Reservoir Rock Classification by Comprehensive Petrophysical Data Integration – Acacus Formation, Jenein-Sud, Tunisia

Petrophysical properties in the Acacus formation are quite variable and inhomogeneous since the reservoir shows substantial diagenetic overprint and layer heterogeneity. To build a sound property model on such conditions it is imperative to establish a petrophysical rock classification concept first by comprehensive integration of log, core and test data. Due to variable diagenetic effects (mainly chloritization and siderite cementation) there is obviously no simple poro-perm relationship in the Acacus sands. Therefore an empirical rock classification approach based on poro-perm to pore-throat relationship has been applied (Winland-R35). Preliminary results of the Winland-R35 quick-look on core data allow the discrimination of four main petrophysical rock types. Mercury intrusion tests (HPMI) carried out on representative samples show rock class specific shapes of capillary pressure curves which endorse the initial classification by Winland-R35. To apply this rock typing concept to the entire reservoir section the correlation of core permeability to irreducible water saturation from NMR log data has been used to derive a permeability estimate which was finally scaled to the permeability thickness derived from DST. The petrophysical rock classification and its specific parameter sets were used to initialize the geo-model as well as to control the spatial distribution of properties.