Transport in heterogeneous porous media

We present a new algorithm for modelling single phase transport of a tracer in porous media which demonstrates that structure on all scales affects macroscopic transport behaviour. We marry the robustness of the continuous time random walk (CTRW) framework with the simplicity of a Monte Carlo approach to reservoir simulation. We simulate transport as a series of particles transitioning between nodes with probability (t).dt that a particle will first arrive at a nearest neighbor in a time t to t + dt. To this end we first determine the mixing rules and transition probability ADE(t) for transport governed by the advection-dispersion equation (ADE) (Rhodes and Blunt, 2006). We validate our algorithm by simulating advective transport in bond percolation clusters at the critical point. We compute the histogram of flow speeds using the velocities from the bonds on the backbone and find the multifractal spectrum for two-dimensional lattices with linear dimension L _ 2000 and in three dimensions for L _ 250. We demonstrate that in the limit of large systems all the negative moments of the velocity distribution become ill-defined. However, to model transport, the velocity histogram should be weighted by the flux to obtain a well-defined mean travel time. Finally, we use CTRWtheory to demonstrate that anomalous transport is observed whose characteristics can be related to the multifractal properties of the system. We next demonstrate a pore-to-reservoir simulation methodology which is consistent across all scales of interest. At the micron scale, we fit a truncated power law (t) for the distribution of particle transition times from pore to pore simulations. To do this we use our transport algorithm on a geologically representative network model of Berea sandstone and compare the results to the explicit modelling of advection and molecular diffusion by Bijeljic and Blunt (2006). We find that the results are similar. We then demonstrate the effect of increasing pore scale heterogeneity on the power law exponent (_) by stretching the distribution of throat radii in our network model. We show that by increasing the spread of velocities within the network we decrease _ making the transport more anomalous - in keeping with the consensus currently in the literature. This (t) is then used to calculate transport on the mm to cm scale. We can then move up to the metre/grid block scale by using the transit time distribution from the mm-cm simulation to model transport in an explicit, geologically representative model of heterogeneity found within a grid block of the reservoir. From these numerical experiments we determine the (t) appropriate for transport on grid block scale systems characterized by Peclet (Pe) number and the type of heterogeneity within the system. This allows us to account for small scale uncertainty by interpreting (t) probabilistically and running simulations for different possible realizations of the reservoir heterogeneity. At the field scale, we represent the reservoir as an unstructured network of nodes connected by links. For each node-to-node transition, we use our upscaled (t) from a simulation of transport at the smaller scale. We account for small-scale uncertainty by parameterising (t) in terms of sub-scale heterogeneity and Peclet number. We demonstrate the methodology by finding a (t) for each scale of interest taking into consideration the relevant physics at that scale and using the appropriate function in a million-cell reservoir model. We show that the macroscopic behaviour can be very different from that predicted by assuming that the ADE operates at the small scale. Small-scale structure dramatically retards the advance of the plume with the particles becoming trapped in the slow moving pores/regions increasing breakthrough times by an order of magnitude compared to those predicted by the ADE

COUNTERING ASOCIAL JUSTICE: CONSUMER CULTURE, STANCE AND A CARTOGRAPHY OF ENCOUNTER

In Social Foundations classrooms, social justice approaches to questions of difference are certainly part of the curriculum. After teaching numerous Social Foundations courses, I encountered several issues related to the way rigid identity categories were complemented by neoliberal narratives that seemed to limit class conversation in troubling ways—particularly in that students had a difficult time articulating a sense of connection with others beyond their circles of acquaintances. This dissertation is an exploration of how I might resolve some of those dilemmas. I problematize the neoliberal subject position as it relates to questions of social justice, and offer that a relational approach to others may be a useful counter. Inspired by several scholars who address theoretical relational curricular possibilities, I designed a course using a consumer culture approach to constructing Other as a conceptual lens through which to begin talking about difference. Using student data from that class, I introduce stance analysis as a way to interpret the data in terms of the ways students either reinscribed or interrupted a sense of neoliberal relationality. Finally, using the methodological approach of social cartography, I created a map wherein students could plot their encounters across difference. This map is intended as a pedagogical heuristic that could be used to destabilize a self-possessed and individualistic neoliberal sense of self. To this end, the map is oriented toward an approach to self and Other that is contingent, ongoing and contextually mediated. I explore the pedagogical implications of the map and suggest that such approaches may be useful for better understanding how we are relationally constituted. I argue that entering social justice conversations from this vantage point may avoid some of the trappings of rigid identity categories without resorting to commonsense neoliberal narratives

Exploring Participation: A Study of Venezuelan Bolivarian Schools

This thesis examines different ways the process of participation is manifested in Venezuelan Bolivarian primary schools. I argue that the notion of participation in development is contested and has been oversimplified by both advocates and detractors. Using the Venezuelan study as an example, I show that in the same project of participatory development both problematic and positive elements of participation will exist. Problematic elements of participation address inadequate understandings of 'community', question the process of consensus building, and highlight the role of proximity to power centers. Promising developments in the Venezuelan case include incorporation of social programs into the schools, new educational quality indicators, and the establishment of a relationship between school curriculum and local development efforts. As these problematic and promising elements simultaneously occur, I suggest that a different approach to evaluating participation in a development context is necessary. This approach, theorized by social geographers, suggests that analysis of how the space of participation emerges would be more beneficial for assessing the merits of participation. From this perspective, continued study of participatory processes might move beyond the current oversimplification

Beyond the balance sheet : performance, participation, and regime support in Latin America

Most studies on regime support focus on performance, or policy outputs, as the principal causal variable. This study challenges this conventional wisdom by focusing on two countries where performance and support do not match. Chile is the economic envy of every country in the region, yet support has been surprisingly anemic since the return of democracy in the early 1990s. By contrast, Venezuela managed to maintain extremely high levels of support during the reign of Hugo Chávez despite severe failures of governance in areas such as economic management, employment, and public security. Resolution of these paradoxes requires turning away from policy decisions and focusing instead on how those decisions are made. Taking inspiration from democratic theory and social psychology, I argue that extensive opportunities for direct participation in the political process engenders in citizens strong feelings of efficacy, a sense of control over the course of politics. Such sentiments increase support both directly and by softening the impact of performance failures. I use a mixed-methods approach to test this theory. Quantitative analysis of survey data confirms the relationships between efficacy, performance, and support. I then show, through both quantitative and qualitative techniques, that participatory programs such as the communal councils in Venezuela have a key role in preserving the legitimacy of that regime, especially in light of the hegemonic and authoritarian practices of chavismo at the national level. Finally, I use experimental data, survey data, and a qualitative analysis of a nascent participatory program in one of Chile’s municipalities to demonstrate that a lack of participatory access lies at the heart of that country’s relatively weak regime support.Governmen

Harm reduction among injecting drug users - evidence of effectiveness

This chapter synthesises and evaluates the available direct evidence relating to the impact of needle and syringe programmes (NSPs), opioid substitution treatment (OST), drug consumption rooms (DCRs), and peer naloxone distribution (PND) on HIV/hepatitis C (HCV) incidence/prevalence, injecting risk behaviour and overdose-related mortality. To achieve this, we conducted a review of reviews; a systematic and explicit method used to identify, select and critically appraise relevant findings from secondary level research (systematic reviews and/or meta-analyses) into an evidence briefing. In the absence of high-quality reviews, appraisal of the evidence was supplemented with a targeted review of the primary literature. We find that there is sufficient review-level evidence that OST reduces HIV transmission, while the evidence in support of NSPs reducing HIV transmission is more tentative, and for DCRs currently insufficient. There is tentative evidence that OST has limited effectiveness in reducing HCV transmission, and insufficient evidence to support or discount NSPs or DCRs' ability to reduce HCV transmission. There is sufficient review-level evidence that NSPs, OST and DCRs reduce self-reported injecting risk behaviour. There is sufficient review evidence that OST reduces risk of overdose mortality, but insufficient evidence to support or discount the effect of DCRs or PND on overdose deaths at the community level. Our review shows evidence in support of a variety of harm reduction interventions but highlights an uneven presence of high-quality review evidence. Future evaluation of harm reduction programmes should prioritise methodologically robust study designs

The Consequences of Information Revealed in Auctions

This paper considers the ramifications of post-auction competition on bidding behavior under different bid announcement policies. In equilibrium, the auctioneer’s announcement policy has two distinct effects. First, announcement entices players to signal information to their post-auction competitors through their bids. Second, announcement can lead to greater bidder participation in certain instances while limiting participation in others. Specifically, the participation effect works against the signalling effect, thus reducing the impact of signalling found in other papers. Revenue, efficiency, and surplus implications of various announcement policies are examined

The Engagement Curve: Populism and Political Engagement in Latin America

Considerable research has been conducted on the relationship between socioeconomic inequality and political engagement. However, there is little consensus on the exact nature of the relationship, and considerable variation in the relationship exists even among countries with similar levels of inequality. This lack of clarity in the literature exists because the impact of inequality on engagement is not constant, but changes depending on the strategic choices of political leaders. Populist leaders, who tend to explicitly connect political and socioeconomic exclusion, can activate latent grievances around inequality. Using data from the Latin American Public Opinion Project, we show that inequality leads to disengagement among the poor in most contexts but increases engagement under populist rule. In other words, a primarily structural relationship is mediated by political variables. Even though the severity of inequality is outside the control of any political actor, leaders’ reaction to inequality can dramatically alter its impact on mass political behavior