bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental and Theoretical Study of Control Strategies for Constant Bottomhole Pressure While Drilling Oil Wells
Authors: Vega M. P. , Vieira F. R. , Folsta M. G. , Leibsohn A. M. , Gandelman R. A.
Published: December 2011

Well construction is a complex job in which annular pressures must be kept inside the operational window (limited by fracture and pore pressure). Monitoring bottomhole pressure to avoid fluctuations out of operational window limits is an extremely important job, in order to guarantee safe conditions during drilling job.

Several operational parameters have a direct impact on bottomhole pressure such as flow rate, rate of penetration, drilling fluid properties, etc. This way, due to the several parameters to be handled, bottomhole pressure control is a complex task and is (nowadays) a manual and very subjective job. Thus, control and automation of drilling operations is a required activity for future challenge of petroleum engineering.

This job presents the results of the implementation of a phenomenological model aiming the development of a classic PI (proportional - Integral) controller for bottomhole pressure during a drilling job. Some strategies were investigated by handling flow rate and a choke opening. An experimental unit was built to study pressure control, when the system is disturbed by an ROP steps or choke openings. Results show a non linear behavior, what requires the system investigation in different operational conditions in order to make a classic PI controller reliable. This fundamental study represents an important step in the understanding the requirements for the implementation of the drilling automation process.
Predicting petrophysical properties using SEM Image
Authors: Suri Yatin
Published: December 2011

Abstract The permeability estimation of reservoir rocks using numerical methods has always been a challenge for petrophysicist. Several models have been developed for its computation of this parameter. As the permeability is entirely controlled by the geometry, the possibility arising of estimating the permeability from quantifiable attributes of the space has always has been a approach. In the present paper, a model is discussed which gives accurate prediction of the permeability based on two dimensional SEM image of a core sample of sedimentary rock. The inputs required for the model are the areas and perimeters measurements from the images of space. The individual conductances are estimated using hydraulic radius approximation. Before using the data obtained from images, stereological corrections are used to convert geometries and various hydraulic corrections are used to account for converging-diverging flow paths. Kirkpatrick's medium approximation is finally used to find the value of the hydraulic conductances of the individual pores. The method has been applied to six data sets of SEM images which include Berea sandstone, consolidated sandstones and carbonate samples. The laboratory determined air permeabilities of these samples ranged from 0.5-400mD. The permeability values predicted by this method are within a factor of two of the values. This method requires least data manipulation and computation and is more accurate than conventional methods such as the Kozeny-Carman equation. The method holds promise of permeability predictions on irregular rock samples like drill cuttings which cannot be in standard lab measurements. Another possible future is to use down-hole borehole imaging technology to provide an image with the appropriate resolution, thereby allowing in-situ permeability estimation, without the need for core samples. Keywords Permeability, Scanning Electron Microscope, Pore Network Modeling, Porosity, Conductance, Sandstones and Carbonates
Comparing the Results of a Full-Scale Buckling-Test Program to Actual Well Data: New Semiempirical Buckling Model and Methods of Reducing Buckling Effects
Authors: Mitchell S.. , Moore N.B.. B. , Franks J.. , Liu G.. , Xiang Y..
Published: December 2011

Buckling and its effects are topics of economic and technical interest as extended reach drilling (ERD) and horizontal wells become critical to maximizing recoverable reserves, particularly in the continental United States and Alaska. Previous work has resulted in important discoveries about drillstring buckling, but to date, little testing has been performed on actual drillpipe in a controlled manner, particularly in measuring drillstring whirl. As a result, there can be disparities between theoretical predictions of buckling effects vs. actual field results. These disparities can result in unrealistically high friction factors required to bring calculated values close to actual data, or in many cases, operational difficulties can result such as high torque, low rate of penetration (ROP), drillstring failures, inability to maintain directional control, or inability to reach the planned depth.

To learn more about drillstring behavior in buckling conditions, a full-scale buckling test fixture was developed to evaluate the effects of buckling on 2⅞-, 3½-, and 4-in. drillpipe while sliding and rotating inside 7-in. casing. The test fixture incorporated a variety of sensors and cameras to characterize torque, drag, vibration, and drillstring deformation under buckling loads. As part of the test program, low-friction nonrotating protectors were also tested to measure performance under buckling conditions.

The test results show that drillstring buckling occurs at far lower loads than predicted by current models, possibly caused by minor deformations inherent in real drillpipe. The results also show that for a given amount of torque or drag, protectors increased the available compressive load by 20 to 30% and substantially reduced vibration caused by drillstring whirl.

The test results were used to develop a new semiempirical buckling model that predicts contact forces resulting from drill-drag modeling software in which it was compared against actual data from a large number and variety of wells. The results show an ability to more accurately predict torque, drag, and vibration caused by buckling and whirl.
Petrophysics of Triple-Porosity Tight Gas Reservoirs With a Link to Gas Productivity
Authors: Deng Hui , Leguizamon Javier , Aguilera Roberto
Published: December 2011

Petrographic work on thin sections from rock samples collected in tight gas sandstones of the western Canada sedimentary basin (WCSB) shows that the sandstones are composed of intergranular, microfracture and slot, and isolated noneffective porosities. The petrographic observations of these triple-porosity rocks have led to a petrophysical interpretation with the use of a triple-porosity model.

Tight gas reservoirs are very complex heterogeneous systems that have been evaluated in the past mostly with single-porosity models. We propose that these types of reservoirs can be represented better by triple-porosity models for more rigorous quantitative petrophysical characterization. The triple-porosity model discussed in this paper fits the petrographic observations very well, leading to a more rigorous characterization of effective and noneffective porosity.

The petrographic and core-calibrated triple-porosity model is then used for well-log interpretation of those wells when these data are not available. The result is a reasonable quantitative characterization of the tight gas reservoir that can be used for improving hydraulic-fracturing design, flow-units determination, reservoir engineering, and simulation studies. The data can be determined at room conditions and simulated conditions of net stress.

It is concluded that honoring with a triple-porosity model the different types of porosities observed in thin sections and cores leads to more-rigorous and -useful petrophysical interpretations that can be linked to gas productivity.
Coupled Facility and Reservoir Simulations to Optimize Strategies for a Mature Field
Authors: Hayder M Ehtesham , Putra Satya A. , Shammari Ahmad T.
Published: December 2011

It is important to employ a good production injection strategy to optimize hydrocarbon recovery from a field. Reservoir constraints on the surface facility change as the field matures. It may be economical to revise the surface facility configurations rather than retaining the initial design of the surface facility to maintain the target production level of the field as reservoir conditions change. If reservoir pressure is not sufficient to maintain natural flow, there may be need for artificial lift mechanisms to keep the well flowing. Careful analysis of interdependence of the surface facility constraints and reservoir conditions are important in designing good quality production injection strategies for these circumstances. Coupled facility and reservoir simulations allow production optimization and determination of the impact of injection or disposal policies on reservoir management. Sometimes there are oscillations in computed production rates, which may be as a result from inaccurate treatment of a coupling algorithm, well management rules, optimization techniques, etc. Excessive fluctuations make the solution impractical to implement. In this paper, we examine the cause of well rate fluctuations in coupled simulations. We were able to keep oscillation levels at a very low level in our simulations by using a small coupling interval and by revising well management rules. We made case studies with reconfiguration of surface facility designs in two large fields to examine if those designs were capable of meeting the required production targets as the reservoir conditions change with time. Surface facility models were built using a commercially available software, which were coupled to Saudi Aramco’s in-house reservoir simulator, POWERS. We examine scenarios where some facilities could be eliminated to reduce cost while maintaining required production target. We study the impact of reconfiguring the surface network and examine how surface constraints might change the overall production rate.
Three-phase Hydrocarbon Thermodynamic Liquid-Liquid-Vapour Equilibrium in CO2 Process
Authors: Lins Abel G. , Nghiem Long X. , Harding Thomas G.
Published: December 2011

Hydrocarbon phase behaviour must be rigorously represented when there is a need to properly account for mass transfer between phases in a porous medium. The overly simplified black-oil formulation, although appropriate for primary depletion and waterflooding, provides inadequate representation of miscible displacement processes. As a result, compositional simulation has evolved to provide thermodynamically consistent means to accurately describe the phases and compositions present within the porous reservoir rocks.

Compositional simulators have become essential modelling tools for CO2 processes in the Petroleum Industry. Advances in computational power have encouraged the development of meaningful improvements and refinements that were not possible until very recently.

CO2 injection into an oil reservoir at low temperatures causes the appearance of a three-phase hydrocarbon thermodynamic Liquid-Liquid-Vapour (LLV) equilibrium. The traditional use of a two-phase flash calculation in this three-phase region may lead to instability problems. Besides, commercial compositional simulators normally do not consider two-phase hydrocarbon Liquid-Liquid (LL) thermodynamic equilibrium that appears in oil reservoirs at low temperatures in the presence of CO2. Instead, it is treated as a Liquid-Vapour (LV) thermodynamic equilibrium and the fluid flux behaviour is not well represented. A compositional simulator must be able to represent adequately the LL hydrocarbon thermodynamic equilibrium when it is present in order to rigorously model the reservoir phase behaviour in the presence of CO2.

A novel procedure has been developed to overcome instabilities which may arise in calculation of multiphase liquid-liquid-vapour (LLV) hydrocarbon phase equilibrium. In addition, a new procedure has been developed for representing the thermodynamic liquid-liquid hydrocarbon equilibrium in a compositional simulator. This new procedure represents the real behaviour of the fluid flux. It is more rigorous than the traditional approach of lumping of the two liquid phases into a pseudo single liquid phase or as a liquid-vapour (LV) thermodynamic equilibrium. The results of this implementation are presented and analyzed in detail.
Shape Factors for Irregularly Shaped Matrix Blocks
Authors: Wuthicharn Katha , Zimmerman Robert W.
Published: December 2011

The shape factor that appears in dual-porosity models of single-phase flow in naturally fractured reservoirs is investigated. Previously derived analytical expressions for a few simple geometries (spheres, cubes, slabs, etc.) are first reviewed. A general numerical procedure is presented that allows the shape factor of an arbitrarily shaped block to be found using a fine-grid simulation of flow into a single matrix block with constant-pressure boundary conditions. From these various results, a scaling law is suggested that expresses the shape factor in terms of the block’s volume V, the block’s outer surface area S, and a diffusion length l. This expression is α = 5S/Vγ, where γ = V1/3 for a three-dimensional block, and γ = A1/2 for a two-dimensional prismatic block with cross-sectional area A. For all cases analyzed, this expression predicts the shape factor within an error of less than 10%. This seems to be the first accurate, general expression available for estimating the shape factors of irregularly shaped matrix blocks such as are formed by the intersection of realistic fracture networks.
Optimizing Development Strategy and Maximizing Field Economic Recovery through Simulation Opportunity Index
Authors: Abd Karim M. Ghazali. , Abd Raub M. Razib.
Published: December 2011

With the rapidly increasing costs of field development, one of the many challenges for any green or brown field development is to optimize the number and locations of development wells that would yield maximum sweep efficiency and recovery. A full field simulation model is generally constructed to assist in optimizing the development plans and in many occasions initial well planning is based on fixed well length, well orientation, well spacing, etc., before any iterative sensitivity runs are performed. It is recognized that in most cases, the decision was heavily influenced by a single reservoir property, such as permeability, without considering the effect of other inter-related parameters, such as movable oil volume, fluid viscosity, hydrocarbon pore volume, reservoir permeability-thickness and residual oil saturation. The need to analyze these variables in a structured and logical manner is therefore a challenge to ensure a technically sound decision making process. In this paper a modified approach, based on techniques already established (Molina et al., 2009), hereinafter called "Simulation Opportunity Index" (SOI) is introduced. It provides an innovative view on how a development strategy is addressed, and subsequently forms the basis of well placement optimization. All steps and equations to generate the desired indexes are discussed in this paper. We have successfully utilized industrial geological modeling software to perform the calculations and eventually generate the three main index properties in a 3D reservoir model. Using an in-house well planning tool, we can place new wells to optimize field development. This paper also presents a case study for a major oil field development in Saudi Arabia. Comparison between conventional approach and this modified technique clearly showed an improved field recovery performance.
Adjusting Modeling Methodologies to Decision Requirements, Reservoir Properties and Recovery Mechanism - Examples from the Shuaiba in Oman
Authors: Warrlich Georg , Amthor Joachim , Abu-Shiekah Issa , Kharusi Ahmed , Kindy Mohammed , Garimella Sai
Published: December 2011

Some of the large carbonate fields in North Oman have been on production for some 40 years. However, substantial contingent volumes exist in these mature fields, highlighting the need to understand the characteristics of the remaining resources and their potential to generate oil and value.

The Petroleum Development Oman (PDO) carbonate oil portfolio can be subdivided into a number of area-themes based on (similar) reservoir types, oil type and reservoir development methods (current and future). In this paper, we illustrate how modeling methodologies can be adjusted for three of these area-themes by focusing on the key subsurface parameters most relevant to the recovery mechanism: Shuaiba fractured carbonates, with heavy oil, under appraisal for steam-assisted GOGDShuaiba matrix carbonates; with thin, transition-zone oil column and light oil, under waterfloodShuaiba matrix carbonates; with reasonable oil column and light oil, under waterflood

Any reservoir modeling methodology is also influenced by the purpose of the models (what decisions it enables), as well as the resources (computation, manpower and time) and data available. The examples described above also differ in these respects: The modeling of a fractured carbonate, heavy-oil reservoir (example A) focused on testing the feasibility of steam-assisted GOGD and required intensive analogue use due to limited data availability. In example B, a transition-zone field where oil saturation, matrix features and relative permeability are key parameters, the modeling supported a waterflood development implementation, consisting of ongoing drilling of 150+ geosteered, horizontal producers & injectors (2 new wells per month). In example C, for a light-oil, reasonable-thick oil column field, waterflood development decision-making on redevelopment options was enabled by multiple-deterministic scenario modeling.
Impact of Heterogeneous Geomechanical Properties on Coupled Geomechanical-Flow Simulation of SAGD
Authors: Khajeh Mohammad Mehdi , Chalaturnyk Rick , Boisvert Jeff
Published: December 2011

In the modern oil industry, geostatistical property models are built for different purposes such as resource estimation and flow simulation. Processing of multiple realizations, obtained from geostatistical simulation techniques, helps assess uncertainty analysis which is important for development planning and decision-making processes.

Each geological model is a combination of structural, facies, and attributes models. In the case of conventional flow simulation (i.e. without considering geomechanical simulation), the petrophysical properties porosity, permeability and saturation, are the only attributes necessary to model. These parameters are included in the fluid flow governing equations. But in the case of dealing with coupled geomechanical-flow simulation, rock mechanical properties are also required.

In the case of conventional simulation process, geostatistical property models have been used widely, but in the case of coupled geomechanical-flow simulation processes, geostatistical modeling for geomechanical attributes has yet to be incorporated. Therefore, uncertainty assessment could be underestimated according to the spatial distribution of these parameters.

In this work, the effect of heterogeneous geomechanical properties on coupled geomechanical-flow simulation process was investigated for a steam assisted gravity drainage (SAGD) process for a heavy oil reservoir in Alberta-Canada.

Cumulative oil Production (COP), Steam Oil Ratio (SOR) and Vertical Deformation Profile (VDP) of the top of reservoir is considered as three simulation output variables. Consideration of heterogeneous models for both flow and geomechanical properties in coupled geomechanical flow simulation of the SAGD process resulted in a range of uncertainties for these three variables. The importance of considering geomechanical properties as heterogeneous models is illustrated by comparing these ranges with the ranges obtained from coupled simulations in which geomechanical properties are considered as homogeneous models. Representative synthetic data of a sand/shale spatial distribution of McMurray formation in Alberta-Canada is considered for the case study.
"Modeling with Intensity" — The Use of Intensity Functions to Condition 3D Geologic Reservoir Models
Authors: LaCroix Pierre , Al-Masrahy Mohammed , Prudden Mark , Loretto Thomas
Published: December 2011

3D seismic acoustic impedance inversion was performed for a Permo-Carboniferous sandstone reservoir interval based on limited well control. The impedance volume was then depth converted and used to target development well locations. The drilling campaign yielded mixed results; some areas of the field showed a high correlation between impedance computed from the wells and that derived from seismic, and other areas showed a low correlation. This difference in correlation presented a challenge when using the impedance model to condition the porosity model. Changes to the impedance volume would be needed in areas of low confidence in the seismic data. To address this problem, the depth-converted impedance volume was rebuilt using a 3D intensity function. This technique assigns appropriate weights to the seismic data in different areas of the field, based on confidence in the seismic data quality. Using this technique produced a more realistic porosity model, when conditioned by the revised impedance model. The subsequent construction of an object-based facies model also used intensity functions to locate seed positions of the sand dune objects, which were then tied to specific impedance ranges in the updated impedance model. Paleosol and sheet-sand facies, unrestricted to specific porosity ranges, were constructed separately using probabilities of occurrence from each well. The separate models were then merged together to produce the final facies model.
Integration of 3D-seismic Impedance into High-resolution Geocellular Models using Non-collocated Downscaling
Authors: Vargas-Guzmán J. A. , Weibel William L. , Mustika Idam , Anbar Qadria
Published: December 2011

The classic integration of seismically-derived attributes into geocellular models by collocated cokriging is revisited, leading to improved geocellular modeling results above the seismic bandwidth in between wells. This paper shows a practical approach to the challenge of downscaling and integration of the seismic acoustic-impedance (seismic AI) attribute by calibrating it to the heterogeneity defined by the log-derived acoustic impedance (log AI). The approach is a reduction of the downscaling method by full cokriging to a simpler stepwise sequential-kriging to estimate the required parameters for stochastic simulation. The proposed approach is to create a downscaled-model AI by combining the low-frequency seismic attribute with a predicted high-frequency component before it is integrated into the porosity model using log well data. The current tools of preference, collocated cokriging and/or collocated co-simulation, assume proportionality between the variogram structures for both the synthetic log AI and the seismic AI. The problem with this assumption is that the modeled attribute may closely resemble the original low resolution data. If the correlation between attributes is significant, then the resulting "downscaled" realizations by collocated methods look diffuse, so they are unsatisfactory for use in high resolution geocellular models. The downscaling approach is redefined in this study by performing analytical computations and verifications with real reservoir data. A proper second-order downscaling approach for seismic AI must be based on full cokriging and non-collocated co-simulation using the logs and seismic. A complete integration should also reproduce the higher-order geological heterogeneity, which is contained in the high-resolution well logs but not normally shown in the seismic attributes. The numerical complications of cokriging and the lack of robust tools in most existing software have motivated the development of practical collocated solutions that can be implemented with less effort. The contribution of this study is that it provides an alternative non-collocated workflow for better representation of the vertical heterogeneity in geocellular models by downscaling seismic prior to integration.
Miscible Gas Injection Tests in Carbonates and its Impact on Field Development
Authors: Kalam Zubair , Al-Rawahi Ali S , Al-Hosani Ismail A , Negahban Shahin , Rehman Abdul Samad
Published: December 2011

Considerations for better ultimate oil recovery and maintaining plateau production beyond the current expectations depend on appropriate EOR methods. Laboratory core floods provide both the recovery characteristics and validity of the microscopic displacements in 1D, and hence the confidence in the choice for macroscopic simulations models and field development options.

Laboratory core floods are typically conducted on long composite of stacked cores to assure good miscibility, minimize experimental uncertainties, and ensure representative reservoir conditions are replicated. This study chose to investigate six miscible gas process displacements on a long composite core of a prolific Cretaceous zone of a giant carbonate reservoir. The displacements were designed to mimic the reservoir advance rates at full reservoir conditions under both conventional vertical floods as well as the challenging horizontal injections. We examine the miscible fluid injection and hydrocarbon recoveries of three fluid systems in tertiary mode, i.e. following a secondary water flood. The injection schemes comprise, a tertiary hydrocarbon gas, a tertiary hydrocarbon / brine WAG and a continuous CO2 gas all at miscible conditions.

The miscible gas injection tests, within the experimental limitations provided recovery profiles and gas process injection characteristics to validate model predictions, and thus enhance confidence in pilot as well as full field development studies based on the underlying reservoir simulation models. Our work highlighted the excellent choice of CO2 as a miscible gas fluid, and dispelled gross uncertainties in conducting such tests in either horizontal or vertical modes. The repeatability of six different secondary water floods confirmed the robust test design, and confidence in the tertiary gas injection measurements.
Visualizing Flow Patterns in Coupled Geomechanical Simulation Using Streamlines
Authors: Parihar Prannay , Datta-Gupta Akhil
Published: December 2011

Reservoir geomechanics is a production induced phenomena that is experienced in large number of fields around the world. Hydrocarbon production changes the pore pressure which in turn alters the in-situ stress state. For reservoirs that are either stress sensitive or where rock is soft and unconsolidated, stresses have appreciable effect on rock properties like porosity and permeability. Anisotropic and isotropic permeability changes impact flow direction and movement of flood front thereby influencing well performance and reservoir productivity. Coupling of geomechanical calculations with multi-phase flow simulation is needed to make reliable predictions on reservoir production response and ultimate recovery. In this paper, geomechanical simulation is combined with streamline tracing to aid in better understanding of reservoir dynamics through visualization of flow patterns in the reservoir.

Specifically, we generate total velocity streamlines and individual phase streamlines for flow fields derived from coupled geomechanical simulation and compare the results with streamline tracing for conventional reservoir simulator to examine the impact of geomechanics on reservoir flow processes. Commercial finite difference simulators are used for flow simulation with and without geomechanical effects and streamline tracing has been done from flux fields using corner point extension of the Pollock algorithm. Our results show that phase and component streamlines in addition to total velocity streamlines can be a valuable reservoir management tool and can provide unique insights into the flow dynamics as well as reservoir mechanisms. The streamlines capture flow directionality, and also provide information on the appearance and disappearance of individual phases and connectivity between injectors and producers.
Barriers that Delimit Risk Perception and Impact Effective Transfer of Safety Training in the Petroleum Industry
Authors: Awolusi O. S.
Published: December 2011

The oil and gas exploration and production industry is a dynamic one, with consequential higher rates of fatalities than the overall U.S. average. The first intervention often used to reduce or manage fatality rate is the implementation of safety training programs, and most are focused on hazard recognition or risk perception. Risk perception is the subjective judgment that people make about the frequency and severity of a particular risk. However, many safety training programs fail to transfer to the workplace, and the way risk is perceived may play a role in this. This study is a review of literature conducted in order to identify barriers that delimit the perception of risk in the petroleum industry to the extent that safety training transfer in the workplace is impacted. The four barriers identified are lack of individual motivation, groupthink, absence of organizational and supervisory leadership initiative, and the encumbrance of regulatory models.
Gravimetric Monitoring of Water Influx Into a Gas Reservoir: A Numerical Study Based on the Ensemble Kalman Filter
Authors: Glegola M.. , Ditmar P.. , Hanea R.G.. G. , Vossepoel F.C.. C. , Arts R.. , Klees R..
Published: December 2011

Water influx into gas fields can reduce recovery factors by 10–40%. Therefore, information about the magnitude and spatial distribution of water influx is essential for efficient management of waterdrive gas reservoirs. Modern geophysical techniques such as gravimetry may provide a direct measure of mass redistribution below the surface, yielding additional and valuable information for reservoir monitoring.

In this paper, we investigate the added value of gravimetric observations for water-influx monitoring into a gas field.

For this purpose, we use data assimilation with the ensemble Kalman filter (EnKF) method. To understand better the limitations of the gravimetric technique, a sensitivity study is performed. For a simplified gas-reservoir model, we assimilate the synthetic gravity measurements and estimate reservoir permeability. The updated reservoir model is used to predict the water-front position. We consider a number of possible scenarios, making various assumptions on the level of gravity measurement noise and on the distance from the gravity observation network to the reservoir formation. The results show that with increasing gravimetric noise and/or distance, the updated model permeability becomes smoother and its variance higher. Finally, we investigate the effect of a combined assimilation of gravity and production data. In the case when only production observations are used, the permeability estimates far from the wells can be erroneous, despite a very accurate history match of the data. In the case when both production and gravity data are combined within a single data assimilation framework, we obtain a considerably improved estimation of the reservoir permeability and an improved understanding of the subsurface mass flow. These results illustrate the complementarity of both types of measurements, and more generally, the experiments show clearly the added value of gravity data for monitoring water influx into a gas field.
Electrokinetics of Limestone Particles and Crude-Oil Droplets in Saline Solutions
Authors: Alotaibi Mohammed B. , Nasr-El-Din Hisham A.
Published: December 2011

Salinity adjustment of waterflooding has been applied recently as an enhanced-oil-recovery (EOR) technique in sandstone and carbonate reservoirs. Reaction mechanisms were different because of the variation in rock mineralogy and reservoir characteristics. Interactions between injection water, crude oil, and limestone particles are still ambiguous. Anions in seawater are believed to have altered carbonate surface potential to negative and, thus, created repulsion forces between crude-oil droplets (negatively charged) and a connate-water layer. As a result, rock wettability was altered toward water-wet.

In this paper, the surface potential of crude oil and limestone particles was studied at 50°C. Ionic strength was varied using formation brine (230K ppm), seawater (54K ppm), shallow aquifer water (5K ppm), and fresh water. Cation (Na+, Ca2+, Mg2+) and anion (SO42−) concentrations were tuned individually in seawater also. The influence of H+ and OH− ions on the suspensions’ surface potential was investigated by diluting seawater and aquifer water with deionized water at different volume ratios. Two-phase (crude oil in water, limestone particles in water) and three-phase (crude oil, and limestone particles in water) tests were performed at pH 8.

The surface potential of oil droplets was strongly affected by 10 vol% diluted seawater, seawater without divalent ions (Ca2+ and Mg2+), and deionized water because of the adsorption of OH− ions at the oil/water (O/W) interface. Sodium sulfate solutions (7,120 ppm) also increased the zeta potential absolute value of oil droplets. The effect of ionic strength on zeta potential was more pronounced in the oil-wet limestone particles than in the intermediate-wet samples. An aqueous layer around crude-oil droplets played a key role in determining droplet charges. Results from this study provide some insights on electrokinetics of limestone particles and oil droplets in different saline solutions. Wettability of the rock and oil recovery are affected directly by the zeta potential of oil droplets and suspensions.
A Simple Formula To Estimate 2D Fracture Connectivity
Authors: Ozkaya Sait I.
Published: December 2011

A simple expression is derived for average fracture intersections per fracture, λ, as the product of fracture density, average length, and angular standard deviation in 2D fracture models. The calculated λ value quite accurately estimates the observed λ values for a variety of cases including one- or two-fracture sets, truncated or not-truncated fractures, and log-normal or power law length distribution. The formula fails to estimate the number of fracture intersections accurately when fractures are clustered. Fracture clusters could either be fault-related fracture corridors or highly fractured layers. In either case, it is necessary to calculate λ for each fracture corridor or each fractured layer with a different fracture density.

The relationship between λ and fracture connectivity was investigated using several stochastic fracture models. λ seems to be a reasonably good estimator of fracture connectivity, which we define as the percentage of fractures within the largest interconnected fracture aggregate. The relationship between the number of fracture intersections and percolation threshold is, however, weak because percolation threshold is dependent on the relative length of fractures with respect to the distance between two opposite ends of a fractured medium.
Pressure-Tolerant Power Electronics for Deep and Ultradeep Water
Authors: Pittini Riccardo , Hernes Magnar
Published: December 2011

This paper presents results from an ongoing research project (SINTEF 2011) on pressure-tolerant power electronics. The main goal of the research is to provide and demonstrate solutions that enable power-electronic converters to operate in pressurized environments. Oil companies have plans for subsea processing of oil and gas. Today's concept considers power-electronic converters in 1-bar vessels. As the depth and the converter power rating increase, these vessels become increasingly bulky and heavy. Pressure-balanced converters would allow lower vessel-wall thickness, thereby giving lower weight, and simpler cooling owing to improved heat conduction through the vessel walls. The new concept considers power-electronic converters placed in vessels completely filled with appropriate dielectric liquid able to operate at pressures from 1 bar up to several hundred bar. Dielectric fluids are required to prove their properties, especially those related to insulation, incompressibility, and heat transport. The methodology presented here considers a mechanical adaptation of components followed by various laboratory experiments for verifying or correcting the proposed solutions (Pittini et al. 2010; Hernes and Pittini 2009; Petterteig et al. 2009).

Standard off-the-shelf components and special pressure-adapted components have been subjected to various provocative pressurization tests up to 300 bar. Tests clarified the need for special adaptation of some components, while others could be used without any modification. Subsequently, a full converter phase leg has been built, submerged in dielectric liquid, and tested in full operation up to 300 bar. This phase leg is based on a press-pack IGBT modified for operation at high pressure. Measurements performed at different pressures demonstrate that there is no relevant difference in terms of electrical parameters between this modified IGBT and a standard IGBT. Long-term tests proved the concept's validity. The next step will be to test bonded IGBT technology in a high-pressure environment, and finally, we will realize a test demonstration to be located at a suitable subsea site.
The Impact of Chinese Purchases of U.S. Government Debt on the Treasury Yield Curve
Authors: Lizardo Radhames A. , Mollick Andre Varella
Published: December 2011

Examining monthly data from May of 1985 to May of 2008, we find that increases in Chinese purchases of U.S government debt lead to decreases in Treasury yields. The effect is stronger as the maturity increases: a one percent increase in purchases of U.S. Treasuries by Chinese investors lowers the two-year (ten-year) Treasury yield by 10 to 38 basis points (39 to 55 basis points) on average, ceteris paribus . Overall, the demand-side variable capturing Chinese purchases of U.S. Treasuries improves the cointegrating properties of U.S. interest rates. In-sample and out-of-sample forecasts reinforce that the model with Chinese purchases greatly outperforms basic models of the yield curve. This study has implications for the business world since we document that Chinese investors contribute to lower U.S. Treasury yields and thus to lower U.S. interest rates in general.
Reward Dominance in Tax-Reporting Experiments: The Role of Context
Authors: Wartick Martha L. , Madeo Silvia A. , Vines Cynthia C.
Published: December 2011

During the past decade, the experimental economics method increasingly has been used to study the impact of tax policy on taxpayer behavior. Experimental economics in taxation typically tests tax applications of expected utility and psychological theory by creating a real microeconomy in the laboratory. A key requirement is strict control over the parameters of the experimental setting and subject preferences. One generally accepted procedure to achieve experimental control is to avoid references to real-world phenomena in instructions to subjects. The reasoning underlying this procedure is that if subjects associate the experiment with real-world phenomena, they may make decisions based on values associated with the real-world context instead of the rewards and penalties of the microeconomy. Despite this, several recent tax-reporting experiments that otherwise conform to the experimental economics method have used explicit tax terminology. In discussing the results of these experiments, the authors and commentators stated that the results probably were not affected by the tax context.

We conducted an experiment to further examine whether the results of a tax-reporting experiment were affected by context. We found that subjects reported significantly more income when the context of the experiment was tax than when the context was nontax. This effect differed, however, depending on the age of the subjects. While subjects 25 years of age and older reported approximately twice as much income in the tax context as they did in the nontax context, subjects under 25 reported only slightly more in the tax context than in the nontax context. These results provide evidence that role playing based on individual subject characteristics occurred when contextual cues were provided.
The Effect of Political Affiliation on Taxpayers' Attitudes Toward Alternative Tax Systems
Authors: McGowan John R.
Published: December 2011

There is a great deal of dissatisfaction with the existing tax system. Prior research has found that self-interest, perceived equity, persuasive messages, tax knowledge, and demographic factors affect taxpayer attitudes. This study contributes to that body of research by examining the effects of another factor that is associated with taxpayer attitudes: their political affiliation. Data obtained from a national telephone survey of homeowners' attitudes toward alternative tax systems are used. Results indicate that political affiliation plays a significant role in taxpayers' attitudes toward both alternative tax systems in general and the proposed flat tax in particular. Specifically, when faced with the choice of alternative tax systems, respondents who identified themselves as having Republican (Democratic, Independent) political af-filiations were more (less) likely to prefer both the flat tax and the sales tax systems over the current system.
The Effect of the Tax Deductibility of Goodwill on Purchase Price Allocations
Authors: Henning Steven L. , Shaw Wayne H.
Published: December 2011

This paper examines whether changes in the tax deductibility of goodwill affected the pricing of acquisitions during the early 1990s. We find that tax deductibility led to a change in purchase-price allocations across asset groups, since an increase in the amount allocated to goodwill was offset by a decrease in the allocation to identifiable assets. Our evidence also suggests that some of the benefits accrued to the target since purchase price increased after the change in the tax status of goodwill. The failure to observe any change in the level or allocation of the purchase price for the tax carryover firms provides additional support that the change for step-up firms was attributable to changes in the tax law and not to other factors.
The Effects of Imputation Systems on Multinational Investment, Financing, and Income-Shifting Strategies
Authors: Babcock Jennifer
Published: December 2011

The United States is one of a few remaining countries to tax distributed corporate earnings twice—once at the corporate level, and again at the individual level. In contrast, many other countries have adopted imputation systems that refund domestic corporate taxes through dividend tax credits. Consequently, foreign-source income, which is often relieved from domestic corporate taxation, is generally ineligible for dividend tax credits.

The paper develops a model to derive the investment, financing, and crossjurisdictional income-shifting incentives of imputation-based multinationals. The model indicates that imputation systems encourage firms to restrict their equity stakes in new foreign investments, and, ultimately, to expand their domestic investments. The results also reveal that imputation systems create incentives for firms to lever highly their foreign operations, use internal debt over equity finance, shift foreign taxable income into home jurisdictions, and to merge with or acquire purely domestic or nonresident owned firms.
Effects of Unitary vs. Nonunitary State Income Taxes on Interstate Resource Allocation: Some Analytical and Simulation Results
Authors: Williams Michael G. , Swenson Charles W. , Lease Terry L.
Published: December 2011

This study examines the optimal location choice decisions of a two-state firm in response to changing state corporate income tax rates and tax structures. Because the firm can engineer its tax liability by manipulating between-state location of sales, property, and payroll, changes in relative state tax rates should result in the firm making such location changes. Results of a model firm simulation, examining various combinations of state tax rates and unitary vs. nonunitary tax structures, found that the firm would make interstate resource changes to minimize company-wide state income taxes.

Important findings of the study are that tax rate changes in nonunitary states may cause little or no change in resources used in that state. Indeed, in one scenario, the resulting resource flows from a tax increase are favorable to the nonunitary state, making a tax increase a win-win situation for the state government (higher tax revenue and more economic activity). In contrast, changes in unitary state tax rates can result in significant resource changes in both the unitary state and in other states. The finding that tax rate cuts are ineffective in nonunitary states implies that these states may be more successful in attracting investment by changes affecting apportionment factors (tax credits for new capital, or new jobs) or by use of nontax incentives.
The Effect of Staff Accountant Objectivity in the Review and Decision Process: A Tax Setting
Authors: Hatfield Richard Charles
Published: December 2011

Prior studies report that less experienced staff accountants are often susceptible to confirmation bias in the evaluation of evidence. This bias results in nonobjective information evaluation by staff-level accountants. This study examines how the perceived objectivity of the staff accountant and the manager's own client advocacy affect the manager's use of the staff accountant's research report when formulating client recommendations. The results suggest that objectivity judgments made by partner-/manager-level accountants are influenced by whether the staff accountant's research report confirms their initial opinion. Further, the confirmatory nature of the research report affects the manner in which the report is incorporated into a client recommendation. Nonconfirming research reports were given more weight than confirming research reports. Preference for client-favorable outcomes was found to affect the weight given to staff accountant research reports as well.
Measuring Corporate Tax Preferences
Authors: Dunbar Amy E. , Sansing Richard C.
Published: December 2011

This paper examines the measurement of corporate tax preferences. It develops a model of corporate investment in which a certain fraction of the investment is immediately expensed. This model is representative of the treatment of costs associated with internally developed intangible assets, which generally are expensed for both financial reporting and tax purposes. Analysis of the model shows that accounting-based measures of tax preferences are deficient because such measures detect only tax preferences that generate book-tax differences. The paper then proposes a new measure in which pre-tax accounting income is replaced by pre-tax stock market returns, which detects tax-favored investments regardless of their financial accounting treatment. A comparison of the two measures for a sample of firms between 1992 and 1996 indicates that tax preferences are substantially higher than accounting-based measures suggest.