A compact and simple estimate of reservoir rock tortuosity

ABSTRACT

This study attempts to develop a simple expression for estimating rock tortuosity, which is important in determining permeability. Historically, attaining this goal has been rather complicated because of some factors: there is confusion in understanding the terms, tortuosity factor and tortuosity; the difficulty in estimating the effective length through which fluids flow, as tortuosity is a complex property precisely obtainable by experimenting on flow through sedimentary samples; and the experimental formulation is relatively difficult. To this end, the authors used the poroelasticity theory to formulate an Archie-like expression and validated the parameter in the equation using a formulated experimental procedure. The underlying hypothesis in the formulation is that the inverse of the pore volume is directly proportional to that of the bulk volume. The differentiation of the equation for porosity yielded an expression relating volumetric strain with the change in porosity, from where a relationship for the reservoir tortuosity was obtained. The results showed an inverse relationship between porosity and tortuosity as confirmed by previous studies. Further, for values of porosity lower than 0.05, the closure effect of the pore space significantly affects the prediction of tortuosity. Thus, the results are applicable to reservoirs with porosity in the range of 0.05–0.29.

KEYWORDS:

• Rock tortuosity
• poroelasticity theory
• porosity
• Archie equation
• pore volume
• permeability

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Disclosure statement

No potential conflict of interest was reported by the authors.