engleski

Observation useful for increase of hydrocarbon fields exploitation period within Croatian part of the Pannonian basin

Approximately 110x106 m3 of oil (100x106 tons) had been recovered from 38 fields in the Croatian part of the Pannonian basin during more than 60 years of exploitation (1941-2003). Based on their cumulative production, number of reservoirs, average porosity and permeability, obtained recovery and depositional characteristics of reservoir rocks, the Croatian hydrocarbon fields may be divided into three groups (oil), or four groups (gas) (Table 1, 2). In the period 1941-1990 the production started in 38 fields, 13 of which before 1959. The peak was reached in 1980-1989 period, when exploitation started in 12 new fields. However, estimations of economic exploitation are optimistic. The longest period is assumed for the 1st group of fields – approx. 55 years, while for 2nd and 3rd group 46 and 36 years of exploitation are expected, respectively. Moreover, in the 1st group the average number of reservoirs is 16 and lithological composition is very favourable, since reservoirs are represented by sandstones of Pannonian and Pontian age. The exception is the Beničanci field with a reservoir in Lower and Middle Miocene breccias. The prognosed exploitation period of gas fields (without fields in the Adriatic off-shore) is between 5 and 23 years. Relatively homogeneous sandstone lithology, including good regional seals like marls, enables increasing of recovery using fluid injection. Also, injection of CO2 is planed in favourable reservoirs (immiscible phases, pressure supported) and two pilot projects are either finished (Šandrovac field in 2001) or planned in near future (Ivanić field in 2008). The water-flooding will probably be dominant secondary method for increasing recovery in the future, especially due to the fact that for the CO2 injection gas transport and careful analysis of fluids interactions in sub-surfaces are necessary. Both approaches can be very easily and successfully applied today due to very good regional tectonic, stratigraphic, depositional and geochemical investigations of the Sava and Drava depressions. It is assumed that over 2-4 times more oil was generated than oil discovered up to now. It means that, at least based on presented statistics, probably some larger fields can be discovered especially in the Drava and Sava depressions.

exploitation period; hydrocarbons; Pannonian basin; Croatia

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