Preliminary communication
Mapping of the Late Miocene sandstone facies using indicator kriging
Kristina Novak Zelenika
; INA-Oil industry, Sector for Geology and Reservoir Management, Šubićeva 29, 10000 Zagreb (Reservoir Geologist)
Tomislav Malvić
; INA-Oil industry, Sector for Geology and Reservoir Management, Šubićeva 29, 10000 Zagreb (Adviser).
Janos Geiger
; University of Szeged, Department of Geology and Paleontology, Egyetem street no. 2, Szeged, Hungary (Associate Professor)
Abstract
Facies mapping is one of very important tasks in modelling of oil and gas reservoirs. Facies type has direct influence on porosity and permeability values, which eventually influence both the migration and accumulation of hydrocarbons. The most numerous reservoirs in the Croatian part of the Pannonian basin major are in the Late Pannonian and Early Pontian sandstones. Various types of these sandstones were formed in turbiditic depositional environment, which had been periodically activated in relatively calm, deeper (mostly up to 200 meters), brackish lake environment with marl sedimentation over the basin plain. Sandstones form sedimentary bodies that are very elongated in approximately NW-SE direction, with sharp transition toward basin marls in bottom and top. On the contrary, lateral transition is gradual, from the clean, medium-grained sandstones, toward fine-grained sandstones or siltites, silty sandstones, marly sandstones, sandy marls and eventually basin marls. Such lateral facies transition in the Kloštar field was analysed, focusing at the largest sandstone oil reservoir ’T’ of Early Pontian age. There were available 19 wells with the newest e-logs and calculated average porosity in reservoirs. With 6 additionally constructed virtual wells using Surfer residual calculation, this made a reliable input dataset. The (litho)facies are analysed through e-logs, porosity map and, eventually, indicator variograms and Indicator Kriging facies map. Transition of porosity values and their probabilities are clearly recognized on the Indicator Kriging maps, and can be correlated with the interpreted depositional environment at the specific well location. This is the first time that Indicator Kriging was applied in Croatian sandstone hydrocarbon reservoirs and result positively confirmed that this interpolation technique is appropriate and useful tool for facies mapping based on subsurface data.
Keywords
facies; sandstone; marl; indicator variogram; indicator kriging; Late Miocene; Sava depression; Croatia
Hrčak ID:
53897
URI
Publication date:
31.5.2010.
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