bluuebunny/crossref_metadata_2025 huggingface dataset:
Proper Modeling of Diffusion in Fractured Reservoirs
Authors: Hoteit Hussein
Published: February 2011

Diffusion may play a key role in a number of oil recovery processes such as heavy oil and naturally fractured reservoirs. In fractured media, several laboratory experiments and numerical studies showed that CO2 injection can improve recovery. Molecular diffusion, gravity drainage, and oil swelling are the main contributing mechanisms. Proper modeling of diffusion of hydrocarbon mixtures at the reservoir PVT and geological conditions is not a trivial task. The challenge is in computing the diffusion coefficients for the non-ideal multicomponent mixtures in oil and gas phases, and in physically accurate modeling of the diffusion driving force. One common approach in most simulators is to use the classical Fick's law which simplifies the multicomponent diffusion fluxes by only considering the main-diffusion (diagonal) terms and neglecting the cross-diffusion (off-diagonal) terms. The diffusion fluxes are assumed independent and the diffusion driving force of each component is proportional to the component self concentration gradient. In this work, we demonstrate analytically and numerically that this simplified approach may have a major inconsistency related the flux balance constraint and, in some applications, it may fail to capture the right direction of diffusion as a result of neglecting the dragging effect. We propose an alternative model based on the generalized Fick's law in which diffusion coefficients are calculated as a function of temperature, pressure, and composition. The proposed approach can be seen equivalent to the Maxwell-Stephan model in which the diffusion driving force is the chemical potential instead of the composition gradient. We also tackle anbook problem that may occur in fractured media when fractures get fully saturated with gas in an under-saturated oil surrounding. Intra-phase gas and oil diffusions will not be initiated due to the discontinuity of phases between the fracture and the rock matrix. The proposed approach in the literature that allows for direct gas-to-oil diffusion may not have a sound bases for issues related to the driving force and the estimation of the mass transfer coefficients. We provide a solution for the cross-phase diffusion flux based on the assumption of having chemical equilibrium at the gas-oil contact. Several numerical examples are provided.
Use of Reduced-order Models for Improved Data Assimilation within an EnKF Context
Authors: He J. , Sarma P. , Durlofsky L. J.
Published: February 2011

Reduced-order modeling represents an attractive framework for accelerating computationally expensive reservoir simulation applications. In this paper we introduce and apply a reduced-order modeling approach for history matching. The method considered, trajectory piecewise linearization (TPWL), has been used previously for production optimization problems, where it has provided large computational speedups. The TPWL model developed here represents simulation results for new geological models in terms of a linearization around previously simulated (training) cases. The high-dimensional state space is projected into a low-dimensional subspace using proper orthogonal decomposition (POD). The geological model is represented in terms of a Karhunen-Loeve expansion of the log-transmissibility field, so both the reservoir states and geological parameters are described in a very concise way. The method is incorporated into an Ensemble Kalman Filter (EnKF) history-matching procedure. The combined technique enables EnKF to be applied using many fewer (high-fidelity) reservoir simulations than would otherwise be required to avoid ensemble collapse. More specifically, it is demonstrated that EnKF results using 50 high-fidelity simulations along with 150 TPWL simulations are much better than those using only 50 high-fidelity simulations and are, in fact, comparable to the results achieved using 200 high-fidelity simulations.
Using Multiscale Regularization to Obtain Realistic Optimal Control Strategies
Authors: Shuai Yuanyuan , White Christopher D. , Zhang Hongchao , Sun Ting
Published: February 2011

Smart well technology is attracting increasing attention because it promises to add operation flexibility and potentially increases oil recovery. However, it remains difficult to find the best strategy for production optimization. One challenge is to find a good optimization algorithm, as some optimization algorithms require prohibitive work to compute the gradients of the objective function with respect to the well controls. These methods also require access to the simulator code, which makes them difficult to use with commercial software. Another challenge is to find a reasonable frequency for well control adjustment: adjusting well controls too frequently imposes unrealistic control burdens on operations, increasing well management cost. Moreover, high-frequency control adjustment increases the risk of optimization algorithms being trapped at local optima as the problem is more under-determined. On the other hand, excessively low-frequency control adjustment may not truly optimize oil recovery.

To address these issues, two simulator-independent optimization algorithms were investigated: ensemble-based optimization (EnOpt) and bound optimization by quadratic approximation (BOBYQA). Multiscale regularization was applied to both to find appropriate frequencies for well control adjustment. In a synthetic case study, if multiscale regularization was not used, then EnOpt converged to a higher net value of production than BOBYQA —even though BOBYQA uses second order Hessian information (EnOpt uses first order gradients). BOBYQA performed comparably only if multiscale regularization was used. After multiscale regularization, both methods obtained net value of production (NVP) that equalled or exceeded unregularized optimization, with simpler well control strategies and convergence in fewer iterations.
Comparison of Two Methods for Speeding up Flash Calculations in Compositional Simulations
Authors: Belkadi Abdelkrim , Yan Wei , Michelsen Michael L. , Stenby Erling H.
Published: February 2011

Flash calculation is the most time consuming part in compositional reservoir simulations and several approaches have been proposed to speed it up. Two recent approaches proposed in the literature are the shadow region method and the Compositional Space Adaptive Tabulation (CSAT) method. The shadow region method reduces the computation time mainly by skipping stability analysis for a large portion of compositions in the single phase region. In the two-phase region, a highly efficient Newton-Raphson algorithm can be employed with initial estimates from the previous step. The CSAT method saves computation time by replacing some of the phase split calculation in the two-phase region with pre-stored flash calculation results. The stored results can be used when the new feed composition is on one of the stored tie lines within a certain tolerance. The number of tie lines stored for comparison and the tolerance set for accepting the feed composition are the key parameters in this method since they will influence the simulation speed and the accuracy of simulation results. Inspired by CSAT, we proposed a Tieline Distance Based Approximation (TDBA) method to get approximate flash results in the two-phase region. The method uses the distance to a previous tieline in the same gridblock to decide whether the approximation should be made. Comparison between the shadow region approach and the approximation approach, including CSAT and TDBA, has been made by using a slimtube simulator where the simulation temperature and the simulation pressure are set constant. It is shown that TDBA can significantly improve the flash calculations in the two-phase region.
On Interplay of Capillary, Gravity, and Viscous Forces on Brine/CO2 Relative Permeability in a Compositional and Parallel Simulation Framework
Authors: Delshad Mojdeh , Kong Xianhui , Wheeler Mary F.
Published: February 2011

The effectiveness of CO2 storage in saline aquifers is governed by interplay of capillary, viscous, and buoyancy forces. Recent experimental data reveals the impact of pressure, temperature, and salinity on interfacial tension (IFT) between CO2 and brine. The dependence of CO2-brine relative permeability and capillary pressure on IFT is also clearly evident in published experimental results. Improved understanding of the mechanisms that control the migration and trapping of CO2 in subsurface is crucial to design future storage projects that warrant long term and safe containment. Simulation studies ignoring the variation in interfacial tension and its effect on petrophysical properties of trapped CO2 saturations, relative permeability and capillary pressure have a poor chance of making accurate predictions of CO2 injectivity and its migration. We have developed and implemented a general relative permeability model that combines effects of pressure gradient, buoyancy, and IFT in an Equation of State (EOS) compositional and parallel simulator. The significance of IFT variations on CO2 migration and trapping is assessed.
A Unified Thermal Wellbore Model for Flexible Simulation of Multiple Tubing Strings
Authors: Stone Terry W. , Bennett James , Edwards David A. , Law David Hin-Sum , Pallister Ian
Published: February 2011

Increasingly, operators around the world are using wells with multiple tubing strings to improve both injection and production of fluids in a reservoir. Many operators are beginning to use this technology for designing and optimizing thermal, heavy oil recovery. For example, steam chamber development in a Steam Assisted Gravity Drainage (SAGD) process along a horizontal well pair is often irregular and dual tubing strings may help to even out both injection and production. Problems that operators have with multiple tubing strings in wells include both their control and design. There is a need for a rigorous, accurate and robust method to model these wells as part of the reservoir simulation stage of field planning and development in order to design these wells to improve and optimize oil production and net present value (NPV).

This paper describes a unified thermal wellbore model that fulfills these requirements. The wellbore model allows flexible control of THP, gas lift rates, injection and production rates for each of the tubing strings. There are additional features for optimizing various aspects of the well operation using instantaneous parameters. Improved accuracy in modeling the multiphase flow of fluids and energy is obtained by allowing the tubing strings to consist of multiple segments and branches containing groups of segments. Each segment has its own set of physical parameters including pressure, temperature, phase holdups and frictional/gravitational/accelerational heads. Any number of segments are allowed, the segments are not confined to the grid and can even be specified outside the grid (up to surface) and a flexible conductive heat transfer facility allows multiple heat transfer paths to exist to and from each segment. Additional facilities are described which allow control and optimization of wells and/or individual tubing strings in addition to controllable devices (ICDs, FCVs) using instantaneous or longer term parameters. Two case studies are presented which illustrate some of the simulation workflows. These studies are based on fluid and reservoir properties and well designs typical of the Surmont reservoir which is part of the McMurray formation in Alberta Canada.
Multiscale Finite Volume Method for Non-Conforming Coarse Grids Arising from Faulted Porous Media
Authors: Hajibeygi H.. , Deb R.. , Jenny P..
Published: February 2011

The multiscale finite volume (MSFV) method is extended to account for non-matching coarse grids arising from faulted porous media. To obtain accurate quantities at the coarse scale, basis and correction functions are computed in extended local domains near the fault regions. With the new framework it is shown that the MSFV results are very close to the fine-scale reference solutions. Finally, to improve the quality and to extend the applicability of the framework, an iterative MSFV method for faulted reservoirs is devised; similar to the recently proposed i-MSFV method for conforming coarse grids by Hajibeygi et al. (2008). Convergence histories of the new i-MSFV method are shown for different homogeneous and heterogeneous test cases. It is concluded that this extension of the MSFV method is very flexible and allows to deal with complex geometries such as faulted reservoirs.
Development of a Transient Mechanistic Two-Phase Flow Model for Wellbores
Authors: Shirdel Mahdy , Sepehrnoori Kamy
Published: February 2011

Two-phase flow occurs during the production of oil and gas in the wellbores. Modeling this phenomenon is important for monitoring well productivity and designing surface facilities. Since transient time period in the producing well is usually shorter than reservoir time steps, stabilized flow is assumed in the wellbore. As such, semi-steady state models are used for modeling wellbore dynamics. However, in the case that flow variations occur in a short period of time (i.e., gas kick during drilling) the use of a transient two-phase model is crucial.

A great deal of research has been conducted to study transient two-phase flow in wellbores. However, there is lack of a comprehensive two-fluid model in the petroleum literature. In this paper, we present an implementation of a pseudo-compositional, thermal, fully implicit, transient two-fluid model for two-phase flow in wellbores. In this model, we solve gas/liquid mass balance, gas/liquid momentum balance, and two-phase energy balance equations to obtain five primary variables: liquid velocity, gas velocity, pressure, holdup, and temperature. This simulator can be used as a stand-alone code or can be used in conjunction with a reservoir simulator to mimic wellbore/reservoir dynamic interactions. In our model, we consider stratified, bubbly, intermittent and annular flow regimes using appropriate closure relations for inter-phase and wall shear stress terms in the momentum equations. In our simulation, we found that the inter-phase and wall shear stress terms for different flow regimes can significantly affect the model's results. In addition, the inter-phase momentum transfer terms mainly influence the holdup value.

The outcome of this research leads to a more accurate simulation of multiphase flow in the wellbore and pipes, which can be applied to the surface facility design, well performance optimization, and wellbore damage estimation.
Comparison of Discrete-Fracture and Dual-Permeability Models for Multiphase Flow in Naturally Fractured Reservoirs
Authors: Moinfar Ali , Narr Wayne , Hui Mun-Hong , Mallison Bradley , Lee Seong H.
Published: February 2011

Two discrete-fracture models (DFMs) based on different, independent numerical techniques have been developed for studying the behavior of naturally fractured reservoirs. One model is based on unstructured gridding with local refinement near fractures, while in the second model fractures are embedded in a structured matrix grid. Both models capture the complexity of a typical fractured reservoir better than conventional dual-permeability models, leading to a more accurate representation of fractured reservoirs.

The accuracy of the DFM approaches is confirmed by their match with a structured, grid-aligned, explicit-fracture model in tests involving capillary imbibition during water flooding and gravity drainage in oil-gas systems. The DFMs are insensitive to grid orientation. Simulations also show consistency and agreement of results of the DFM methods in synthetic models with complex fracture patterns. Our simulations indicate that conventional dual-permeability approaches are appropriate when the fracture system is very sparse relative to the grid spacing. In these situations a DFM can be used as the basis for defining dual-permeability model parameters. However, conventional dual-permeability approaches are inadequate in the presence of high localized anisotropy and preferential channeling. When used with general purpose reservoir simulators, both DFMs show computational performance that is comparable to that of dual-permeability models.
New Frontiers in Large Scale Reservoir Simulation
Authors: Dogru Ali H. , Fung Larry S. , Middya Usuf , Al-Shaalan Tareq M. , Byer Tom , Hoy H. , Hahn W. A. , Al-Zamel Nabil , Pita J. , Hemanthkumar K. , Mezghani M. , Al-Mana Abdulrahman , Tan J. , Dreiman W. , Fugl A. , Al-Baiz Abdulaziz
Published: February 2011

Giant reservoirs of Middle East contain substantial portion of the world's total hydrocarbons. Accurate simulation of these reservoirs requires as many as billion cells. A billion-cell parallel reservoir simulator was first presented in 2009.

This paper discusses the progress in the past two years and future projections.

In addition to black oil models, paper presents a large full field compositional model involving over billion unknowns. Throughout the paper grid size effects, computational work distribution and parallel scalability are discussed and illustrated. Paper also presents futuristic technologies for building and analyzing large simulation models.
Good Practice in Controlling Employees' Exposure to Noise and Vibration in the Oil and Gas Industries
Authors: Appleton Bruce
Published: February 2011

There are notable examples of good practice in control of noise and vibration in the offshore oil and gas industry. However, it is often the case that the EC directives' requirements for eliminating or controlling exposures to noise and hand-arm vibration (HAV) are not fully implemented in the industry. There are many technical challenges presented by life extension projects. Much of this work may involve significant exposure, but it may also present opportunities to eliminate and control exposures better. Similarly, the construction of new installations provides scope for incorporating good design from the outset.

HSE has encountered recent examples of refit and new build where both engineering design and operational input have been sought. However, the emphasis often remains very much on assessment rather than taking appropriate control actions. Noise and vibration control is not a new science. Noise from process and plant can often be an indicator of (or even mask) plant condition and condition monitoring is now an increasingly sophisticated science. We therefore need to change the perception of this being a ‘health problem’ to being an engineering challenge, for which good engineering design and good practice provide the best solutions. In many cases, this can involve incorporation of simple, well-established principles.

Whilst the major focus of the oil and gas industry is rightly on key issues such as integrity and safe operation, there is still a need to address issues that have serious health implications. Within its broader inspection programme, HSE is examining the way the industry is controlling noise and vibration. It is also looking at good examples of project management where control of noise and vibration has been incorporated. Such examples of good practice provide encouragement and education to others in the industry. This paper describes the approach being taken by HSE in the UK.
Multiyear Nutrient Removal Performance of Three Constructed Wetlands Intercepting Tile Drain Flows from Grazed Pastures
Authors: Tanner Chris C. , Sukias James P. S.
Published: February 2011

Subsurface tile drain flows can be a major source of nutrient loss from agricultural landscapes. This study quantifies flows and nitrogen and phosphorus yields from tile drains at three intensively grazed dairy pasture sites over 3‐ to 5‐yr periods and evaluates the capacity of constructed wetlands occupying 0.66 to 1.6% of the drained catchments to reduce nutrient loads. Continuous flow records are combined with automated flow‐proportional sampling of nutrient concentrations to calculate tile drain nutrient yields and wetland mass removal rates. Annual drainage water yields ranged from 193 to 564 mm (16–51% of rainfall) at two rain‐fed sites and from 827 to 853 mm (43–51% of rainfall + irrigation) at an irrigated site. Annually, the tile drains exported 14 to 109 kg ha−1 of total N (TN), of which 58 to 90% was nitrate‐N. Constructed wetlands intercepting these flows removed 30 to 369 g TN m−2 (7–63%) of influent loadings annually. Seasonal percentage nitrate‐N and TN removal were negatively associated with wetland N mass loadings. Wetland P removal was poor in all wetlands, with 12 to 115% more total P exported annually overall than received. Annually, the tile drains exported 0.12 to 1.38 kg ha−1 of total P, of which 15 to 93% was dissolved reactive P. Additional measures are required to reduce these losses or provide supplementary P removal. Wetland N removal performance could be improved by modifying drainage systems to release flows more gradually and improving irrigation practices to reduce drainage losses.
Dairy Slurry Application Method Impacts Ammonia Emission and Nitrate Leaching in No‐Till Corn Silage
Authors: Powell J. M. , Jokela W. E. , Misselbrook T. H.
Published: February 2011

Reducing ammonia (NH3) emissions through slurry incorporation or other soil management techniques may increase nitrate (NO3) leaching, so quantifying potential losses from these alternative pathways is essential to improving slurry N management. Slurry N losses, as NH3 or NO3, were evaluated over 4 yr in south‐central Wisconsin. Slurry (i.e., dairy cow [Bos taurus] manure from a storage pit) was applied each spring at a single rate (∼75 m3 ha−1) in one of three ways: surface broadcast (SURF), surface broadcast followed by partial incorporation using an aerator implement (AER‐INC), and injection (INJ). Ammonia emissions were measured during the 120 h following slurry application using chambers, and NO3 leaching was monitored in drainage lysimeters. Yield and N uptake of oat (Avena sativa L.), corn (Zea mays L.), and winter rye (Secale cereale L.) were measured each year, and at trial's end soils were sampled in 15‐ to 30‐cm increments to 90‐cm depth. There were significant tradeoffs in slurry N loss among pathways: annual mean NH3–N emission across all treatments was 5.3, 38.3, 12.4, and 21.8 kg ha−1 and annual mean NO3–N leaching across all treatments was 24.1, 0.9, 16.9, and 7.3 kg ha−1 during Years 1, 2, 3, and 4, respectively. Slurry N loss amounted to 27.1% of applied N from the SURF treatment (20.5% as NH3–N and 6.6% as NO3–N), 23.3% from AER‐INC (12.0% as NH3–N and 11.3% as NO3–N), and 9.1% from INJ (4.4% as NH3–N and 4.7% as NO3–N). Although slurry incorporation decreased slurry N loss, the conserved slurry N did not significantly impact crop yield, crop N uptake, or soil properties at trial's end.
Subsurface Application of Poultry Litter and Its Influence on Nutrient Losses in Runoff Water from Permanent Pastures
Authors: Watts D. B. , Way T. R. , Torbert H. A.
Published: February 2011

Environmental pressure to reduce nutrient losses from agricultural fields has increased in recent years. To abate this nutrient loss to the environment, better management practices and new technologies need to be developed. Thus, research was conducted to evaluate if subsurface banding poultry litter (PL) would reduce nitrogen (N) and phosphorus (P) loss in surface water runoff using a four‐row prototype implement. Rainfall simulations were conducted to create a 40‐min runoff event in an established bermudagrass (Cynodon dactylon L.) pasture on soil types common to the Coastal Plain and Piedmont regions. The Coastal Plain soil type was a Marvyn loamy sand (fine‐loamy, kaolinitic, thermic Typic Kanhapludults) and the Piedmont soil type was a Hard Labor loamy sand (fine, kaolinitic, thermic Oxyaquic Kanhapludults). Treatments consisted of surface‐ and subsurface‐applied PL at a rate of 9 Mg ha−1, surface broadcast–applied commercial fertilizer (CF; urea and triple superphosphate blend) at the equivalent N (330 kg N ha−1) and P (315 kg N ha−1) content of PL, and a nonfertilized control. The greatest loss for inorganic N, total N, dissolved reactive P (DRP), and total P occurred with the surface broadcast treatments, with CF contributing to the greatest loss. Nutrient losses from the subsurface banded treatment reduced N and P in surface water runoff to levels of the control. Subsurface banding of PL reduced concentrations of inorganic N 91%, total N 90%, DRP 86%, and total P 86% in runoff water compared with surface broadcasted PL. These results show that subsurface band–applied PL can greatly reduce the impact of N and P loss to the environment compared with conventional surface‐applied PL and CF practices.
Ammonia Volatilization from Surface‐Banded and Broadcast Application of Liquid Dairy Manure on Grass Forage
Authors: Pfluke Paul D. , Jokela William E. , Bosworth Sidney C.
Published: February 2011

Manure can provide valuable nutrients, especially N, for grass forage, but high NH3 volatilization losses from standard surface‐broadcast application limits N availability and raises environmental concerns. Eight field trials were conducted to evaluate the emission of NH3 from liquid dairy manure, either surface broadcast or applied in narrow surface bands with a trailing‐foot implement. Manure was applied using both techniques at rates of approximately 25 and 50 m3 ha−1 on either orchardgrass (Dactylis glomerata L.) on a well‐drained silt loam or reed canarygrass (Phalaris arundinacea L.) on a somewhat poorly drained clay soil. Ammonia emission was measured with a dynamic chamber/equilibrium concentration technique. High NH3 emission rates in broadcast treatments, especially at the high rate (2 to 13 kg ha−1 h−1), occurred during the first few hours after spreading, followed by a rapid reduction to low levels (<0.5 kg ha−1 h−1 in most cases) by 24 h after spreading and in subsequent days. Band treatments often followed the same pattern but with initial rates substantially lower and with a less dramatic decrease over time. Total estimated NH3 losses from broadcast application, as a percent of total ammoniacal N (TAN) applied, averaged 39% (range of 20 to 59%) from the high manure rate and 25% (range of 9 to 52%) from the low rate. Band spreading reduced total NH3 losses by an average of 52 and 29% for the high and low manure rates, respectively. Results show that the trailing‐foot band application method can reduce NH3 losses and conserve N for perennial forage production.
Modeling the Risk of Phosphorus Runoff Following Single and Split Phosphorus Fertilizer Applications in Two Contrasting Catchments
Authors: Burkitt Lucy L. , Dougherty Warwick J. , Corkrey Ross , Broad Shane T.
Published: February 2011

The potential loss of P in runoff is a function of the combined effects of fertilizer–soil interactions and climatic characteristics. In this study, we applied a Bayesian approach to experimental data to model the annualized long‐term risk of P runoff following single and split P fertilizer applications using two example catchments with contrasting rainfall/runoff patterns. Split P fertilizer strategies are commonly used in intensive pasture production in Australia and our results showed that three applications of 13.3 kg P ha−1 resulted in a greater risk of P runoff compared with a single application of 40 kg P ha−1 when long‐term surface runoff data were incorporated into a Bayesian P risk model. Splitting P fertilizer applications increased the likelihood of a coincidence of fertilizer application and runoff occurring. We found that the overall risk of P runoff is also increased in catchments where the rainfall/runoff pattern is less predictable, compared with catchments where rainfall/runoff is winter dominant. The findings of our study also question the effectiveness of current recommendations to avoid applying fertilizer if runoff is likely to occur in the next few days, as we found that total P concentrations at the half‐life were still very high (18.2 and 8.2 mg P L−1) following single and split P treatments, respectively. Data from the current study also highlight that omitting P fertilizer on soils that already have adequate soil test P concentrations is an effective method of reducing P loss in surface runoff. If P fertilizer must be applied, we recommend less frequent applications and only during periods of the year when the risk of surface P runoff is low.
Monitoring Nitrogen Loading and Retention in an Urban Stormwater Detention Pond
Authors: Rosenzweig Bernice R. , Smith James A. , Baeck Mary Lynn , Jaffé Peter R.
Published: February 2011

Stormwater detention ponds have become ubiquitous in urbanized areas and have been suggested as potential hotspots of N transformation within urban watersheds. As a result, there is a great deal of interest in their use as structural best management practices to reduce the excessive N export from these watersheds. We conducted continuous monitoring of the influent and effluent N loads of a stormwater detention pond located on the Princeton University campus in Princeton, New Jersey. Our monitoring was conducted during four 21‐d periods representing the four seasons of the northeastern United States. Water quality samples were collected and analyzed for nitrate (NO3−) during all four monitoring periods. During two of these periods, loads of ammonium (NH4+), dissolved organic N, and particulate N (PN) were measured. Our results show that NO3− dominated the influent N load, particularly in dry weather inflows to the detention pond. However, PN, which is often neglected in stormwater quality monitoring, made up as much as 30% of the total load and an even greater fraction during storm events. The results of our monitoring suggest that seasonal variation may play an important role in N retention within the detention pond. Although retention of NO3−, the most dominant fraction of N in the influent stormwater, was observed during the summer sampling period, no significant NO3− retention was observed during the spring or the two cold‐weather sampling periods.
Surface Water and Groundwater Nitrogen Dynamics in a Well Drained Riparian Forest within a Poorly Drained Agricultural Landscape
Authors: Davis Jennifer H. , Griffith Stephen M. , Wigington Parker J.
Published: February 2011

The effectiveness of riparian zones in mitigating nutrients in ground and surface water depends on the climate, management, and hydrogeomorphology of a site. The purpose of this study was to determine the efficacy of a well drained, mixed‐deciduous riparian forest to buffer a river from N originating from a poorly drained grass seed cropping system. The study site was adjacent to the Calapooia River in the Willamette Valley, Oregon. Water was found to move from the rapid drainage of swale surface water. During winter hydrological events, the riparian forest also received river water. Low nitrate (NO3−) concentrations (0.2–0.4 mg NO3−–N L−1) in the shallow groundwater of the cropping system were associated with low rates of mineralization and nitrification (33 kg N ha−1 yr−1) and high grass seed crop uptake of N (155 kg N ha−1 yr−1). The riparian forest soil had higher rates of mineralization (117 kg N ha−1 yr−1) that produced quantities of soil N that were within the range of literature values for plant uptake, leading to relatively low concentrations of shallow groundwater NO3− (0.6–1.8 mg NO3−–N L−1). The swale that dissected the cropping system and riparian area was found to have the highest rates of denitrification and to contribute dissolved organic C to the river. Given the dynamic nature of the hydrology of the Calapooia River study site, data suggest that the riparian forest plays a role not only in reducing export of NO3− from the cropping system to the river but also in processing nutrients from river water.
Interactions between Soil Texture and Placement of Dairy Slurry Application: II. Leaching of Phosphorus Forms
Authors: Glæsner Nadia , Kjaergaard Charlotte , Rubæk Gitte H. , Magid Jakob
Published: February 2011

Managing phosphorus (P) losses in soil leachate following land application of manure is key to curbing eutrophication in many regions. We compared P leaching from columns of variably textured, intact soils (20 cm diam., 20 cm high) subjected to surface application or injection of dairy cattle (Bos taurus L.) manure slurry. Surface application of slurry increased P leaching losses relative to baseline losses, but losses declined with increasing active flow volume. After elution of one pore volume, leaching averaged 0.54 kg P ha−1 from the loam, 0.38 kg P ha−1 from the sandy loam, and 0.22 kg P ha−1 from the loamy sand following surface application. Injection decreased leaching of all P forms compared with surface application by an average of 0.26 kg P ha−1 in loam and 0.23 kg P ha−1 in sandy loam, but only by 0.03 kg P ha−1 in loamy sand. Lower leaching losses were attributed to physical retention of particulate P and dissolved organic P, caused by placing slurry away from active flow paths in the fine‐textured soil columns, as well as to chemical retention of dissolved inorganic P, caused by better contact between slurry P and soil adsorption sites. Dissolved organic P was less retained in soil after slurry application than other P forms. On these soils with low to intermediate P status, slurry injection lowered P leaching losses from clay‐rich soil, but not from the sandy soils, highlighting the importance of soil texture in managing P losses following slurry application.
Adsorption of Isoxaflutole Degradates to Aluminum and Iron Hydrous Oxides
Authors: Wu Si Hyun , Goyne Keith W. , Lerch Robert N. , Lin Chung‐Ho
Published: February 2011

Isoxaflutole is a preemergence herbicide that has been marketed as a substitute for atrazine. It is rapidly transformed to a more stable and soluble diketonitrile degradate (DKN) after field application and can further degrade to a benzoic acid degradate (BA) within soil. However, no previous research has been conducted to investigate DKN and BA sorption to metal oxide minerals. The primary objective of this research was to elucidate the interactions of DKN and BA with synthetic hydrous aluminum and iron oxides (HAO and HFO, respectively) to understand how variably charged minerals may influence adsorption of these compounds in soil. The herbicide degradates did adsorb to HAO and HFO, and the data were well described by the Freundlich model (R2 > 0.91), with N values ranging from 0.89 to 1.2. Adsorption isotherms and Kd values demonstrate that BA is adsorbed to HFO to a greater extent than other degradate–mineral combinations that were studied. The degree of hysteresis between adsorption/desorption isotherms was characterized as slight (hysteresis index values <1.7), suggesting weak DKN and BA retention to HFO and HAO oxide surfaces. Degradate adsorption was observed to greatly diminish as suspension pH increased. Attenuated total reflectance–Fourier transform infrared spectra show no evidence that DKN or BA adsorb to mineral surfaces as inner‐sphere complexes under hydrated conditions. Instead, DKN and BA adsorb to positively charged metal oxide surfaces as outer‐sphere or diffuse ion swarm complexes via electrostatic attraction. This research indicates that metal oxides may serve as important retardants for DKN and BA migration through acidic soils enriched with aluminum and iron oxides.
Subsurface Application of Poultry Litter in Pasture and No‐Till Soils
Authors: Pote D. H. , Way T. R. , Kleinman P. J. A. , Moore P. A. , Meisinger J. J. , Sistani K. R. , Saporito L .S. , Allen A. L. , Feyereisen G. W.
Published: February 2011

Poultry litter provides a rich nutrient source for crops, but the usual practice of surface‐applying litter can degrade water quality by allowing nutrients to be transported from fields in surface runoff while much of the ammonia (NH3)–N escapes into the atmosphere. Our goal was to improve on conventional litter application methods to decrease associated nutrient losses to air and water while increasing soil productivity. We developed and tested a knifing technique to directly apply dry poultry litter beneath the surface of pastures. Results showed that subsurface litter application decreased NH3–N volatilization and nutrient losses in runoff more than 90% (compared with surface‐applied litter) to levels statistically as low as those from control (no litter) plots. Given this success, two advanced tractor‐drawn prototypes were developed to subsurface apply poultry litter in field research. The two prototypes have been tested in pasture and no‐till experiments and are both effective in improving nutrient‐use efficiency compared with surface‐applied litter, increasing crop yields (possibly by retaining more nitrogen in the soil), and decreasing nutrient losses, often to near background (control plot) levels. A paired‐watershed study showed that cumulative phosphorus losses in runoff from continuously grazed perennial pastures were decreased by 55% over a 3‐yr period if the annual poultry litter applications were subsurface applied rather than surface broadcast. Results highlight opportunities and challenges for commercial adoption of subsurface poultry litter application in pasture and no‐till systems.
Novel Manure Management Technologies in No‐Till and Forage Systems: Introduction to the Special Series
Authors: Maguire Rory O. , Kleinman Peter J. A. , Beegle Douglas B.
Published: February 2011

Surface application of manures leaves nitrogen (N) and phosphorus (P) susceptible to being lost in runoff, and N can also be lost to the atmosphere through ammonia (NH3) volatilization. Tillage immediately after surface application of manure moves manure nutrients under the soil surface, where they are less vulnerable to runoff and volatilization loss. Tillage, however, destroys soil structure, can lead to soil erosion, and is incompatible with forage and no‐till systems. A variety of technologies are now available to place manure nutrients under the soil surface, but these are not widely used as surface broadcasting is cheap and long established as the standard method for land application of manure. This collection of papers includes agronomic, environmental, and economic assessments of subsurface manure application technologies, many of which clearly show benefits when compared with surface broadcasting. However, there remain significant gaps in our current knowledge, some related to the site‐specific nature of technological performance, others related to the nascent and incomplete nature of the assessment process. Thus, while we know that we can improve land application of manure and the sustainability of farming systems with alternatives to surface broadcasting, many questions remain concerning which technologies work best for particular soils, manure types, and farming and cropping systems.
Fate of Prions in Soil: A Review
Authors: Smith Christen B. , Booth Clarissa J. , Pedersen Joel A.
Published: February 2011

Prions are the etiological agents of transmissible spongiform encephalopathies (TSEs), a class of fatal neurodegenerative diseases affecting humans and other mammals. The pathogenic prion protein is a misfolded form of the host‐encoded prion protein and represents the predominant, if not sole, component of the infectious agent. Environmental routes of TSE transmission are implicated in epizootics of sheep scrapie and chronic wasting disease (CWD) of deer, elk, and moose. Soil represents a plausible environmental reservoir of scrapie and CWD agents, which can persist in the environment for years. Attachment to soil particles likely influences the persistence and infectivity of prions in the environment. Effective methods to inactivate TSE agents in soil are currently lacking, and the effects of natural degradation mechanisms on TSE infectivity are largely unknown. An improved understanding of the processes affecting the mobility, persistence, and bioavailability of prions in soil is needed for the management of TSE‐contaminated environments.
Impact of Precipitation Spatial Resolution on the Hydrological Response of an Integrated Distributed Water Resources Model
Authors: Fu Suhua , Sonnenborg Torben O. , Jensen Karsten H. , He Xin
Published: February 2011

Precipitation is a key input variable to hydrological models, and the spatial variability of the input is expected to impact the hydrological response predicted by a distributed model. In this study, the effect of spatial resolution of precipitation on runoff, recharge and groundwater head was analyzed in the Alergaarde catchment in Denmark. Six different precipitation spatial resolutions were used as inputs to a physically based, distributed hydrological model, the MIKE SHE model. The results showed that the resolution of precipitation input had no apparent effect on annual water balance of the total catchment and runoff discharge hydrograph at watershed outlet. On the other hand, groundwater recharge and groundwater head were both affected. The impact of the spatial resolution of precipitation input is reduced with increasing catchment size. The effect on stream discharge is relatively low for a catchment size above 250 km2, and the effect is negligible when the entire catchment area of approximately 1000 km2 is considered. In the present case the highest resolution of 500 m was found to result in the best representation of the hydrological response at subcatchment scale. Stream discharge, groundwater recharge, and groundwater head were also affected by the method for correction of systematic errors in precipitation measurements. The results underscored the importance of using a spatial resolution of the precipitation input that captures the overall precipitation characteristics for the considered catchment or subcatchment. As long as the average precipitation of the considered catchment or subcatchment is accurately estimated, the spatial resolution seems less important when the integrated response in the form of stream flow is considered.
Visualizing Unsaturated Flow Phenomena Using High‐Resolution Reflection Ground Penetrating Radar
Authors: Haarder Eline B. , Looms Majken C. , Jensen Karsten H. , Nielsen Lars
Published: February 2011

Unsaturated flow phenomena, such as unstable wetting fronts and preferential flow, cannot be investigated using small‐scale sampling. Dye tracer experiments can help visualize the dynamics of water flow but are destructive and therefore irreproducible. We investigated the applicability of high‐resolution ground penetrating radar (GPR) for nondestructive visualization of unsaturated flow patterns arising from a forced infiltration experiment. Synthetic studies using a reflection GPR two‐dimensional finite difference time domain modeling code indicated that differences in water content caused by preferential flow and fingering could be resolved. Moisture content contrasts down to approximately 2.5% within the top 2 m were detectable, but with increasing degrees of heterogeneity in the subsurface it becomes difficult to distinguish these moisture content changes. We conducted a field experiment in which 100 mm (900 L) of Brilliant Blue dyed water was infiltrated across a 3‐ by 3‐m area in relatively homogenous and undisturbed sandy alluvial sediments. Reflection GPR data were collected before and after infiltration. Dye‐staining patterns, revealed by excavating a 2‐m‐deep trench through the infiltration area, were compared with changes in the GPR data. Reflection amplitude changes as well as reflection delay revealed significant differences within the dye‐stained area. The GPR data provided information about the unsaturated flow below the extent of the dye staining, and the results of the synthetic GPR modeling, as well as the observed changes in the real GPR data set, underline the potential of reflection GPR as a nondestructive method to map unsaturated flow phenomena.
Nonuniform Groundwater Discharge across a Streambed: Heat as a Tracer
Authors: Jensen Jannick Kolbjørn , Engesgaard Peter
Published: February 2011

Time series analysis of continuous streambed temperature during a period of 47 d revealed that discharge to a stream is nonuniform, with strongly increasing vertical fluxes throughout the top 20 cm of the streambed–aquifer interface. An analytical solution to the transient heat transport equation was used to analyze several pairs of observed amplitude damping with depth. A nonuniform pattern in discharge across the stream width was also observed, which could have been caused by lateral or horizontal flow. Head measurements in a meadow area and below the stream showed strong convergence of flow near the streambed. Seepage meter measurements in the middle of the stream often resulted in highly variable flux estimates, which could have been caused by hyporheic flow due to the presence of a gravel layer. Discharge and recharge to the stream at the bank near the meadow was relatively steady throughout the period. On the other hand, discharge to the stream at the opposite bank near a steep hillslope decreased significantly toward the end of the period (early June), which was attributed to a drop in the water table on this side of the stream. The results from the time series analysis were compared with seepage meter measurements and the results from a steady‐state analytical solution to the heat transport equation. The different methods agreed on the pattern of discharge across the stream width, and the mean values during the studied period generally agreed well but with different ranges.
Quantifying Transient Soil Moisture Dynamics Using Multipoint Direct‐Current Resistivity in Homogeneous Sand
Authors: Franz Trenton E. , Nolan Jay , Nordbotten Jan M. , Caylor Kelly K. , Slater Lee D.
Published: February 2011

Direct measurements of soil moisture are extremely difficult to obtain between the spatial scales of point measurements and remote sensing. Nevertheless, the spatiotemporal distribution of soil moisture remains a key variable in hydrology. In this study, we explored the use of multipoint direct‐current resistivity to examine spatiotemporal changes in soil moisture following a rapid infiltration event into a large macropore. The methodology was selected because the time scale of flow processes in the homogeneous isotropic sand prevented the use of imaging techniques. Selection of an appropriate electrode array was critical for collecting the required high‐resolution spatiotemporal resistivity measurements in a 1.44‐m‐diameter tank. Direct placement of a dense array of electrodes in the sand allowed us to use geostatistical methods for spatial interpolation, thereby removing the inherent uncertainty resulting from inversion mechanics (i.e., smoothness constraints for underconstrained problems). Instead, conversion of resistivity to saturation was directly performed using Archie's law. We compared the observations to a two‐dimensional, axisymmetric, numerical solution of the system using the HYDRUS 2D/3D software, and to a semianalytical solution to estimate soil hydraulic properties. We found satisfactory comparisons among the observations and the numerical and semianalytical solutions of the system, which indicates that these techniques may be applicable to field‐scale estimates of effective hydraulic properties. Subject to limiting initial conditions, boundary conditions, and material properties, the results of the semianalytical solution are encouraging for capturing general hillslope‐scale dynamics at longer temporal scales toward a greater understanding of emergent patterns in dryland ecosystems.