Aumann C.A.,Alberta Research Council
Environmental Modelling and Software | Year: 2011
This paper focuses on an approach for constructing credibility in models used to evaluate environmental policies. Credibility is defined as adequacy relative to an intended use. The proposed approach is located within a broader policy assessment framework and is general enough to function in both scientific and policy assessment contexts. A model assessment framework is introduced and linked to current understanding of mental models in cognitive psychology to provide a possible explanation of how stakeholders come to view modeling results as credible. Since policy evaluation is about an unknown and unknowable future, data to assess model performance will be limited. A number of options are suggested for how credibility can be constructed in such situations. The argument presented depends primarily on i) the hierarchical levels of simulation models, ii) the ability to apply model assessment criteria specified across these hierarchical levels, and iii) the public nature of these criteria relative to the mental models of stakeholders enables debate about the adequacy of the criteria relative to the intended purpose of the policy appraisal. Taken together these aspects enables stakeholders to reach agreement on necessary and desirable performance criteria for the modeling results to be credible. © 2009 Elsevier Ltd.
Gibson J.J.,Alberta Research Council |
Reid R.,Indian and Northern Affairs Canada
Journal of Hydrology | Year: 2010
Stable isotopes of water, oxygen-18 and deuterium, were measured at biweekly to monthly intervals during the open-water season in a small, headwater lake (Pocket Lake, 4.8 ha) near Yellowknife Northwest Territories, and concurrently in a nearby string-of-lakes watershed (Baker Creek, 137 km2) situated in the subarctic Precambrian Shield region. As measured in water samples collected over a 12 year period (1997-2008), the levels of evaporative isotopic enrichment in both lake and watershed outflow were differentially offset, and seasonal variations were found in both to be driven by variations in open-water evaporation. Systematic differences measured in the magnitude of the offset between the lake and watershed outflow are interpreted as being caused by changes in the effective drainage area contributing to runoff. Based on the observed and extremely consistent relationship between isotopic compositions of lake water and watershed outflow (r2 = 0.849, p < 0.001) we extend the analysis of open-water evaporation losses and effective drainage areas back to 1991 when less-frequent water sampling at the sites commenced. This 18-year record serves to demonstrate for the first time the expected variability in the evaporation and transpiration partitioning, upper limits on the effective drainage area, and isotopic signals transferred downstream in a typical shield drainage system within the Mackenzie Basin. © 2009 Elsevier B.V.
Yuan J.-Y.,Osum Oil Sands Corporation |
McFarlane R.,Alberta Research Council
Journal of Canadian Petroleum Technology | Year: 2011
The impact of steam quality, circulation rate and pressure difference between the well pair during SAGD initialization using steam circulation was explored through the use of numerical simulations employing a discretized wellbore model. These operating parameters appear to affect uniformity of reservoir heating, occurrence of steam breakthrough and time required to establish communication between the well pair. The simulation results indicate that, for the given tubing and liner sizes and reservoir properties, relatively lower circulation rates at high-steam quality are more favourable for faster initialization and development of uniform temperature between the horizontal well pair. At lower steam qualities, however, higher circulation rates appear more favourable. The use of high-steam quality in combination with high-circulation rates leads to slower rates of initialization, less uniform heating along the length of the wells and possibility of premature steam breakthrough at the heel. It was also found that having a higher steam quality in the lower well than in the upper well could lead to faster initialization and more uniform heating between the well pair. Although a large pressure difference is not encouraged, a small pressure difference, offsetting the natural hydraulic pressure (50 kPa), appears to be more favourable for faster and more uniform initialization.
Burdukova E.,University of Melbourne |
Li H.,Alberta Research Council |
Ishida N.,Japan National Institute of Advanced Industrial Science and Technology |
O'Shea J.-P.,University of Melbourne |
Franks G.V.,University of Melbourne
Journal of Colloid and Interface Science | Year: 2010
Poly (N-isopropylacrylamide) (PNIPAM) is a temperature responsive polymer. At temperature below its lower critical solution temperature (LCST 32 °C) PNIPAM is soluble in water and hydrophilic. At temperature above the LCST, the polymer becomes hydrophobic and insoluble in water. At temperatures above the LCST, PNIPAM has been shown to induce flotation of previously hydrophilic minerals. The mechanism is believed to be an increase in particle hydrophobicity when PNIPAM adsorbs to the particle surfaces at high temperature. This paper investigates the interaction forces between bare silica surfaces in PNIPAM solutions. The influence of three phase contact angles on these interactions, in the presence of polymers of different molecular weights, is also examined. It was found that the presence of PNIPAM on silica surfaces significantly increases their hydrophobicity at a temperature above the LCST. The AFM measurements of surface forces at high temperature also showed that strong adhesion is present between the PNIPAM coated surfaces, which is absent in the absence of polymer. These findings lead to the conclusion that the detected attractive force and subsequent adhesion result from hydrophobic attraction induced by PNIPAM at temperature above the LCST. © 2009 Elsevier Inc. All rights reserved.
McFarlane R.A.,Alberta Research Council |
Gray M.R.,University of Alberta |
Shaw J.M.,University of Alberta
Fluid Phase Equilibria | Year: 2010
The Peng-Robinson cubic equation of state (CEOS) is widely used to predict thermodynamic properties of pure fluids and mixtures. The usual implementation of this CEOS requires critical properties of each pure component and combining rules for mixtures. Determining critical properties for components of heavy asymmetric mixtures such as bitumen is a challenge due to thermolysis at elevated temperatures. Group contribution (GC) methods were applied for the determination of critical properties of molecular representations developed by Sheremata for Athabasca vacuum tower bottoms (VTB). In contrast to other GC methods evaluated, the Marrero-Gani GC method yielded estimated critical properties with realistic, non-negative values, followed more consistent trends with molar mass and yielded normal boiling points consistent with high temperature simulated distillation data. Application of classical mixing rules to a heavy asymmetric mixture such as bitumen yields saturated liquid density and bubble pressure estimates in qualitative agreement with experimental data. However the errors are too large for engineering calculations. In this work, new composite mixing rules for computing co-volumes of asymmetric mixtures are developed and evaluated. For example, composite mixing rules give improved bubble point predictions for the binary mixture ethane + n-tetratetracontane. For VTB and VTB + decane mixtures the new composite mixing rules showed encouraging results in predicting bubble point pressures and liquid phase densities. © 2010 Elsevier B.V. All rights reserved.