In this fifth lecture, definitions such as permeability, porosity, heterogeneity and anisotropy are explained.
The ability of a solid to transmit fluid is called permeability. This permeability is defined by Darcy’s law an can be influenced by properties like grain size, grain sorting, grain roundness and the texture of the rock. An example of that is the fact that rounder grains lead to higher permeability’s.
The ability of a solid to store fluid is called porosity. Voids within the solid make it possible for liquid to be encapsulated by the solid. Processes like compaction decrease the porosity due to the effects of loading. All processes that can be undergone by a potential rock reservoir with burial are summarized as diagenesis.
Lateral and vertical changes in rock properties, called heterogeneity, can result in changes of physical properties, called anisotropy. These layers, and with that the differences in reservoir quality, can be identified using well logs.
Next, it is explained that petroleum geologists should use well data, seismic data and geological knowledge to build a 3D reservoir model. In Delft University of Technology, a process based simulation of barrier bar development as a function of fluctuating see levels is developed. A demonstration of this program can be seen here.
The final part of this lecture is on carbonates, which are significantly different from classic reservoir rocks. One of the big differences is that most of the material is biogenic. It is not uncommon that carbonates are both the source and the reservoir rock. Carbonate depositional settings and a great variety of carbonate pore types, which influences the permeability, are discussed.