A new small drill hole minipermeameter probe for in situ permeability measurement: Fluid mechanics and geometrical factors

Considerable heterogeneity is evident when permeability measurements are made on small scales, either in the field or in the laboratory on field samples. Small‐scale permeability measurements have commonly been made by inducing multidimensional gas flow through a sample with various configurations of the conventional surface‐sealing gas minipermeameter. In order to reduce weathering and seal‐quality problems, a new minipermeameter probe was designed for field application within small diameter holes drilled into an outcrop. We briefly describe the small drill hole minipermeameter, while developing in detail the associated data analysis methodology for performing in situ permeability measurements with this new probe. Analysis of field data, which consists of gas injection pressure and mass flow rate, is based on a numerical solution in cylindrical coordinates of the ideal gas flow equation, assuming homogeneous and isotropic conditions over the averaging volume of the measurements. In the following development the semianalytical inverse solution for permeability will be derived for the new small drill hole minipermeameter probe, which varies from that of the conventional surface‐sealing minipermeameter probe only in the choice of the appropriate characteristic length and in the magnitude of the associated geometrical factor.