Fluvial reservoirs are difficult to model due to the high permeability contrast between the sandstone bodies and the overbank deposits and the complex geometry of the permeable (sandstone bodies) and impermeable zones (overbank deposits). A set of fluvial meandering models has been generated using FLUMY. The models represent a range of Net-to-Gross ratios and sandstone body geometries. In order to quantify the effect of sample size on effective properties, the models are evaluated based on the statistical moments of the probability distributions of porosity and single-phase permeability as a function of sample size. The porosity and permeability show a high spread at small sample volumes, but the spread reduces as the sample size increases. A normalized standard deviation, the coefficient of variation, has been used as a criterion for the variability of the probability distributions. The coefficient of variation of the porosity and the horizontal permeability show a monotonic decline as a function of sample size. The coefficient of variation of the vertical permeability does not show a monotonic decline. This is caused by a drastic decrease of the mean of the vertical permeability with increasing sample volume. The mean of the horizontal permeability also decreases with increasing sample size, but to a lesser extent. The mean of the probability distributions of permeability as a function of sample size converges much earlier than the standard deviation. This convergence indicates that we can determine the effective properties at the Representative Elementary Volume (REV), without reaching REV. The convergence of the mean could potentially be used as a criterion for the relevant spatial scale of upscaling from the fine scale static model to the coarse scale model. Furthermore, if cells are uncorrelated at a scale where the mean of the permeability is not a function of sample volume anymore, random attribution of properties can be used to populate dynamic grid cells.

Geothermal energy is strongly dependent on the geothermal gradient; this means that with increasing depth an increase in temperature is found. The targeted formation of our research is the Hardegsen which reaches depths of around three kilometers in the West Netherlands Basin. At three kilometers depth the temperature is around 90 C˚ which is interesting for geothermal exploitation. However, rock at increasing depth generally shows a decrease in reservoir properties. This study investigates whether the reservoir properties of the Hardegsen formation at a depth of three kilometers are still interesting for geothermal exploitation. This is done by determining to what extent the Hardegsen has been influenced by depositional history, diagenetic processes and inversion. Determining the reservoir properties is done by studying a data set that consists of core descriptions, core plug measurements, gamma ray logs, microscopy analysis, literature studies and a field study. From the core plug measurements a simple model was created describing how porosity and permeability of the Hardegsen behave with increasing depth. The Hardegsen succession in the West Netherlands Basin consists mainly out of (cross-bedded) arkosic fine to medium grained sandstones intercalated by 0.2-1 meter thick laterally consistent shales and shaly/silty very fine sands. High minus-porosities (up to 45 %) are reported which could have played an important role in the preservation of the reservoir properties. Core plug measurements show that the Hardegsen has good prospects for a potential reservoir with porosities ranging from 10-20% and permeability’s ranging from 50-1000 mD. The presence of the laterally consistent shale and sandy/silty very fine sand layers is heavily dependent on the location in the reservoir. This research shows absence of these layers in wells that are located closer to the basin margin. Since these layers decrease vertical flow drastically, further investigation of the extent of these layers is needed to give a better prediction of the quality of the reservoir as a whole.