bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mechanisms for High Displacement Efficiency of Low-Temperature CO2 Floods
Authors: Okuno R.. , Johns R.T.. T. , Sepehrnoori K.. 
Published: July 2011

Summary
CO2 floods at temperatures typically below 120°F can involve complex phase behavior, where a third CO2-rich liquid (L2) phase coexists with the oleic (L1) and gaseous (V) phases. Results of slimtube measurements in the literature show that an oil displacement by CO2 can achieve high displacement efficiency of more than 90% when three hydrocarbon phases coexist during the displacement. However, the mechanism for the high-displacement efficiency is uncertain because the complex interaction of phase behavior with flow during the displacement is not fully understood.
In this paper, we present the first detailed study of three-phase behavior predictions and displacement efficiency for low-temperature CO2 floods. Four-component EOS models are initially used to investigate systematically the effects of pressure, temperature, and oil properties on development of three-phase regions and displacement efficiency. Multicomponent oil displacements by CO2 are then considered. We use a compositional reservoir simulator capable of robust three-phase equilibrium calculations.
Results show that high displacement efficiency of low-temperature CO2 floods is a consequence of both condensing and vaporizing behavior. The L2 phase serves as a buffer between the immiscible V and L1 phases within the three-phase region. Components in the L1 phase first transfer efficiently to the L2 phase near a lower critical endpoint (LCEP). These oil components then transfer to the V phase near an upper critical endpoint (UCEP) at the trailing edge of the three-phase region. The CEPs are defined where two of the three coexisting phases merge in the presence of the other immiscible phase. Unlike two-phase displacements, condensation and vaporization of intermediate components occur simultaneously within the three-phase region. The simultaneous condensing/vaporizing behavior involving the CEPs is also confirmed for simulations of several west Texas oil displacements. Quaternary fluid models can predict qualitatively the complex displacements because four is the minimum number of components to develop CEP behavior in composition space at a fixed temperature and pressure.
Survey of Stranded Gas and Delivered Costs to Europe of Selected Gas Resources
Authors: Attanasi E.D.. D. , Freeman P.A.. A. 
Published: July 2011

SummaryTwo important trends affecting the expected growth of global gas markets are (1) the shift by many industrialized countries from coal-fired electricity generation to the use of natural gas to generate electricity and (2) the industrialization of the heavily populated Asian countries of India and China. This paper surveys discovered gas in stranded conventional gas accumulations and presents estimates of the cost of developing and producing stranded gas in selected countries. Stranded gas is natural gas in discovered or identified fields that is not currently commercially producible for either physical or economic reasons. Published reserves of gas at the global level do not distinguish between volumes of gas in producing fields and volumes in nonproducing fields. Data on stranded gas reported here—that is the volumes, geographical distribution, and size distributions of stranded gas fields at the country and regional level—are based on the examination of individual-field data and represent a significant improvement in information available to industry and government decision makers. Globally, stranded gas is pervasive, but large volumes in large accumulations are concentrated in only a few areas.The cost component of the paper focuses on stranded conventional gas accumulations in Africa and South America that have the potential to augment supplies to Europe. The methods described for the computation of extraction and transport costs are innovative in that they use information on the sizes and geographical distribution of the identified stranded gas fields. The costs are based on industry data specific to the country and geologic basin where the stranded gas is located. Gas supplies to Europe can be increased significantly at competitive costs by the development of stranded gas. Net extraction costs of producing the identified gas depend critically on the natural-gas-liquids (NGLs) content, the prevailing prices of liquids, the size of the gas accumulation, and the deposit's location. The diversity of the distribution of stranded gas is one obstacle to the exercise of market power by the Gas Exporting Countries Forum (GECF).
Modeling Gas-Phase Mass Transfer Between Fracture and Matrix in Naturally Fractured Reservoirs
Authors: Jamili A.. , Willhite G.P.. P. , Green D.W.. W. 
Published: July 2011

Summary
Gas injection in naturally fractured reservoirs maintains the reservoir pressure and increases oil recovery primarily by gravity drainage and to a lesser extent by mass transfer between the flowing gas in the fracture and the porous matrix. Although gravity drainage has been studied extensively, there has been limited research on mass-transfer mechanisms between the gas flowing in the fracture and fluids in the porous matrix.
This paper presents a mathematical model that describes the mass transfer between a gas flowing in a fracture and a matrix block. The model accounts for diffusion and convection mechanisms in both gas and liquid phases in the porous matrix. The injected gas diffuses into the porous matrix through gas and liquid phases, causing the vaporization of oil in the porous matrix, which is transported by convection and diffusion to the gas flowing in the fracture. Compositions of equilibrium phases are computed using the Peng-Robinson EOS.
The mathematical model was validated by comparing calculations to two sets of experimental data reported in the literature (Morel et. al. 1990; Le Romancer et. al. 1994), one involving nitrogen (N2) flow in the fracture and the second with carbon dioxide (CO2) flow. The matrix was a chalk. The resident fluid in the porous matrix was a mixture of methane and pentane. In the N2-diffusion experiment, liquid and vapor phases were initially present, while in the CO2 experiment, the matrix was saturated with liquid-hydrocarbon and water phases.
Calculated results were compared with the experimental data, including recovery of each component, saturation profiles, and pressure gradient between matrix and fracture. Agreement was generally good. The simulation revealed the presence of countercurrent flow inside the block. Diffusion was the main mass-transfer mechanism between matrix and fracture during N2 injection. In the CO2 experiment, diffusion and convection were both important.
Permanent Abandonment of a North Sea Well Using Unconsolidated Well-Plugging Material
Authors: Saasen Arild , Wold Sturla , Ribesen Bjørn Thore , Tran Tu Nhat , Huse Arve , Rygg Vidar , Grannes Ingvar , Svindland Alf 
Published: July 2011

Summary
The traditional plug-and-abandonment (P&A) method of exploration wells in the North Sea is to set a series of cement plugs to isolate the pressurized zones from each other and from surface. This paper describes a North Sea P&A field case. In this case, an alternative method was used with a Bingham-plastic unconsolidated plugging material with high solids concentrations. This alternative method addresses well-integrity issues such as those caused by shrinking of cement or gas migration during setting, fracturing after setting, or long-term degradation by exposure to heat and chemical substances in the well.
The gas-tight well-barrier element described here does not set up after placement and does not shrink. Furthermore, it cannot fracture even when shear forces exceed its strength. When this happens, the material floats and shear forces are reduced below yield strength, causing the plug to reshape. Because this is a purely mechanical process, the transition between solid and fluid phase is repeatedly reversible (in principle, an infinite number of times).
The plug is thermodynamically stable because its sealing property is decided by the solids particle-size distribution (PSD) and bound water only. The closely packed particles and absence of free water mean that the entire column is kept homogeneous and no internal redistribution of particles may occur. Hence, the permanent gas-tight barrier will prevent influx through the wellbore.
In the field case, a successful implementation of the technology was obtained. The field case shows how the fast and efficient placement of the plug contributes to overall cost reduction. The paper explains how the well-barrier element complies with Norwegian requirements for permanent P&A; these requirements also apply to the UK sector (NORSOK D-010 2004; Oil and Gas UK 2009). Operational procedures are also presented in some detail.
Qualifying Seismic as a "Reliable Technology"—An Example of Downdip Water-Contact Location
Authors: Sidle R.E.. E. , Lee W.J.. J. 
Published: July 2011

Summary
The term "reliable technology" was added to the lexicon of oil and gas reserves estimation with the updated regulations published by the US Securities and Exchange Commission in late 2008 (US Securities and Exchange Commission 2008). A previous paper (Sidle and Lee 2010) described an approach to the demonstration that a technology satisfied the criteria of a reliable technology. This paper builds on the use of the scientific method, as described in the previous paper, by examining a real-life example of seismic interpretation to define water contacts downdip of hydrocarbon-column penetrations.
Complex technologies, such as seismic, require careful and detailed calibration and testing to demonstrate the consistency and repeatability needed to qualify as a reliable technology. However, this complexity need not preclude that technology from use as reliable. Proper analysis of the science behind the technology and testing to demonstrate those circumstances that allow reliable conclusions from the technology will permit even a complex technology to be qualified as acceptable.
The example used is from the Gulf of Mexico (GoM) deep water. It gives the results from several turbidite sand reservoirs in multiple fields to demonstrate the conditions under which certain seismic can be shown as reliable. The learnings from these applications allow the development of a "reliability qualification checklist" that defines the conditions under which the seismic data are definitive. Then, it describes the final testing of the "reliable data" to determine when a seismically interpreted water contact is sufficiently conclusive to be reasonably certain.
This paper will provide a useful description of how the qualification of a technology can be planned, tested, and conclusions drawn. It will provide examples of constraints that develop from the theoretical analysis and testing results and show how these constraints can be incorporated into a set of limitations on the application of the technology. While certain elements of the technology are discussed in this paper, it is not the authors’ intent to provide an exhaustive description of the seismic theory and methods used for this example. Rather, the paper will focus on the reliability demonstration process.
Hydrogen Sulfide Absorption Phenomena in Brine/Oil Mixtures
Authors: Zea Luis , Cooper David , Kumar Ranganathan 
Published: July 2011

Summary
Brine and oil absorb hydrogen sulfide (H2S) under pressure in the underground oil reservoir and then undergo a decompression during the extraction process, during which a certain amount of H2S is released from the liquid phase. This paper reports experimental data on how much of the corrosive gas is absorbed into different brine/oil mixtures [0, 33, 66, and 100% water cuts (WCs)]. Different reservoir-simulation scenarios were created at 20 and 70 atm at room temperature. H2S gas concentration was varied as tests were conducted with 50, 100, and 300 ppm in nitrogen. These experiments took place in an autoclave system that simulates the hydrostatic process that occurs inside a reservoir. This paper also reports Henry's law constants for H2S in different WCs. It is found that for all WCs, total pressure plays only a minor role in the absorption phenomena when the initial H2S concentration is increased. In addition, the highest mass-absorption ratios are found at lower H2S concentrations.
Discretization, Simulation, and Swanson's (Inaccurate) Mean
Authors: Bickel J. Eric , Lake Larry W. , Lehman John 
Published: July 2011

SummarySwanson's mean (SM) is heavily used within the oil and gas industry to approximate continuous probability distributions such as the log-normal. In this paper, we document the errors induced by this practice, which, as we show, has no theoretical justification for any distribution other than the normal. In parallel, we review methods to discretize continuous distributions and compare these methods to Monte Carlo (MC) simulation. We demonstrate that the best discretization methods have an accuracy equivalent to that of tens of thousands of MC trials.
CO2 Breakthrough vs. Gas-Processing Facilities: Qualitative Appraisal
Authors: Belhaj Hadi , Abdulwahab Haytham 
Published: July 2011

Summary
This study describes how gas-processing facilities are impacted by injected CO2 returning to surface through production streams, with the goal to improve profitability of the enhanced-oil-recovery (EOR) project by postponing the expenses of handling returning CO2. In the short term, mixing the incremental oil that has a higher CO2 content with the remaining production streams of lower CO2 content will allow the existing gas-processing facilities to accommodate the returning CO2. In the long term, the compression capacity should be increased and acid gas should be enriched with H2S before being fed to sulphur-recovery units. Another alternative is to isolate the impact of CO2 on the existing facilities by using an exclusive separation train, reinjecting the associated gas (or the acid part of it) and sending the sweet part to existing facilities for natural-gas-liquid (NGL) recovery--provided that the capacity is available. Enrichment units can be used to extract H2S from acid gas for sulphur recovery in existing units, provided that the capacity is available, while pure CO2 can be injected. Cryogenic fractionation will be required to separate mixtures of ethane and CO2.
A New Model for Modern Production-Decline Analysis of Gas/Condensate Reservoirs
Authors: Sureshjani M. Heidari , Gerami Shahab 
Published: July 2011

Summary
Modern production-decline analysis is a robust technique for analysis of production data from a well under variable operating conditions. It uses production rates and flowing pressures to provide reliable estimates of recoverable reserves and fluid in place. The mathematics behind this technique is similar to that of pressure-transient theory; however, the focus is different. It deals with long-term variable production data instead of short-term constant-rate transient data.
Using modern decline analysis for two-phase-flow conditions (e.g., gas/condensate reservoirs) is under question because of the single-phase-flow assumption in the development of a "material-balance time" function. This is a time function that converts any decline (e.g., exponential decline) to harmonic decline to account for variable operating conditions. The purpose of this work is to develop a model to use the concepts of modern techniques for analyzing production data of single-porosity gas/condensate reservoirs. For this purpose, the governing flow equation is linearized, using appropriately defined pseudopressure and pseudotime functions. Then, the solution is obtained for constant-well-rate condition. This is followed by employing the superposition theorem to account for variable well pressure/rate conditions, resulting in definition of two-phase material-balance pseudotime. The solution developed here is coupled with an appropriate material-balance equation and used to estimate the average reservoir pressure and original gas in place from analyzing production data. The dependency of relative permeability on capillary number and non-Darcy flow is included in the formulation.
Verification of the proposed method is obtained with the analysis of synthetic production data using a series of fine-grid compositional numerical simulations over a typical range of gas/condensate-reservoir parameters.
Changes in BMI, Duration of Overweight and Obesity, and Glucose Metabolism: 45 Years of Follow-up of a Birth Cohort
Authors: Power Chris , Thomas Claudia 
Published: July 2011

OBJECTIVE
Long-term implications of childhood obesity and BMI change over the life course for risk of type 2 diabetes remain uncertain. The objective was to establish whether there are effects on adult glucose metabolism of 1) sensitive periods of BMI gain or 2) long duration of overweight and obesity.

RESEARCH DESIGN AND METHODS
Participants in the 1958 British birth cohort with child to adult BMI and glycosylated hemoglobin (HbA1c) at 45 years (n = 7,855).

RESULTS
Prevalence of type 2 diabetes or HbA1c ≥7 was 2%. BMI gains in child- and adulthood were associated with higher HbA1c: for every SD of 5-year BMI increase from 0 to 7 years, there was a 75% (95% CI 1.42–2.16) increased risk of HbA1c ≥7, increasing to a 4.7-fold (3.12–7.00) risk for the interval 23–33 years. Associations for BMI gain in adulthood were related to attained BMI but were independent for the longer period birth (or 7 years) to 45 years. Duration of obesity was also associated with HbA1c; compared with the never obese, those with childhood onset had a 23.9-fold risk (13.5–42.1) of HbA1c ≥7%; odds ratios were 16.0 (10.6–24.2) and 2.99 (1.77–5.03), respectively, for young and midadulthood onset. Similar trends by onset age were found in mean HbA1c levels and for onset of overweight. Those with the earliest age of onset had higher BMI and waist circumference at 45 years, which markedly explained the associations for onset age and HbA1c.

CONCLUSIONS
Excessive BMI gain across the life span and earlier onset of overweight/obesity are associated with impaired glucose metabolism, in part through attained adult BMI.
Type 1 Diabetes and Interferon Therapy
Authors: Nakamura Kan , Kawasaki Eiji , Imagawa Akihisa , Awata Takuya , Ikegami Hiroshi , Uchigata Yasuko , Kobayashi Tetsuro , Shimada Akira , Nakanishi Koji , Makino Hideichi , Maruyama Taro , Hanafusa Toshiaki ,   the Research Committee on Type 1 Diabetes of the Japan Diabetes Society
Published: July 2011

OBJECTIVEInterferon therapy can trigger induction of several autoimmune diseases, including type 1 diabetes. To assess the clinical, immunologic, and genetic characteristics of type 1 diabetes induced by interferon therapy, we conducted a nationwide cross-sectional survey.RESEARCH DESIGN AND METHODSClinical characteristics, anti-islet autoantibodies, and HLA-DR typing were examined in 91 patients for whom type 1 diabetes developed during or shortly after interferon therapy.RESULTSMedian age at the onset of type 1 diabetes was 56 (interquartile range 48–63) years and mean ± SD BMI was 20.8 ± 2.7 kg/m2. The time period from the initiation of interferon therapy to type 1 diabetes onset in patients receiving pegylated interferon and ribavirin was significantly shorter than that in patients with nonpegylated interferon single therapy (P &lt; 0.05). Anti-islet autoantibodies were detected in 94.5% of patients at diabetes onset. Type 1 diabetes susceptibility HLA-DRs in the Japanese population, DR4 and DR9, were also associated with interferon treatment–related type 1 diabetes. Furthermore, the prevalence of HLA-DR13 was significantly higher in interferon treatment–related type 1 diabetes than in healthy control subjects (odds ratio 3.80 [95% CI 2.20–7.55]; P &lt; 0.0001) and classical type 1 diabetes (2.15 [1.17–3.93]; P &lt; 0.05).CONCLUSIONSAnti-islet autoantibodies should be investigated before and during interferon therapy to identify subjects at high risk of type 1 diabetes. Stronger antiviral treatment may induce earlier development of type 1 diabetes. Furthermore, patients who develop interferon-induced type 1 diabetes are genetically susceptible.
Clinical Usefulness of Different Lipid Measures for Prediction of Coronary Heart Disease in Type 2 Diabetes
Authors: Eliasson Björn , Cederholm Jan , Eeg-Olofsson Katarina , Svensson Anne-Marie , Zethelius Björn , Gudbjörnsdottir Soffia ,   on behalf of the National Diabetes Register
Published: July 2011

OBJECTIVE
We assessed the association between different blood lipid measures and risk of fatal/nonfatal coronary heart disease (CHD).

RESEARCH DESIGN AND METHODS
We conducted an observational study of patients with type 2 diabetes from the Swedish National Diabetes Register. Baseline LDL cholesterol, non-HDL cholesterol, ratio of non-HDL to HDL cholesterol (non-HDL:HDL), and ratio of triacylglycerol to HDL cholesterol (TG:HDL) was measured in 18,673 patients aged 30–70 years, followed for a mean of 4.8 years from 2003 to 2007.

RESULTS
Hazard ratios (HRs) for CHD per 1-SD increment in lipid measures were 1.23 with non-HDL:HDL, 1.20 with non-HDL cholesterol, 1.17 with LDL cholesterol, and 1.15 with TG:HDL (all P &lt; 0.001 when adjusted for clinical characteristics and nonlipid risk factors). The best global model fit was found with non-HDL:HDL. When patients within the lowest tertile of a lipid measure were compared with those with all lipid measures within the highest tertile, the adjusted HR for CHD was 0.62 with non-HDL:HDL &lt;3.5 mmol/L, 0.65 with non-HDL cholesterol &lt;3.3 mmol/L, and 0.70 with LDL cholesterol &lt;2.5 mmol/L (all P &lt; 0.001). The lowest tertile of LDL and non-HDL cholesterol corresponded with treatment targets according to U.S. and European guidelines. HRs for CHD were 0.52, 0.62, and 0.66 with the lowest deciles of non-HDL:HDL, non-HDL cholesterol, and LDL cholesterol ≤1.8 mmol/L (all P &lt; 0.001). Mean TG:HDL was considerably lower in patients within the lowest tertile of non-HDL:HDL, 0.82 ± 0.47, than in those within the lowest tertile of LDL cholesterol (&lt;2.5 mmol/L), 1.49 ± 1.03.

CONCLUSIONS
Non-HDL:HDL had a stronger effect on CHD risk than LDL cholesterol, and low TG:HDL values were more often seen within the lowest non-HDL:HDL tertile than within the lowest LDL cholesterol tertile. LDL cholesterol was not the best predictor of CHD risk in type 2 diabetes.