Rock Properties of a Petroleum Reservoir: Get along with Darcy’s Law?

ABSTRACT The reservoir rock and fluid properties play a crucial role in dictating the resulting multi-phase fluid flow in a petroleum reservoir. The primary purpose of this article is to investigate whether the applied rock properties in a petroleum reservoir really get along with the widely used Darcian approach. It is to be noted that the drainage characterisation of a petroleum reservoir keeps accommodating various rock and fluid properties emanating from very different scales, and the concept of Representative Elementary Volume (REV), while applying continuum-based Darcy’s law, is no longer given any due significance. As a result, upscaling the observed processes from the laboratory scale to a real field-scale scenario has become a major challenge in petroleum reservoir applications. In the present article, the following properties have been taken into consideration under the Darcian approach: porosity, permeability, wettability, capillary pressure and relative permeability. The findings of the present study include that porosity, being a statistical quantity, needs to be averaged with utmost care, while reservoir permeability cannot be averaged simply, as it is basically a tensor. Capillary pressure and wettability, being pore-scale processes, cannot be directly accommodated in the Darcian approach. Relative permeability remains to deviate significantly from the Darcian perspective, and as a result, the Darcian approach has a limitation in its applicability towards multi-phase fluid flow.