Abstract. Minipermeameters are rapidly becoming a popular tool for collecting localized measurements of permeability in both laboratory and field studies. While one of the main advantages of minipermeameters is their ability to collect data on various support volumes, there have been only limited attempts to analyze their size and geometry. We define the support volume of minipermeameter measurements as a region containing 90% of the total gas flow, i.e., a region bounded by the 10% streamline. Using our new semianalytical solutions for the Stokes' stream function, we demonstrate that the support volume has a shape of the semitoroid adjacent to the sample surface. Hence there is a blind spot directly below the minipermeameter, which is not probed by the measurement. We demonstrate that the support volume of the minipermeameter measurements decreases with the tip-seal's ratio (a ratio of the inner tip-seal radius to the outer tip-seal radius), while the size of the corresponding blind spot increases.
IntroductionDelineation of the spatial distribution of permeability in water-and oil-bearing formations is one of the major challenges in hydrogeology and petroleum engineering. Specifically, this is an ill-posed inverse problem, and hence it is inherently difficult to solve. Mathematical models that provide a means to extract permeability data indirectly from experimental measurements of dependent quantities (e.g., pressure head and flow rates) do so by defining a related well-posed problem through some form of regularization. The necessary presence of this regularization, which may not be stated explicitly, is likely a critical factor in the recent debate over the scale dependence of permeability measurements. Consequently, there is a growing interest in experimental procedures that possess well-defined regions of investigation or support volumes.Minipermeameters seem well suited for this purpose because they induce a localized flow by injecting gas into a sample through a small tip seal. Although these devices were first described by Dykstra and Parsons [1950], it was not until recently that Goggin et al. [1988] proposed a mathematical model for the application of the minipermeameter to localized permeability measurements. In particular, for the case of steady state gas flow, Goggin et al. [1988] introduced a coefficient of proportionality into an integral form of Darcy's law. Dubbed the geometric factor, this coefficient allowed the permeability to be inferred from the injection rate and the corresponding gas pressure. The experimental aspect of this work focused on measuring the permeability of core samples; thus the support volume was defined by the sensitivity of the geometric factor to the sample size. Specifically, the support volume was deter-