The Sava Depression is located in the Northern Croatia, representing southern geotectonical border of the Pannonian Basin toward Adriatic Carbonate Platform. The depression is well-known hydrocarbon province with several large Croatian oil and gas fields. The analytical target for calculation of hydrocarbon existence probability was the lithostratigraphic formation Ivanić-Grad of Upper Pannonian age. The analysed area was divided in squares of size 5x5 km, totally 74 cells. Probability of hydrocarbon existence had been estimated for each cell (value similar to term Probability Of Success – POS). That was calculated for six geological categories: existence of (1) hydrocarbons (2) reservoirs (3) source rocks (4) traps, and (5) quality of reservoirs (6) exploration level based on number of wells. Each of categories could be estimated with three values: 3 for clearly proved category from excellent data, 2 for weak or poor evidences for category and 1 in case without evidences. If there was no available data or measurements in particular category, that value had not been estimated. The categories 1-5 had been estimated based on (a) field files, (b) a few regional well-known published papers, (c) relevant PhD thesis and (d) expert opinions. In the case ofexploration level (category 6) the mark 3 had been used in the case with more than 10 wells in cell, mark 2 for 5-10 wells, and mark 1 for 1-5 wells. The further calculation is based on summing (in Excel table) values of all categories, using following ponders: 2 for category 1, 1.5 for categories 2, 4, 5 and 1 for categories 3 and 6. The maximum value of total probability value is 25.5 (existence of hydrocarbons is sure) and minimal 8.5 (there is no probability of discovering hydrocarbons). The calculated value is finally transformed in probability on the well-known POS scale, i.e. between 0 (for 8.5) and 1 (for sum 25.5). Such POS was calculated for each of 74 cells and graphically represented in coloured map, using five probability classes (0-20, 20-40, 40-60, 60-80 and 80-100% of POS). Results are presented mostly through discriminant cells, i.e. values can be significantly different in neighbouring cells. It is why because field area (2.57-54.86 square km) is often lower than area of cell (25 square km), and reservoir surrounding probability is already included in analysed cell. Also, sandstone borders cuts some marginal cells. |