Abstract

Reservoirs are characterized by complex pore systems consisting of several distinct pore types. Each pore type is characterized by a unique geometry. Geometric elements can be expressed analytically through image analysis of the pore system as observed in thin section. Quantification of key geometric elements allows direct calculation of permeability and capillary pressure using thin sections of small samples (sidewall cores and cuttings). Additionally, permeability can be calculated for each pore type.

Analysis of 3 sandstone reservoirs from Indonesia demonstrates the inherent complexity of reservoir pore systems. These reservoirs are characterized by a mixture of 4 to 6 pore types. Pore types genetically include several varieties of intergranular, intragranular and dissolution porosity. Pore system complexity increases with decreasing total porosity. Log responses and the results of routine core analyses do not reveal important details of pore system complexity. This complexity has impact on recovery efficiency at all stages of production, including EOR.

The ability to derive accurate permeability and capillary pressure information from sidewall cores of these reservoirs reduces the need for extensive conventional coring programs. A combination of conventional cores (in key wells) and sidewall cores (in most wells) is recommended as a cost-effective alternative.