bluuebunny/crossref_metadata_2025_split huggingface dataset:
Parallel Numerical Reservoir Simulations of Nonisothermal Compositional Flow and Chemistry
Authors: Delshad M.. , Thomas S.G.. G. , Wheeler M.F.. F. 
Published: January 2011

Summary
This paper describes an efficient numerical scheme for nonisothermal compositional flow coupled to chemistry. An iterative implicit-pressure/explicit-composition (IMPEC) method is applied to solve the flow problem using a volume-balance-convergence criterion. A backward-Euler mixed finite-element method (FEM) with lowest-order RT0 elements is applied to solve the pressure equation, and a component local mass-preserving explicit scheme is used to update concentrations. Chemical reactions are solved using explicit Runge-Kutta (RK) ordinary-differential-equation (ODE) integration schemes. A higher-order Godunov method and a backward-Euler mixed FEM are applied for thermal advection and conduction, respectively, in a time-split scheme.
One of the major applications of the method is in the modeling of field-scale carbon dioxide (CO2) sequestration as an enhanced-oil-recovery (EOR) process or for containment in deep saline aquifers where chemical reactions and temperature variations may have an effect on the flow and transport of CO2. Leakage patterns when CO2 is injected near leaky abandoned wells, the displacement of methane from depleted gas reservoirs, and accurate modeling of geochemical reactions involving injected CO2 are other applications of interest.
Results of a benchmark problem in multiphase flow with several hydrocarbon components in formations with highly heterogeneous permeability on very fine grids, as well as a large-scale parallel implementation of modeling CO2 sequestration, are presented to justify the practical use of the model. A parallel efficiency of approximately 80% was observed on up to 512 cores in the benchmark study. Results from a problem simulating injection of CO2 in deep aquifers including nonisothermal and chemical effects are also presented. The results indicate a good agreement of the solutions with published data, where available.
Numerical modeling and simulation of CO2 sequestration plays a major role in future site selections and in designing storage facilities for effective CO2 containment. The main contribution of this paper lies in providing a parallel and efficient method of simulating challenging compositional flow problems, such as in the study of CO2 sequestration, as well as flow coupled to thermal and geochemical effects.
Barite Nucleation and Inhibition at 0 to 200°C With and Without Thermodynamic Hydrate Inhibitors
Authors: Fan Chunfang , Kan Amy T. , Zhang Ping , Tomson Mason B. 
Published: January 2011

Summary
In this study, we modified the commonly employed dynamic-tube-blocking methodology and built an apparatus to study the nucleation kinetics of barite-scale formation at high temperatures in the presence and absence of scale inhibitors. Barite formation was detected by monitoring pressure change over a micrometer-sized in-line filter, and this has been proved to be an easy and accurate method to study mineral-scale-nucleation kinetics at high temperatures. Additionally, we investigated the nucleation kinetics of barite at 0–25°C with and without thermodynamic hydrate inhibitors. By using this modified dynamic-tube-blocking technique, we successfully measured the nucleation kinetics of barite in 1M NaCl solutions over a temperature range from 25 to 200°C and at various supersaturation conditions. We also evaluated the inhibition efficiency of barite precipitation at this high temperature range. On the basis of the experimental results, the relationship of precipitation kinetics of barite as a function of temperature and saturation index was established. The inhibition efficiency of the phosphonate inhibitor [bis-hexamethylenetriamine-penta (methylene phosphonic) acid (BHPMP)] on barite precipitation has been evaluated over the same range of conditions. The Ca2+ effect on the inhibition efficiency of BHPMP at a low temperature (4°C) and at high temperatures (175–200°C) was investigated also. Results of this study have been incorporated into the scale-prediction software ScaleSoftPitzer.
pH-Sensitive Polymers for Novel Conformance-Control and Polymer-Flood Applications
Authors: Choi Suk Kyoon , Sharma Mukul M. , Bryant Steven L. , Huh Chun 
Published: January 2011

SummaryNovel conformance-control and polymer-flood applications that exploit the pH sensitivity of partially hydrolyzed polyacrylamide (HPAM) are proposed. The key feature of this process is the injection of the HPAM solution under acidic conditions. The low pH makes polymer molecules coil tightly, resulting in a very low polymer-solution viscosity. This allows the polymer solution to be injected into the reservoir at a substantially reduced injection pressure. Once injected, the acid reacts with the formation minerals to cause a spontaneous pH increase, uncoiling the polymer chains and causing a large increase in solution viscosity. Such a viscosity-control scheme can be exploited for placement of a concentrated polymer solution in high-permeability zones, where it later viscosifies to divert subsequently injected fluids (in-depth conformance control), or to reduce the high pressure drop near the wellbore during polymer injection (injectivity improvement).Extensive laboratory experiments were systematically performed and interpreted to evaluate the novel applications of pH-sensitive HPAM. The evaluations require (a) quantification of steady-shear viscosities, (b) characterization of geochemical reactions with acids, and (c) transport evaluation of HPAM solutions in cores. Rheological measurements show that shear viscosities of HPAM solution have a pronounced, but reversible, dependence on pH. The peak pHs observed in several shut-ins guarantee that spontaneous geochemical reactions can return the polymer solution to its original high viscosity. The use of a weak acid is the key. Coreflood results show that the HPAM solution under acidic conditions can be propagated through cores with much higher mobility than at neutral pH. However, low-pH conditions increase adsorption (polymer loss) and require additional chemical cost (for acid). The optimum injection formulation (polymer concentration, injection pH) will depend on the specific reservoir mineralogy, permeability, salinity, and injection conditions.
Exponential Growth in San Juan Basin Fruitland Coalbed Permeability With Reservoir Drawdown: Model Match and New Insights
Authors: Shi J.-Q.. -Q. , Durucan S.. 
Published: January 2011

Summary
The exponential-growth behavior of coalbed permeability with reservoir pressure depletion has been observed previously at the Fairway wells in the San Juan basin. More recently, the exponential trend has also been confirmed for a group of 10 wells in a region northeast of Fairway. Increase in the absolute permeability of coalbeds is a result of matrix shrinkage caused by gas desorption, which becomes a dominant factor on cleat permeability over the effective-stress effect during reservoir production.
A permeability model previously developed by the authors has been revisited in an effort to match the recently published field-permeability data. The Shi and Durucan (S&D) permeability model (2004, 2005a) makes use of a stress permeability relationship reported in the literature for an idealized geometry (matchsticks), in which the permeability varies exponentially with changes in the effective horizontal stress through the use of a constant cleat (pore) compressibility parameter. In this study, a stress-dependent cleat volume compressibility defined by an initial compressibility with a negative exponential decline rate was adopted. By tuning these two parameters, it was possible to achieve a close match to all the field-permeability data by use of a common set of reservoir properties (elastic properties and matrix-shrinkage parameters) that are consistent with the available field and laboratory data in the literature.
The matching of the field-permeability data in these two regions of the San Juan basin in this study has further validated the updated S&D permeability model (now with variable cleat-volume compressibility). It has also provided theoretical support for the observed near-exponential growth behavior of coalbed permeability in a producing reservoir. Furthermore, the model has shed new light on the permeability behavior: (1) The exponential growth occurs when the reservoir pressure is reduced to a level generally below the permeability-recovery pressure (the reservoir pressure at which the initial permeability is recovered); (2) The reservoir permeability in these two regions would remain relatively flat at reservoir pressures above the permeability recovery pressure.
Identification and Characterization of High-Conductive Layers in Waterfloods
Authors: Izgec B.. , Kabir C.S.. S. 
Published: January 2011

Summary
This study expands upon the use of modified-Hall analysis (MHA) to discern the characteristics of a high-permeability channel. Briefly, the modified-Hall plot uses three curves involving improved Hall-integral (H-I) and the two derivatives, analytic and numeric. Ordinarily, the derivative curves overlay on the integral curve during matrix injection, but separate lower when fracturing occurs. This work presents a method to identify and characterize high-conductive layers or channels between injector and producer pairs with the MHA. The distance separating the integral and derivative curves provides the required information to quantify channel properties. A simple analytical solution is presented for transforming the separation distance into channel permeabilitythickness product.
The analytic derivative is based on the radial-flow-pattern assumption and the numeric derivative is correlated to the pressure response. Therefore, a comparison of these two curves reveals clues about the maturity of a waterflood at a given time. Several simulated examples verified the channel-property-estimation algorithm and identified the distinctive derivative signatures for channeling and fracturing situations. This method is also useful for identification of wormhole propagation during sand production in unconsolidated formations.
Advanced Gas Material Balance in Simplified Format
Authors: Moghadam Samane , Jeje Oluyemisi , Mattar Louis 
Published: January 2011

Summary
Material balance has long been used in reservoir engineering practice as a simple yet powerful tool to determine the original gas in place (G). The conventional format of the gas material balance equation is the simple straight line plot of p/Z vs. cumulative gas production (Gp), which can be extrapolated to zero p/Z to obtain G. The graphical simplicity of this method makes it popular. The method was developed for a "volumetric" gas reservoir. It assumes a constant pore volume (PV) of gas and accounts for the energy of gas expansion, but it ignores other sources of energy, such as the effects of formation compressibility, residual fluids expansion and aquifer support. It also does not include other sources of gas storage, such as connected reservoirs or adsorption in coal/shale. In the past, researchers have introduced modified gas material balance equations to account for these other sources of energy. However, the simplicity of the p/Z straight line is lost in the resulting complexity of these equations.
In this paper, a new format of the gas material balance equation is presented, which recaptures the simplicity of the straight line while accounting for all the drive mechanisms. It uses a p/Z** instead of p/Z. The effect of each of the previously mentioned drive mechanisms appears as an effective compressibility term in the new gas material balance equation. Also, the physical meaning of the effective compressibilities are explained and compared with the concept of drive indices. Furthermore, the gas material balance is used to derive a generalized rigorous total compressibility in the presence of all the previously mentioned drive mechanisms, which is important in calculating the pseudotime used in rate transient analysis of production data.
The Influence of Heterogeneity, Wetting, and Viscosity Ratio on Oil Recovery From Vertically Fractured Reservoirs
Authors: Salimi Hamidreza , Bruining Johannes 
Published: January 2011

Summary
We use upscaling through homogenization to predict oil recovery from fractured reservoirs consisting of matrix columns, also called vertically fractured reservoirs (VFRs), for a variety of conditions. The upscaled VFR model overcomes limitations of the dual-porosity model, including the use of a shape factor. The purpose of this paper is to investigate three main physical aspects of multiphase flow in fractured reservoirs: reservoir wettability, viscosity ratio, and heterogeneity in rock/fluid properties. The main characteristic that determines reservoir behavior is the Péclet number that expresses the ratio of the average imbibition time divided by the residence time of the fluids in the fractures. The second characteristic dimensionless number is the gravity number.
Upscaled VFR simulations, aimed at studying the mentioned features, add new insights. First, we discuss the results at low Péclet numbers. For only small gravity numbers, the effect of contact angle, delay time for the nonequilibrium capillary effect, the heterogeneity of the matrix-column size, and the matrix permeability can be ignored without appreciable loss of accuracy. The ultimate oil recovery for mixed-wet VFRs is approximately equal to the Amott index, and the oil production does not depend on the absolute value of the phase viscosity but on viscosity ratio. However, large gravity numbers enhance underriding, aggravated by large contact angles, longer delay times, and higher viscosity ratios. Layering can lead to an improvement or deterioration, depending on the fracture aperture and permeability distribution. At low Péclet numbers, the fractured reservoir behaves very similarly to a conventional reservoir and depends largely on the viscosity ratio and the gravity number. At high Péclet numbers, after water breakthrough, the oil recovery appears to be proportional to the cosine of the contact angle and inversely proportional to the sum of the oil and water viscosity. In addition, the mixed-wetting effect is more pronounced; there are significant influences of delay time (nonequilibrium effects), matrix permeability, matrix-column size, and the column-size distribution on oil recovery. At low gravity numbers and an effective length/thickness ratio larger than 10, the oil recovery is independent of the vertical-fracture-aperture distribution. For the same amount of injected water, the recovery at low Péclet numbers is larger than the recovery at high Péclet numbers.
The Mechanism of Flow in Reservoir Regions Dominated by Gravity Segregation
Authors: Hales Hugh B. , Cook Kari M. 
Published: January 2011

Summary
The flow in regions of oil and gas reservoirs that are dominated by gravity segregation can occur through two different mechanisms. First, all reservoir fluid phases, possibly oil, gas and water, might move through the same pores. One or more phases might move upward while the others move countercurrently downward, in the same pores. If such a mechanism were valid, Darcy's law could be applied uniformly over large areas of the reservoir to provide average-phase velocities, just as if the flows were the result of pressure-induced convection. However, a second mechanism is also possible. The phases might be segregated such that some pores carry the upward flowing phases, while other pores carry downward flows. When this mechanism is valid, Darcy's law applies only locally to the upward or downward regions of flow.
The two mechanisms result in substantially different phase velocities. Simulators, including those available commercially, generally assume the first mechanism (i.e., uniform, countercurrent flow throughout each simulation cell). This paper describes an experimental study in which two-phase flow velocities were measured as the phases moved through a bed of small, uniform glass beads, as the result of gravitational forces only. The resulting velocities were more consistent with those predicted for segregated flows of Mechanism 2 compared with those of the commonly assumed homogeneous flows of Mechanism 1. These results suggest that greater accuracy in reservoir simulation may be achieved by including segregated flow in areas of the reservoir where gravity segregation predominates.
Polycentric Polity: Genuine vs. Spurious Federalism
Authors: Eusepi Giuseppe , Wagner Richard E. 
Published: January 2011

Abstract
Federalism is commonly described in contradictory fashion as involving both competition and decentralization. These descriptions may appear similar on the surface, but they emanate from contradictory analytical orientations. Competition entails a polycentric arrangement of competitors where there is no locus of control over the arrangement. In contrast, decentralization is a monocentric arrangement that involves a locus of control. To treat federalism as a method for decentralizing governments leads to a spurious form of federalism because the object that has been identified is not genuinely a competitively organized system of government. Genuine federalism requires a polycentric arrangement that is organized through openly competitive processes. In contrast, the spurious form of federalism allows hierarchy to trump open competition.
Introduction: Ex Uno Plures. Welfare Without Illusion
Authors: Brennan Geoffrey , Eusepi Giuseppe 
Published: January 2011

Abstract
Two competing visions of federalism have long held sway. The first is centered on the idea of an administrative system of delegation based on a geographic partitioning of the polity. The second view sees federalism as a bottom-up structure in which the larger polity is a construct of the smaller polities of which it is composed. In this edited collection, the object is to use these rival visions of a federal structure as a lens through which to analyze the various interconnections between the welfare state and its financing. Specifically, the claim is that the effects of federalism cannot be fully understood without consideration of the vision of federalism that the participants in their various roles adopt. The works collected in this special issue represent a selection of the papers presented at the conference “Ex Uno Plures. Welfare without Illusion,” held in September 2009 at the Faculty of Economics of Sapienza University of Rome, Italy, organized by the European Center for the Study of Public Choice (ECSPC).
Federalism, Budget Deficits and Public Debt: On the Reform of Germany's Fiscal Constitution
Authors: Feld Lars P. , Baskaran Thushyanthan 
Published: January 2011

Abstract
In 2009, new debt restrictions in the Grundgesetz (the German constitution) and in federal legislation passed both chambers of the German parliament by two-thirds majorities, imposing a more rigid debt regime on federal and Länder (states’) fiscal policies than previous constitutional provisions entailed. In this paper, the new provisions are evaluated against the background of the problems of German fiscal federalism that they are supposed to solve, as well as the possible solutions discussed in constitutional economics. We thereby mainly draw on recent evidence from Switzerland. This reform is an important step to remedy the shortcomings of German fiscal federalism, but we argue that it needs to be complemented by tax autonomy for the German Länder.
Raising vs. Leveling in the Social Organization of Welfare
Authors: Wagner Richard E. 
Published: January 2011

AbstractThis paper contrasts raising and leveling as alternative conceptual frameworks regarding the social organization of welfare. At least since Richard Musgrave’s (1959) tripartite organization of the theory of public finance, most fiscal scholars have treated the redistributive activities of governments as necessarily belonging to the national level of government. More significantly perhaps, that literature has treated the problem of promoting welfare as one of leveling incomes through programs of taxing-and-transferring. In contrast, this paper treats the problem of promoting welfare as one of raising incomes. This alternative formulation leads, in turn, to an alternative orientation toward the relationship between federalism and welfare. In particular, there is good reason to think that genuinely competitive federalism offers a sounder institutional framework for the promotion of raising than can redistribution through a central government, mostly because the knowledge that is required for a program of raising is distributed and incapable of meaningful summarization through aggregation.
Federalism as an Effective Antidote to Terrorism
Authors: Frey Bruno S. 
Published: January 2011

Abstract
Many governments as well as terrorist experts see the use of military and police forces as the only way to effectively counter terrorism. The most effective negative sanctions are considered to be military strikes, aggressive actions (including kidnapping and killing) against individuals known or suspected of being terrorists, or against persons supporting and harboring terrorists. Overt and covert military and paramilitary action is also thought advisable to pre-empt and prevent actions by terrorist groups, as well as against states suspected of hosting or tolerating terrorists. This paper argues that decentralization constitutes a powerful antidote as it strongly reduces the incentives for terrorists to attack and because the expected damage suffered is much smaller than in a centralized society. It moreover strengthens society, as economic, political and social decentralization (or polycentricity) is an essential element of a free and vigorous society. This in turn makes a society less vulnerable to terrorist attacks. Indeed, terrorism has no chance of success against a society that actively guards its fundamental liberal institutions, of which decentralized decision-making forms an essential part.
The Global Effects of Subglobal Climate Policies
Authors: Boehringer Christoph , Fischer Carolyn , Rosendahl Knut Einar 
Published: January 2011

Abstract
Individual countries are in the process of legislating responses to the challenges posed by climate change. The prospect of rising carbon prices raises concerns in these nations about the effects on the competitiveness of their own energy-intensive industries and the potential for carbon leakage, particularly leakage to emerging economies that lack comparable regulation. In response, certain developed countries are proposing controversial trade-related measures and allowance allocation designs to complement their climate policies. Missing from much of the debate on trade-related measures is a broader understanding of how climate policies implemented unilaterally (or subglobally) affect all countries in the global trading system. Arguably, the largest impacts are from the targeted carbon pricing itself, which generates macroeconomic effects, terms-of-trade changes, and shifts in global energy demand and prices; it also changes the relative prices of certain energy-intensive goods. This paper studies how climate policies implemented in certain major economies (the European Union and the United States) affect the global distribution of economic and environmental outcomes and how these outcomes may be altered by complementary policies aimed at addressing carbon leakage.