Unsaturated Hydraulic Conductivity Measurements with Centrifuges: A Review

Abstract

531G are often faced with making quantitative predictions of the migration of multiple fl uids through the subsurface. Software packages for simulating multiphase fl uid fl ow through porous media are well developed (e.g., ECLIPSE Schlumberger reservoir simulator, HYDRUS-1D and 2D [Šimůnek et al., 1998, 1999], and STOMP [White and Oostrom, 2000]) and fi nd wide applications in both research and industry. Among the physical properties of the porous medium that are required as model inputs, the capillary pressure and unsaturated hydraulic conductivity (or relative permeability) vs. fl uid saturation functions are often considered the most critical (Christiansen, 2001). Accurate and effi cient measurements of these functions are therefore of considerable importance for ensuring accurate simulations.Th e advantages of measuring the capillary pressure and relative permeability functions on core samples using centrifuges have been recognized from as early as the beginning of the 20th century (Briggs and McLane, 1907;Gardner, 1937). Th e fact that the centrifugal acceleration is many times greater than Earth's gravitational acceleration and that it acts equally on all fl uids throughout the sample (which accelerates the adaptation to changes in boundary conditions) is seen as an attractive way to speed up multiphase fl uid fl ow experiments. Besides this advantage, the fl ow and transport processes take place under more ideal and controlled conditions than experiments conducted under normal gravity, leading to more accurate measurements that extend across a wider range of saturations (Nimmo, 1990;Nakajima and Stadler, 2006).Conventional permeameter techniques for measuring the intrinsic permeability, k, under normal gravity conditions have also been applied to a centrifugal fi eld. A clear distinction is made between experiments in which water is supplied from an internal or an external source, and if the fl ow experiment is conducted under constant-or falling-head conditions (Nimmo et al., 2002). Th e relevant analytical equations describing saturated fl ow under these diff erent combinations of experimental conditions were presented in Nimmo and Mello (1991) and Nimmo et al. (2002).Centrifuge techniques for measuring the relative permeability function can be divided into steady-and transient-state methods. In steady-state centrifuge experiments, the sample and fl uids are subject to a time-invariant centrifugal acceleration. Pressure and fl ow conditions at the inlet end face (the sample face closest to the center of rotation) are set so that steady-state fl ow conditions develop for the wetting fl uid with time. Two steady-state methods, referred to by Nimmo et al. (2002) as internal fl ow control (IFC) and unsaturated fl ow apparatus (UFA), have been used for multiphase fl ow applications. A: IFC, internal fl ow control; UFA, unsaturated fl ow apparatus. R AConduc ng drainage or imbibi on experiments in a centrifugal force fi eld has long been recognized as a valid and efficient way to determine capillary pressure-...

Inverse determination of saturated and relative permeability with a bench-scale centrifuge

“…As the samples are thin, we neglect the occurrence of a drying shock. [12] Denote by S e = θ −θ r θ s −θ r the effective saturation where θ s is the volumetric water content at saturation and θ r the residual volumetric water content. We have S e ∈ (0, 1), since θ ∈ (θ r , θ s ).…”

“…where k(h) is k (S e (h)) from (12). Several numerical solution methods have been proposed to solve (13).…”

Non-destructive Analysis of Oil-Contaminated Soil Core Samples by X-ray Computed Tomography and Low-Field Nuclear Magnetic Resonance Relaxometry: a Case Study

“…6) is important hydrological information for the site. This information is useful in formulating an adequate plan for a possible subsequent destructive analysis of the cores (e.g., time-consuming hydraulic permeability test using centrifugal force; van den Berg et al 2009). Although no aquitard was detected at the site consisting of medium to coarse sand grains (Fig.…”

Unsaturated Permeability and Retention Curve Determination From In-Flight Weight Measurements in a Bench-Scale Centrifuge

“…This was initiated by Hassler and Brunner (1945). A detailed overview on the development of this method can be found in several articles (Nimmo 1990;Nimmo et al 2002; Van den Berg et al 2009) and the citations therein. Nimmo et al (1991) showed that steady-state unsaturated flow is possible in a centrifuge, allowing for the performance of accurate outflow experiments using equilibria values.…”