The researches and practice show that the permeability is often apparently related to direction

hence permeability is a kind of vector. The geological origins of directional permeability are expounded. Some confusable viewpoints

which occur when understanding and using the vector properties of permeability

are analyzed and put right. Also it is revealed that the resultant vector of two permeability vectors in two different directions can not serve as the rock permeability of the direction to which the resultant vector point; and the projection of a permeability vector can not be used as the permeability of the projection direction. Furthermore

A quantitative calculation model is deduced for anisotropic permeability. The horizontal permeability in any direction could be calculated by virtue of this model. Moreover

this calculation model of permeability could be used to compute the directional transmissibility in numerical reservoir simulation

and to design the well spaces in different directions for anisotropic reservoir.