"Solving a Puzzle" — An Integrated Approach to Revitalize a Neogene Turbidite Play in SW Pannonian Basin, Hungary

Nemeth, Andras; Vincze, Marianna

Two gas discoveries were made by application of a complex tectono-sedimentological model and a critical revision and synthesis of old G&G data. The study area has been explored since the 1940s targeting Mesozoic reservoirs in structural traps, with additional discoveries in Upper Miocene turbidite series above basement structures. All the fields are mature or depleted by now. To revitalize the exploration and exploitation of the area, we initiated a new approach focusing on stratigraphic traps within the Upper Miocene turbidites.

As a first step, a 3-D seismic survey was conducted covering an E-W striking ridge with accumulations and a graben north to the ridge serving as a HC-kitchen. Based on the interpretation of the 3-D cube, a complex depositional model was elaborated for the Upper Miocene sediments, identifying shelf, slope and basin paleoenviroments and a sediment influx from NE to SW. Characteristics of the system are narrow shelf and strong sediment supply that resulted in sand rich turbidites. Based on seismic attribute anomalies, nearly 30 leads were identified within the turbidite series. An integrated analysis of the HC system led us to focus on the northern flank of the ridge, where post-depositional uplift and tilting of the turbidite succession provided favorable trapping conditions.

One of our most promising prospects, however, was significantly weakened by an old dry well situated at the edge of the turbidite lobe. To solve this contradiction, we carefully checked both the elements of our evaluation and the old data. The well, drilled during WWII, was part of an appraisal phase of a basement oil field. In the 1960s, however, similar appraisal wells were tested to find further possibilities above the depleted basement pool. The results were two small gas discoveries from Upper Miocene sandstones. This led us to the conclusion that some penetrated HC pools remained hidden for the early explorators.

We also encountered some contradictions at another prospect located next to a depleted Upper Miocene sandstone pool, below its initially supposed GWC. We put every piece of the HC-puzzle in the right place by redefining the field contour and critically revising old test results.

Drilling our prospects resulted in discoveries, demonstrating that key to success is not only the state-of-the art technology but a critical synthesis of all available information, followed by a brave decision.

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013