bluuebunny/crossref_metadata_2025 huggingface dataset:
FreezeFrac Improves the Productivity of Gas Shales
Authors: Enayatpour S. , Van Oort E. , Patzek T.
Published: September 2013

With rapid depletion of conventional petroleum supplies and due to energy security concerns, the world is increasingly turning its attention to unconventional hydrocarbon reservers such as oil shales, gas shales, tight gas sands, coalbed methane, and gas hydrates. Despite the abundant unconventional reservers, the production is still hindered by many obstacles including lack of technology and knowledge of the physics of flow in tight porous media. Flowing the tightly-locked hydrocarbon to the well in such formations, unlike the conventionals, requires a large number of inter-connecting pathways for flow. The existing in-situ cracks in rock have to be connected in order for the hydrocarbon to flow into the wellbore. In this paper we go over the basic mechanisms of rock fracture in micro and Macro levels and then study the two parameters whose variations could reduce the effective stress and lead to rock fracturing. We then discuss the effect of inhomogeneity on the fracture load and show that the dominant load for thermal fracturing is the tensile stress. There are three governing equations of stress, heat transfer, and flow which should be solved in a coupled fashion, for which we are using the finite element software packages. Assuming that thermal cracks increase the permeability of rock in the near wellbore zone by 10-10,000 times, we show the impact of rock stimulation by thermal shock on cumulative production of gas from a sample case of a wellbore placed in a tight formation. The improved recovery for the sample case is 16%.
A New Model for Geomechanical Seismicity Based Reservoir Characterization Including Reservoir Discontinuity Orientations
Authors: Hosseini S. Mehran , Aminzadeh Fred
Published: September 2013

Seismicity based reservoir characterization (SBRC) is a reservoir characterization method based on seismic events. This paper focuses on seismicity based permeability estimation which has been used in the oil and gas industry for more than a decade. However, the geomechanical processes behind this phenomenon have not been fully considered in the permeability estimation. A new model for SBRC based on radial pore pressure diffusion in the reservoir and Mohr-Coulomb failure criteria is proposed. This model includes reservoir stress state, fault friction coefficient and discontinuity orientations which were not included in the previously published models. Seismic data from the German Continental Deep Drilling Project (KTB) is used to test the validity of the new model. Our model predicts KTB's reservoir permeability to range between 10−17 to 10−16 m2, which perfectly matches the reported permeability in the literature for KTB and is bounded by the crust permeability limits measured in different studies worldwide. Based on the events front, reservoir discontinuity orientations can also be characterized. Sensitivity analyses of the effects of fault friction coefficient and geometry on estimated permeability showed significant dependency of the estimated permeability on the mentioned parameters. Previous SBRC models did not include permeability estimation dependency on reservoir geomechanical properties and reservoir discontinuity orientations. The new model captures the physics of microseismic activities due to fluid injection and includes geomechanical and reservoir discontinuity properties that were not included in previously published models. Using the new model, based on the events front, one can characterize the orientation of discontinuities that can be activated due to fluid injection which can be used as a new method for fracture network characterization in a fractured reservoir.
Analytical Solutions for Gas Displacements with Bifurcating Phase Behavior
Authors: Khorsandi Saeid , Johns Russell T. , Ahmadi Kaveh
Published: September 2013

Minimum miscibility pressure (MMP) is one of the most important parameters in the design of a successful gas flooding process. The most reliable methods to calculate the MMP are based on slim-tube experiments, 1-D slim-tube simulations, mixing cell calculations, and the analytical methods known as the method of characteristics (MOC). The calculation of MMP using MOC is the fastest method because it relies solely on finding the key tie lines in the displacement path. The MOC method for MMP estimation in its current form assumes that the composition path is a series of shocks from one key tie line to the next. For some oils, however, these key tie lines do not control miscibility and the MMP calculated using the key tie line approach can be significantly in error. The error can be as high as 5,000 psia for heavier oils or CO2 displacements at low temperature where three-phase hydrocarbon regions can exist (L1-L2-V). At higher pressures, the two- or three-phase region can split (or bifurcate) into two separate two-phase regions (L1-L2 and L1-V regions). Thus, for the MMP calculation from MOC to be correct we must calculate the entire composition path for this complex phase behavior, instead of relying on the shock assumption from one key tie line to the next.

In this paper the MOC composition route is developed completely for the bifurcating phase behavior displacement using a simplified pseudoternary system that is analogous to the complex phase behavior observed for several real displacements with CO2. We develop the MOC analytical solutions by honoring all constraints required for a unique solution; velocity, mass balance, entropy, and solution continuity. The results show that a combination of shocks and rarefaction waves exist along the nontie-line path, unlike previous MOC solutions reported to date. We show that by considering the entire composition path, not just the key tie lines, the calculated MMP agrees with the mixing cell method. We also show that in this complex ternary displacement the displacement mechanism has features of both a condensing and vaporizing drive, which was thought to be possible only for gas floods with four or more components. For pure CO2 injection the solution also becomes discontinuous for oils that lie on the tie-line envelope curve. Finally, we show that shock paths within the two-phase region are generally curved in composition space and that there is no MMP for some oil compositions considered in the displacements by CO2. Recovery can be large even though the MMP is not reached.
Using Completion Diagnostics to Optimize Completion Designs in Several Horizontal Shale Plays
Authors: Johnson M. D. , Pechiney J. J. , Warren M. N. , Woodroof R. A. , Leonard R. S. , Moore C. P.
Published: September 2013

Abstract

Horizontal shale gas and oil completion designs have evolved over the last several years. Effective completion design has become extremely important in developing these shale plays. In general, the industry has moved towards longer laterals, more stages, closer spacing between entry points, and increased proppant and fluid volumes. The use of completion diagnostics can be applied to supplement production data and stimulation modeling in optimizing the completion designs and reducing the slope of the learning curve in these emerging shale plays. Fluid and proppant tracer technologies and production profiling have been successfully employed in this optimization process. This paper will present several case histories demonstrating how these completion diagnostic tools have been successfully deployed to assess stimulation effectiveness. Case histories will be presented from the Marcellus, Eagle Ford, Haynesville, and Woodford shales in which these technologies have been employed to characterize proppant placement and load fluid clean-up and to quantify fluid and proppant communication between wells. In these case histories, the diagnostic results were used to evaluate perforation design, fluid and proppant placement as a function of the perforating scheme, lateral coverage, and fluid clean-up as it relates to lateral length, wellbore trajectory, changes in lithology, and frac fluid design.

This paper will characterize and validate the role of completion diagnostics in the completion optimization process.
Eagle Ford Shale: Hydraulic Fracturing, Completion and Production Trends, Part III
Authors: Centurion Sergio , Cade Randall , Luo Xin Lucy , Junca-Laplace Jean-Philippe
Published: September 2013

The Eagle Ford Shale, as one of the most active unconventional reservoirs in the US, began heavy development in 2009. One of the attractive aspects of the Eagle Ford, which has heightened interest and helped to accelerate development, is substantial liquids production, along with solution gas. However the resultant multiphase fluid production, along with reservoir heterogeneity that is typical of most unconventional reservoirs, adds complexity and risk to development, especially for completions.

One technique that has the potential for reducing risk is learning from historical completion trends. Even though the Eagle Ford play is quite new, more than 4,000 horizontal wells have been drilled and all have been hydraulically fractured. The resultant large and growing data resource invites data mining to uncover trends and insights.

The ground work for this case study was laid first in SPE 149258 (2011) and then in SPE 158501 (2012). This last paper summarized production, completion techniques and hydraulic fracturing stages performed in 57 Eagle Ford wells. Since the previous papers, many new wells have been completed, considerably expanding the data available for analysis. Completion volumes, well architecture and reservoir character are analyzed. The entire data set is mapped in an effort to understand anomalies and trends. As the successful development of this reservoir has relied in the combination of horizontal drilling, multistage completions and hydraulic fracturing, the results should be valuable for understanding and optimizing completions in the Eagle Ford and similar shales.
Reservoir-Condition Pore-Scale Imaging Of Supercritical Carbon Dioxide
Authors: Andrew Matthew , Bijeljic Branko , Blunt Martin J.
Published: September 2013

We present the results from a novel experimental apparatus that can image – at the micron scale – fluid displacements at elevated temperatures and pressures. The images are acquired using a micro-CT scanner (Xradia Versa 500) that has been adapted to allow core flood experiments to be conducted in situ, allowing continuous imaging at resolutions down to around 1 µm. A small cylindrical core – approximately 6 mm in diameter – is placed in a carbon fibre core holder that allows high pressures and temperatures to be imposed, while remaining largely transparent to x-rays. Fluids are injected into this mini-core holder, with flexible tubing to allow the core to rotate during scanning.

We use this apparatus to study the displacement of supercritical carbon dioxide by brine, with application to carbon storage in aquifers. We study displacement in carbonate and sandstone rocks. Experiments in carbonates introduce additional challenges, since the carbon dioxide, brine and rock need to pre-equilibrated to prevent dissolution of carbon dioxide and chemical reaction (dissolution) with the rock during the experiments: this then reproduces conditions in the centre of a carbon dioxide plume where local thermodynamic equilibrium has been reached.

We study displacement in Ketton limestone and Bentheimer sandstone. Both rocks have large inter-granular pores. In Ketton there is also significant intra-granular micro-porosity that remains brine-saturated during the experiments. We study primary drainage (injection of carbon dioxide) followed by secondary imbibition (injection of brine). We image the distribution of the phases during and at the end of the experiment.

We show that significant quantities of carbon dioxide can be trapped as a residual phase in the pore space of both rock types, with a saturation matching that measured in core-scale (cm scale) experiments (0.202±0.012 in Ketton and 0.320±0.009 in Bentheimer). Trapped ganglia of all sizes are observed, with an approximately power-law distribution of size. The exponents for the power laws are larger than expected through percolation theory (2.189 as against measured values of 2.39±0.12 in Ketton and 3.0±0.3 in Bentheimer). We can observe how the supercritical carbon dioxide is displaced at the pore scale during waterflooding, providing a benchmark dataset for pore-scale modelling and further analysis.

Overall, this work presents a novel methodology for in situ reservoir-condition pore-scale multi-phase flow analysis, accounting for phase exchange and chemical reaction. In application to carbon storage, we show that significant amounts of carbon dioxide can be trapped as a residual phase in both quartz and calcite rich rocks.
Design Methodology for Swellable Elastomer Packers for Well Construction Operations
Authors: Evers Rutger , Koløy Tom Rune , Abrahamsen Terje
Published: September 2013

Since the introduction of swellable technology to the oilfield in 2001, its acceptance has grown significantly, and the scope of applications has expanded accordingly. Most of its usage has been in applications in horizontal, multi-zone fracturing, and in combination with inflow control devices (ICDs) and screens during the completion phase of the wells.

One application that is gaining interest globally is the use of swellable tools during the well construction phase. The main objective here has been to provide extra sealing capability in addition to that of the cement sheath to prevent a micro-annulus or a mud channel when the packers are cemented in. In certain cases, swellable elastomer packers (SEPs) are designed to provide a full redundant seal above the top of cement (TOC).

There are several reasons why SEPs and cementing operations are a good fit; primarily, the application of the technology is simple to implement, and allows pipe movement during the cement job. One other advantage is the fact that no specialized personnel are required for packer installation.

However, several implications to the use of SEPs in combination with a cement job must be considered:

Packer design and impact on cement placement; the packer must not impact the cement placement, as the main objective of a cement job is to get the cement slurry placed properly. Impact of swelling rubber on cement matrix once the cement is in place, it is important to know whether the SEP will impact the hydration process (setting) of the cement, changing the properties of the set cement. Bonding at the cement/rubber interface; the bond at the cement/rubber interface must be confirmed.

This paper discusses the issues above, and benefits that can be expected when SEPs are used during well construction. Two case histories will be presented to illustrate the use of SEPs during the well construction phase.
Deepwater Wells Top Hole Cement Volume Evaluation using Innovative Hole Size Inversion from LWD Propagation Resistivity Measurements
Authors: Peternell Ana , Dooply Mohammed , Leveque Soazig , Tovar Gioconda , Horkowitz Jack
Published: September 2013

Following the Gulf of Mexico Deepwater drilling moratorium in 2010, the industry focus towards well integrity assurance has significantly increased. Several new and updated regulations and best practices have been published in the last two years, including API Standard 65 – Part 2 and API RP 96. These two industry accepted standards highlighted that determining the hole volume to confirm the cement slurry volume, to fill-up the annulus to the designed top of cement, is one of the many factors impacting cement placement success during well construction process.

A new solution for riserless section was developed based on existing Logging While Drilling (LWD) electromagnetic propagation resistivity measurements, which meets the requirement to understand hole volume drilled with water based mud in deepwater environment.

Historically, deriving an accurate caliper from LWD electromagnetic propagation resistivity measurements has never been easy due to big uncertainty of mud resistivity (Li et al, 2003). The implementation of a novel simultaneous inversion model and forward modeling database from standard 2-Mhz propagation resistivity, for water-based mud (WBM) and large boreholes, provided the solution to overcome that uncertainty (Whyte et al, 2012).

This novel solution was specifically developed to address the needs for the riserless top-hole sections of high cost deepwater wells: from cement volume calculations, identification of borehole degradation through time, and new opportunities for identification of shallow water flows using the full capacity from the inversion process.

The extensive validation of this innovative approach with wireline mechanical calipers in numerous hole sections resulted in far better results than initially anticipated (Whyte et al, 2012). The information obtained provided significant insights into the reliability and limitations of the current algorithm. The ability to monitor the borehole size while drilling, as well as analyzing the reaming and trip out passes from recorded data, makes this measurement a valuable source of time-lapse information. The next validation process consisted in the comparison between cement volumes computed using these measurements against identification of cement returns during riserless cementing operations in deepwater wells.

The LWD caliper derived from propagation resistivity measurement was analyzed in more than a dozen of wells in Gulf of Mexico. Spefic case studies covering the drilling and cementing operations are presented in this paper.
Hydraulic Fracture Propagation from Infill Horizontal Wells
Authors: Roussel Nico P. , Florez Horacio A. , Rodriguez Adolfo A.
Published: September 2013

As pressure increases or decreases non-uniformly as a result of well injection/production, stresses vary anisotropically in the reservoir. The principal stresses, which govern the propagation direction of hydraulic fractures, are thus modified not only in magnitude but also in direction. Previous modeling efforts and field observations have demonstrated the impact of stress reorientation on the refracturing of vertical wells and the multi-stage fracturing of horizontal wells.

Using a state-of-the-art coupled symmetric Galerkin boundary-element method (SGBEM) and finite-element method (FEM) model, we simulate the impact of prior production from offset wells on the propagation direction of fractures initiated from an infill horizontal well. Geomechanical calculations demonstrate the occurrence of stress reversal in the infill region following a period of production from the offset wells in the order of years. The numerically simulated hydraulic fracture network in the infill well is shown to contact a smaller reservoir area past the onset time of stress reversal, as the induced fractures gradually turn to orient parallel to the infill well. The risk is to see the performance of the infill well drop compared to the offset wells. On the other hand, a window of opportunity exists when the horizontal stress contrast is reduced compared to in-situ, thus favoring the interaction with natural fractures and enhancing fracture complexity.

These new observations have significant implications for field development strategies, hydraulic fracturing design, well placement and spacing, as well as the timing of infill-well stimulation, especially in shale plays where poroelastic stress reorientation is sustained over the life of the reservoir.
Defining Three Regions of Hydraulic Fracture Connectivity, in Unconventional Reservoirs, Help Designing Completions with Improved Long-term Productivity
Authors: Suarez-Rivera Roberto , Behrmann Larry , Green Sid , Burghardt Jeff , Stanchits Sergey , Edelman Eric , Surdi Aniket
Published: September 2013

Using large-scale hydraulic fracturing experiments on tight shale outcrops we identified three dominant regions controlling stage production: (1) the connector between the wellbore and the fracture system, (2) the near-wellbore fracture and (3) the far-wellbore fracture network. The particular nature of these regions may change depending on the play, the reservoir fabric, its relation to the in-situ stress, and the distribution of rock properties. However, these regions are always well differentiated. Understanding the role of each of these components, to hydrocarbon production, is fundamental to identify the dominant sources of loss of fracture conductivity and accelerated production decline. The conditions promoting the loss of fracture conductivity, fracture face permeability and surface area in contact with the reservoir vary significantly along the length of the hydraulic fracture. By separating the induced fractured area into three characteristic regions of reservoir contact, we isolate the dominant drivers of loss of production per region, and obtain the best compromise for sustained stage productivity. We used large-scale hydraulic fracturing experiments to develop and validate the concept. These were integrated with scaled-down measurements of fracture conductivity, proppant embedment and the effect of rock-fluid sensitivity. We find that the critical conditions for productivity for the wellbore-connector depends on mechanical stability considerations and are independent of reservoir quality. The critical conditions for productivity from the near-wellbore fracture are solids retention in the proppant pack, and reduction of fracture face permeability due to proppant embedment. The critical conditions for productivity from the far-wellbore fracture are loss of surface area and retention of fracture conductivity. Results provide a framework for improving fracture design for improved long-term productivity. This is achieved by understanding the conflicting requirements between three regions of flow within the fracture and selecting the optimal compromise between these.
Selecting the Optimal Spacing Pilot Design for Unconventional Resource Optimization
Authors: Coopersmith Ellen , Burkholder Kent , Schulze Jan , Monette Scott
Published: September 2013

Spacing pilots are the most discussed and debated pilots considered for unconventional resource plays because they provide the greatest opportunity to maximize the value derived from an asset by optimizing the number of development wells. Determining optimal spacing early in a field's development allows companies to affect the largest amount of acreage. Determining the optimal spacing late may result in under or overdevelopment of all or large portion of the acreage.

Interestingly, spacing pilots in unconventional plays tend to differ from those in conventional, which is a matter of debate and caution addressed in this paper. Conventional field spacing pilots are often trying to understand drainage from individual wellbores, to answer the question of how many wells are needed to produce the estimated resource in a given acreage tract; in which case, the fewer the wells, the higher the value. In unconventional reservoirs, however, the industry tends to take a very different approach. A typical well performance type curve is forecast for a given well and completion design. Unconventional spacing pilots are then designed to try to understand the minimum distance between lateral wellbores before interference occurs and the wells produce each other's resources, thereby degrading type curve performance. In this case, the more wells, the higher the value.

The challenge lies in the early and efficient evaluation of different spacing pilot designs. This is due in part to the inherent complexities involved with unconventional resources: the fact that the optimum spacing is linked both to existing geologic uncertainties and uncertainties in the effectiveness of the well and completion design.

This paper presents a step-wise approach to design and value unconventional spacing pilots, using a typical case study example. The paper demonstrates (1) how to frame spacing pilot design alternatives, (2) forecast the uncertainty reduction potential of each design, and (3) evaluate the business case for the different alternatives. Each step is distinct and necessary to guide the evaluation of this decision. Tips and pitfalls are described and the field optimization decision tree structure necessary to capture the impact of optimal spacing is discussed.
Technology as an Enabler
Authors: Williams W. M. , Hauser M. K. , Woodall D. , Ershaghi I.
Published: September 2013

This paper is focused on how technology can significantly accelerate and improve operations, enable petro-technical and business decisions and workflows, and improve real-time access to information and experts. This approach is fundamental to how Chevron is evolving the managment of its upstream businesses. Examples are included to demonstrate how improving work flows and enabling them with technology relies on innovation and integration of people and processes. We'll also show how information can help to create pragmatic solutions that quickly allow us to realize value. By improving performance, increasing efficiency, and streamlining decision making, critical resources can recapture the time and capacity required to help us innovate into the future. As part of the Data Visualization, we'll discuss the petrotechnical integration framework for data visualization, surveillance, analysis, and reporting. We'll show how a web-based workflow petrotechnical portal can provide data access and visualization. This portal is a map-based GIS tool that connects high-value data from our petrotechnical systems of record and exposes it to facilitate decision-making. The context for the web-based tool and its role are shown in the program-level macro workflow. We'll discuss how this technology is enabling faster and broader access to data that currently exists in silos, and how it will afford high-quality analysis.
The Use of a Probabilistic Methodology to Generate and Manage the Production Forecast for Accomplishing Company's Level Goals
Authors: Castaño R. , Medina C.
Published: September 2013

The purpose of this paper is to present a methodology to generate a Company's production forecast by applying probabilistic tools to consider uncertainties and their impact on the outcome. Those uncertainties are in the category of technical, operational, social and environmental variables.

By analysing the entire production process at a company level, it was noted that it was required a comprehensive tool for forecasting, defining priorities, goal settings, production system analysis, decision making and performance evaluation. A probabilistic methodology was outlined to take into account uncertainty and interdependence of variables from different order, such as technical (decline, initial rate for new wells, EOR response, workover results), operational (downtime, drilling schedule, access to remote locations, oil evacuation), social (external blockage) and environmental (licensing time and conditions). All these variables are included in the generation of multiple production scenarios using Monte Carlo simulation and probabilistic trees. The probabilistic workflow generates production forecasts starting from each single well up to the Company level. It uses as input the results from conventional tools like reservoir simulation, DCA, Nodal analysis, maintenance plans, failure statistics, etc.

The probabilistic methodology can be used as a management tool that allows defining allencompassing production targets and to focus efforts and resources on the topics that generate greater potential deviation on production behaviour. A key contribution is the capacity to perform sensitivities for the impact of each variable and visualize it as a tornado analysis to define priorities and action plans that are reflected in Team and individual goals throughout the Balance Score Card methodology. As a result, this probabilistic methodology notably contributes to reach the production and unit operating cost target.

This methodology has been applied and improved during 3 years to make it more automatic, to assess risks, to link it to action plans and to combine it with other planning tools such us budgeting, oil transport and sales forecast.
Modelling of Cyclic Hysteresis of Three-Phase Relative Permeability during Water-Alternating-Gas (WAG) Injection
Authors: Shahverdi Hamidreza , Sohrabi Mehran
Published: September 2013

Multiphase flow takes place in many petroleum reservoirs in particular mature fields and reservoirs under fluid (e.g., gas, WAG) injection. The numerical simulation of such reservoirs requires knowledge of flow functions (i.e. relative permeability and capillary pressure). Since experimental measurement of fluid permeabilities in particular under three-phase flow conditions is very time consuming and difficult, many correlations and models have been developed and are widely used instead of measured data.

In this study, we have used the results of a comprehensive set of water-alternating-gas (WAG) injection coreflood experiments performed under different wettability conditions and core permeability values in order to obtain relative permeabilites of oil, water and gas under reservoir pressure and temperature. Three-phase relative permeability of each phase was obtained by history matching the measured production and differential pressure obtained in the laboratory. The results of the experiments revealed significant cyclic hysteresis effects in gas and oil relative permeability.

We proposed new formulations and methodology for modelling of cyclic hysteresis of three-phase relative permeability during WAG injection. This technique is a direct method which uses measured three-phase kr data obtained from first cycle of WAG to predict the relative permeability of the subsequent cycles. The integrity of this technique has been validated against the three-phase kr data obtained from our WAG experiments

We also assess the validity of the WAG hysteresis model available in reservoir simulators against our three-phase relative permeability data in order to evaluate its performance.
Application and Benefits of Degradable Technology in Open-hole Fracturing
Authors: Aviles I. , Marya M. , Hernandez T. Reyes , Dunne T. , Dardis M. , Baihly J.
Published: September 2013

The introduction of a new technology is critical for operators to expand their completion options, increase efficiency, and drive profitably in challenging environments. For unconventional reservoirs, open-hole fracturing has been key for the economic success of new ventures. With the increase in activity of liquids rich plays, there is a growing need for new technology developments for open-hole fracturing systems that further optimize these completions.

Using a combination of open-hole packers and sliding sleeves, open-hole fracturing tools successfully segment horizontal sections of the reservoir to be stimulated individually. In order to achieve isolation, seats of increasing diameters are placed inside the completion at each fracturing sleeve. These seats catch a ball that performs the function of opening the sleeve for fracturing purposes and isolating the completion below the stage. After the stimulation job is performed, the balls should ideally flow back to surface. Unfortunately, as seen in the field and described in the literature, this is often not the case. Balls frequently remain in the completion without coming to surface. In some cases depending on ball and seat material, balls may actually get stuck in the ball seats completely isolating production from the stages below. Many operators have found this to be a root cause of production problems and they are forced to take the added cost and risk of milling out the balls and seats.

A new degradable material has been developed for use on frac balls that are used in said open-hole completions. Balls made of this material can handle pressure differentials beyond the current market offering without deformation. After fracturing, these balls degrade away opening up the flow path of the well without intervention. The degradation time is a function of temperature and water chemistry (including brine), but 1 to 4 days is a typical degradation time. No other requirements are needed for the degradation process to occur.

This paper discusses a new degradable metal technology and its application in open-hole fracturing.
Successful Implementation of Engineered Fiber Based Loss Circulation Control Solution to Effectively Cure Losses While Drilling, Cementing and Work Over Operations in Oman
Authors: Jain Bipin , Khattak Mohammad Arif , Mesa Alvaro Martin , Al Kalbani Sultan , Meyer Arnoud , Aghbari Salim , Al-Salti Anwar , Hennette Benjamin , Khaldi Mohammed , Al-Yaqoubi Ali , Al-Sharji Hamed
Published: September 2013

Oman is a hotspot for drilling activity and wells are being drilled in different environments varying from Deep exploration and development for gas and oil and water injection/disposal. One challenge tops all other challenges: Lost Circulation. Due to the fractured/fissured nature of the formation and low existing reservoir pressures, all major operators are suffering from lost circulation challenges. Some of the challenges include: Mud losses while drilling leading to cost overruns and HSE concerns, primary cement job failure due to not getting the cement up to the desired height resulting in subsequent sustained casing pressure and corrosion, not able to perform work over activity on certain wells due to losses. Enormous quantities of water are required to maintain well control, and due to the limitation of water availability all over Oman, this becomes another critical issue. An Engineered fiber-based Loss Circulation pill has proved successful to address these challenges in multiple fields for Petroleum Development Oman.

Drilling shallow wells in Oman through the naturally fractured limestone formation of Natih, usually results in significant losses of up to 55 m3/h (346 bbl/h) even with a low density drilling fluid of 1,033 to 1,070kg/m3 (8.6 to 8.9lbm/gal). Packoffs are often observed due to the swelling shale section, which leads to several attempts with kick-off plugs and sidetracking. Engineered fibers pills enabled total returns to surface when no other loss circulation solution had worked before. This also enabled to bring cement all the way to surface using 1,410kg/m3 (11.8lbm/gal).

In another field, a work over rig was mobilized to perform a well kill operation and pullout. Due to total losses through perforations into the reservoir, the well kill could not be completed. In addition, every time the water level fell gas started to flow in the well. After 17 attempts and 8 loss circulation material pills, a total of 763m3 (4,800bbl) of well-supply water had been pumped. An engineered fiber pill at 1,474kg/m3 (12.3lbm/gal) was designed and bullheaded into the perforations. The pressures while pumping and squeezing rose to 11,031kPa (1,600psi). The well was shut and observed for 3 hours without any pressure increase indicating losses were cured and gas flow stopped.

Engineered fibers have proved their value in all sorts of lost circulation applications in North Oman. These pills have been successfully used to mitigate losses while drilling, while cementing, during mud circulation before cement job when the casing is on bottom and in work over jobs in depleted reservoirs. With the level of success achieved with such treatments, in some fields it has become a standard practice for curing losses.
Lower Tertiary - A Comprehensive Well Completion Design Methodology to Overcome Reservoir Challenges
Authors: Chavez Marco A , Garcia Gonzalo A , Pogoson Oje Li , "Lisa" Yu , Cardona Andres H , Nelson Roy N.
Published: September 2013

In developing an encompassing well completion design, an integrated, comprehensive solution study was under taken for the Lower Tertiary, mainly Wilcox Formation in the Gulf of Mexico. The study included reservoir characterization, optimized hydraulic 3D fracture design and modeling, nodal analysis and production forecasting and reservoir simulation to determine optimum well completion requirements such as internal tubing diameter, completion tool inner strings and downhole control valve sizes.

Preliminary studies from the Wilcox Formation were taken into consideration. Assuming a 3000-ft. MD gross height for the Wilcox formation, a representative LAS file containing the main curves for this formation was stretched out to have representative curves for the gamma ray, resistivity, neutron porosity, density, sonic delta compressional and values of core permeability.

The pore pressure and stress gradients were defined for each of the zones selected for stimulation. The stress profile was calculated implementing the Gamma Ray Index (GRI) and VShale on a per-foot basis for the zones selected withthe gamma ray curve and the assumed input values for sand and shale.

The mechanical properties were calculated from correlations for Vp and Vs utilizing the Vsh values as defined above, which in turn determined the dynamic values for Young Modulus and Poisson on the same per-foot foundation. Additional calculations were performed to determine the static values of the same characteristics for each of the selected zone depths.

The optimum well completion configuration was determined by evaluating: the fracture design (optimum treatment schedule for each zone) and minimizing pressure losses in the production tubing. Well completion reservoir simulations assisting to estimate the flow velocity during the well life. The production system was designed to not exceed the critical erosion velocity of the downhole equipment.

The study supports re-defining the well completion design requirements (maximum ratings) for ultra-deep water, high pressure and temperature applications.
Batched evaluation of linear tabled logic programs
Authors: Areias Miguel , Rocha Ricardo
Published: September 2013

Logic Programming languages, such as Prolog, provide a highlevel, declarative
approach to programming. Despite the power, flexibility and good performance
that Prolog systems have achieved, some deficiencies in Prolog?s evaluation
strategy - SLD resolution - limit the potential of the logic programming
paradigm. Tabled evaluation is a recognized and powerful technique that
overcomes SLD?s susceptibility in dealing with recursion and redundant
sub-computations. In a tabled evaluation, there are several points where we
may have to choose between different tabling operations. The decision on
which operation to perform is determined by the scheduling algorithm. The two
most successful tabling scheduling algorithms are local scheduling and
batched scheduling. In previous work, we have developed a framework, on top
of the Yap Prolog system, that supports the combination of different linear
tabling strategies for local scheduling. In this work, we propose the
extension of our framework to support batched scheduling. In particular, we
are interested in the two most successful linear tabling strategies, the DRA
and DRE strategies. To the best of our knowledge, no other Prolog system
supports both strategies simultaneously for batched scheduling. Our
experimental results show that the combination of the DRA and DRE strategies
can effectively reduce the execution time for batched evaluation.
Physiological tolerance to uncompensated heat stress in soldiers: Effects of various types of body cooling systems
Authors: Jovanovic Dalibor , Karkalic Radovan , Zeba Snjezana , Pavlovic Miroslav , Radakovic Sonja
Published: September 2013

Background/Aim. In military services, emergency situations when soldiers are
exposed to a combination of nuclear, biological and chemical (NBC)
contamination combined with heat stress, are frequent and complex. In these
specific conditions, usage of personal body cooling systems may be effective
in reducing heat stress. The present study was conducted in order to evaluate
the efficiency of four various types of contemporary personal body cooling
systems based on the ?Phase Change Material? (PCM), and its effects on
soldiers? subjective comfort and physiological performance during exertional
heat stress in hot environments. Methods. Ten male soldiers were voluntarily
subjected to exertional heat stress tests (EHSTs) consisted of walking on a
treadmill (5.5 km/h) in hot conditions (40?C) in climatic chamber, wearing
NBC isolating impermeable protective suits. One of the tests was performed
without any additional cooling solution (NOCOOL), and four tests were
performed while using different types of cooling systems: three in a form of
vests and one as underwear. Physiological strain was determined by the mean
skin temperature (Tsk), tympanic temperature (Tty), and heart rate values
(HR), while sweat rates (SwR) indicated changes in hydration status. Results.
In all the cases EHST induced physiological response manifested through
increasing Tty, HR and SwR. Compared to NOCOOL tests, when using cooling
vests, Tty and Tsk were significantly lower (on 35th min, for 0.44 ? 0.03 and
0.49 ? 0.05?C, respectively; p < 0.05), as well as the average SwR (0.17 ?
0.03 L/m2/h). When using underwear, the values of given parameters were not
significantly different compared to NOCOOL tests. Conclusions. Using a body
cooling system based on PCM in the form of vest under NBC protective clothes
during physical activity in hot conditions, reduces sweating and alleviates
heat stress manifested by increased core and skin temperatures and heart rate
values. These effects directly improve heat tolerance, hydration state,
decrease in the risk of heat illness, and extends the duration of soldiers?
exposure to extreme conditions.
Patterns of Language Use in Accounting Narratives and Their Impact on Investment-Related Judgments and Decisions
Authors: Riley Tracey J. , Semin Gün R. , Yen Alex C.
Published: September 2013

Recent research has examined the role of accounting narratives on investors' judgments and decisions. This study extends this line of inquiry by examining the effects of language categories on investors' judgments and decisions—the notion that narratives written with different predicates (verbs versus adjectives/nouns) will have a differential effect on investors. We use a language classification system, the Linguistic Category Model (LCM), to identify linguistic categories that vary on the dimension of abstractness/concreteness. First, the validity of the LCM in an accounting context is tested by analyzing quarterly earnings press releases. Results show that the language in press releases is more concrete (abstract) when the associated financial information is positive (negative). Second, an experiment to examine the effect of language categories on investors' judgments and decisions is conducted. The findings indicate that investors are least (most) likely to invest when a negatively (positively) valenced narrative is written concretely.
Truck Redesign Case: Simulating the Target Costing Process in a Product Design Environment
Authors: Everaert Patricia , Swenson Dan W.
Published: September 2013

This active learning exercise simulates the target costing process and demonstrates how a management theory (goal setting theory) is relevant to a business improvement initiative (target costing). As part of the target costing simulation, student participants work in teams to address a business issue (product development) that moves across functional boundaries. The simulation begins with students learning how to assemble a model truck and calculate its product cost using activity-based costing. Students are then divided into teams and instructed to reduce the truck's cost through a redesign exercise, subject to certain customer requirements and quality constraints. Typically, the teams achieve cost reduction by eliminating unnecessary parts, by using less expensive parts, and by using less part variety. This exercise provides a unique opportunity for students to actively participate in a redesign exercise. It results in student teams creating a wide variety of truck designs with vastly different product costs. The case ends by having a discussion about target costing, goal setting theory, and the implications of the target costing simulation.

This simulation contains a number of specific learning objectives. First, students learn how the greatest opportunity for cost reduction occurs during the product design stage of the product development cycle. Second, students see firsthand how design-change decisions affect a product's costs, and the role of the cost information in guiding those decisions. Third, students experience the cross-functional interaction that occurs between sales and marketing, design engineering, and accounting during product development. Finally, this exercise helps students understand the concept of target costing. The simulation is appropriate for undergraduate or graduate management accounting classes.

Data Availability:  For more information about this case, contact the first author at Patricia.Everaert@UGent.be.
Insider Entrenchment and CEO Compensation: Evidence from Initial Public Offering Firms
Authors: Forst Arno , Park Myung Seok , Wier Benson
Published: September 2013

We examine how insider entrenching governance choices of firms conducting their initial public offering (IPOs) influence the CEOs compensation contracts post-IPO. Using ten legal provisions affecting insider entrenchment, we find that entrenching governance decisions have a significant effect on CEO compensation post-IPO. Specifically, we observe a positive association between entrenchment and levels of post-IPO salary, total compensation, and pay-for-performance sensitivity. We also find a negative relation between entrenchment and the proportion of CEOs' salary to total compensation. Our observed relationships are principally driven by takeover readiness provision choices rather than voting rights limitation choices. Our results are robust to controlling for potential confounding effects.

JEL Classifications: M41; M52; G34; G32.
Model for End-stage Liver Disease (MELD) in spontaneous bacterial peritonitis –a clinical study at a tertiary health center in Nepal
Authors: Pathak Rahul , Niraula Kiran , Khadga Prem Krishna , Singh Kumar Vikram , Sharma Ishwar
Published: September 2013

Background and Aims: The aim of this study was to assess the predictive value of different variables including the Model of End-stage Liver Disease (MELD) scores in hospitalized patients with spontaneous bacterial peritonitis (SBP) and its correlation with adverse outcomes. Methods: A cross-sectional study of 73 patients diagnosed with cirrhosis, ascites, and spontaneous bacterial peritonitis admitted to a gastroenterology department from February 2010 to November 2012. MELD scores were calculated using laboratory parameters and the United Network of Organ Sharing (UNOS) internet MELD tool. Results: Categorical variables and mortality status were analyzed for association by chi-square test. MELD scores and all-cause mortality were found to be positively correlated. Mortality was higher among the groups with MELD scores greater than 15. Upon stratification of the groups by mortality status, only age and urea level were novel and consistent predictors of mortality. Conclusions: In this Nepalese sample of cirrhotic patients, MELD scores along with age and urea level were confirmed as significant predictors of mortality. DOI: http://dx.doi.org/10.3126/jaim.v2i2.8776  J ournal of Advances in Internal Medicine 2013;02(02):47-51
Falsely Elevated Acetaminophen Levels in the Setting of Hyperbilirubinemia
Authors: Parekh Parth J , Manser Thomas J
Published: September 2013

A 51-year-old male with a history of heavy alcohol abuse presented with alcoholic hepatitis and acute renal failure. Although he denied acetaminophen (APAP) ingestion, he was found to have elevated APAP levels that persisted and actually increased despite treatment with N-acetylcysteine. Review of the literature reveals that falsely elevated APAP levels may rarely occur with patients suffering from liver failure and felt to be related to severe hyperbilirubinemia. Interpretation of APAP levels in patients with severe liver disease and hyperbilirubinemia may be difficult and lead to diagnostic and therapeutic confusion. DOI: http://dx.doi.org/10.3126/jaim.v2i2.8782   Journal of Advances in Internal Medicine 2013;02(02):74-77