GAS MINIPERMEAMETRY

Gas minipermeameters have been used in the field and laboratory for the last thirty years by hydrologists, sedimentologists, and petroleum scientists and engineers. Permeameters obviously measure permeability but some miniperm designs can also measure porosity. Miniperms typically inject gas through a local source ( eg. a "tip seal") and measure pressure and flow rate. Example miniperm applications include facies classification, estimation of spatial correlation structure and scale, and upscaling behavior. Sampled materials include unlithified and lithified coarse silts, sands, and fine gravel. Smaller or larger grain sizes present addition challenges to miniperms, as do carbonates and fractured rock, and are not typically sampled using this technology. We review permeameter designs, operating procedures, and applications, and investigate the effects of permeameter tip-seal size and local heterogeneity. We present maps of the relative influence of different portions of the sampled domain on the estimated permeability (spatial weighting functions) and explore the bias induced by initial water saturation. We end with an encouraging assessment of the future scientific and engineering utility of this interesting instrument.