual reservoir environments to increase production and sequester CO₂.

The Nagylengyel Field is situated in the Zala Sub-basin of the Pannonian Basin, western Hungary, and contains a STOIIP of 275 MMBO in the Upper Cretaceous Ugod Formation. It is unusual as the carbonate reservoir has a tight matrix so production depends on karstic fractures and caverns. The field is split into 15 separate compartments (Fig. 1). Production under strong aquifer drive peaked at ~22,530 BOPD in 1955 and had declined to 1127 BOPD with a water-cut of ~87% by 1987.

The first of three stages of fieldwide CO₂ injection began in 1988 following a successful pilot in 1980 in Block V-VI. An extensive program of well recompletions and new injectors to replace wells with poor casing was completed in Block I-IV. Gas was injected through two injectors, and another nine were added to balance the GOC. The oil bank was driven down to a limit of 1947 m TVDSS to keep it above the original OWC (Fig. 2). By 1990 oil production had increased to 5000 BOPD. Gas injection ceased and blow-down of the gas-cap began in January 1993. The produced gas was reinjected without compressors into Blocks VII, VIII and Block X South as part of the second stage of the project.

The use of CO₂ injection resulted in an incremental production from Block I-IV of ~1.25 MMBO per year between 1989 and 1995. By 2005, 88.8 BCF of CO₂ had been injected and stage III of the project was in preliminary design. By 2008, incremental oil produced had reached 18.9 MMBO. Total incremental oil from the CO₂ injection is expected to be 29.8 MMBO.

The Digital Analogue Knowledge System (DAKS™) contains many global oil and gas analogues specifically focused on heavy oil fields. Use these analogues to benchmark your own field, and delve into C&C Reservoirs Reservoir Evaluation Reports to discover best practices from top performing reservoirs that can be applied to your own assets.