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OBSERVATIONS USEFUL FOR INCREASE OF HYDROCARBON FIELDS EXPLOITATION PERIOD WITHIN A CROATIAN PART OF THE PANNONIAN BASIN

AUTHOR/S: J. VELIC, T. MALVIC, M. CVETKOVIC, M. WEISSER, V. CURI
Sunday 1 August 2010 by Libadmin2008

8th International Scientific Conference - SGEM2008, www.sgem.org, SGEM2008 Conference Proceedings/ ISBN: 954-918181-2, June 16-20, 2008, Vol. 1, 567-574 pp

ABSTRACT

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.

Keywords: exploitation period, hydrocarbons, Pannonian basin, Croatia.