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

Abstract

[1] 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 surfacesealing minipermeameter probe only in the choice of the appropriate characteristic length and in the magnitude of the associated geometrical factor.

Fault Zone Deformation Overprints Permeability of Nonwelded Ignimbrite: Chalk Cove Fault, Bishop Tuff, Bishop, California

“…Detailed outcrop mapping and microstructural analyses were used to characterize the structural geometry of the Chalk Cove fault zone and to provide context for in situ gas permeability studies. A small‐drillhole minipermeameter probe (Molz et al, 2002; Dinwiddie et al, 2003; Dinwiddie, 2005) and a constant‐head liquid permeameter (Reynolds and Elrick, 1986) were used to measure both the gas and liquid permeability (as approximations to the intrinsic permeability) of deformed and nondeformed nonwelded to sintered ignimbrite adjacent to the Chalk Cove fault. Liquid permeability was measured to support the reasonableness of the more spatially detailed gas permeability data.…”

“…The lack of cohesion of friable nonwelded ignimbrite leads to difficulties during sample collection, making standard sampling methods impractical. The small‐drillhole minipermeameter probe (Molz et al, 2002; Dinwiddie et al, 2003; Dinwiddie, 2005) was developed for in situ application inside a small hole drilled into an outcrop to circumvent such sampling difficulties.…”

“…After steady‐state conditions are achieved, several pressure and flow rate pairs are recorded. Given an assumption of homogeneity within the averaging volume, the measured injection pressure, flow rate, and a numerically determined geometrical factor describing the flow system (Dinwiddie et al, 2003), the effective gas permeability of the porous medium surrounding the drill hole (Molz et al, 2003) is calculated with the standard semianalytical inverse solution (Dinwiddie et al, 2003). Pressure and flow rate data pairs from each location are analyzed for the presence of high‐velocity flow effects, and corrections are made if warranted.…”

Stochastic fractal‐based models of heterogeneity in subsurface hydrology: Origins, applications, limitations, and future research questions

“…As shown in the analysis by Lu and Molz [2001], the histogram for the entire ln( k ) data set is distinctly non‐Gaussian and, as usual, resembles a Levy distribution. However, Lu et al [2002b] present an analysis of data from the interdune facies as well as a preliminary analysis of more recent data collected from a bioturbated sandstone facies in Utah that was collected using the new drill hole gas minipermeameter [ Dinwiddie et al , 2003]. The cumulative distribution functions from both single‐facies data sets appear more Gaussian.…”

“…This is due to surface roughness, which inhibits a good seal, the difficulty of manually maintaining a steady and repeatable sealing pressure, and the fact that an unprepared surface is often weathered and not representative of the interior rock properties. These considerations motivated Dinwiddie et al [2003] to develop and analyze the small drill hole minipermeameter probe (Figure 12). This probe is well suited for field use in drillable rock, because drilling produces a smooth and nonweathered surface, and the normal force applied by the annular seal to the walls of the drill hole is robust and easily controlled by a mechanical torque wheel.…”