A novel model for reservoir rock tortuosity estimation

Abstract

This work presents a simple and novel model for determining the tortuosity of a porous, permeable rock – the ratio of a streamline path-length between two points to the straight-line distance between those points – a parameter which enables an estimate of permeability. Previous research on this topic has resulted in elaborate or complex models, partly due to confusion in terminology between tortuosity and tortuosity factor, and partly due to the difficulty in estimating the streamline path-length along which fluids flow. Tortuosity is a useful parameter that must be estimated from precise laboratory measurements of fluid flow through rock samples but from which the resulting empirical relationship is relatively arbitrary. This paper uses a poro geometry elasticity approach to create an innovative formulation and to determine the parameters in the model from precise experimental measurements. The underlying assumption in the formalism is that the inverse of the tortuosity factor is directly proportional to that of the porosity. The variation of tortuosity with respect to porosity results in an equation relating surface area strain with varying porosity values, and the reservoir tortuosity was conducted. The analysis shows an inverse relationship between tortuosity and porosity, as observed in the experimental data. I find that pore-thsurface arearoat occlusion significantly impacts pore connectivity for tight reservoir and reduces the prediction accuracy of tortuosity. I therefore conclude that the tortuosity model from this study is applicable to different reservoirs.