bluuebunny/crossref_metadata_2025 huggingface dataset:
Cell Excitability Necessary for Male Mating Behavior inCaenorhabditis elegansIs Coordinated by Interactions Between Big Current and Ether-A-Go-Go Family K+ Channels
Authors: LeBoeuf Brigitte , Garcia L Rene
Published: December 2011

Variations in K+ channel composition allow for differences in cell excitability and, at an organismal level, provide flexibility to behavioral regulation. When the function of a K+ channel is disrupted, the remaining K+ channels might incompletely compensate, manifesting as abnormal organismal behavior. In this study, we explored how different K+ channels interact to regulate the neuromuscular circuitry used by Caenorhabditis elegans males to protract their copulatory spicules from their tail and insert them into the hermaphrodite’s vulva during mating. We determined that the big current K+ channel (BK)/SLO-1 genetically interacts with ether-a-go-go (EAG)/EGL-2 and EAG-related gene/UNC-103 K+ channels to control spicule protraction. Through rescue experiments, we show that specific slo-1 isoforms affect spicule protraction. Gene expression studies show that slo-1 and egl-2 expression can be upregulated in a calcium/calmodulin-dependent protein kinase II-dependent manner to compensate for the loss of unc-103 and conversely, unc-103 can partially compensate for the loss of SLO-1 function. In conclusion, an interaction between BK and EAG family K+ channels produces the muscle excitability levels that regulate the timing of spicule protraction and the success of male mating behavior.
A Case‐crossover Study of Transient Risk Factors for Occupational Traumatic Hand Injuries in Incheon, Korea
Authors: Choi Won‐Jun , Cho Sung‐Il , Han Sang‐Hwan
Published: December 2011

A Case‐crossover Study of Transient Risk Factors for Occupational Traumatic Hand Injuries in Incheon, Korea: Won‐Jun CHOI, et al. Department of Ocean and Underwater Medicine, Maritime Medical Center, ROK Navy, Korea—

Objectives

A casecrossover study was conducted to identify transient risk factors for occupational acute hand injuries.

Methods

In total, 98 subjects were recruited from a hospital specializing in occupational accidents and trauma. Patients who had injured fingers, hands or wrists during work were interviewed within 30 days after their accidents.

Results

The relative risks for each factor were as follows: 22.9 for unusual or malfunctioning machines (95% confidence interval [CI] 14.4–36.4), 3.3 for wearing gloves (95% CI 1.9–5.7), 5.7 for unusual tasks (95% CI 3.8–8.8), 12.1 for altered work methods (95% CI 8.4–17.6), 4.1 for rushing (95% CI 2.6–6.3), 12.9 for being distracted (95% CI 7.9–20.9), 1.2 for feeling ill (95% CI 0.4–3.6) and 1.0 for working overtime (95% CI 0.6–1.6).

Conclusion

The results suggest that some transient risk factors were associated with occupational acute hand injuries. These risk factors are probably preventable, and modifying unsafe or unusual conditions is important to reduce occupational traumatic hand injuries.
Spirituality and Resistance
Authors: Barnhill David
Published: December 2011

Avatar shares key narrative features with Ursula Le Guin’s 1972 novel The Word for World is Forest, including a depleted earth, exploitive resource extraction on another planet, and a successful revolt by the natives. Natives live in harmony with a natural world that is considered sacred and has both animistic and Gaian properties. Both works present a radical critique of modern Western society. There also are fundamental differences: The Word for World is Forest does not portray a Terran leading the revolt or joining the indigenous society, there is no romance between a Terran and a native, and the violence by the natives is unheroic and culturally damaging. While The Word for World is Forest is a dystopian novel, Avatar is apocalyptic. Both also have utopian elements, though Avatar is more optimistic than The Word for World is Forest, with its more nuanced view of our political situation.
Clarifying the spiritual values of forests and their role in sustainable forest management
Authors: Clark William A.
Published: December 2011

People value forests for many reasons. Historically, market and utilitarian values predominated both in forestry practice and the academic literature. Since the 1980s, forest professionals and researchers have given greater attention to less tangible forest values, including spiritual values. In reviewing the literature and searching the web, I found there is a broad awareness, but an overall lack of denition, of the spiritual value of forests. This lack of clarity hinders incorporating spiritual values into the practice

of sustainable forest management. I attempt to clarify spiritual values as they apply to forests. Rather than viewing them as a single concept, I propose four broad categories of spiritual values as they relate to forests: intrinsic sacredness, associated sacredness (forests as the loci of significant spiritual history or culture), refection of God’s glory, and a place to experience transcendence.
Cinema of the Not-Yet
Authors: Ivakhiv Adrian
Published: December 2011

Drawing on Ernst Bloch’s writings on utopia, Michel Foucault’s notion of heterotopia, and the ‘affective turn’ in social theory, I argue that cinema is by its nature heterotopic: it creates worlds that are other than the ‘real world’ but that relate to that world in multiple and contradictory ways. The landscapes and people portrayed in ?lm are affectively charged in ways that alter viewers’ relationship to the real objects denoted or signi?ed by them. But it is the larger context of social and cultural movements that mobilizes or fails to mobilize this affective charge to draw out its critical utopian potentials. I examine four ?lms from the 1970s—Deliverance, The Wicker Man, Jonah Who Will Be 25 in the Year 2000, and Stalker—as examples of richly heterotopic ?lms that elicited utopian as well as dystopian affects in their audiences, and I discuss some ways in which American environmentalists, British Pagans, Europe’s ‘generation of ’68’, and Soviet citizens worked with these affects to imagine change in their respective societies.
Transitivity System and Process Types in Persian
Authors: Bahman Zhila
Published: December 2011

This paper focuses on the ideational function of language and the TRANSITIVITY system of Persian and attempts to give, in general, a functional description of the grammar of the clause as representation and to identify, in particular, different process types and participant roles in Persian. In the identification of the characteristics of Persian experiential grammar, this paper will further focus on the verbal morphology and describe its role in the recognition of different participants in various process types by foregrounding the ways through which the Persian clauses represent some kind of bond or agreement between the process and one experiential participant. This co-relation between the verbal group and the experiential participant will also be illustrated in terms of voice.
A discourse semantic approach to Old English narrative texts
Authors: Hong Hyo-Chang
Published: December 2011

With a few exceptions such as Michael Cummings (1995, 2010), Martin Davies (1996) and David Banks (2008), older stages of English have not received much attention in in Systemic Functional Linguistics (SFL). Motivated by Coffin’s research on the language of history (1997, 2006), this paper attempts to examine the possibility of classifying OE texts into different genre types based on Martin & Rose’s genre classification model (2008) and to investigate discourse semantic features contributing to such classifications; in particular, with regards to the mystery particle ‘þa’ (Longacre, 1976). It reports on the way in which the discourse semantic systems of conjunction and appraisal play a key role in the generic classification of the OE texts examined.
The Genre of Foyers in the Contemporary Highrise
Authors: McMurtrie Robert
Published: December 2011

The term genre is usually associated with literary and filmic texts; however, this article also considers other communicative events such as foyers as text types. While it might seem quite obvious to note that the fundamental purpose of foyers is to shuttle users back and forth between the entrance and the elevator, it is more intriguing to discern the ways in which this function is achieved. By using the theoretical framework developed within the discipline of systemic functional linguistics and by employing the analytical tool of intertextuality, this article undertakes a comparative semiotic reading of the foyers of Harry Seidler’s corporate and residential highrises in Sydney, Australia, in order to explicate the generic structure of foyers, to elucidate the similarities and differences between his foyers and to foreground the ideological stance that Seidler has consistently taken throughout his oeuvre.L
Where is the hard news?
Authors: Rossette Fiona
Published: December 2011

This article examines the French press in light of the news/commentary distinction, both in terms of discourse structure and variation in authorial voice. It is demonstrated that while news is the genre “by default” in press-reporting in the Anglo-Saxon world, elements generally reserved in English for commentary appear in French news. Main examples are taken from the French dailies Le Monde, Libération and Le Figaro, and are compared with articles from The Times, The Guardian and The Independent. Structurally, French news diverges from the nucleus-satellite model and contains more logical conjunction. Explicit structuring is also carried out through extensive layers of paratext. In terms of authorial voice, French news contains more instances of inscribed appraisal, and can also promote greater proximity between writer and reader. This study provides a glimpse of the very distinctive tone of the French press, and raises the question of whether subjectivity is perceived in the same way in different languages.
Method of numerical correction of errors occasioned by delay of records during the monitoring of environmental variables of interest for animal production
Authors: Gabriel Filho Luís R. A. , Pereira Danilo F. , Barato Fernando F. , De Magalhães Marcelo M.
Published: December 2011

Thermal and air conditions inside animal facilities change during the day due to the influence of the external environment. For statistical and geostatistical analyses to be representative, a large number of points spatially distributed in the facility area must be monitored. This work suggests that the time variation of environmental variables of interest for animal production, monitored within animal facility, can be modeled accurately from discrete-time records. The aim of this study was to develop a numerical method to correct the temporal variations of these environmental variables, transforming the data so that such observations are independent of the time spent during the measurement. The proposed method approached values recorded with time delays to those expected at the exact moment of interest, if the data were measured simultaneously at the moment at all points distributed spatially. The correction model for numerical environmental variables was validated for environmental air temperature parameter, and the values corrected by the method did not differ by Tukey's test at 5% significance of real values recorded by data loggers.
Decomposition kinetics of gaseous ozone in peanuts
Authors: Alencar Ernandes R. de , Faroni Lêda R. D. , Martins Marcio A. , Costa André R. da , Cecon Paulo R.
Published: December 2011

This study was conducted to evaluate the decomposition kinetics of gaseous ozone in peanut grains. This evaluation was made with 1-kg peanut samples, moisture contents being 7.1 and 10.5% wet basis (w.b.), placed in 3-liter glass containers. The peanut grains were ozonated at the concentration of 450 µg L-1, at 25 and 35 ºC, with gas flow rates of 1.0 and 3.0 L min-1. Time of saturation was determined by quantifying the residual concentration of ozone after the gas passed through the grains to constant mass. The decomposition kinetics of ozone was evaluated after the grain mass was ozone-saturated. For the peanut grains whose moisture content was 7.1% (w.b.), at 25 and 35ºC and with flow rates of 1.0 and 3.0 L min-1, the values obtained for time of saturation of gaseous ozone ranged between 173 and 192 min; the concentration of saturation was approximately 260 µg L-1. For the grains whose moisture content was 10.5% (w.b.), a higher residual concentration of gaseous ozone was obtained at 25 ºC, that of 190 µg L-1. As regards the half-life of ozone, the highest value obtained was equivalent to 7.7 min for grains ozonated at 25 ºC, while for those with moisture content of 10.5% at 35 ºC, half-life was 3.2 min. In the process of ozone decomposition in peanut grains, temperature was concluded to be the key factor. An increase of 10 ºC in the temperature of the grains results in a decrease of at least 43% in the half-life of ozone.
Sensibility analysis of the pearl model for pesticide leaching in the State of Mato Grosso do Sul, Brazil
Authors: Scorza Júnior Rômulo P. , Silva João P. da
Published: December 2011

For an accurate use of pesticide leaching models it is necessary to assess the sensitivity of input parameters. The aim of this work was to carry out sensitivity analysis of the pesticide leaching model PEARL for contrasting soil types of Dourados river watershed in the state of Mato Grosso do Sul, Brazil. Sensitivity analysis was done by carrying out many simulations with different input parameters and calculating their influence on the output values. The approach used was called one-at-a-time sensitivity analysis, which consists in varying independently input parameters one at a time and keeping all others constant with the standard scenario. Sensitivity analysis was automated using SESAN tool that was linked to the PEARL model. Results have shown that only soil characteristics influenced the simulated water flux resulting in none variation of this variable for scenarios with different pesticides and same soil. All input parameters that showed the greatest sensitivity with regard to leached pesticide are related to soil and pesticide properties. Sensitivity of all input parameters was scenario dependent, confirming the need of using more than one standard scenario for sensitivity analysis of pesticide leaching models.
Biomatemática: métodos e limitações
Authors: Piqueira José Roberto Castilho
Published: December 2011

Este trabalho trata de uma visão panorâmica dos principais métodos utilizados, atualmente, na modelagem matemática de processos biológicos. Esses métodos são muito variados, com enfoques que, às vezes, são determinísticos, utilizando a teoria dos sistemas dinâmicos e, às vezes, são probabilísticos, lançando mão das equações diferenciais estocásticas. Em todos eles, entretanto, três fatores inerentes aos processos biológicos não podem deixar de ser considerados: a complexidade, a imprevisibilidade e a diversidade de escalas temporais.
Um olhar histórico sobre a questão regional e os serviços básicos de saúde no Estado de São Paulo
Authors: Mello Guilherme Arantes , Ibañez Nelson , Viana Ana Luiza d'Ávila
Published: December 2011

Com notável vigor, nos últimos anos, o debate da saúde pública brasileira tem sedimentado a ideia de que a organização regional da atenção primária à saúde é um passo inicial obrigatório para a consecução dos princípios da universalidade, equidade e integralidade do Sistema Único de Saúde (SUS). Ideário que contrapõe em definitivo o peso histórico mobilizado pela descentralização como essência do processo de organização dos serviços nos estados, mas explicita a insuficiência do modelo burocrático de gestão e dos papéis clássicos das instâncias governamentais, com reflexo particular na aptidão gerencial das Secretarias de Estado da Saúde. Sendo assim, este artigo busca contribuir com uma visão histórica geral da trajetória, as concepções, as mudanças gerenciais e o papel da instância estadual na conformação da organização regional e dos serviços básicos de saúde no estado de São Paulo. Sob o referencial da história do discurso e balizado pela introdução do modelo dos centros de saúde distritais nos anos 1920 como origem mais remota do discurso contemporâneo da atenção básica, o texto se estrutura sobre a identificação de quatro fases dinâmicas, marcadas por reformas que alteram de modo incisivo a questão regional e dos serviços básicos no estado.
The Great Achievement in Well Control of one of the Iranian Wells
Authors: Makvandi Mehran , Shahbazi Khalil , Bahmani Heaidar
Published: December 2011

Well control is one of the crucial tasks in drilling oil or gas reservoirs. It affects the overall cost of completing a well and in some cases leads to fatalities and numerous damages to environment.

During drilling 12 1/4″ hole size at depth of 615m, well 24 of Naft shahr located in the Western part of Iran was blown out in 2010. The entire drilling rig got fire and due to extreme temperature, substructure and wellhead were buried by mast, rig floor, top drive and drawworks. The temperature at the wellhead was estimated to be almost 950°C and pressure around 900 psi. These added to the difficulty of the kill operation. Moreover, the seepage of gas in the area around the well made the operation for the personnel very difficult.

Two parallel approaches were employed to control the well. They consisted of well capping (top kill) and relief wells (bottom kill). With a close observation of the process and a precise program, the top kill technique worked out and the well was controlled after an unbelievable time period of 38 days. One of the main issues in this operation was the removal of large debris around the wellhead.

In this paper, the details of the steps taken during the 38 days including the engineering design of the both approaches, the preparation of the area, removal of the debris, employing stinger and smoke stack, and the utilization of relief well as a development well are presented.
A Comparison of Polymer Flooding With In-Depth Profile Modification
Authors: Seright R. S. , Zhang Guoyin , Akanni Olatokunbo O. , Wang Dongmei
Published: December 2011

For stratified reservoirs with free crossflow and where fractures do not cause severe channeling, improved sweep is often needed after water breakthrough. For moderately viscous oils, polymer flooding is an option for this type of reservoir. However, in recent years, an in-depth profile modification method had been commercialized where a block is placed in the high-permeability zone(s). This sophisticated idea requires (1) the blocking agent must have a low viscosity (ideally a unit-mobility displacement) during placement, (2) the rear of the blocking-agent bank in the high-permeability zone(s) must outrun the front of the blocking-agent bank in adjacent less-permeable zones, and (3) an effective block to flow must form at the appropriate location in the high-permeability zone(s). Achieving these objectives is challenging but has been accomplished in at least one field test. This paper asks: When is this in-depth profile modification process a superior choice over conventional polymer flooding?

Using simulation and analytical studies, we examined oil recovery efficiency for the two processes as a function of (1) permeability contrast, (2) relative zone thickness, (3) oil viscosity, (4) polymer solution viscosity, (5) polymer or blockingagent bank size, and (5) relative costs for polymer versus blocking agent. The results reveal that in-depth profile modification is most appropriate for high permeability contrasts (e.g. 10:1), high thickness ratios (e.g., less-permeable zones being 10 times thicker than high-permeability zones), and relatively low oil viscosities. Because of the high cost of the blocking agent (relative to conventional polymers), economics favor small blocking-agent bank sizes (e.g. 5% of the pore volume in the high-permeability layer). Even though short-term economics may favor in-depth profile modification, ultimate recovery may be considerably less than from a traditional polymer flood.
Worldwide Classification and Reporting Requirements for Geothermal Resources
Authors: Falcone G. , De Witt G. J. , Teodoriu C.
Published: December 2011

The increased awareness and interest in renewable resources has raised the need to standardize the reporting requirements for geothermal resources that can be applied worldwide. As no agreed standards, guidelines or codes exist, there remains too much latitude in geothermal assessment, which leads to more resource uncertainty, more investment risk and less confidence in development. Standardizing the reporting of geothermal resources is a major challenge as it is difficult to define what the target actually is: the source, the reservoir, the fluids, the stored heat, the recoverable volume, the recoverable heat, the recoverable power, or the net profit. Formulating an agreed procedure to classify geothermal resources is further complicated by changing environmental, policy and regulatory constraints around the globe.

This paper provides a detailed review of published geothermal classifications, which contrasts and compares them with reporting requirements from the petroleum and mining industries. Present day techniques of computing geothermal resources provide only ballpark estimates at best. The classification and quantification of different geothermal occurrences will differ, depending on their static thermal energy in place, recoverable thermal energy, or net transformed energy.

An integrated approach to estimate geothermal resources is suggested that would couple the modeling of volumes and flows at subsurface and surface conditions, possibly allowing the future inclusion of technological advances to exploit geothermal resources that were previously reported to be sub-commercial.
Predicting Production From the Marcellus Shale With Two-Layer Dynamic Inflow Performance Curves
Authors: Cook Joshua
Published: December 2011

This paper discusses a modeling technique that can be used to predict the gas production from Marcellus Shale wells. The fundamental concept is to model the relationship between pressure and production over time using inflow performance relationships and volumetric calculations. The model can be adjusted to fit the production values and then used to predict production on that well or on offsetting wells based on the pressures that are expected.

The introduction of this paper provides a general description of the characteristics and production volumes that are typical of horizontal Marcellus wells.

The theory separates the reservoir into two systems; the stimulated reservoir and the matrix reservoir. From these systems inflow performance relationships, decline curves, and volumetric calculations are used to build the model. Over time, the inflow performance curves will change. With this model, an inflow performance curve can be generated at any point in the life of the well.

By creating a model for a well, a prediction can be made of the well’s production if conditions change. This could be extremely helpful in modeling pipeline and compression systems or evaluating wells under changing conditions. It can also be used to estimate potential production from curtailed wells. Over time, the model may also be used to indicate if damage or enhancements have occurred or if chemical, mechanical or stimulation treatments were effective.

The technique could easily be applied to other similarly designed wells. This could include other shale wells, CBM wells or wells in naturally fractured reservoirs.

This paper presents a theory that is a "first run" concept, based on previous work, theories, and observations. The technique presented can be expanded and refined by future researchers.
Experimental PVT Property Analyses for Athabasca Bitumen
Authors: Ashrafi Mohammad , Souraki Yaser , Karimaie Hassan , Torsaeter Ole , Bjorkvik Bard J.
Published: December 2011

Extra heavy oil and bitumen reservoirs constitute huge volumes around the world and are attracting attention as alternative energy resources while the light oil reserves diminish. Thermal recovery and steam based methods are the most widely used recovery methods applicable to these highly viscous deposits. Study of steam injection in porous media containing viscous oil requires a good understanding of the physical properties of both reservoir rock and fluid. In particular, there are some bitumen properties that are needed for simulation studies and the most reliable source for these data is laboratory tests. This paper presents experimental study of some PVT properties of Athabasca crude oil to help provide input data for further numerical studies.

Viscosity of Athabasca heavy crude was measured using a rotational viscometer up to 300 °C. This viscosity data is a more reliable input for simulation purposes. Athabasca oil was characterized by gas chromatography analysis to C39+. No significant amount of components lighter than C9 was observed. Whole sample molar mass was measured to 534 g/mol by cryoscopy. Density at standard conditions of 1 atm and 60 °F was measured to 1.0129 g/cm3 by a density measuring cell. Density and molar mass of the C39+ fraction were also determined. Density measurements were performed in the temperature range 120–195 °C as well where the density was found to vary in the range 0.95–0.90 g/cm3. A formula was derived based on experimental density data to predict Athabasca bitumen density in the temperature and pressure range studied. The interfacial tension between oil and steam was measured in the temperature range 120–220 °C by the pendant drop method. The interfacial tension was determined to be between 25 and 18 mN/m with a decreasing trend in the temperature range studied. The results presented here can be used as reference data for studies related to Athabasca bitumen.
Microseismic and Microscopic Analysis of Laboratory Induced Hydraulic Fractures
Authors: Chitrala Yashwanth , Moreno Camilo , Sondergeld Carl , Rai Chandra
Published: December 2011

Microseismic (MS) monitoring of hydraulic fractures using either the downhole or surface geophones has become a common practice. The same setup may be used for the multi-stage fractures. The main limitations in using these data to understand hydraulic fracturing results are: the sensor location which is far away from the source, limited azimuthal coverage and inadequate velocity models. Analysis becomes more complex when we start dealing with anisotropic reservoirs. Typically the service companies produce the spatial and temporal plots of hypocenters without estimates of uncertainty leading the engineer to believe the hypocenter locations are exact. The hypocenter location problem becomes more complex in anisotropic shale reservoirs. Hypocenter locations are often determined from the arrival times of P-wave and S-waves and a known velocity model. The difference in the velocity structure and the complex fracture network make accurate fracture mapping difficult. In this paper, we report on a series of laboratory hydraulic fracturing studies performed on sandstone and a strongly foliated metamorphic rock, pyrophyllite. Microseismic events associated with the hydraulic fracturing are dominated by shear failure; fracture orientation is controlled as predicted by applied stresses in isotropic materials. However, in anisotropic materials the hydraulic fracture direction is influenced by the magnitude of anisotropy but is predictable when the anisotropic elastic constants are known. Visual evidence supports the hypocenter locations and focal mechanism determinations. Scanning Electron Microscope (SEM) observations reveal the nonlinear and nonplanar nature of the induced fractures. The fracture trace confirms the wider aperture at the injection point and the frequent occurrence of the terminations and bifurcations farther along the fracture front.
Fracture Treatment Optimization Via Points of Diminishing Return as Determined by Seismic Moment Tensor Inversion
Authors: Mace Kaitlyn , Urbancic Ted , Baig Adam
Published: December 2011

We introduce the concept of Fracture Treatment Optimization (FTO) to find and analyze the Point of Diminishing Return (PDR) of stimulations. The approach is based upon locating the opening and closing points of fractures as identified through Seismic Moment Tensor Inversion (SMTI) analyses of microseismic data collected during treatments. By using SMTI data, it is postulated that the size of a treatment, the proppant concentrations and amounts, types of fluid pumped and amounts, the rates of treatment, and disposition of the fracture network may be analyzed to determine if they are optimal for the formation and the stress conditions of each individual fracture stage. As described, FTO is performed as a post-treatment approach to characterize the effectiveness of the treatment process. The PDR is identified by analyzing the SMTI data for each event in time and compared to the fracture treatment data. We show, through example, how the SMTI data can be used to establish when the transition between fractures with opening components of failure and those including significant closure components of failure. We suggest that these states are indicative of reaching a PDR thereby allowing for changes to the treatment to be considered. In the examples provided, we identify apparent PDRs due to leakoff dominated pad stages which are too large and when proppant is added too late in the stage. Additional PDRs are identified in the treatment when an energy balance has been reached, where leakoff and fluid injection is at equilibrium. At this point we suggest that introducing a change in energy or proppant concentrations can optimize the treatment. This empirical optimization allows for potentially more economic and efficient stimulations in subsequent hydraulic fracture treatments in the field.
Porosity and Permeability Changes in Sandstones and Carbonates Under Stress and Their Correlation to Rock Texture
Authors: Petunin V. V. , Yin X. , Tutuncu A. N.
Published: December 2011

The porosity and permeability of carbonate and sandstone cores were measured using a CMS-300 permeameter under a variety of stresses. Stress-permeability correlations showed significant variations with rock type. Porosity decay was similar between the rock types. The difference in the stress-permeability behaviors is explained by the difference in the pore structure.

Permeability loss during reservoir depressurization has important consequences on production. Laboratory quantification of stress-dependent permeability conducted in this study provided useful data for reservoir models. In addition, the correlation between stress-permeability behavior and rock type is helpful in establishing a bridge between microscopic structure and geomechanics.

In sandstone cores, the permeability decayed by 10–20% with increasing stress while the porosity decreased by about 3%, similar to what is expected from a Carman-Kozeny-type correlation. In some carbonate cores tested, the permeability was altered by an order of magnitude with the same porosity reduction. Cores with artificial fractures behaved similarly to un-fractured carbonates. These results indicate that the porosity in carbonates can be divided into a conductive portion that controls the permeability through the Carman-Kozeny equation, and a non-conductive (vuggy) portion that has limited effect on fluid flow, similar to the division between fracture porosity and matrix porosity in fractured rocks. The porosity-permeability relationship of carbonates was used to separate the conductive and non-conductive (vuggy) porosities. The vugginess of carbonate samples were projected to be 25–90% of the total effective porosity. Microscopic imaging shows favorable initial agreement with model projections.

Reservoir rock properties are not static when they are being produced. Instead, pores change their shapes and sizes with varying stress conditions. Understanding those changes are valuable in their own right but this geomechanical response also indicates important features of the rock. This research not only characterized the stress-permeability behaviors of sandstone and carbonates, but also successfully correlated them to their characteristic texture. The method of characterization of vugginess through a geomechanical test is new, and this principle can be applied to fractured rock samples to find not only the compressibility of rock but also the fracture and matrix porosities.
Shale Reservoir Properties from Digital Rock Physics
Authors: Walls Joel D. , Diaz Elizabeth
Published: December 2011

A majority of the whole core samples recovered in the US today come from shale (mudstone) reservoirs. A primary reason for so much shale coring is that shale petrophysical models require rigorous core calibration to provide reliable data for reservoir quality, hydrocarbon-in-place, and hydraulic fracturing potential. However, the uncertainty in interpreting shale well log data is sometimes matched or exceeded by the uncertainty observed in traditional methods of analyzing core samples. Most commercial core analysis methods in use today were developed decades ago for sandstones and carbonates exceeding 1 millidarcy in permeability. High quality organic-rich shale on the other hand is usually lower than 0.001 millidarcy. This extreme low permeability creates substantial challenges for existing methods and has contributed to the rapid rise of a new approach to reservoir evaluation called Digital Rock Physics or DRP.

DRP merges three key technologies that have evolved rapidly over the last decade. One is a high-resolution diagnostic imaging method that permits detailed examination of the internal structure of rock samples over a wide range of scales. The second is advanced numerical methods for simulating complex physical phenomenon and the third is high speed, massively parallel computation using powerful graphical processing units (GPU’s) that were originally developed for computer gaming and animation.

Based on pore-scale images from a wide range of organic shales, it can be seen that organic material is present in a variety of forms. Three primary forms, non-porous, spongy, and pendular are commonly observed. Non-porous organic components fill all of the available non-mineral space leaving virtually no porosity or fluid flow path. Porous or "spongy" organic material is commonly encountered in thermally mature gas shales. Pendular organic material appears to fill the small inter-granular and grain contact regions, leaving open pore space in the larger voids. These pore types are largely controlled by kerogen type and thermal maturity, and they exert large influence on the porosity, permeability, and overall shale reservoir quality.
Shear Dilatancy in Unconsolidated Laboratory Samples Improves Relative Permeability Performance
Authors: Khan Hasnain A. , Olson Jon E. , Holder Jon
Published: December 2011

Steam Assisted Gravity Drainage (SAGD) can cause dilatant shear failure in unconsolidated heavy oil reservoirs. Our experimental work documents changes induced by such shear failure in absolute permeability, relative permeability to oil and water, and residual saturations. Tests were performed on 2 inch diameter synthetic specimens made from lower fine to medium grain size Ottawa sand formed with wet vibration to an initial porosity of about 32%. Loading paths included triaxial compression and radial extension. Axial and volumetric strains were measured directly during deformation, and single and two phase permeability tests were executed at axial strains of 1 to 10%. Triaxial compression tests followed a path of increasing mean stress (under constant confining stress) while radial extension tests provided a decreasing mean stress loading path (reducing confining stress under constant axial stress). The relative permeability was determined by the unsteady state method for relative permeability endpoint assessment. Results show similar absolute permeability trends to those published by others, but our multiphase measurements appear unique. Relative permeabilities are more strongly influenced by shearing, with water relative permeabilities being increase by as much as a factor of 2. The effect seems to be slightly greater for finer grain sand than for the medium grain size. Absolute permeability changes were greatest for the samples with the lowest initial porosity, which would include those that were poorer sorted. Poorer sorting of the sand pack seems to reduce the impact on relative permeability changes, however. Residual oil saturations were reduced from 0.28 to 0.13 in the lower fine Ottawa sample, suggesting the possibility for significant improvement in oil recovery when the sand is sheared. During triaxial testing, it was interesting to note that at 50 psi effective confining stress, absolute permeability increased with shearing, but at 200 psi effective confining stress, absolute permeability was reduced, even though the volumetric strain was still dilatant. In addition to providing new data on the magnitude of absolute permeability and multiphase flow properties for unconsolidated sands, this paper also demonstrates that dilatant shear failure does not guarantee increased flow capacity for such rocks.
Bayesian Probabilistic Decline Curve Analysis Quantifies Shale Gas Reserves Uncertainty
Authors: Gong Xinglai , Gonzalez Raul , McVay Duane , Hart Jeff
Published: December 2011

Several analytical decline curve models have been developed recently for shale gas wells (Anderson et al. 2010; Ilk et al. 2008; Valko and Lee 2010). However, despite the considerable uncertainty associated with forecasting shale gas production, these authors either do not quantify the reserves uncertainty in shale gas wells or fail to demonstrate that their probabilistic forecasts are well calibrated. Jochen and Spivey (1996) and Cheng et al.(2010) developed bootstrap methods that can generate probabilistic decline forecasts and quantify reserves uncertainty. Forecasts with the Modified Bootstrap Method (Cheng et al. 2010) provide good coverage of the true reserves. However, it is not time efficient because it requires hundreds of Newton iterations for each well. In this work, we introduce a Bayesian methodology for probabilistic decline curve analysis that quantifies reserves uncertainty reliably, quickly, and without modifying the historical production data. We analyzed 167 horizontal gas wells with more than 7 years of production in the Barnett shale to validate the methodology.

In this Bayesian methodology, the decline curve parameters qi,Di, and b are assumed to be random variables instead of parameters to be modified to obtain a best fit. A Markov chain of the decline curve parameters is constructed using MCMC with the Metropolis algorithm. In the test of 167 Barnett shale horizontal gas wells, we assume that the first half of production is known and the second half of production is unknown and acts as "future production." Approximately 85% of the 167 wells’ "future production" falls in the range of P90 and P10 reserves generated by this Bayesian methodology, indicating the method is well calibrated, and the Bayesian method is 13 times faster than the modified bootstrap method.

The proposed Bayesian methodology provides a means to generate probabilistic decline curve forecasts and quantify the reserves uncertainty in shale gas plays quickly and reliably. This Bayesian methodology can also be applied with other analytical decline curve models if desired.
Measuring the Impact of Geomechanical Heterogeneity in Organic Shales on Hydraulic Fracture Initiation and Propagation
Authors: Waters George , Zhao Ruhao
Published: December 2011

The placement of multiple hydraulic fractures along cased and cemented horizontal wellbores drilled in the direction of minimum horizontal stress is the most common completion methodology used in the development of organic shales today. Multiple perforation clusters are included in each stimulation treatment to optimize time and efficiency. This does not necessarily result in optimized productivity as many perforation clusters are frequently determined not to be contributing to production when these wellbores are evaluated with horizontal production logs.

The ability to initiate, propagate and place proppant through the near-well region of a hydraulic fracture is a function of stresses around the borehole and the orientation of the borehole relative to the principle stress field. The near-well stresses are influenced by the anisotropic geomechanical medium pervasive in organic shales. This anisotropy can dramatically alter the stress field and must be taken into account if productivity is to be optimized along a horizontal wellbore.

Field data from the Barnett Shale is evaluated to estimate the impact of this anisotropy on the ability to initiate and place hydraulic fractures through the near-well region. Fracture initiation and near-well closure pressures are measured and compared to those predicted by accounting for geomechanical anisotropy. These results are used to develop guidelines for effective perforation placement. Such techniques can be used to improve well productivity.
Novel Wellbore Strengthening Enables Drilling of Exploration Well in a Highly Depleted Formation
Authors: Friday Otutu
Published: December 2011

Operators all over the world are still facing the challenge of having to drill through highly pressure depleted formations in order to drill to lower lying hydrocarbon bearing zones especially in terms of wellbore stability and loss circulation. Stability of boreholes in these scenarios requires a careful consideration of in-situ stresses, rock strength, pore pressure, wellbore fluid pressure and drilling fluid characteristics. Managing lost circulation with stability offormations is one of the most difficult scenarios that needs proper engineering. Before a depleted zone can be cased-off, it has to be successfully drilled. Drilling through highly depleted sands can result in problems such as lost circulation, differential sticking, difficult logging and/or not being able to reach the well objective depth, wellbore instability resulting in significant and expensive non-productive time (NPT) and costly remediation process, in addition to the loss of costly mineral oil-based mud used for drilling.

Remedies such as squeezes, cement plugs, expandable liner and casing while drilling can be costly solutions and are not always successful.

Key factors in the successful drilling of study wells included special drilling fluid design, rock mechanics study, pro-active use of bore hole strengthening technology, integration of supplier and operator expertise, and excellent communication between all parties involved.

The study showed that enhanced formation strength can allow sufficient tolerance to overbalance pressure leading to the use of higher mud weight due to the widening of mud weight window especially when an exploration objective is to be drilled below depleted formations.

This paper presents the result of the use of a novel system used in improving the formation strength characteristics in a depleted environment.
C7+ Characterization of Heavy Oil Based on Crude Assay Data
Authors: Ghasemi M. , Alavian S. A. , Whitson C. H.
Published: December 2011

The description of heptanes and heavier components (C7+) in reservoir fluids can be important for equation of state (EOS) predictions of phase and volumetric behavior. This paper describes a procedure for C7+ characterization of heavy oil based on crude assay data which are typically measured for refining and marketing applications.

C7+ characterization is defined as (1) modeling the molar distribution that quantifies molar (mass) amounts and molecular weights of discrete plus fractions, (2) estimating specific gravity and normal boiling point of plus fractions, and (3) estimating EOS and viscosity-model parameters Tc, pc, ω, Vc, s (volume shift) and binary interaction parameters (BIPs) kij of plus fractions.

From crude assay data, we use the mass fractions and overall sample molecular weight to determine the parameters for gamma molar distribution parameters – shape (α), lower bound (η) and average plus molecular weight (Mo) in the gamma distribution model. The molar distribution model, together with measured assay-cut specific gravity and boiling point data, are used to determine parameters in the Soreide correlation describing specific gravity-molecular weight relationship. The inter-correlation of assay data is also affected by correlation used between molecular weight, boiling point, and specific gravity. We use a parameter, fTwu, where fTwu=1 honors the Twu correlation exactly, while fTwu= 0 honors a pure-paraffinic correlation between molecular weight and boiling point (independent of specific gravity).

Viscosities of each fraction are correlated against measured data and/or standard-pressure liquid viscosity estimates from the Orrick-Erbar correlation. We use the Lorentz-Bray-Clark (LBC) correlation, where fraction critical volumes are adjusted to give consistency between the LBC estimates for each fraction individually. This approach to determining the critical volumes has proven useful in making the LBC more predictive for overall oil mixture viscosities at reservoir conditions.
An Innovative Approach for Pore Pressure Prediction and Drilling Optimization in an Abnormally Subpressured Basin
Authors: Contreras Oscar , Hareland Geir , Aguilera Roberto
Published: December 2011

Up to now, an indirect generalized method to predict pore pressure under subpressured conditions has not been reported in the literature. In this work, an innovative procedure is presented for estimation of pore pressure and optimization of wells drilled in the abnormally subpressured Deep Basin of the Western Canada Sedimentary Basin (WCSB). The procedure starts with detailed evaluation of 5 wells drilled in a township that covers the study area. Pore Pressure was calculated from Sonic Logs and the Modified D Exponent using Eaton’s Method (Eaton, 1975), which proved to be the most effective approach for abnormal subpressured conditions over a variety of methods tested (Contreras et al., 2011). The optimization procedure was carried out using the Apparent Rock Strength Log (ARSL), which is an effective indicator of formation-drillability and very sensitive to the pore pressure. Next, optimization of individual sections in each well was carried out to determine the optimum types of bits and operational parameters for the lowest cost of drilling.

An artificial intelligence function was implemented to set up the optimum combination of parameters in such a way that the rate of penetration (ROP) (m/h) was increased after a number of simulation runs while controlling the bit wear. Especial attention was focused on tight gas reservoirs for selection of the most suitable parameters that increase the quality of drill cuttings. It was concluded that the rollercone bit IADC 547 with at least 0.73 horsepower in the bit per square inch provides the best quality of cuttings for the Nikanassin Group. This is of paramount importance for increasing accuracy in the quantitative determination of permeability and porosity from cuttings particularly in those tight gas reservoirs where the amount of cores is very limited.

It is concluded that wells in the Deep Basin of the WCSB can be drilled efficiently with 7 bit runs while keeping the cuttings quality, bit wear and well stability at a significantly high average ROP of 13 m/h. Another conclusion is that the normal trend methods from sonic logs are the most effective approach when dealing with an abnormally subpressured basin.