Browsing by Subject "Hydraulic conductivity"

Now showing 1 - 9 of 9

Centrifuge measurement of two-phase transient flow in rigid porous media
(2016-08) Blake, Calvin Russell; Zornberg, Jorge G.; Mohanty, Kishore K
Gravity driven multi-phase flow in porous media is an important mode of fluid transport in several geologic settings. Some applications where gravity drainage may play an important role in the movement of a fluid can include primary oil recovery from a petroleum reservoir or water flow into the ground surface. Because of the similarities between a single-gravity environment and a centrifugal environment, measurements of two-phase flow are often conducted in the centrifuge to observe the behavior of the whole system under gravity-like conditions while reducing the time of measurement. In this study, measurements of transient fluid outflow from sandstone cores were conducted in the centrifuge using air as the invading phase. The draining phase in these experiments comprised three different brines and a light mineral oil. Hydraulic conductivity functions and capillary pressure curves were determined from this data using a numerical history matching technique, and the results were compared with two prevailing analytical models. The results of this study corroborate previous findings that a full numerical history match can easily predict more realistic hydraulic conductivity functions than the prevailing analytical models.
Data-driven uncertainty quantification for predictive subsurface flow and transport modeling
(2019-02-06) He, Jiachuan; Dawson, Clinton N.; Landis, Chad; Bui, Tan; Ghattas, Omar
Specification of hydraulic conductivity as a model parameter in groundwater flow and transport equations is an essential step in predictive simulations. It is often infeasible in practice to characterize this model parameter at all points in space due to complex hydrogeological environments leading to significant parameter uncertainties. Quantifying these uncertainties requires the formulation and solution of an inverse problem using data corresponding to observable model responses. Several types of inverse problems may be formulated under various physical and statistical assumptions on the model parameters, model response, and the data. Solutions to most types of inverse problems require large numbers of model evaluations. In this study, we incorporate the use of surrogate models based on support vector machines to increase the number of samples used in approximating a solution to an inverse problem at a relatively low computational cost. To test the global capabilities of this type of surrogate model for quantifying uncertainties, we use a framework for constructing pullback and push-forward probability measures to study the data-to-parameter-to-prediction propagation of uncertainties under minimal statistical assumptions. Additionally, we demonstrate that it is possible to build a support vector machine using relatively low-dimensional representations of the hydraulic conductivity to propagate distributions. The numerical examples further demonstrate that we can make reliable probabilistic predictions of contaminant concentration at spatial locations corresponding to data not used in the solution to the inverse problem. This dissertation is based on the article entitled Data-driven uncertainty quantification for predictive flow and transport modeling using support vector machines by Jiachuan He, Steven Mattis, Troy Butler and Clint Dawson [32]. This material is based upon work supported by the U.S. Department of Energy Office of Science, Office of Advanced Scientific Computing Research, Applied Mathematics program under Award Number DE-SC0009286 as part of the DiaMonD Multifaceted Mathematics Integrated Capability Center.
Effect of bentonite swelling on hydraulic conductivity of sand-bentonite mixtures (SBMs)
(2014-05) Spears, Amber; El Mohtar, Chadi Said
The hydraulic conductivity of sand-bentonite mixtures (SBMs) was measured to investigate the effects of mixing method, uniformity, and hydration of the mixtures. Triaxial tests were completed to determine the hydraulic conductivity of each specimen. Specimens using Ottawa sand and Wyoming bentonite, prepared with dry and suspension mixing conditions that altered the degree of hydration and swelling of bentonite, had varying bentonite content by percentage dry weight of sand. The conclusions of this experiment can be applied to the construction of cut off walls used in levees to mitigate groundwater seepage through underlying pervious layers. Eleven sand-bentonite specimens were tested in this study: nine were prepared using dry mixing and two were prepared using suspension mixing. The results do not show strong correlations between hydraulic conductivity and bentonite content, mixing method, clay void ratio, or time. Therefore, further investigation of the results was necessary. The bentonite void ratio (clay void ratio) assumes that bentonite is fully swelled for both blocked and partially blocked flow. Blocked flow occurs when the swelled bentonite blocks all the sand voids, forcing the water to flow within the bentonite voids. However, the results in this study shows that the concept of clay void ratio doesn’t capture the performance of SBMs when the bentonite is partially swelled; therefore, a new concept of effective clay void ratio was introduced to account for bentonite partial swelling. The effective clay void ratio determines the volume of swelled clay as a function of the volume of fully swelled bentonite. This is useful when comparing results with literature or predicting hydraulic conductivity in cases where only partial swelling of bentonite is expected.
The effect of expanded shale lightweight aggregates on the hydraulic drainage properties of clays
(2013-05) Mechleb, Ghadi; Gilbert, Robert B. (Robert Bruce), 1965-
Fine grained soils, in particular clays of high plasticity, are known to have very low values of hydraulic conductivity. This low permeability causes several problems related to vegetation growth and stormwater runoff. One way to improve the permeability of clay soils is by using coarse aggregates as a fill material. Recently, Expanded Shale has been widely applied as an amendment to improve drainage properties of clayey soils. However, limited effort has been made to quantify the effect of Expanded Shale on the hydraulic conductivity or on the volume change of fine grained soils. Specifically, the field and laboratory tests required to quantify the amounts of Expanded Shale to be mixed with clays to obtain desired hydraulic conductivity values have not been conducted. This paper presents the results of a series of laboratory fixed-wall permeameter tests conducted on naturally occurring clay deposits in the Austin area with different plasticity. The testing program comprised of clay samples with different quantities of Expanded Shale aggregates by volume, ranging between 0 and 50%, and compacted at two different compaction efforts (60% and 100% of the standard Proctor compaction effort). The laboratory test results indicate that the hydraulic conductivity of the three soils increases by at least an order of magnitude when the Expanded Shale is mixed in quantities between 25 to 30% by volume depending on the compaction effort. Expanded Shale amended samples also showed lower swelling potential with increasing amendment quantities. Moreover, when the clay with the higher plasticity was mixed with 25% Expanded Shale, the compression and recompression ratios decreased by 25% and 15% respectively.
Hydraulic conductivity measurement of permeable friction course (PFC) experiencing two-dimensional nonlinear flow effects
(2010-05) Klenzendorf, Joshua Brandon; Charbeneau, Randall J.; Barrett, Michael E.; Maidment, David R.; McKinney, Daene C.; Sepehrnoori, Kamy; Sharp, Jr., John M.
Permeable Friction Course (PFC) is a layer of porous asphalt pavement with a thickness of up to 50 millimeters overlain on a conventional impervious hot mix asphalt or Portland cement concrete roadway surface. PFC is used for its driver safety and improved stormwater quality benefits associated with its ability to drain rainfall runoff from the roadway surface. PFC has recently been approved as a stormwater best management practice in the State of Texas. The drainage properties of PFC are typically considered to be governed primarily by two hydraulic properties: porosity and hydraulic conductivity. Both of these hydraulic properties are expected to change over the life of the PFC layer due to clogging of the pore space by trapped sediment. Therefore, proper measurement of the hydraulic properties can be problematic. Laboratory and field tests are necessary for accurately determining the hydraulic conductivity of the PFC layer in order to ensure whether the driver safety and water quality benefits will persist in the future. During testing, PFC experiences a nonlinear flow relationship which can be modeled using the Forchheimer equation. Due to the two-dimensional flow patterns created during testing, the hydraulic conductivity cannot be directly measured. Therefore, numerical modeling of the two-dimensional nonlinear flow relationship is required to convert the measureable flow characteristics into the theoretical flow characteristics in order to properly determine the isotropic hydraulic conductivity. This numerical model utilizes a new scalar quantity, defined as the hydraulic conductivity ratio, to allow for proper modeling of nonlinear flow in two-dimensional cylindrical coordinates. PFC core specimens have been extracted from three different roadway locations around Austin, Texas for the past four years (2007 to 2010). Porosity values of the core specimens range from 12% to 23%, and the porosity data suggest a statistical decrease over time due to trapped sediment in the pore space. A series of constant head tests used in the laboratory and a falling head test used in the field are recommended for measurement of PFC hydraulic characteristics using a modified Forchheimer equation. Through numerical modeling, regressions equations are presented to estimate the hydraulic conductivity and nonlinear Forchheimer coefficient from the measureable hydraulic characteristics determined during experimental testing. Hydraulic conductivity values determined for laboratory core specimens range from 0.02 centimeters per second (cm/s) to nearly 3 cm/s. Field measurements of in-situ hydraulic conductivity vary over a range from 0.6 cm/s to 3.6 cm/s. The results of this research provide well-defined laboratory and field methods for measurement of the isotropic hydraulic conductivity of PFC experiencing two-dimensional nonlinear flow and characterized by the Forchheimer equation. This methodology utilizes a numerical model which presents a proper solution for nonlinear flow in two-dimensions.
Intra-meander groundwater-surface water interactions in a losing experimental stream
(2010-08) Nowinski, John David; Cardenas, Meinhard Bayani, 1977-; Sharp, John M.; Bennett, Philip C.
Groundwater-surface water interactions between streams and shallow alluvial aquifers can significantly affect their thermal and chemical regimes and thus are critical for effective management of water resources and riparian ecosystems. Of particular significance is the hyporheic zone, an area delineated by subsurface flow paths that begin and end in surface water bodies. Although detailed work has examined hyporheic flow in the vertical dimension, some studies have suggested that the drop in a stream’s elevation as it flows downstream can laterally extend the hyporheic zone. This study examines intra-meander hyporheic flow using extensive field measurements in a full-scale experimental stream-aquifer system. Synoptic head measurements from 2008 and 2009 and a lithium tracer test were conducted to determine the extent and nature of hyporheic flow within the meander. Permeability was measured and sediment cores were analyzed from 2008 to 2009 to assess aquifer properties. Finally, transient head and temperature measurements were collected during flooding events to assess the sensitivity of intra-meander hyporheic flow and temperature to stream discharge. Results verify that hyporheic flow through meanders occurs, but show that it is sensitive to whether a stream is gaining or losing water to the subsurface overall. In addition, permeability and core grain size results indicate moderate heterogeneity in permeability can occur in aquifers composed of relatively uniform sediment. Results also demonstrate that permeability in alluvial aquifers can evolve through time. Such evolution may be driven by groundwater flow, which transports fine particles from areas where porosity and permeability are relatively high and deposits them where they are relatively low, thus creating a positive feedback loop. Finally, measurements during flooding indicate that steady-state hyporheic flow and the thermal regime within the aquifer are largely insensitive to stream discharge. Together, these results expand upon previous field studies of intra-meander hyporheic flow and verify previous modeling work, although they demonstrate a level of complexity within these systems that should be considered in future work.
Mechanical and Hydraulic Behavior of Acid Fractures - Experimental Studies and Mathematical Modeling
(1997-12) Gong, Ming; Hill, Daniel A.
Acid fracturing is a well stimulation method commonly used in carbonate reservoirs. In the process, an HCl solution, sometimes viscosified or emulsified, is injected into the formation above the fracture pressure to create a fracture or to open existing natural fractures. Acid etches the fracture faces unevenly, leaving a conductive pathway for reservoir fluids to flow into the wellbore. The key to a successful acid fracturing is the achievement of acid penetration and the creation of sufficient fracture conductivity. Much research has been done to study the acid penetration in acid fracturing. However, the hydraulic conductivity created by acid etching is not well understood. There is an empirical correlation available to evaluate acid fracture conductivity, which was reported by Nierode and Kruk over 20 years ago. Acid etching is a stochastic process and the resulting hydraulic mechanisms of acid fractures are complex. The conductivity is affected by the aperture and contact area of the fracture under closure stress. The damage of the rock strength at the fracture surfaces by acid adds complexity to the prediction of hydraulic conductivity of acid fractures. The leakoff of acid into the formation through the fracture faces makes the situation even more complex. Acid contact time, acid leakoff, rock mechanical properties, and formation heterogeneity all affect the creation of hydraulic conductivity of an acid fracture. This work explores the mechanisms of hydraulic conductivity of acid fracture in two ways. The first is a systematic experimental study of the creation of acid fracture conductivity, including characterization of surface roughness created by acid etching, investigation of the damage of rock compressive strength by acidizing, and measurement of hydraulic conductivity under closure stress. To study the effect of rock mechanical properties on the creation of hydraulic conductivity of acid fracture, important mechanical properties of the rock sample have been carefully measured. In order to understand the damage of rock strength by acid, the microstructures at the grain scale of core samples have been examined. Experimental data have shown that longer acid contact results in rougher fracture surface and, in tum, higher hydraulic conductivity. The second focus of this work is the mathematical modeling of acid fracture conductivity. Several different theoretical models for fracture conductivity have been reviewed and examined. Based on our experimental results, a new fracture deformation model was derived with a consideration of both the surface roughness and the rock mechanical properties. The roughness of acid etched surfaces as well as the rock strength have been correlated to acidizing conditions. The fracture closure under stress is modeled with. the plastic deformation of asperities. Finally, a cubic law is used to calculate the fracture conductivity. The prediction of acid fracture conductivity using this model with appropriate parameters shows excellent agreement with experimental data.
Post-permeation stability of modified bentonite suspensions under increasing hydraulic gradients
(2013-08) El-Khattab, May Mohammad; El Mohtar, Chadi Said
Slurry wall is a geotechnical engineering application to control the migration of contaminants by retarding groundwater flow. Sand-bentonite slurry walls are commonly used as levees and containment liners. The performance of bentonite slurry in sand-bentonite slurry walls was investigated by studying the rheological properties of bentonite suspensions, the penetration length of bentonite slurry into clean sand, and stability of the trench under in-situ hydraulic gradients. In this study, the rheological parameters of bentonite suspensions were measured at various bentonite fractions by weight from 6 to 12% with 0-3% of sodium pyrophosphate; an ionic additive to control the rheological properties of the bentonite slurries. The penetrability of the bentonite slurries through Ottawa sand was studied by injecting the slurries into sand columns at different bentonite fractions. The injection tests were performed with the permeameters having different diameters to eliminate any bias on test results due to the different size of permeameter. An empirical correlation for predicting the penetration length of bentonite slurry based on apparent viscosity, yield stress, effective particle size, relative density, and injection pressures was updated by taking into account the effects of the permeameter diameter size. Moreover, the stability of sand-bentonite slurry walls was inspected by studying the hydraulic performance of sand permeated with bentonite suspensions under increasing hydraulic gradients. The critical hydraulic gradient at which washing out of bentonite suspensions is initiated was examined. For specimens with bentonite contents less than the threshold value, the flow occurred through the sand voids and minimal washing out occurred. On the other hand, when the bentonite content was high enough to fill up all the void space between the sand particles, the flow was controlled by the clay void ratio. In this case, washing out did occur with increasing gradients accompanied by an increase in hydraulic conductivity. Accordingly, a relation between the yield stress of bentonite suspensions and the critical hydraulic conductivity was developed.
Using coefficient of consolidation to assess response time and reading accuracy of piezometers in grouted boreholes in fat clays
(2015-05) Brewster, Alexander C.; El Mohtar, Chadi Said; Gilbert, Robert B. (Robert Bruce), 1965-
Reading accuracy of a piezometer in a fully grouted borehole has typically been assessed by comparing the hydraulic conductivity of the grout (K[subscript grout]) to that of the soil (K[subscript soil]). The field conditions of interest to this study represent the case of a relatively permeable cement – bentonite grout (the fill material of choice for borehole applications) being installed in a relatively impermeable fat clay. The soil and grout are assumed to be incompressible and fully saturated with an incompressible fluid. Using a steady state approach, error is defined for a given K[subscript grout]/K[subscript soil] ratio. Each of the three studies that investigate K[subscript grout]/K[subscript soil] propose a significantly different failure criterion. An experimental program was developed, with the critical area of focus being on the highly inconsistent K[subscript grout]/K[subscript soil] criteria used to predict grouted piezometer reading error. This study investigated the merits of coefficient of consolidation (c[subscript v]) theory in predicted such errors. It was discovered that pressure pulses (like those experienced within a grouted borehole) migrate through a specimen under a different gradient than those experienced in a typical consolidation environment. This discovery extends beyond existing literature, which makes no distinction between consolidation and pressure propagation. As such, a new term has been coined: the coefficient of pore pressure propagation (C[subscript p]). C[subscript p] was found to be characterized as a single-valued function of C[subscript v], making it a particularly useful term (i.e. calculating C[subscript v] allows for C[subscript p] to be accurately predicted). The testing program consisted of CRS and triaxial approaches that measured the K, C[subscript p] (attained from pulse tests), and C[subscript v] (attained from conventional consolidation tests) as a function of consolidation pressure and volumetric water content. These parameters were successfully measured for sands, sand-bentonite mixtures (SBM), and fire clay specimens. It was discovered that a C[subscript p] framework is better suited to assess reading error than the prevailing K theory. Experimental data demonstrates that pressure equalization rates within the grout are highly dependent on stiffness and degree of saturation, neither of which is adequately captured in the K data. Furthermore, relying on K theory led to widely varying predictions of response time that were experimentally determined to be inaccurate. A numerical model was developed using the C[subscript p] theory. Even in a reasonably conservative state, the model predicts that no currently-available cement-bentonite grouts are suitable for use in a fat clay installation. If future studies fail to identify a viable grout for such installations, the fully grouted method may need to be abandoned altogether for installations in fat clays.