The influence of geological factors such as degree of diagenesis, grain size, anisotropy and degree of failure on the gas permeability of sedimentary rocks in triaxial state of stress is described in this paper. There is significant relationship between the anisotropy of rocks and gas permeability. Increasing of the petrographical anisotropy (occurrence of layers and lamins) increase the differences between the results of gas permeability measured on the samples oriented parallel or perpendicular to the layers. The influence of degree of diagenesis on permeability of sedimentary rocks is evident. It is obvious that a higher diagenesis can lead to a lower permeability. The influence of degree of failure was studied during triaxial load testing. It is possible to divide the influence of degree of failure into two parts in this case. At first the decrease of porous system led to decrease in the permeability in consequence of the axial loading. A rise in permeability occurred before reaching peak strength and rapid rise in permeability has been observed during post peak phase oftesting.
Gas permeability of rocks is due to the presence of communicative pores in the material. It is obvious that the quality and quantity of the pores influence the permeability of the material. There is very good correlation between gas permeability and state of stress of the rock sample, and between gas permeability and absorptive capacity or porosity (Konecny et aI., 1999). However, some geological factors can also influence the porous medium. It is very important to know the grain size, anisotropy of the rock, degree of diagenesis and degree of failure to appreciate the possibility ofthe migration ofthe gases through the rock.
The gas permeability measurement was performed on the triaxial cell KTK 100.
