bluuebunny/crossref_metadata_2025 huggingface dataset:
Prevalence and Covariates of Severe Under Nutrition among Tribal and Non-Tribal Preschoolers from Ahmednagar District, Maharashtra, India
Authors: Nagargoje Kondiram M. , Waghray Kavita
Published: April 2016

The study aimed to assess the level of under nutrition among children of 0-6 year age as influenced by their communities, gender, age group, caste and socio economic status of parents. All 14 Tahasils of Ahmednagar District of Maharashtra State, India were considered for the study. Preschoolers of 0-6 year age with<Median-3SD weight for age by WHO standards and were in grade III and IV level of under nutrition by IAP classifications were the participants. The higher proportion of girls and particularly children from tribal and socially deprived castes viz. Scheduled Tribes (ST), Scheduled Caste (SC) and Nomadic Tribes (NT) were found severely under nourished. More children of age group 12-35 months were found to be severely under nourished. The lower and middle socio economic status and severe under nutrition exhibited strong association.
Posterior Tibial Slope: Effect on, and Interaction with, Knee Kinematics
Authors: Ahmad Riaz , Patel Amit , Mandalia Vipul , Toms Andrew
Published: April 2016

➢ Posterior tibial slope should be measured on a long lateral or an expanded lateral radiograph.

➢ Posterior tibial slope decreases the quadriceps force needed to exert knee extension moment.

➢ Posterior tibial slope parallel to natural tibial slope minimizes tibial component subsidence.

➢ Posterior tibial slope should be increased rather than releasing the posterior cruciate ligament (PCL) to restore normal kinematics in a knee that is tight in flexion.

➢ Larger tibial slope widens the flexion gap in posterior stabilized total knee replacement.
The Impact of Thermodynamic Hydrate Inhibitors (MEG and Methanol) on Scale Dissolver Performance
Authors: Williams Helen , Herrmann Timo , Jordan Myles , McCallum Catriona
Published: April 2016

The use of dissolvers to remove scale deposits formed during water production is a relatively common practice for both onshore and offshore hydrocarbon extraction. Acids are commonly used for carbonate deposits, whilst chelant chemistries are deployed for dissolution of sulphate scales. The development of subsea fields presents challenges of deployment of such treatments down flow/test lines, with accurate volumes and movement of solids. In addition, there is the risk of hydrate formation during shut-in of the production wells, which generally means that thermodynamic hydrate inhibitors are applied ahead of the dissolver pill and possibly during the reflow of the spent dissolver pill while the well is heating up to normal operating conditions.

This study investigates the impact of two common thermodynamic hydrate inhibitors (methanol and monoethylene glycol or MEG) on the performance of two dissolver chemistries, one organic acid and one chelant. Tests were conducted at 50 °C with no methanol or MEG present, when methanol or MEG was present in the dissolver solution prior to reaction with scale (applied ahead of a dissolver pill), and finally with methanol or MEG applied to the reacted dissolver (simulating thermodynamic hydrate protection during reflow of the well).

The results from the study show an unexpected and significant reduction in dissolver performance with methanol or MEG added to the dissolver solution before, and also after reaction with the scale samples. When the hydrate inhibitor was added to the mix at the beginning of the test, the amount of scale dissolved was reduced in every test, with methanol having the biggest effect. The results were similar when the solvent was added to the reacting dissolver when the test was underway. Distinctive differences between MEG and methanol on the performance of organic acid dissolver were observed. Furthermore, different trends in dissolution performance became apparent with the chelant dissolver.

The findings from this study clearly show the need for careful design of subsea dissolver applications to prevent reduced chemical performance in the presence of thermodynamic hydrate inhibitors such as methanol and MEG.
Iron Sulfide Scale Control: A Novel Chemical for Growth Inhibition and Dispersion
Authors: Bhandari N. , Kan A. T. , Ruan G. G. , Liu Y. , Zhang F. , Yan F. , Alsaiari H. A. , Zhang Z. , Dai Z. , Lu Y. , Deng G. , Tomson M. B.
Published: April 2016

Formation of iron sulfide scale has been a serious flow assurance problem in sour-gas wells and other similar production scenarios. Compared to carbonate and sulfate scales, iron sulfide (FeS) is difficult to inhibit and various risks are associated with chemical removal. Hydrochloric acid and acetic acid are most common chemicals for sulfides dissolution but severe damage to the completion metallurgy, generation of H2S byproduct and its potential toxicity and possibility of re-precipitation of FeS limit its applicability. Other commercial dissolvers, iron chelators, biocides as well as dispersants have been reported, however, efficacy of these chemicals preventing iron sulfide scaling is poor and often uneconomically high concentrations are required. Despite its huge industrial importance and interest, an efficient chemical control of iron sulfide scale formation in oil and gas production is still an elusive goal.  This study seeks to identify chemical compound(s) to inhibit iron sulfide scale formation.

In order to identify the effective chemical treatment of iron sulfide scale, a strictly anoxic static experimental setup was designed and various chemicals of different functional groups as well as a range of molecular weights were evaluated. Our laboratory studies indicate that a polymeric compound containing amide functionality showed a promising effect by preventing of iron sulfide scale deposition at threshold quantities. Specifically, the polymer did not prevent the formation of the iron sulfide particles; however, it significantly influenced the growth and aggregation of the iron sulfide particles. In addition, the polymer kept the particles well dispersed for an extended period and prevented the formation of iron sulfide pads at the water-oil interface. The effect of temperature (up to 90 °C), pH, TDS on polymer efficiency on iron sulfide scale control as well as calcium tolerance were investigated and results indicate that the performance is not significantly influenced. Using various analytical techniques, underlying principle of growth inhibition and dispersion properties has been identified. It is believed that this polymer will provide a novel chemistry of controlling the metal-sulfide scale.
Effect of Hydrodynamic Pressure on Mineral Precipitation Kinetics and Scaling Risk at HPHT
Authors: Bhandari N. , Kan A. T. , Dai Z. , Zhang F. , Yan F. , Ruan G. G. , Alsaiari H. A. , Zhang Z. , Liu Y. , Lu Y. , Deng G. , Tomson M. B.
Published: April 2016

Sulfate minerals (barite, anhydrite and celestite) can be of technological hindrance as a result of scale formation especially at those productions where sea water injection involves. Situation could become even more challenging when producing from high-pressure/high-temperature (HP/HT) wells since it demands the highest-performance equipment's and accurate understanding of brine chemistries. Because of the lack of relevant experimental data, prediction of mineral scaling risk is generally being made assuming that there is no additional kinetic effect of the pressure even at ultra-high pressure level. Therefore, this study seeks to investigate whether there is additional risk involved due to the kinetic effect of the pressure. Just as there is a kinetic activation energy, E‡, we have measured a corresponding activation volume, V‡. Specifically, it aims to experimentally determine the magnitude of the effect of the pressure on sulfate mineral scaling kinetics at deep-water production environment.

To accomplish the goal, a flow-through apparatus has been developed to perform precipitation reaction of barite, anhydrite and celestite at range of pressures (15- 15,000 psia), temperature (up to 2000C), and at various TDS levels. Mineral nucleation (precipitation) kinetics as a function of the pressure was investigated under similar thermodynamic driving force (supersaturation level). Based on the experimental data, a robust semi-empirical barite nucleation model that correlates the precipitation kinetics (induction time) to T, P, SI was developed. The nucleation model is used to estimate the barite precipitation kinetics using simulated field conditions with and without including the kinetic effect of the pressure. Our results indicate that these sulfate mineral nucleation kinetic is a strong function of applied pressure. In fact, the actual mineral nucleation time at elevated pressure (e.g. 15,000 psia) could be more than two orders of magnitude faster than expected when kinetic effect of the pressure is neglected. We believe that our findings could potentially provide some insights to discrepancies between our prediction and field observations.
Prediction and Experimental Determination of the Solubility of Exotic Scales at High Temperatures - Zinc Sulfide
Authors: Figueroa D. C. , Fosbøl Philip Loldrup , Thomsen Kaj
Published: April 2016

The presence of "exotic" scale such as Zinc Sulfide (ZnS), Lead Sulfide (PbS) and Iron Sulfide (FeS) in HP/HT reservoirs has been identified. "Exotic" scale materials come as a new challenge in HP/HT reservoirs. This has led to the development of more advanced tools to predict their behavior at extreme conditions. The aim of this work is to include ZnS into the group of scale materials that can be modeled with the Extended UNIQUAC model.

Solubility data for ZnS are scarce in the open literature. In order to improve the available data, we study the experimental behavior of ZnS solubility at high temperatures. The determination of the solubility of ZnS is carried out at temperatures up to 250°C. Zinc sulfide (99.99%) and ultra-pure water are placed in a vial in a reduced oxygen atmosphere. The sample is placed in a controlled bath and stirred until equilibrium is attained. The suspension is filtered at the same process temperature and diluted immediately. Afterwards the aqueous solution is analyzed using Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) as analytical technique. The concentrations of Zn2+ and S2− ions are analyzed. The experimental data are used for parameter estimation in the Extended UNIQUAC model presented by Villafafila et al. (2005); (2006).

The solid-liquid phase equilibria of the system is represented using the Extended UNIQUAC model. This model is chosen due to its versatility and fewer number of parameters (two parameters per species plus two parameters per species pair) to be estimated compared to other models (Pitzer's model). It is observed that ZnS solubility increases with increasing the temperature. This temperature dependency is very well represented by the Extended UNIQUAC model. The model is capable of predicting experimental data within the experimental error.

The agreement between experimental data and the Extended UNIQUAC model shows that this thermodynamic model is a promising tool capable of determining the occurrence of ZnS scaling in HP/HT reservoirs. This methodology can be extended to other scaling materials (PbS, FeS), making the Extended UNIQUAC model a leading model in predicting scaling in HP/HT reservoirs.
Pioneering a New Method to Prevent Scale in Deep Water, High Pressure Reservoirs - A Gulf of Mexico Case Study
Authors: Hebert Jeff , Leasure Josh
Published: April 2016

Production of hydrocarbons in deep water reservoirs involves the economical flow of hydrocarbons from the reservoir to the point of sale. One important consideration is effectively preventing / handling solid deposits which can be both organic (i.e. paraffin, asphaltenes) and inorganic (i.e. calcite, barite, halite) in nature. These deposits can cause catastrophic blockage in pipelines, subsea equipment and impair fracture conductivity and well performance. To prevent deposition and lost production inhibitor chemicals are typically delivered downhole via tubulars, injected at points along flow lines and risers and as an additive to fracturing fluids. Installing and maintaining such injection systems in these very challenging environments can be expensive to the operator of such facilities.

A new delivery system has been developed which utilizes an infused and encapsulated ultra-high strength porous proppant (UHSPP). The stresses of these deep, high pressure reservoirs requires proppant that can resist closures up to 20,000 psi and previous attempts of using solid inhibitors in these environments have typically sacrificed conductivity. The use of this UHSPP does not negatively impact conductivity and allows for delivery of inhibitors in previously unreachable areas. The delivery system allows inhibitor chemicals to be released at a slow, controlled rate when the proppant comes in contact with produced fluids and results in a highly efficient, reservoir based chemical delivery system. Typical treatments are designed to last for years of production.

This paper will present a case study of the use of this new technology in owery tertiary wells in the Gulf of Mexico. These wells have been treated with an inorganic scale inhibitor using a multi-functional UHSPP. This paper will also describe how substrate type and pore structure can be engineered to maintain conductivity at very high closure stresses. It will also show how semi-permeable membranes can be tailored to specifically control the release of these inhibitors upon contact with production fluids.

This paper will prove useful for all completion, production and facility engineers engaged in offshore operations, and can also be adapted similarly to onshore wells. The cost savings from utilizing a UHSPP delivered chemical system can provide a significant reduction in operating expenses.
Scale Squeeze Placement Options in Subsea Multi-Lateral Horizontal Wells Completed With Sliding Sleeve Technology
Authors: Jordan Myles , Ishkov Oleg , Vazquez Oscar , Mackay Eric
Published: April 2016

The deployment of scale squeeze treatments in subsea horizontal wells has always presented a challenge in terms of understanding the location of injected fluids vs the location of the produced water where scale formation will occur. Over the years software packages such as Eclipse has been able to provide valuable information on the possible placement options for such wells when production logging tool (PLT) data have not been available. The development of multi-lateral drilling/completion technology has further complicated the placement challenges in such wells.

In this paper Eclipse simulation data has been linked to SQUEEZE designs software for two subsea production wells completed with multi laterals and sliding sleeves to allow selective placement of the squeeze treatment. The objective of the study was to evaluate the options of bullhead deployment in terms of both laterals being open during the squeeze vs two squeeze stages being sized and selectively placed into each lateral again via bullhead deployment, but this time using the sliding sleeve technology to divert the chemical.

Information on cross flow issues, the pump rates required to allow effective placement are presented, along with the differences in chemical volumes, pump time and soak times required for the two potential treatment options. The finding from this study show the clear advantages in terms of treatment volumes, reduced clean up time and extended treatment life (reduced intervention frequency) of bullhead deployment of two squeeze steps, one to each lateral, achieved by utilizing the sliding sleeve technology in these two production wells.
Study of Thermal Stability of Scale Inhibitors and its Impact on Processing Plants
Authors: Rosa Katia Regina , Bezerra Maria Carmen , Fontes Rosane Alves , Ponzio Eduardo Ariel , Rocha Anderson Araújo
Published: April 2016

Petroleum, which is one of the most complex mixtures existing in nature, is equilibrated and coexists with the aqueous phase at reservoir conditions. However, depending on the oil viscosity, strong emulsions may be formed due to the high shear imposed by the production process. As a consequence higher temperatures conditions are necessary for the oil separation treatment. Therefore it is important to assure that scale inhibitors are thermally stable and able to act in what are considered extreme temperatures such as the ones used in heat exchangers, for example 16 °C. This work aimed to evaluate the influence of temperature in the scale inhibition activity for different active materials of chemical inhibitors, such as: Nitrilotris (methylene) tri phosphonic acid (NTP), Diethylenetriamine penta (methylphosphonic acid) (DETPMP), and polyvinyl sulphonate (PVS). Aqueous inhibitor solutions were aged in the temperature conditions between 60 to 160 °C for different times (6, 12 and 24 hours). Raman spectroscopy, NMR (31P, 1H and 13C) and FT-MS techniques were used to characterize chemical species from aged and original inhibitor solutions. Different from previous works, these techniques allow identification of some degradations products. Additionally, dynamic performance tests were conducted to evaluate scale inhibitor performance of the solutions. Results of the chemical characterization of the original and thermally aged PVS showed no compositional differences. Dynamic testing for barium sulphate scale showed that minimum effective concentrations remained constant in all assays. However, for the NTP and DETPMP products, at the highest temperature (160 °C, after 24 hours of testing) some degradation products were identified, such as methyl phosphonic acid, and especially, amino methyl phosphonic acid. As a consequence of the structural breakdown of the phosphonate molecules, confirmed by chemical analysis using FT-MS and NMR, the efficiency of inhibition of barium sulphate scale was reduced. The paper presents a methodology to evaluate and understand the behavior of different chemical inhibitors for extreme temperature conditions and highlights the demand for new stable molecules for high temperatures.
Estimation of Transport Diffusivity of Natural Gas in Organic Matter Using Molecular Dynamics Simulation
Authors: He Shuai , Ning Yang , Chen Tianluo , Liu Honglin , Wang Hongyan , Qin Guan
Published: April 2016

Due to the uncertainty in shale reservoir simulation, increasing attention has been drawn to the investigation of nano-scale transport behavior in heterogeneous shale rocks. Molecular dynamics simulation has become a widely-used simulation technique to investigate molecular behaviors at nanoscale. In this paper, we combined one of the state-of-art pore characterization techniques with molecular dynamics simulation to study the natural gas transport behavior in complex nano-pore networks in organic matter. Representative kerogen molecule is selected based on thermal maturity and the origin. Methane molecule is chosen to represent natural gas. Equilibrium molecular dynamic simulations have been performed to construct kerogen clusters and the structural properties of the organic matter have been studied. As a building block, the amorphous kerogen clusters were inserted into the digital rock obtained from focused ion beam scanning electron microscopy (FIB-SEM). Then, non-equilibrium molecular dynamics simulations were performed to study the transport behavior of natural gas in the reconstructed nano-scale digital rock. The transport diffusivity coefficients were thus determined by following the Fick's first-order diffusion equation. The proposed method provides a new insight into the understanding of nano-scale transport behavior of natural gas in shales, which is crucial to the prediction of long-term production performance and reserve estimation in larger-scale reservoir simulation.
Stability Analysis and Equilibrium Considerations in Tight Formations
Authors: Sherafati Marjan , Jessen Kristian
Published: April 2016

Despite the large potential of unconventional resources, many unknowns still exist regarding the physics controlling the extraction processes in these settings. These include accurate representation of phase equilibrium in tight formations and effective implementation of relevant models in simulation tools. In this work, we analyze the numerical aspects of including capillarity phenomena in VLE calculations in an effort to arrive at robust and efficient algorithms for stability analysis that can be used in compositional modeling/simulation of unconventional reservoirs.

When a fluid is confined in pore spaces of nanometer size, significant interfacial curvatures may occur that can result in large capillary pressures between the liquid and vapor phases: The pressure difference between the two phases will likely affect the vapor-liquid equilibrium state. Previous efforts have shown that this effect is negligible for conventional reservoirs (with pores in the micron range) and current commercial reservoir simulators ignore the effect of capillary pressure in the VLE calculations. However, experimental and modeling efforts have shown that ignoring capillary pressure in the VLE calculations will not be a valid approximation for unconventional (tight) reservoirs.

In this work, we specifically look at the effects of including capillary pressure in stability analysis. While the equality of chemical potentials is a necessary condition for equilibrium, it is not a sufficient one. A sufficient condition for equilibrium is the minimization of Gibbs energy, and the latter can be tested using the tangent plane distance (TPD) criteria. We show that stability analysis testing based on the TPD criteria remains valid for systems with large capillary pressures and propose effective/robust algorithms for stability testing. The proposed algorithms are tested for multicomponent reservoir fluid systems over a range of relevant T, P and pore radii.
Capillary Pressure Effect on Hydrocarbon Phase Behavior in Unconventional Reservoirs
Authors: Zhang Yuan , Lashgari Hamid R. , Di Yuan , Sepehrnoori Kamy
Published: April 2016

Small pore sizes on the order of nanometers in the shale gas and tight oil reservoir formations can lead to a large capillary pressure. The presence of capillary pressure significantly affects both the thermodynamic behavior of fluid mixtures and the fluid flow process. Although there have been some attempts to study the effect of capillary pressure on phase behavior, it has not been clearly understood in the application considering multiple components in tight oil reservoirs. In this work, we present a methodology to calculate the phase behavior of CO2/hydrocarbon systems in the presence of capillary pressure. We modify the Peng-Robinson equation of state considering inequalities of hydrocarbon liquid and vapor pressures. The criterion of Gibbs free energy minimization and Rachford-Rice flash calculation are applied in the phase equilibrium calculation. The Young-Laplace equation is utilized to calculate capillary pressure. The Newton-Raphson method is used to solve the nonlinear phase equilibrium equations. We validate the methodology against two experimental measurements and a published numerical model. Subsequently, binary mixture and one typical fluid from the Bakken Formation are used to study the influence of capillarity in the unconventional reservoir. The simulation results indicate that capillary pressure plays an important role in the phase equilibrium calculation when pore size is less than 50 nm. Additionally, the bubble-point pressure of Bakken oil reduces nearby 500 psi when the nano-pore size is 10 nm. The developed method can address the thermodynamics governing unconventional reservoirs and provide better understanding of the phase behavior of CO2/hydrocarbon systems in the case of CO2 injection into unconventional reservoirs.
Rock Characterization in Unconventional Reservoirs: A Comparative Study of Bakken, Eagle Ford, and Niobrara Formations
Authors: Cho Younki , Eker Erdinc , Uzun Ilkay , Yin Xiaolong , Kazemi Hossein
Published: April 2016

Liquid-rich shale reservoirs contribute immensely to the United States oil and gas production. Because Bakken, Lower Eagle Ford, and Niobrara formations have different mineralogy, pore structure, organic content, and fluid compositions, it is critical to differentiate the unique characteristics of each formation for field development and oil and gas production. The latter information is also useful in well stimulation design and hydraulic fracturing.

This paper presents an experimental study of mineralogy, pore-size distribution, pore geometry, and spatial correlation between minerals and pores to identify the effect of micro-scale properties on flow behavior. Porosity and permeability of several core samples from the Middle Bakken, Lower Eagle Ford, and Niobrara formations were studied and the results, using mercury injection capillary pressure (MICP), X-Ray diffraction (XRD), and scanning electron microscopy (SEM), were shown. Finally, a workflow that estimates cementation factor combining the results obtained from MICP measurements and GRI crushed core analysis will be presented.
A Practical and Rigorous Approach for Production Data Analysis in Unconventional Wells
Authors: Holy R. W. , Ozkan E.
Published: April 2016

A new approach for production data analysis in unconventional reservoirs is presented. Unlike the existing decline-curve analysis methods, this approach is not empirical and it is theoretically rigorous. The basis of the approach is an anomalous diffusion model for the performance of fractured horizontal wells surrounded by a stimulated reservoir volume. In the anomalous diffusion model, instead of Darcy's Law, a more general constitutional relation is used to incorporate the non-local and hereditary nature of flow in highly heterogeneous nanoporous media. The sub- or super-diffusive state of flow can be deduced from the slope of the straight line on the log-log plot of rate vs. time. Nonnecessity of a detailed description of the intrinsic properties and spatial distribution of matrix and fracture constitutes the practical advantage of the model. The reduced number of parameters can be conveniently estimated from production data and used in the anomalous diffusion model to predict future production. In this paper, a one-dimensional numerical model is implemented and applied to two Barnett shale gas wells and compared to common empirical models. It is shown that, even with limited completion, reservoir, and production data, the anomalous diffusion model has the potential to capture the production characteristics. Moreover, the model can be used to run sensitivities on actual system variables such as hydraulic fracture length, height and spacing, as well as to account for changing operating conditions.
Hydraulic Fracturing Placement Issues on Horizontal Wells in the Mancos Shale, San Juan Basin: Case Study of Possible Causes, Solutions, and Results
Authors: McCarthy Caitlin , Garcia Mariano
Published: April 2016

The Mancos shale in the San Juan basin can present challenging conditions when hydraulic fracturing treatments are performed in horizontal wells. Some of the issues while completing a well in the Mancos can be caused by overall geomechanics and reservoir properties; for example, high horizontal stress anisotropy and the presence of discontinuities, such as microfractures and lamination. This paper presents three case studies in which hydraulic fracturing placement issues were explored.

Normally, the interactions of geomechanics and reservoir properties cause high treating pressures or premature screenouts, as presented in previous publications. Ramurthy et al. (2009a, 2009b) and Potocki (2012) explain how and why properties, such as process zone stress (PZS), pressure-dependent leakoff (PDL), and geomechanics, can affect the hydraulic fracturing conditions and production results. Depending on how the well is completed, these challenging conditions can be either enhanced or minimized. When the reservoir and geomechanics are not taken into consideration in the completion design of the well, issues can occur during the hydraulic fracturing of the formation.

Issues including screenouts, pressure outs, and high pressure while trying to initiate the fracture can lead to the formation not allowing the placement of the designed treatment, improper stimulation of the reservoir, excessive completion costs, and more commonly than not, poor production. This paper presents three case studies. In all three studies, similar reservoir characteristics and geomechanical conditions occur, which pose challenging obstacles for both completion and production. The challenges were each addressed in different ways, resulting in different outcomes. In one case, no action was taken to mitigate these obstacles. In the second case, the area was studied using analysis service data, treatment data, and public information. This knowledge was applied to assist in the completion of the treatment without issues. In a more recent case, in a well with similar conditions as the two previous studies, only a portion of the recommendations were applied, with mixed results.

This paper presents the knowledge gained from the three case studies conducted in the Mancos shale, San Juan basin. General suggestions are presented when similar conditions are encountered while completing a well.
Pore-Scale Permeability Calculation Using CFD and DSMC Techniques
Authors: Mohammadmoradi Peyman , Kantzas Apostolos
Published: April 2016

Numerical experiments are performed to evaluate the capability and examine the computational costs and tradeoffs of numerical and analytical approaches for apparent gas permeability calculation. Considering the dominancy of capillary force in pore level studies, two-phase distribution maps are constructed within micro and nano-scale scale media using a quasi-static technique. The distribution profile of the non-wetting phase is then extracted to predict the effective permeability and analyze the effect of water saturation. To investigate the effect of gas slippage on the accuracy of the results, both Computational Fluid Dynamics (CFD) and Direct Simulation Monte Carlo (DSMC) techniques are applied in a wide gas pressure range. The results reveal that the continuum theory is valid for a specific pore size and gas pressure range and its accuracy is strongly dependent on the Knudsen number value. DSMC simulation case studies demonstrate that in case of proper medium characterization, a tuned Klinkenberg correlation is capable of providing satisfying predictions within both slippage and transition flow regimes.
Modeling PVT Behavior of Gas-Condensate System Under Pore Confinement Effects: Implications for Rate-Transient Analysis of Gas-Condensate Shale Plays
Authors: Haghshenas B. , Qanbari F. , Clarkson C. R. , Chen S. N
Published: April 2016

Rate-transient analysis (RTA) is a robust technique for evaluating reservoir/stimulation properties and for forecasting production from shale reservoirs. However, knowledge of fluid storage and flow mechanisms, and controlling rock and fluid parameters, is critical for obtaining meaningful information from RTA.

It is common practice to use PVT data measured in laboratories (i.e. bulk fluid properties) for reservoir modeling and production data analysis purposes. These measurement techniques were developed for conventional reservoirs and cannot explain some of the anomalous fluid production behaviors observed for shale gas-condensate wells, such as long-term constant gas/oil ratio (GOR) trends. One explanation for this behavior is that the PVT properties of fluids are affected by confinement in nano-scale pores, and hence deviate from bulk fluid properties.

In order to study the effects of pore confinement on fluid properties in shales, the simplified local density (SLD) model is used. The SLD model can be used to estimate fluid density gradients from pore wall to pore center, and therefore explicitly considers pore geometry in adsorption modeling. This model can also be used to adjust the confined fluid critical properties, phase envelope and viscosity. Significant shifts in phase envelope and fluid properties due to pore confinement are observed in this work. Importantly, the corrected equation-of-state predicts a later onset for condensate dropout in shale reservoirs than for bulk systems. The SLD model is also used to estimate adsorbed layer thickness, which in turn is used to modify flow calculations.

The corrections for fluid properties, adsorbed layer thickness and non-Darcy flow are then analytically incorporated into transient linear flow analysis of nanoporous shale gas-condensate wells. Analysis of simulated cases using the "corrected" (for pore confinement effects) and "uncorrected" RTA is performed to quantify errors associated with the latter.

This study demonstrates that failure to account for pore confinement effects on fluid properties and fluid flow results in errors in linear flow parameter estimation using RTA, but the error depends on the fluid composition, pore size, permeability and pressure. The effects of pore confinement should therefore be considered for proper evaluation of shale gas-condensate reservoirs using analytical or numerical methods.
Simultaneous Estimation of Intrinsic Permeability, Effective Porosity, PoreVolume Compressibility, and Klinkenberg-Slip Factor of Ultra-Tight Rock Samples Based on Laboratory Pressure-Step-Decay Method
Authors: Dadmohammadi Y. , Misra S. , Sondergeld C. H. , Rai C. S.
Published: April 2016

Conventional laboratory characterization of ultra-tight reservoir rock samples involves separate laboratory measurements on different core plugs or on crushed rock samples. Heterogeneity and anisotropy of ultra-tight reservoir samples adversely influence the laboratory correlation among various measured and estimated petrophysical properties.

We apply an inversion algorithm to simultaneously estimate the intrinsic permeability, effective porosity at ambient condition, pore-volume compressibility, and Klinkenberg-slip factor of an ultra-tight pyrophyllite sample from a single laboratory-based pressure-step-decay measurement. In doing so, we circumvent the effects of heterogeneity and account for the pore-pressure dependency of apparent permeability and effective porosity. Moreover, the time and resource requirements are drastically reduced in comparison to those required when performing multiple experiments that separately estimate the aforementioned petrophysical properties.

The inversion algorithm is valid for nitrogen injection pressure in the range of 50 to 500 psi. The algorithm assumes ideal-gas behavior of the injected nitrogen, 1D isothermal laminar gas flow, homogeneity of the core, pressure-independent gas viscosity, inverse-pressure dependence of the apparent permeability, pressure-independent Klinkenberg-slip factor, non-negligible pore-volume compressibility, pressure-dependent effective porosity, negligible inertial effects, negligibly small pressure gradients, and time-invariant confining pressure.

Estimated apparent permeability and effective porosity of the pyrophyllite samples exhibit strong pore- pressure dependence; consequently, both the properties vary substantially along the sample length during the pressure-step-decay measurement. On an average, the effective porosity of the pyrophyllite samples increased by 100% and the apparent permeability decreased by 75% when the pore pressure increased from 50 psi to 500 psi during the measurement. The average values ki, ϕ0, Cp, and b of the nine pyrophyllite samples were estimated to be 40 nd, 0.03, 2×10−3 psi−1, and 100 psi, respectively.
Optimization of Chock Valves for Fracture Clean-up in Tight Gas Condensate Reservoirs
Authors: Zhang Kai , Liu Qingquan , Wang Kun , Jing Gary , Zhang Shihan , Zhan Jie , Wu Keliu , Chen Shengnan , Chen Zhangxin
Published: April 2016

Hydraulic fracturing is a vital technique to unlock tight gas condensate reservoirs. The efficiency of clean-up in tight gas condensate reservoirs has a tremendous effect on well delivery. During hydraulic fracturing flowback operations, only part of fracturing fluids flows back to the surface, resulting in discrepancies between the expected fracture length and the effective production fracture length. A reasonable choke size during fracture clean-up can help to maximize the fracture conductivity.

In order to get a maximum amount of fracturing fluids flowing back to the surface and a least amount of proppants flowing back, optimization of a chock valve in operations is investigated. Furthermore, effects of a proppant size and well types including vertical and horizontal wells on chock valve adjustments are presented.

A chock is adjusted by gradually increasing its diameter as fractures start to close. In addition, the chock size needs to be bigger in a horizontal well than that in a vertical well under the same conditions. If the fracture width close to a proppant size, the chock size will be bigger as the proppant diameter increases; if the fracture width is much larger than the diameter of the proppants, the chock size will be larger with a larger diameter of proppants prior to fracture closure. However, the optimum chock size will be smaller with a larger size of proppants after fracture closure.
A New Approach for Permeability Prediction With NMR Measurements in Tight Formations
Authors: Di Jianwei , Jensen Jerry L.
Published: April 2016

Prediction of extremely low permeability in tight reservoirs poses major challenges with traditional methods. Several studies have proposed nuclear magnetic resonance (NMR) permeability predictors, but these often give large errors when applied in tight formations. In this report, we describe a new method with NMR well-log measurements that decomposes the T2 spectrum into, at most, three Gaussian components. On the basis of parameters from the decomposition, we build a pore-size-based lithofacies model to predict whole-core horizontal permeability. With these parameters, we also modify the empirical Timur-Coates equation (TIM) to predict permeability.

The NMR decomposition allows us to predict proportions of shale and silt. Applied to the tight Cardium formation, the parameters correlate strongly with core image and X-Ray-diffraction (XRD) results. In addition to Cardium data, we apply our approach to published data sets with good results, showing that the model gives accurate lithofacies-proportion estimates.

To calibrate the model, Cardium probe permeameter data are used to identify facies permeabilities. Arithmetic-averaged permeability with the NMR-based model was calculated to compare with whole-core horizontal permeability. Monte Carlo analysis confirms the agreement between the model and core-permeability values. Our model provides a “bridge” to relate permeability between the probe scale (<1 cm laminations) and core size (>15 cm thin beds).

Without the NMR well-log decomposition, Cardium TIM permeability predictions are in error by more than one order of magnitude in most intervals. The major challenge with the TIM model is obtaining an accurate T2 cutoff value. Compared with core-measured bound-water saturations, the default 33 ms value is too large for our tight samples. Our NMR decomposition, however, shows good correlation with measured bound-water saturations. With several core samples and NMR parameters, we modified the TIM model and found that it provides very good permeability predictions.
Carotid Intima-Media Thickness and Incident ESRD: The Atherosclerosis Risk in Communities (ARIC) Study
Authors: Pang Yuanjie , Sang Yingying , Ballew Shoshana H. , Grams Morgan E. , Heiss Gerardo , Coresh Josef , Matsushita Kunihiro
Published: April 2016

Background and objectives

Carotid intima-media thickness has been reported to predict kidney function decline. However, whether carotid intima-media thickness is associated with a hard kidney end point, ESRD, has not been investigated.

Design, setting, participants, & measurements

We studied 13,197 Atherosclerosis Risk in Communities participants at visit 1 (1987–1989) without history of cardiovascular disease, including coronary heart disease, stroke, and heart failure, at baseline and assessed whether carotid intima-media thickness measured by B-mode ultrasound is associated with ESRD risk using Cox proportional hazards models. Regarding carotid intima-media thickness parameters, we investigated the mean and maximum values of overall and segment-specific (common, bifurcation, and internal carotid arteries) measurements.

Results

Mean age was 54.0 (SD=5.7) years old, and there were 3373 (25.6%) blacks and 7370 (55.8%) women. During a median follow-up of 22.7 years, 433 participants developed ESRD (1.4/1000 person-years). After adjusting for shared risk factors for atherosclerosis and kidney disease, including baseline kidney function, carotid intima-media thickness was significantly associated with ESRD risk (hazard ratio [HR] between quartiles 4 and 1, 1.46; 95% confidence interval [95% CI], 1.02 to 2.08 for overall mean intima-media thickness and HR between quartiles 4 and 1, 1.75; 95% CI, 1.24 to 2.48 for overall maximum intima-media thickness). The associations were largely consistent in demographic and clinical subgroups. When we explored segment–specific intima-media thicknesses, the associations with ESRD were most robust for bifurcation carotid (e.g., adjusted HR between quartiles 4 and 1 of mean intima-media thickness, 1.49; 95% CI, 1.04 to 2.13 for bifurcation; adjusted HR between quartiles 4 and 1 of mean intima-media thickness, 1.36; 95% CI, 0.94 to 1.97 for common; and adjusted HR between quartiles 4 and 1 of mean intima-media thickness, 0.93; 95% CI, 0.67 to 1.29 for internal).

Conclusions

Carotid intima-media thickness was independently associated with incident ESRD in the general population, suggesting the shared etiology of atherosclerosis and ESRD.
Comparison of sequential and single extraction in order to estimate environmental impact of metals from fly ash
Authors: Tasic Aleksandra , Sredovic-Ignjatovic Ivana , Ignjatovic Ljubisa , Ilic Marija , Antic Malisa
Published: April 2016

The aim of this paper was to simulate leaching of metals from fly ash in
different environmental conditions using ultrasound and microwave-assisted
extraction techniques. Single-agent extraction and sequential extraction
procedures were used to determine the levels of different metals leaching.
The concentration of metals (Al, Fe, Mn, Cd, Co, Cr, Ni, Pb, Cu, As, Be) in
fly ash extracts were measured by Inductively Coupled Plasma-Atomic Emission
Spectrometry. Single-agent extractions of metals were conducted during
sonication times of 10, 20, 30, 40 and 50 min. Single-agent extraction with
deionized water was also undertaken by exposing samples to microwave
radiation at the temperature of 50?C. The sequential extraction was
undertaken according to the BCR procedure which was modified and applied to
study the partitioning of metals in coal fly ash. The microwave-assisted
sequential extraction was performed at different extraction temperatures: 50,
100 and 150?C. The partitioning of metals between the individual fractions
was investigated and discussed. The efficiency of the extraction process for
each step was examined. In addition, the results of the microwave-assisted
sequential extraction are compared to the results obtained by standard ASTM
method. The mobility of most elements contained in fly ash is markedly pH
sensitive.
microRNA-182 Mediates Sirt1-Induced Diabetic Corneal Nerve Regeneration
Authors: Wang Ye , Zhao Xiaowen , Wu Xiaoming , Dai Yunhai , Chen Peng , Xie Lixin
Published: April 2016

Sensory neurons are particularly susceptible to neuronal damage in diabetes, and silent mating type information regulation 2 homolog 1 (Sirt1) has been recently identified as a key gene in neuroprotection and wound healing. We found that the expression of Sirt1 was downregulated in trigeminal sensory neurons of diabetic mice. A microRNA microarray analysis identified microRNA-182 (miR-182) as a Sirt1 downstream effector, and the expression level of miR-182 was increased by Sirt1 overexpression in trigeminal neurons; Sirt1 bound to the promoter of miR-182 and regulated its transcription. We also revealed that miR-182 enhanced neurite outgrowth in isolated trigeminal sensory neurons and overcame the detrimental effects of hyperglycemia by stimulating corneal nerve regeneration by decreasing the expression of one of its target genes, NOX4. Furthermore, the effects of miR-182 on corneal nerve regeneration are associated with a functional recovery of corneal sensation in hyperglycemic conditions. These data demonstrate that miR-182 is a key regulator in diabetic corneal nerve regeneration through targeting NOX4, suggesting that miR-182 might be a potential target for the treatment of diabetic sensory nerve regeneration and diabetic keratopathy.
Development and Validation of a Model for Training Equine Phlebotomy and Intramuscular Injection Skills
Authors: Williamson Julie A. , Dascanio John J. , Christmann Undine , Johnson Jason W. , Rohleder Bradley , Titus Lydia
Published: April 2016

Simulation in veterinary education offers a solution for bridging the gap between observation and performance of clinical skills. An equine neck model was created that allows repetitive practice of jugular phlebotomy, intramuscular (IM) injection, and intravenous catheterization. The aim of this study was to validate the model for jugular phlebotomy and IM injection. We surveyed experienced veterinarians on the model's realism and the comprehensiveness of its features. In a randomized experimental study, we compared the learning outcomes of first-year veterinary students trained on the model (n=48) and students trained on equine head-neck cadavers (n=45). There was no difference in post-training performance of phlebotomy on the live horse between cadaver-trained students and model-trained students when assessed by a checklist (cadaver 6.87±0.33; model 6.89±0.77; p=.99) or a global rating scale (cadaver 5.23±0.87; model 5.32±0.77; p=.78). No difference was found between post-training scores for IM injection when assessed by checklist (cadaver 6.87±0.34; model 6.89±0.31; p=.76) or global rating scale (cadaver 5.23±0.87; model 5.32±0.77; p=.75). Veterinarians (n=7) found this low-fidelity model acceptable and supported its use as a training tool for veterinary students. Students reported in a post-lab survey that they felt models were as helpful as cadavers for learning the procedures. These results support the use of the model as a component of first-year veterinary student curriculum.
Structural Damage Localization by the Principal Eigenvector of Modal Flexibility Change
Authors: Li Cui-Hong , Yang Qiu-Wei , Sun Bing-Xiang
Published: April 2016

Using the principal eigenvector (PE) of modal flexibility change, a new vibration-based algorithm for structural defect localization was presented in this paper. From theoretical investigations, it was proven that the PE of modal flexibility variation has a turning point with a sharp peak in its curvature at the damage location. A three-span continuous beam was used as an example to illustrate the feasibility and superiority of the proposed PE algorithm for damage localization. Furthermore, defect localization was also performed using the well-known uniform load surface approach for comparison. Numerical results demonstrated that the PE algorithm can locate structural defects with good accuracy, whereas the ULS approach occasionally missed one or two defect locations. It was found that the PE algorithm may be promising for structural defect assessment.