Permeability, Relative Permeability, Microscopic Displacement Efficiency, and Pore Geometry of M_1 Bimodal Pore Systems in Arab D Limestone

Pore geometrical parameters for the M_1 petrophysical rock type of the Arab D limestone in Ghawar field have been related to static and dynamic reservoir properties and geological facies (Clerke et al. 2008). The M_1 bimodal pore system is the most common and important member of a new set of ultimate recovery petrophysical rock types (URPRT), which uses a new pore system classification for the Arab D limestone. The dynamic reservoir property results for the bimodal M_1 are reviewed here. The roles played by the pore system parameters describing the macropores (M) and micropores (Type 1) within the M_1 in permeability, imbibition oil relative permeability, and microscopic displacement efficiency are examined in detail. All pore systems are analyzed by the Thomeer method using an extensive mercury injection capillary pressure (MICP) data set in conjunction with dynamic experiments performed on samples prepared using the same wettability restoration. Effects commonly ascribed to wettability changes are observed by changes in the distribution of porosity between the M and Type I subsystems. An extensive study of the pore systems of the Ghawar Arab D limestone gathered a large and comprehensive MICP data set (484 samples) (Clerke et al. 2008; Cantrell and Hagerty 1999, 2003; Clerke 2003, 2004; Ahr et al. 2005). All MICP data were type-curve matched by Thomeer functions (Clerke et al. 2008; Thomeer 1960). The study of this carefully prepared MICP data is the foundation for a new pore system classification. The new classification is built upon intrinsic, fundamental, and separate maximum pore-throat diameter modal elements named "porositons" (Clerke 2008; Ahr et al. 2005). Porositons are stable and recurring modes in the statistics of the Thomeer maximum pore-throat diameter of these carbonate pore systems. Porositon combinations are used to construct meaningful petrophysical rock types. Petrophysical rock types (PRTs) are defined by Clerke et al. (2008) as objects or combinations of objects that are present in the 3D space of the Thomeer pore-system parameters. Porositons are a new PRT object type; other PRT objects are clusters, trends, and surfaces. By constructing PRTs from porositons, strong relationships are found connecting the geological facies, PRTs, and reservoir-flow properties of these complex multimodal carbonate rocks (Clerke et al. 2008). These relationships demonstrate that these PRTs are important for defining ultimate recovery.