We initiate pore-scale modeling of The Geysers to characterize the formation's pore space. For this purpose, we analyze the drainage data obtained from mercury intrusion for different samples where the variation of the capillary pressure with wetting phase saturation shows a non-plateau-like trend. The non-plateau-like trend is inconsistent with cyclic pore models such as the regular lattice model, in which the random assignment of the pore size to a lattice results in a plateau-like variation of the capillary pressure with wetting phase in drainage. Our study reveals that we can capture the pore space of The Geysers using acyclic void models. The connectivity of pores is limited in acyclic models and there is only a single path between two pores when they are connected. To capture the pore space, we determine the number of pore throats required to model the drainage results. We also use the characterized acyclic models to analyze the single-phase flow behavior of The Geysers at pore scale. Our analysis of the single-phase permeability suggests that the fluid flow is controlled primarily by a small fraction of the pores whose characteristic sizes are notably larger than others, although the data are not sufficient to eliminate the possible contribution of other pores with smaller characteristic sizes. This study could have major implications for understanding transport phenomena in The Geysers at pore scale. (C) 2015 Elsevier Ltd. All rights reserved.