bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Summary
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

SummarySalinity 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

Summary
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

Summary
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.
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.