Abstract There have been three attempts since the 70s to explore the offshore extension of Golfo San Jorge Basin, a prolific onshore province in Patagonia (Argentina) with more than 100 years of activity. Although some non commercial accumulations were found, none of these attempts was successful to find a discovery with enough oil resources to make an offshore development project viable. In this study we will discuss the reasons for this failure, and the keys for a new attempt in the area.
Besides high crude oil prices have been a triggering factor in this renewed interest, new petroleum system models have allowed the definition of undrilled areas with potential for a feasible offshore development. A number of prospects and leads with moderate geological risk have been defined in these undrilled areas.
The low productivity of Golfo San Jorge reservoirs restricts the possible development options. Chubut Group reservoirs are mainly composed of thin and disconnected fluvial sandstones, with limited petrophysical conditions, leading to multiple independent traps with different reservoir pressures, hydrocarbon types and fluid contacts. Thus, new technologies to be applied in reservoir and production engineering represent a real challenge for the economy of the project.
Different engineering options including new technologies for drilling, testing and production are under study and will be applied to make this new attemp a success. The new reserves consequently incorporated would replace the natural decline of production in the mature onshore areas.
Introduction The San Jorge Basin is located in Patagonia (southern Argentina), between 45° and 47° S and 65° and 71° W, and covers an areal extent of 170,000 km2. Two thirds of the basin occurs onshore, where more than 450 M m3 of oil have been produced. The remaining one third extends offshore. Water level increases rapidly close to the shore area up to 100 meters and remains constant all over the Golfo domain (fig.1)
Fig 1: Location of the study area
The offshore San Jorge basin involved three unsuccessful exploratory periods; consequently, it was not been possible to perform any production project up to date.
The first stage (AGIP, Tenneco and Sinclair between 1971 and 1973) comprised a bad quality 2D seismic survey and the drilling of 17 exploratory wells in the outer zones of the basin. These external areas are characterized by long-distance migration and low hydrocarbon charge (heavy oils and gas). There were three uneconomic discoveries in this stage (Marta, Petrel and Batitú).
The second exploratory stage (YPF between 1977 and 1978) involved a bad quality 2D seismic survey and the drilling of 7 wells following the high production belt tendency of the onshore oil fields, in poorly defined near-shore structures.
There were four uneconomic discoveries with productions from Mina del Carmen formation.