3D GEOSTATISTICAL MODELING OF FACIES AND PETROPHYSICAL PROPERTIES OF THE UPPER KHARTAM OUTCROP OF KHUFF FORMATION, CENTRAL SAUDI ARABIA

Oolitic grainstones can contain significant hydrocarbon reserves. The heterogeneity in carbonate reservoir ascribes to the depositional and digenetic processes. Within the studied interval, facies were analyzed and grouped into four depositional sub-environment which stacked in five cycle sets (4th order sequences). The porosity and permeability were measured from core plug of outcrop samples. However, the measured porosity and permeability values showed patterns of distributions when statistically analyzed based on the rock typing and stratigraphic intervals. Based on the outcrop observations, the 3D framework was constructed which comprises of five zones separated by six surfaces. In the context of depositional environment, these zones are; foreshoal and shoal (zones 1 and 2), shoal and backshoal (zones 3 and 4) and tidal flat deposits (zone 5). The sea level within these zones was relatively high, fluctuated and dropped within deposits of zones 1 and 2, zones 3 and 4 and zone 5, respectively. In the context of 3D modelling, lithofacies within each zone was populated separately by using different geostatistical algorithm. Based on the relative sea level, the dominated lithofacies and the presence or absence of marine fauna, the studied interval was subdivided into three broad intervals. These intervals are; lower (zones 1 and 2), middle (zones 3 and 4) and the upper interval (zone 5). The porosity evolution was investigated within each zone and incorporated within the 3D outcrop model. The results showed how the incorporation of the porosity scenarios within the 3D framework can provide a realistic and to some extent the exact vertical stacking of reservoir units. This approach could be applied to predict and enhance the reservoir quality in the analogous oolitic reservoir