bluuebunny/crossref_metadata_2025 huggingface dataset:
Leveraging Stranded Gas to Energize Temporary Power Solutions and Support Artificial Lift
Authors: Dickert David
Published: September 2014

Unconventional oil and gas developers are currently enduring economic and environmental pressures to produce oil and gas efficiently, safely, and cost-effectively in the remotely located operations of North America's shale plays. By employing alternative fuels, such as stranded natural gas found at the field, to power generators, operators can cut costs, increase production efficiency, and reduce harmful emissions levels.

However, common misconceptions about the ability to effectively use natural gas to power operations inhibit the adoption of this solution by much the oil and gas industry. This paper will present several common challenges to wider use of natural gas power. We will also provide case study examples to demonstrate how alternatively fueled temporary power generation is a viable option for getting operations up and running quickly and maintaining desired production levels.
Shale Oil Production Challenges in Beam Pumping Being Solved with Premium Sucker Rod Designs
Authors: Alvarez Gustavo , Ruiz Rodrigo , Few Jim
Published: September 2014

The shale oil wells are usually able to start producing high fluid rates with enough energy to free flow naturally. After this stage, a high rate artificial lift systems such as ESP or Gas lift is required. But because of the rapid depletion of the stimulated zone during the first year (between 60 – 80% in Eagle Ford), the most flexible form of artificial lift available is used, the beam pumping.

Because the pump depth could reach between 4,000 up to 12,000 ft, the beam pumping system is limited in flow rate. A big surface pumping unit and high strength rod are necessary. Other complex challenges to overcome are the combination of crooked or highly deviated well bore, high GOR, propant or sand flow back and the presence of H2S. Small tubing completions in shale wells, with 2 3/8″ tubing installations, pushes the system to provide high fluid velocity with effective solids transportation in low rates and more inexpensive equipment but with sucker rod diameter restriction to 7/8″ slimhole couplings.

Optimizing artificial lift equipment selection, sizing, and design will ensure longevity of the equipment and continued production. A premium sucker rod connection has a design that allows the use of 7/8″ and ¾″ strings tapers with KD material to work in corrosive environments with regular size pumping units and lighter strings with guides when necessary in wells where 1″ and high strength rods should be the conventional alternative.

This paper explains the experiences of more than 150 strings installed and the benefits achieved in the Eagle Ford.
Accuracy of Nitrogen Temperature Correction Factors
Authors: Sutton Robert P.
Published: September 2014

Nitrogen gas is used to charge the domes in gas lift valves and some downhole safety valves to provide the closing force to shut the valve. The design pressure and temperature conditions in the well must be calibrated to the shop conditions where the valve is set up and tested. Shop conditions are typically established at 60°F so the nitrogen pressure at operating conditions in the well must be corrected to this temperature; hence, the name "temperature correction factor." Currently, the use of 60°F is an industry standard, although earlier shop-conversions pre-1980's offered calibration temperatures of both 60 and 80°F. The significance of the current shop standard is examined and an explanation is offered confirming the standard.

Early downhole design injection pressure conditions were typically in the range of 500-1,000 psig which formed the basis for the development of early tables and charts used within the industry. As more challenging conditions were encountered, the accuracy of these resources diminished and new methods were developed that form the basis of the procedures that are in part used today. These methods were developed using published nitrogen Z factor data that expanded the calibaration range to 3,000 psig and 300°F. The new methods used 2nd and 3rd order polynomial equations as a basis for the model. The usage of these types of polynomial equations for models does not offer an accurate extrapolation as the boundary conditions are approached or exceeded. Currently, the industry is pursuing equipment with design pressures of 20,000 psig so the use of existing models for extreme conditions is suspect. A detailed analysis of the calculation methodology and accuracy of the published temperature correction factor methods at operating conditions ranging up to 15,000 psig and 400°F is presented. As an alternative, a new equation-of-state (EOS) based method for nitrogen PVT properties is also offered to accurately determine temperature correction factors. This method is easily implemented in existing software programs as the only the coefficients in a commonly-used, natural gas EOS are updated to accurately reflect nitrogen PVT properties to 15,000 psig and 400°F.
Accelerated Learning Through Collaboration in a PCP Application: An Australian Case Study
Authors: Sheldon John , Vecere Chuck , Knafl Matt , Johnson Jon , Setiadi Bagus
Published: September 2014

Four major operators with significant coal seam gas (CSG) holdings in Queensland, Australia identified Progressing Cavity Pumps (PCPs) as one of the preferred artificial lift technologies to deliquify coal seams and allow the adsorbed coal seam gas to be produced to surface. Each operator also acknowledged the need to accelerate their understanding of PCP technology in order to effectively overcome the unique challenges of this application. To address this need, since early 2012, these operators have met semi-annually to share reliability data on their PCP installations and the experience gained in their field operations. It was found that, through these semi-annual meetings, learnings were accelerated. Possible solutions to key challenges were identified during the meetings, trialled in the field and evaluated for success. The results were then shared with the other operators. This paper describes the process that was used to highlight challenges and identify potential solutions. It also presents examples of solutions that proved to be effective. This collaborative effort shows that challenges can be overcome in a shortened time period, if experience and operational data is shared among operators in similar applications.
ESP Recirculation System in Artificial Sump
Authors: Bridges Jeffrey , Storts Brent , Reid Leslie
Published: September 2014

Artificial Lift Case Study: A Mississippian Lime well was tested on an electrical submersible pump (ESP) after previous installations were unsatisfactory.

The three main objectives of the test were: (1) to determine if the run life and production of an ESP system could be increased on a gas-slugging well; (2) to implement a downhole recirculation system inside an artificial sump; and (3) to monitor the economic impact of the installation of the ESP unit to the well.

The challenges for the ESP system for this specific test included: (i) low liquid inflow during severe gas slugging; (ii) high gas/liquid ratio (>800 SCF/BBL); (iii) difficult startup conditions; (iv) thermal and mechanical damage to motor lead extensions.

Due to these challenges, using traditional gas-separation and gas-handling technology was considered a disadvantage. A downhole recirculation system inside an artificial sump was used as an alternative method to prevent potential gas locking, to circulate fluid to keep the motor cool, and to enhance reservoir drawdown.

This paper presents basic principles of the application of ESP systems in a gassy and gas-slugging well, principles of implementing a downhole recirculation system, and uncommon techniques to effectively operate an ESP unit in gas-slugging wells. Historical design challenges system-specific design/operation, and production results of the tested well are also presented.
Systematic Study of Bakken Well Performance over Three Well Completion Design Eras
Authors: Yan Changhui , Luo Guofan , Ehlig-Economides C. A.
Published: September 2014

Oil production from the Bakken formation has been active for 60 years and has applied three well completion design strategies in three different eras: mainly hydraulically fractured vertical wells before 1987, horizontal wells before 1991, and mainly multiple transverse fracture horizontal wells since 2006. Reported production data enables comparisons of well performance during these eras.

This study employs the log-log graph of rate (q) versus material balance time (Q/q) to diagnose transient (slope −¼ or −½) and boundary dominated flow (BDF) (slope −1) behavior. Wells from the 3 eras show mainly 3 types of flow regime sequences seen as straight trends on the log-log graph of rate versus material balance time: −¼ to −1, −½ to −1 and −¼ to −½ to −1. Flow geometries corresponding to various flow regime sequences are related to specific well and formation characteristics. Then we extrapolate the BDF behavior to estimate the EUR for each well when possible.

We observed that both the average well EUR and the average well rate at start of BDF behavior is highest for the multiple transverse fracture horizontal well completion design. This project also investigates the behavior of the GOR versus material balance time (MBT). Three types of GOR behavior were observed: constant, constant followed by sharp increase, or scattered. In all three eras, the EUR was highest in wells with constant GOR behavior followed by sharp increase. The sharp increase likely signals flow below the bubble point pressure. The lower EUR in wells that did not produce below the bubble point pressure shows that solution gas drive behavior enhances the EUR. Lower EUR in wells with scattered GOR behavior may be attributed to unstable well production.

This study shows how to use long term production behavior to gain important insights about well designs and why some wells have higher EUR and rate behavior.
Temporal Evolution of the Geometrical and Transport Properties of a Fracture-Proppant System under Increasing Mechanical Loading
Authors: Chen Cheng , Martysevich Vladimir , O'Connell Pete , Hu Dandan , Matzar Luis
Published: September 2014

A fracture-proppant system is used to mimic the interaction between the rock matrix and proppants during the process of fracture closing attributed to pore pressure reduction during hydrocarbon production. Effects of rock type and bedding plane direction are investigated. High-strength sintered bauxite proppants are placed into simulated hydraulic fractures in sandstone and shale rock. There are two bedding plane directions in shale rock; one is 90°, which is perpendicular to the fracture, while the other is 0°, which is parallel to the fracture. Increasing mechanical loading is imposed to close the fracture. Micron-scale X-ray tomography is used to visualize the internal structure. Cutting-edge imaging processing methods are applied to extract patterns of both the fracture and matrix. A pore-scale lattice Boltzmann (LB) simulator, optimized using graphics processing unit (GPU) parallel computing, is used to simulate the permeability tensor inside the fracture. Significant proppant embedment is observed in the sandstone rock when the effective stress is increased to 4,200 psi. Consequently, fracture porosity is reduced by nearly 70%, and permeability is reduced by two orders of magnitude. Embedded proppants are unable to create microscopic fractures on the matrix surface because of the low bonding strength between grains. In the shale rock with 90° bedding planes, when the effective stress is increased to 3,000 psi, significant microscopic fractures on the matrix surface are created because the lamination structure of the matrix is opened. In the shale rock with 0° bedding planes, noticeable microscopic fractures on the matrix surface are not observed until the effective stress is increased to 6,990 psi. Proppant embedment is insignificant because of the high bonding strength between fine grains. Significant anisotropy in the permeability tensor is observed during all experiments. This study is the first to use cutting-edge imaging and modeling methods to quantitatively study the interaction between proppants and the rock matrix during the stress increase process. It has important applications, which help sustain production with adequate fracture conductivity in deep reservoirs (e.g., the Haynesville shale).
A New Methodology to Forecast Solution Gas Production in Tight Oil Reservoirs
Authors: Yu Shaoyong
Published: September 2014

Due to favorable economics, more and more oil companies are now drilling multi-stage fractured horizontal wells to develop tight oil reservoirs. While oil production forecasting in these wells has historically been the primary focus of most operators, gas (solution gas) production forecasting has been largely neglected. There are two distinct reasons for this oversight: First, when compared to oil production, solution gas rates typically have a much lower impact on overall economics. Second, solution gas production is often very difficult to forecast due to abnormal GOR's which are typically caused by incorrect gas rate measurements.

This paper presents a simple methodology to predict solution gas production based on forecasted oil production. This methodology introduces a new specialized plot which can be used to determine various parameters necessary to forecast solution gas production without any costly PVT and pressure history data. Additionally, this paper presents a step-by-step procedure used to analyze the available history to obtain an accurate representation of GOR performance. This data in turn can be used to predict solution gas production.

Missing data and/or incorrect gas measurements are common issues that can directly affect a well's GOR history. The methodology presented in this paper will outline the steps required to repair this kind of bad data and ultimately generate a reasonable GOR forecast that is representative of a well's true performance.

This methodology was initially validated using synthetic data (generated by a commercial simulator) and has been subsequently tested on over one thousand oil wells that are producing from tight formations such as the Bakken, Niobrara and Wolfcamp in the USA and the Cardium in Canada. Each test was carried out by hindcasting – using the early part of production data to history-match the later part of history. This methodology has consistently resulted in good agreement between the forecast and the real field data.

A number of practical examples from different reservoirs have been presented in this paper to illustrate/validate this new methodology.
Horizontal Well Injection Profiling Using Distributed Temperature Sensing
Authors: Foo David , Krislock Jeremy , Meador Trevor , Cheng Teresa
Published: September 2014

As industry moves towards waterflooding horizontal wells, monitoring and maintaining the injection profiles has emerged as a reservoir management issue. Heterogeneities in the reservoir, completion design, and completion problems can all contribute to non-uniform injection and a corresponding drop in waterflood efficiency. Knowing where the water is being injected along the length of a horizontal water injection well is critical to maximizing secondary recovery. Operators need to monitor for channeling of water injection between horizontal injectors and horizontal producers and gather information capable of determining the best way to remediate problems. Operators have begun using distributed temperature sensing (DTS) to measure the temperature along a horizontal well and infer the injection profile from that data. Based on this information, a workover can be done to redistribute the injection, resulting in lower watercuts at the producers and improving the secondary recovery factor.

This paper covers the techniques used to determine the injection profile with DTS, focusing on a case history from the Cardium formation in the Pembina area of Alberta. The well and reservoir conditions are summarized, the completion is reviewed (with microseismic data showing fracture geometry on the injection well), the injection profiling methods are covered, and the results are shown. The operator's remedial efforts are then covered, along with preliminary results.
Reservoir and Drilling Engineering Combined Effort to Develop a Naturally Fractured Over Pressured Shale Formation: Understanding and Operational Specific Procedures
Authors: Badessich Matias Fernandez , Krasuk Raul
Published: September 2014

In the area of this study, the Quintuco-Vaca Muerta complex is an ultra-low permeability, highly over pressured, laminated calcareous and shaly rock that extends over 5000 km2 with an average gross thickness of 700 m. It overlies some 30 meters of what is known as the kitchen of Vaca Muerta, a world-class, high TOC source rock, the main source rock for the Neuquen basin in Argentina. Whenever found naturally fractured, it can produce high quality oil at attractive initial choked rates as high as 1500 bopd.

Historically, throughout many drilling campaigns, it has been very difficult to anticipate where it will have enough good reservoir properties such as to grant a commercial completion. Many times in the past decades, as soon as the wells showed important kicks during the drilling phase in Quintuco-Vaca Muerta, the wells were completed without any further evidences other than high initial productivity indexes. This led more often than not, to wrong decisions and the completions turned out to be sub-economical.

Drilling operations through this geological sequence present severe well control related problems such as difficulties anticipating pore pressures, predicting fluid influx levels and mainly the fact that an increase in mud weight in most of the wells, instead of leading to well control, exacerbates formation fluid kicks and influx pressure.

Combining geological knowledge, production history, downhole pressure while drilling (PWD), surface underbalanced drilling (UBD), mud logging data and drilling experience, a specific underbalanced drilling methodology was developed assuming one main hypothesis which is that in some areas of the field, the formation is naturally fractured and it is potentially critically stressed. This drilling methodology defines how the optimum mud weight is identified, how to deal with formation fluid influx and the well killing procedure; additionally a "dynamic soft well shut-in method" was defined.

An integrated effort of drilling and reservoir engineering allowed the operator to design and execute a meaningful short reservoir limit test that facilitated the evaluation in real time of the size of the accumulation and the reaching of an informed decision on whether or not to complete the well from this interval.
Analysis of Multi-Well and Stage-by-Stage Flowback from Multi-Fractured Horizontal Wells
Authors: Williams-Kovacs J. D. , Clarkson C. R.
Published: September 2014

As a result of low gas prices and recent reductions in natural gas liquids prices, unconventional light oil reservoirs remain a primary target for exploration and development in North America. Due to the low permeability of such reservoirs, well-life tends to be dominated by transient linear flow from the matrix to the fractures which may last several years. This flow period is affected by hydraulic fracture properties, therefore operators are looking for new methods to characterize hydraulic fractures, particularly early in the well life. In previous studies by the authors it has been shown that high-frequency flowback flow rates and flowing pressures can be modeled to obtain key hydraulic fracture parameters (i.e. half-length and conductivity). Although commingled data is commonly gathered, technology exists to collect individual stage data.

In this work, we advance the analytical procedure presented by Clarkson and Williams-Kovacs (2013b) and Williams-Kovacs and Clarkson (2013c) for analyzing pre- and post-breakthrough of formation fluid during flowback of light tight oil wells by investigating multi-well and stage-by-stage flowback. Studies have shown that there may be significant communication both between stages and between wells on a given pad (or beyond) during the flowback period but not during long-term production. In order to accurately model the flowback period this communication must be accounted for in order to properly assess individual well hydraulic fracture properties. Building upon the analytical models developed previously for single well flowback from unconventional light tight oil wells, we employ the "communicating tanks" concept to account for stage (or inter-well) interaction. Proper allocation and transfer of fluids between stages, if they are communicating, is necessary to ensure that the fracture volume assigned to each stage/well is correct. Our work demonstrates that if individual stage/well flowback data is analyzed without accounting for communication, derived reservoir properties (i.e. fracture halflength) are in significant error. As a result, future well performance predictions, and attempts to optimize fracture stimulations, will also be in error.

Our new methods are tested against both simulated and field examples. Stage-by-stage flowback is demonstrated using simulated data, while multi-well flowback will be demonstrated using field data from a multi-well pad.
Quantification of Proppant Distribution Effect on Well Productivity and Recovery Factor of Hydraulically Fractured Unconventional Reservoirs
Authors: Sierra Leopoldo , Sahai Rakshit (Raki) , Mayerhofer Michael
Published: September 2014

The most common completion methodology the industry uses to help maximize productivity and fluid recovery in unconventional reservoirs consists of placing multiple, optimally spaced transverse fractures in horizontal wells, navigating along the direction of minimum principle horizontal stress. In this type of completion, well productivity and fluid recovery can be maximized when the following conditions are met:

Horizontal wellbore navigates optimally in the reservoir. Generated fracture connects the entire productive pay zone. Transverse fractures are optimally spaced. Proppant is well-distributed throughout the created fracture.

With respect to the actual completion strategy, the first two conditions are met using proper geological interpretation and measurements of fracture height growth (e.g., microseismic); the third condition depends on economics and cluster efficiency. However, the distribution of proppant within the hydraulic fractures is usually ignored, particularly for cases in which low-viscosity fracturing fluids are used for stimulation.

By performing extensive simulations for gas-producing reservoirs with a wide range of unconventional reservoir permeabilities, this paper quantifies the impact of proppant distribution on well productivity and the recovery factor (RF). For cases in which proppant distribution is not optimized, previously published extensive simulations demonstrate that the RF and productivity are significantly affected.
Experimental and Numerical Study on Spontaneous Imbibition of Fracturing Fluids in Shale Gas Formation
Authors: Zhou Z. , Hoffman B. , Bearinger D. , Li X.
Published: September 2014

During some hydraulic fracturing processes, it is found that only 10% to 50% of fracturing fluids is recovered. This paper investigates how much of the remaining fracturing fluids are imbibed by shale rocks as a function of time, and also investigates the influence of various parameters on the imbibition process including: lithology, reservoir characteristics, and fluid properties. In addition, based on the experimental results, a numerical model is developed to estimate the amount and rate of spontaneous imbibition during fracturing over the entire fracture face.

The rock samples are from the Horn River formation. The fracturing fluids used in the experiments include 2% KCL, 0.07% friction reducer and 2% KCL substitute. Distilled water is also used in experiments as control groups. Through spontaneous imbibition experiments, the relationships between imbibed weight of fluid and time show that the content of clay is the most important factor which affects the total amount imbibed. Shale matrix with high clay content can imbibe volume of fluid greater than its measured porous space because of the clay's strong ability to expand and hold water. Small porosity with less total organic carbon (TOC) results in the highest imbibed rate. Contact angle results show the stronger water wet shale samples have a faster imbibed rate. Temperature also influence amount of imbibition. The total imbibed volume decreases as the environment temperature rises.

From this paper, it can help optimally design fracturing fluid for different conditions of shale formation to reduce fluid loss. We find that 2% KCL and 2% KCL substitute fracturing fluid are imbibed 10% to 40% less than 0.07% friction reducer in shale formation with high clay content; while in shale formation with low clay content, the opposite occurs. 0.07% friction reducer is imbibed 10% to 30% less than 2% KCL, but has similar imbibed amount with 2% KCL substitute.

The numerical model results are matched with the experiment results in order to estimate relative permeability and initial water saturation in the model which can represent the properties of rocks. This model can use to estimate the total imbibed volume along fracture faces through spontaneous imbibition.
Linking Rock Mechanic Petrophysics to Proppant Selection in the Wolfcamp: Capitalizing on Log Based Value of Information
Authors: Prochnow S. , Brown R. L. , Rexilius J. P. , Fields M. J.
Published: September 2014

Value of information for petrophysical data in unconventional plays can be extended far beyond perforation placement, but can also be used to develop strategic plans for the selection of costly proppants. Proppant is the single most expensive feature of Midland Basin Wolfcamp completions, especially in deeper (>10,000 ft. TVD) zones that are under high stress. Wire line petrophysical data has recently been adopted as a critical element in proppant capital stewardship.In particular, dipole sonic logs in the Wolfcamp play now provide critical closure stress information for the decision to attempt hydraulic fracturing of a zone and the selection of appropriate proppant for those zones. New proppant selection criteria relate zone stress to required hydraulic fracture conductivity given the expected formation permeability and production capacity. Before this study, frac stages and proppants were chosen on a paucity of available completion records. This resulted in a strategy to use ceramic proppants in all zones below 10,000 ft., or roughly > 6,500 psi closure stress. The incorporation of petrophysical log analysis has refined the process by which the prescription of expensive proppants and frac stages are made and ultimately reduces cost. Dipole sonic data is now collected every square mile of the active development area. The sonic data is converted into estimates of fracture gradient (psi*ft−1), minimum horizontal stress (psi), and closure pressure (psi). Average porosity of pay ranges from 6.3% (P10) to 9.5% (P90) in the mudstone prone Cline formation, while the ramp carbonates constituting the Strawn and Bend formations ranges from 3.2% (P10) to 12.8% (P90). Core analysis suggests the corresponding permeability are around 0.19 MD (P10) to 0.71 MD (P90) for the Cline while the Strawn and Bend range from 0.02 MD to 8.06 MD (P90). Log based, average P90 minimum horizontal stress in deep Pennsylvanian zones ranges from 7,743 psi (Cline Fm), 7,389 (Strawn Fm), to 9,783 (Atoka Fm). These relationships suggest that white sand provides adequate frac conductivity for 35% to 45% wells completing in the Upper Atoka and Atoka-Bend zones, or when average porosity is less than 7.5%. Likewise, the Strawn can be completed with white sand 80% of the time instead of ceramic because the zone has lower permeability and closure stress. The Cline formation should ceramic proppant only about 10% of the time. This method of prescribing the ideal proppant considering both sonic-based stress and formation permeability is projected to save around $96,000 per well. This translates to 6.4 million dollars for 67 wells to be drilled in Queen Anne's Field from the 2nd through 4th quarter 2014. This is a huge incremental value enabled by adding sonic logs and petrophysical analysis to the completion design paradigms.
Integrated Reservoir Characterization and 3D Modeling of the Monteith Formation: Tight Gas Sandstones in the Western Canada Sedimentary Basin, Alberta, Canada
Authors: Zambrano Liliana , Ramirez John Freddy , Pedersen Per Kent , Aguilera Roberto
Published: September 2014

The Monteith Formation is an important tight gas reservoir in the Deep Basin, Alberta, and consists of a progradational succession of shallow marine sediments, non-marine carbonaceous and coaly, coastal plain facies, and coarse-grained fluvial deposits, from base to top, respectively. This study compares rock properties and production performance of the uppermost lithostratigraphic unit ("Monteith A") and the lowermost portion ("Monteith C") of the Monteith Formation in the Western Canada Sedimentary Basin (WCSB) in Alberta.

The study is based on multi-scale description and characterization techniques using cores and drill cuttings, including multiple laboratory measurements of key reservoir parameters such as porosity and permeability. A second stage of the study involves the use of laboratory measurements obtained from cores and drill cuttings and their integration with well logs to produce a numerical 3D model of the study area. The 3D model is used to history match gas production, and forecast performance of new wells in those areas where the geologic model indicates potential for gas production. The ultimate goal is to provide a better understanding of the distribution of reservoir properties in the study area, for developing drilling prospects and their production potential. In addition to that, the reservoir modeling stage is carried out by implementing a recently developed methodology that integrates a Variable Shape Distribution (VSD) model, capable of capturing different reservoir properties through the whole scale spectrum without any data truncation. This new methodology introduces an extension of the VSD approach for reservoir simulation purposes.

The results are showing that the Monteith A unit has better rock quality than the shallow marine sandstones of the Monteith C interval. This is most likey due to larger pore throat apertures ranging between 0.5 and 1 microns, relatively higher proportion of preserved intergranular pore space within these coarser-grained framework grains. Furthermore, the best production performance is found from wells that are actually producing from the uppermost interval. The resulting 3D reservoir model will allow to improve field development strategies for this and other similar unconventional gas reservoir in the Deep Basin of Alberta.
Rate-Decline Analysis For Fracture-Dominated Shale Reservoirs: Part 2
Authors: Duong Anh N.
Published: September 2014

When it comes to forecasting production from shale plays that are subject to multistage hydraulic fracturing, most modeling approaches do not apply throughout the life of a well. The Duong decline method, introduced in 2010, is no exception. When a well reaches the stage of boundary-dominated flow (BDF), the method's limitations become clear.

Part 2 of the Duong method proposes to extend the approach in order to apply it to the long-term performance of wells that are influenced by various fracture fabrics, well spacing, and fluid types such as gas and saturated and unsaturated oil production. In addition to overcoming its own limitations, the extended method is also intended to rectify limitations associated with other commonly used production forecasting methods. The outcome of this work should generate a model that accounts for the physical processes of flow regimes in horizontal wells with multistage hydraulic fracturing.

This extension employs empirical, analytical, and numerical solutions to represent a depletion model that consists of multiple realistic flow regimes. The method uses the Duong diagnostic plot, log(q/Gp) versus log(t), to normalize the constant rate and constant pressure analytical solutions during both linear flow and BDF. This forms an equivalent Fetkovich-type curve for unconventionals and serves as the base curve for identifying the start time of fracture interference among the fractures and in connection with the Arps' b values. Results from numerical simulation modeling are used to fill in long-term production estimates affected by various fracture geometries, well drilling spacing units, and fluid types. Type-curve parameters include start fracture interference time and fluid influx ratio for each depletion system. The fluid influx ratio based on permeabilities, fracture distance and half-length, and well spacing ranges from zero to one, where zero represents an isolated system and one represents transient conditions.

The outcome of this work should help the industry not only to forecast rate production more accurately, but to better understand decline prediction in tight oil and shale gas reservoirs. The paper also discusses methods to estimate input parameters for forecasting, using factors such as permeabilities, fracture interference time, stimulated-rock volume (SRV), and fracture half-length from production history and completion data. The paper applies field and simulation data to demonstrate the use of the new extension.
Relation Between Track Irregularity of Speed-Increased Railway and Dynamic Speed Limits Through Simulation
Authors: Zhi-Chen Wang , Ying Song , Jian-Xi Wang
Published: September 2014

Based on the vehicle-track coupled dynamics theory and the corresponding simulation software ADAMS/Rail
software package, a vehicle-track coupling system model is established, and the track irregularity is introduced to the
coupling system model as an excitation source. Firstly, the dynamic responses of speed-increased railway vehicle and
track components due to different types of track irregularity are obtained. Secondly, the sensitive wavelength of different
track irregularities in high-speed operation is discussed. Finally, suggestions about the maximum operation speed to meet
the standards value of daily maintenance target, comfortable value, emergency repair and speed management target are
put forward.
Study on Pre-Warning Method of the Lateral Security of Heavy Vehicle in
Deteriorative Weather
Authors: Zhao Zhi-Guo , Chen Min , Chen Nan , Zhao Yong-Bing , Chen Xin
Published: September 2014

The lateral security of heavy vehicle in deteriorative weather is one of the main causes of accidents of vehicles
on roads. Road safety has become a subject of great concern to institutions of higher education and scientific research
institutions. There are important theoretical and practical significances to explore applicable and effective lateral safety
warning methods of heavy vehicles. One of the purposes of this paper is to provide a good theoretical basis for the core
technology of heavy vehicle safety features for our country's independent research and development. Aiming at the issue
of lateral security of heavy vehicle for road conditions in deteriorative weather, this paper constructs the framework of the
lateral security pre-warning system of heavy vehicles based on cooperative vehicle infrastructure. Moreover, it establishes
vehicle lateral security statics model through analysis of the force of the car in the slope with section bending and states
the parameters of vehicles for no rollover. The side slip is indexed to calculate critical speed of vehicles in a bend. This
paper also analyzes the influence of road friction coefficient, the road gradient and the turning radius on the lateral
security of the vehicle with critical speed on the asphalt pavement with surface conditions ranging from wet, dry, snowing
or icy. The calculation results show that the bad weather road conditions, road friction coefficient and turning radius have
obvious influence on the lateral security critical speed. Experimental results indicate that the critical speed error warning
is within 4% and it meets the design requirements.
Research on Urban Rail Train Passenger Door System Fault Diagnosis
Using PCA and Rough Set
Authors: Shuai Lin , Limin Jia , Yong Qin , Bo Yu , Yanhui Wang
Published: September 2014

Train passenger door is the key system for operation and maintenance of urban rail train. In this paper, working
process of the passenger door system of urban rail train is analyzed and the mathematical model is established. Firstly,
the method of parameter estimation is used to obtain physical parameters of doors in different working conditions. Then
fault diagnosis experiment is carried out on train passenger door with principal component analysis and rough set theory.
In the end, fault diagnosed accuracies under different time settings of opening and closing profiles with the test rig are
verified.
The Risk Analysis and Evaluation of Urban Underground Logistics System Development Based on the Grey Analytic Hierarchy Process
Authors: Xiao Hong , Cheng Xiaoliang , Zou Cilan
Published: September 2014

Urban underground logistics system is a newly emerging concept, and there is no molded sample project to
provide reference information. So there exists much uncertainty in its development, and such uncertainty will have some
impact on overall development of the system. In this paper, gray analytic hierarchy process analysis will be used to
evaluate the risk factors in the development of urban underground logistics system. And then, we use the empirical
analysis to quantify the risk of the development of urban underground logistics and provide references for the
development of urban underground logistics system.
Abiotic Effects on Effluent Dissolved Organic Nitrogen Along an Estuarine Transect
Authors: Funkey Carolina P. , Latour Robert J. , Bronk Deborah A.
Published: September 2014

Biological nutrient removal is a process commonly used in water resource recovery facilities to reduce dissolved inorganic nitrogen (DIN) concentrations in effluent; this process is less effective at removing all of the effluent dissolved organic nitrogen (EDON). The goal of this study was to investigate the fate of EDON after it undergoes the disinfection process and enters receiving waters. The authors quantified the abiotic effects of effluent exposure to sunlight, increased salinity, and a combination of the two factors. Effluent dissolved organic nitrogen showed significant breakdown during the disinfection process (UV and chlorine) and when exposed to sunlight and increasing salinity. Approximately 7% of the EDON was transformed to DIN and dissolved primary amines after exposure to 9 hours of sunlight and a salinity increase from 0 to 33. The production of DIN and primary amines should be taken into account when considering sources of labile nitrogen to aquatic ecosystems.
Effects of fluxing agents on gasification reactivity and gas composition of high ash fusion temperature coal
Authors: Zhao Ruifang , Wang Yulong , Bai Yonghui , Zuo Yongfei , Yan Lunjing , Li Fan
Published: September 2014

A Na-based fluxing agent Na2O (NBFA) and a composite fluxing agent (mixture
of CaO and Fe2O3 with mass ratio of 3:1, CFA for short) were used to decrease
the ash fusion temperature of the Dongshan and Xishan coal from Shanxi of
China and make these coal meet the requirements of the specific gasification
process. The main constituents of the fluxing agents used in this study can
play a catalyst role in coal gasification. So it is necessary to understand
the effect of fluxing agents on coal gasification reactivity and gas
composition. The results showed that the ash fusion temperature of the two
coal used decreased to the lowest point due to the eutectic phenomenon when 5
wt% of CFA or NBFA was added. Simultaneously, the gas molar ratio of H2/CO
changed when CFA was added. A key application was thus found where the gas
molar ratio of H2/CO can be adjusted by controlling the fluxing agent amount
to meet the synthetic requirements for different chemical products.
Econometric modelling of unemployment in Serbia during period 2008-2013
Authors: Anic Aleksandra , Mladenovic Zorica
Published: September 2014

The purpose of the paper is to econometrically exploit the characteristics of
unemployment in Serbia upon the start of the 2008 economic crisis. The
methodological framework is based on the cointegrated vector autoregressive
model that consists of the following macroeconomic variables: unemployment
rate, prices, nominal wages and nominal exchange rate. These variables are
unit-root processes and their relationship is examined within the
multivariate cointegrated time series set-up. Following the deductive
modelling approach, we reached the specification that explains unemployment
rate by real wages. The results show the negative consequences of the
economic crisis to the labour market, with an extremely high increase in the
unemployment rate. Strong negative impact of real wages on unemployment rate
is additionally confirmed by its dynamic effects throughout the impulse
response function.
Debris and friction of self-ligating and conventional orthodontic brackets after clinical use
Authors: Araújo Raíssa Costa , Bichara Lívia Monteiro , de Araujo Adriana Monteiro , Normando David
Published: September 2014

Objective: 

To compare the degree of debris and friction of conventional and self-ligating orthodontic brackets before and after clinical use.

Materials and Methods: 

Two sets of three conventional and self-ligating brackets were bonded from the first molar to the first premolar in eight individuals, for a total of 16 sets per type of brackets. A passive segment of 0.019 × 0.025-inch stainless steel archwire was inserted into each group of brackets. Frictional force and debris level were evaluated as received and after 8 weeks of intraoral exposure. Two-way analysis of variance and Wilcoxon signed-rank test were applied at P < .05.

Results: 

After the intraoral exposure, there was a significant increase of debris accumulation in both systems of brackets (P < .05). However, the self-ligating brackets showed a higher amount of debris compared with the conventional brackets. The frictional force in conventional brackets was significantly higher when compared with self-ligating brackets before clinical use (P < .001). Clinical exposure for 8 weeks provided a significant increase of friction (P < .001) on both systems. In the self-ligating system, the mean of friction increase was 0.21 N (191%), while 0.52 N (47.2%) was observed for the conventional system.

Conclusion: 

Self-ligating and conventional brackets, when exposed to the intraoral environment, showed a significant increase in frictional force during the sliding mechanics. Debris accumulation was higher for the self-ligating system.
Deletion of Both Rab-GTPase–Activating Proteins TBC1D1 and TBC1D4 in Mice Eliminates Insulin- and AICAR-Stimulated Glucose Transport
Authors: Chadt Alexandra , Immisch Anja , de Wendt Christian , Springer Christian , Zhou Zhou , Stermann Torben , Holman Geoffrey D. , Loffing-Cueni Dominique , Loffing Johannes , Joost Hans-Georg , Al-Hasani Hadi
Published: September 2014

The Rab-GTPase–activating proteins TBC1D1 and TBC1D4 (AS160) were previously shown to regulate GLUT4 translocation in response to activation of AKT and AMP-dependent kinase. However, knockout mice lacking either Tbc1d1 or Tbc1d4 displayed only partially impaired insulin-stimulated glucose uptake in fat and muscle tissue. The aim of this study was to determine the impact of the combined inactivation of Tbc1d1 and Tbc1d4 on glucose metabolism in double-deficient (D1/4KO) mice. D1/4KO mice displayed normal fasting glucose concentrations but had reduced tolerance to intraperitoneally administered glucose, insulin, and AICAR. D1/4KO mice showed reduced respiratory quotient, indicating increased use of lipids as fuel. These mice also consistently showed elevated fatty acid oxidation in isolated skeletal muscle, whereas insulin-stimulated glucose uptake in muscle and adipose cells was almost completely abolished. In skeletal muscle and white adipose tissue, the abundance of GLUT4 protein, but not GLUT4 mRNA, was substantially reduced. Cell surface labeling of GLUTs indicated that RabGAP deficiency impairs retention of GLUT4 in intracellular vesicles in the basal state. Our results show that TBC1D1 and TBC1D4 together play essential roles in insulin-stimulated glucose uptake and substrate preference in skeletal muscle and adipose cells.
Ask1 Gene Deletion Blocks Maternal Diabetes–Induced Endoplasmic Reticulum Stress in the Developing Embryo by Disrupting the Unfolded Protein Response Signalosome
Authors: Wang Fang , Wu Yanqing , Gu Hui , Reece E. Albert , Fang Shengyun , Gabbay-Benziv Rinat , Aberdeen Graham , Yang Peixin
Published: September 2014

Apoptosis signal–regulating kinase 1 (ASK1) is activated by various stresses. The link between ASK1 activation and endoplasmic reticulum (ER) stress, two causal events in diabetic embryopathy, has not been determined. We sought to investigate whether ASK1 is involved in the unfolded protein response (UPR) that leads to ER stress. Deleting Ask1 abrogated diabetes-induced UPR by suppressing phosphorylation of inositol-requiring enzyme 1α (IRE1α), and double-stranded RNA-activated protein kinase (PKR)-like ER kinase (PERK) blocked the mitochondrial translocation of proapoptotic Bcl-2 members and ER stress. ASK1 participated in the IRE1α signalosome, and removing ASK1 abrogated the proapoptotic kinase activity of IRE1α. Ask1 deletion suppressed diabetes-induced IRE1α endoriboneclease activities, which led to X-box binding protein 1 mRNA cleavage, an ER stress marker, decreased expression of microRNAs, and increased expression of a miR-17 target, thioredoxin-interacting protein (Txnip), a thioredoxin binding protein, which enhanced ASK1 activation by disrupting the thioredoxin-ASK1 complexes. ASK1 is essential for the assembly and function of the IRE1α signalosome, which forms a positive feedback loop with ASK1 through Txnip. ASK1 knockdown in C17.2 neural stem cells diminished high glucose– or tunicamycin-induced IRE1α activation, which further supports our hypothesis that ASK1 plays a causal role in diabetes-induced ER stress and apoptosis.
Inorganic Nitrate Promotes the Browning of White Adipose Tissue Through the Nitrate-Nitrite-Nitric Oxide Pathway
Authors: Roberts Lee D. , Ashmore Tom , Kotwica Aleksandra O. , Murfitt Steven A. , Fernandez Bernadette O. , Feelisch Martin , Murray Andrew J. , Griffin Julian L.
Published: September 2014

Inorganic nitrate was once considered an oxidation end product of nitric oxide metabolism with little biological activity. However, recent studies have demonstrated that dietary nitrate can modulate mitochondrial function in man and is effective in reversing features of the metabolic syndrome in mice. Using a combined histological, metabolomics, and transcriptional and protein analysis approach, we mechanistically defined that nitrate not only increases the expression of thermogenic genes in brown adipose tissue but also induces the expression of brown adipocyte–specific genes and proteins in white adipose tissue, substantially increasing oxygen consumption and fatty acid β-oxidation in adipocytes. Nitrate induces these phenotypic changes through a mechanism distinct from known physiological small molecule activators of browning, the recently identified nitrate-nitrite-nitric oxide pathway. The nitrate-induced browning effect was enhanced in hypoxia, a serious comorbidity affecting white adipose tissue in obese individuals, and corrected impaired brown adipocyte–specific gene expression in white adipose tissue in a murine model of obesity. Because resulting beige/brite cells exhibit antiobesity and antidiabetic effects, nitrate may be an effective means of inducing the browning response in adipose tissue to treat the metabolic syndrome.