engleski

One-dimensional variogram and statistical analysis in reservoir units of the Bjelovar sag, Croatia

Porosity behaviour is analysed in vertical dimension regarding potential reservoir units of the Mosti, Poljana and Pepelana lithostratigraphic members in the Bjelovar sag. Analyses are performed on location with a sufficient number of laboratory porosity-value measurements. The most constant lithology is observed in the Mosti member. Average of the most favorable corrected porosity and range values are calculated on the Galovac-Pavljani field (7.99 % and 0.64 m) for the Mosti member. Poljana sandstones are characterised with the most pronounced lithology changes, and very often represent poor permeable or impermeable sediments. The highest corrected values are again calculated on the Galovac-Pavljani field (23.3 % and 0.57 m), and the lowest very close on the Velika Ciglena (8.95 % and 0.21 m), what is in accordance with lithology described in well files. Pepelana sandstones have more uniform lithology than Poljana sandstones. The most favorable reservoir properties are described in the Šandrovac field, where are documented generally the highest corrected values of 29.99 % and 0.95 m. The most lithological uniformity is described on the Velika Ciglena (range 1.03 m) and Galovac-Pavljani (range 1.73 m) locations. The performed analysis is applied to the characterization of reservoir units and reservoirs in the Bjelovar sag on locations with enough large input dataset. Corrected porosities represent the lowest expected values in observed reservoir unit/pool. Corrected ranges describe extrapolation limits for porosity values in the same reservoir.

geostatistics; variogram analysis; corrected porosity and range; the Bjelovar sag

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