Measurement of fracture aperture fields using transmitted light: An evaluation of measurement errors and their influence on simulations of flow and transport through a single fracture

Abstract

Abstract. Understanding of single-phase and multiphase flow and transport in fractures can be greatly enhanced through experimentation in transparent systems (analogs or replicas) where light transmission techniques yield quantitative measurements of aperture, solute concentration, and phase saturation fields. Here we quantify aperture field measurement error and demonstrate the influence of this error on the results of flow and transport simulations (hypothesized experimental results) through saturated and partially saturated fractures. We find that precision and accuracy can be balanced to greatly improve the technique and present a measurement protocol to obtain a minimum error field. Simulation results show an increased sensitivity to error as we move from flow to transport and from saturated to partially saturated conditions. Significant sensitivity under partially saturated conditions results in differences in channeling and multiple-peaked breakthrough curves. These results emphasize the critical importance of defining and minimizing error for studies of flow and transport in single fractures. While light transmission methods for measuring aperture fields have been applied previously [e.g., Glass and Nicholl, 1995; Persoft and Pruess, 1995; Brown et al., 1998], they have not been thoroughly evaluated with respect to error and therefore yield data of ambiguous quality. Additionally, the influence of this error on our interpretation of the underlying physics within a particular single-phase or multiphase experiment has yet to be considered. The appropriate design of experiments required to advance our understanding of the fundamental physics demands that both of these evaluations be accomplished. In this paper, we evaluate aperture field measurement error for the light transmission technique, outline a measurement protocol to obtain a minimum error field (optimal field), and demonstrate the influence of accuracy on hypothesized experimental results using simulations of flow and transport through saturated and partially saturated fractures.To enhance our understanding of the light transmission technique, we independently evaluate each source of error that contributes to the total measurement error. We find reducing measurement error requires balancing precision (random error) and accuracy (systematic or bias error) to minimize the total error for a particular fracture and light transmission apparatus. With this understanding we formulate a general protocol for measuring aperture fields. For our system, measurements on a representative "baseline" rough-walled fracture yielded an estimated root-mean-square (

Numerical simulations for the effects of normal loading on particle transport in rock fractures during shear

“…Assuming that the flow of an incompressible fluid through the fracture follows the cubic law, in a steady state, the governing equation can be written as (2) where Q is the source/sink term (positive when fluid is flowing into the fracture), and T xx and T yy are the fracture transmissivity [L ] in x-and y-directions, respectively. In this paper, the local transmissivity at each element of the FEM model of the fracture is assumed to be equal in x-and y-directions for simplicity and is defined by…”

“…Many efforts have also been made to test fluid flow and tracer transport processes in rock fractures, with or without flow visualization and normal loading [1][2][3]. It was found that fluid flows in rock fractures through connected and tortuous channels that bypass the contacts areas.…”

Factors controlling satiated relative permeability in a partially‐saturated horizontal fracture

“…At any given stage of its development, phase geometry is a history dependent product of competition between local capillary, viscous, and gravity forces [Glass et al, 1995]. In a statistically homogeneous horizontal fracture much larger than the spatial correlation length of the aperture field, slow steady displacement along the plane of the fracture leads to a satiated condition where the invading phase spans the fracture in all directions, and the remaining defending phase is fully entrapped [Glass et al, 1998].…”

Saturated flow in a single fracture: evaluation of the Reynolds Equation in measured aperture fields

“…In the absence of the large-scale channeling that would result from system-scale heterogeneity, local aper- We measured aperture fields using light transmission theory first proposed by Glass et al [1991]. The measurement protocol outlined by Detwiler et al [1999] was employed to minimize and quantify measurement errors that result from a combination of image noise, nonlinear dye absorbance, and refraction within the fracture. In this protocol, we first measure the aperture field (normalized to its mean) and evaluate the total root mean squared (RMS) error; mean aperture and associated error are measured independently.…”

“…In each of our analog fractures, the entire aperture field (-15 x 30 cm) is measured at high resolution (-0.015 cm, which corresponds to 5 or more points per correlation length) at the time of the hydraulic measurements. To measure aperture fields, we used light absorption techniques [Detwiler et al, 1999] that significantly improve on earlier approaches and yield a well defined measurement error for the aperture field. We considered three different test fractures: a Hele-Shaw cell constructed from very smooth glass plates; a rough-walled fracture constructed from two textured glass plates; and a rough-walled fracture constructed from one textured and one smooth glass plate.…”