bluuebunny/crossref_metadata_2025_split huggingface dataset:
Improving Characterization and History Matching Using Entropy Weighted Ensemble Kalman Filter for Non-Gaussian Distributions
Authors: Nejadi Siavash , Trivedi Japan J , Leung Juliana 
Published: May 2011

Abstract
The Ensemble Kalman Filter (EnKF) has gained popularity over recent years as a Monte-Carlo based technique for assisted history matching and real time updating of reservoir models. The EnKF procedure utilizes an ensemble of model states (e.g. realizations of reservoir properties such as porosity and permeability) to approximate the covariance matrices used in the updating process. EnKF works efficiently with Gaussian variables and linear dynamics, but it often fails to preserve the reference probability distribution of the model parameters and to achieve an acceptable production data match where the system dynamics are strongly nonlinear, especially of the type related to multiphase flow, or if non-Gaussian prior models are used.
In order to alleviate these drawbacks, we investigated various weighted averaging techniques for computing the ensemble mean by introducing a weighting factor to each ensemble; two new formulations were implemented. The first weighting factor was calculated based on the mismatch in entropy of the model parameters, a normalized measure of the spread of a given probability distribution. The second weighting factor was computed using the forecast mismatch. In addition, both weights could be applied at a single updating step for reducing the forecast mismatch and maintaining the prior distribution simultaneously.
The performance of traditional EnKF and these weighted EnKF methods were evaluated by performing various simulation studies with different reservoir heterogeneity. The qualities of the final matching results were assessed by computing the experimental histogram and variograms of the final ensemble, as well as the Root Mean Square Error (RMSE) of the predicted data mismatch.
The results reveal that reasonable improvement in the efficiency of the EnKF is achieved by suggested weighted techniques. The RMSE of the predicted data is improved, and the quantity of spurious model parameters is reduced at each updating step. Taking advantage of the entropy based weighting factor assists the filter to preserve the reference distribution. The improvement indicates that the Entropy weighted EnKF (EWEnKF) has a significant potential to resolve the shortfall of traditional EnKF in reservoir characterization and history matching of challenging reservoirs with non-Gaussian distributions.
Reservoir Management Using Streamline-Based Flood Efficiency Maps and Application to Rate Optimization
Authors: Park Han-Young , Datta-Gupta Akhil 
Published: May 2011

Abstract
3-D streamlines provide an effective tool for reservoir management because of their ability to display reservoir flow and well connections in a physically intuitive manner. Streamlines have been extensively used to investigate the interaction between heterogeneity and well patterns and also for rate allocation and pattern balancing. More recently, streamlines have been used in conjunction with constrained optimization techniques for improving waterflood performance via rate control. Field scale rate optimization problems, however, involve highly complex reservoir models, production and facilities constraints and a large number of unknowns, making them inaccessible for routine waterflood management.
In this paper we provide a simple and easy to use workflow for waterflood rate optimization using streamline-based flood efficiency maps that display the flux and time of flight distribution amongst producing wells. We demonstrate the use of flood efficiency map to optimize the injection/production rates to maximize waterflood sweep efficiency by equalizing the average time of flight (TOF) amongst the producing wells in regional basis. Our optimization approach is extremely efficient because it relies on simple analytic calculations to compute weighting factors for injection and production rates to minimize the TOF variance amongst producing wells. Because the approach does not rely on formal and complex optimization tools, it is particularly well-suited for large-scale field application. Also, the approach can be used with both streamline and finite difference simulators. For finite-difference simulations, the streamlines and time of flight are derived from the flux field generated by the simulator. Multiple examples are presented to support the robustness and efficiency of the proposed waterflood management scheme. These include 2D synthetic examples for validation and a 3D field application.
Simulation Study of 2-D SAGD Experiment and Sensitivity Analysis of Laboratory Parameters
Authors: Ashrafi Mohammad , Souraki Yaser , Karimaie Hassan , Torsaeter Ole , Kleppe Jon 
Published: May 2011

Abstract
Bitumen resources constitute a high portion of the total world oil resources. The main recovery mechanism for these high viscous fluids is to reduce their viscosity by the application of heat, mostly by introducing steam.
Among different steam injection schemes, steam assisted gravity drainage (SAGD) has become the method of choice applicable to bitumen and oil sand reservoirs. In these extra heavy oil reservoirs the reservoir has almost no injectivity due to high oil viscosity, and therefore conventional steam flooding is hard to conduct. SAGD, however, reduces the viscosity of bitumen in place and the heated bitumen drains due to gravity forces towards the production well and is then being produced.
Our simulation study is based on the experimental work done by Chung (1988) and the simulation model of this experiment by Chow (1993). Chung's physical experiment was a 2-D model to simulate SAGD experiment in laboratory.
A reservoir simulation model was built using a numerical thermal reservoir simulator. The model was then tested and validated with Chung's physical model. Having a valid model, sensitivity analysis was run to examine the effect of different simulation parameters on recovery and steam oil ratio.
The sensitivity parameters tested are steam temperature and quality, the permeability of the model, both horizontal and vertical, different well placement schemes, and the effect of grid refinement. High permeability was found to have a profound effect on recovery.
Different steam temperatures and qualities were examined. The best injection condition was found to be 130 °C and 90% quality, beyond which no increased recovery was achieved.
Different injector and producer placements were tested. Placing injector and producer diagonally in the model showed the best horizontal sweep efficiency in the laboratory model.
The Chung's experiment was done with Cold Lake crude oil. Our model was tested using bitumen with higher viscosity from Athabasca and results showed that in order to get the same recovery as in the Cold Lake case; the temperature must be increased to 140 °C as compared to 100 °C for the case with lower viscosity oil.
Petrophysics of Triple Porosity Tight Gas Reservoirs with a Link to Gas Productivity
Authors: Deng Hui , Leguizamon Javier , Aguilera Roberto 
Published: May 2011

Abstract
Petrographie 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 + slot, and isolated non-effective 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 better represented by triple-porosity models for more rigorous quantitative petrophysical characterization. The triple porosity model discussed in this paper fits very well the petrographic observations leading to a more rigorous characterization of effective and non-effective porosity.
The petrography and core-calibrated triple porosity model is then used for well log interpretation of those wells where 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 lead to more rigorous and useful petrophysical interpretations that can be linked to gas productivity.
Acoustic Wave Testing System for Monitoring the Vapor Chamber in Vapor Extraction Process
Authors: Zhou W. , Paranjape R. , Asghari K. 
Published: May 2011

Abstract
The acoustic wave detection system is considered a non-destructive monitoring system to estimate distances using measurement of the time-of-flight of an ultrasonic wave. In this paper, a comprehensive experimental study was conducted to investigate the feasibility of the acoustic wave detection system in monitoring the shape and position of the gas phase in the vapor extraction process. For this purpose, various stages of vapor chamber evolution in the Vapex process were experimentally simulated by changing the shape of air balloons buried in simulated porous media in a lab scale model. Then, an array of ultrasound transducers and receivers were used to measure time-of-flights at different stages of the vapor chamber growth. Finally, the collected data were fed into a signal processing program developed in this study to determine the shape of the vapor chamber. Conducted analysis in this study include: sound speed testing in different porous media, signal attenuation tests in different porous media, imaging of different simulated vapor chambers in different porous media, and the acquisition and analysis experiments. Results show that acoustic wave detection can be used for accurate mapping of the position and shape of the vapor chamber in the studied process. Monitoring the shape and growth of the vapor chamber provides valuable information for optimizing oil production in order to maximize oil recovery. This is the first attempt at using acoustic wave detection techniques in monitoring the phase movement in the Vapex process. Results of this study show that this technique can be potentially used for this purpose.
Efficiency of Oil Recovery by Low Salinity Water Flooding in Sandstone Reservoirs
Authors: Nasralla Ramez A. , Alotaibi Mohammed B. , Nasr-El-Din Hisham A. 
Published: May 2011

Abstract
Low salinity water is a promising technique for improving oil recovery in sandstone reservoirs. However, the optimum conditions that improve oil recovery by low salinity flooding are uncertain due to the lack of understanding of fluid-rock interaction mechanisms. In this study, several coreflood experiments were conducted to explain the mechanisms involved when recovering oil with low salinity water.
Core flood experiments were run to determine the effect of water salinity on oil recovery in the secondary and tertiary modes. Deionized water and three different brines (from 5,000 to 174,000 mg/l) were tested; these brines represent a Middle East field case. Two different types of crude oils were used to investigate the effect of oil composition on the applicability of low salinity water flooding. All experiments were conducted on 5 to 6 in. long outcrop Berea sandstone cores. Core flood effluent was sampled regularly to follow rock-fluid interactions, and it was achieved by measuring the concentration of different cations.
Core flood tests indicated that injection of deionized water in the secondary mode resulted in a significant improvement in oil recovery, up to 22%, compared to seawater. However, no additional oil was recovered in the tertiary mode. This paper contributes to the understanding of cation exchange caused by low salinity water injection, and how this exchange alters the wettability of the rock and reduces the electrostatic attraction forces between oil and rock. Likewise, we discuss formation damage that might occur during low salinity waterflooding in Berea sandstone, and investigate the contribution of formation damage to oil recovery improvement.
Residual Trapping in Simultaneous Injection of CO2 and Brine in Saline Aquifers
Authors: Javaheri Mohammad , Jessen Kristian 
Published: May 2011

Abstract
Disposal of carbon dioxide (CO2) into saline aquifers appears to be one of the best CO2 sequestration options in terms of capacity and technology. Injected CO2 migrates invariably upwards due to buoyancy forces. In most common aquifer settings, the density difference between CO2 and brine is sufficiently high that gravity force is a pre-dominant factor that controls the upward migration of a CO2 plume. Any scheme that can retard the vertical movement of the plume can enhance the entrapment of the injected CO2 and reduce the risk of potential leakage back into the atmosphere.
An appealing scheme for sequestration projects in aquifers involves simultaneous injection of brine and CO2 from vertical wells, where brine is injected in the upper part of injection well(s) and CO2 is injected in the lower portion of the well(s). This scheme inhibits the rapid upward migration of CO2, since the injected CO2 is forced to move horizontally during the injection period. The horizontal displacement increases the volume of the aquifer that is contacted by the injected CO2, and hence, the residual entrapment of the CO2-rich phase can be increased significantly. The upward migration of CO2 away from the injector occurs predominantly in a counter-current flow mode.
In this study, we compare residual entrapment of CO2 for the simultaneous injection of CO2 and brine in four different aquifer settings. The four aquifer settings are selected from the classification scheme proposed by Kopp et al. (2009). It is shown that for large gravity numbers, there is a significant difference between the four aquifer settings in terms of storage capacity with warm aquifers having the least storage capacity and cold aquifers providing the largest storage capacity. The distance at which segregation of brine and CO2 is complete, not only depends on the gravity number, but also on the aquifer setting. It is indicated that residual entrapment of CO2 depends on brine injection rate and higher rates of brine (lower gravity number) increase the fraction of CO2 that is trapped in a residual phase. Finally, we demonstrate that the reduction in the relative permeability of both phases, due to counter-current flow, has a major impact on the sweep efficiency of the injected CO2 and hence impact both the distance traveled before full segregation and the level of residual entrapment.
Tapered-Bean Steam Chokes Revisited
Authors: Castrup Suzanne , Latif Faisal , Kalbani Ali Al 
Published: May 2011

Abstract
Controlling and monitoring flow rates at continuous and cyclic steam injection wells are important elements of reservoir heat management. For nearly 30 years, critical flow chokes have proven to be the most reliable and cost-effective means of controlling steam injection into heavy oil reservoirs. Flow control efficiency has been further improved with tapered-bore bean inserts to achieve critical flow with only 10% to 15% pressure loss across the choke.
For the past 10 years, the standard steam choke assembly has consisted of a 1-inch outer diameter (O.D.) by 6-inch long bean with 6° tapered-bore inserted in a 2-inch O.D. cage nipple or housing. Larger diameter cage nipples and bean inserts have been required for steam injection rates exceeding 500 b/d. More recently, a cost-cutting practice has been employed using shorter tapered-beans inserted in standard choke assemblies.
This paper presents the results of field tests conducted to evaluate the effectiveness of shorter tapered-bean length for controlling steam injection rates. Transition from subcritical to critical flow and overall pressure loss for different tapered-bean lengths are presented. A modified Thornhill-Craver flow rate equation is provided for critical and subcritical flow regions. Calculated and measured rates are compared and their relative uncertainties are assessed.
Geochemical Allocation of Commingled Oil Production or Commingled Gas Production
Authors: McCaffrey Mark A. , Ohms Danielle H. , Werner Michael , Stone Christopher , Baskin David K. , Patterson Brooks A. 
Published: May 2011

Abstract
We have made substantial improvements to the previously published methods for geochemical allocation of commingled oil production and/or commingled gas production. This new method has allowed allocation of commingled production from wells at less than 2–5% of the cost of production logging. Four case studies are shown here. In the first two studies, commingling of the wells was subject to approval of the Alaska Oil and Gas Conservation Commission (AOGCC). Before agreeing to the use of geochemical allocation, the AOGCC required the well operator to perform multi-month trial studies in which the wells were monitored both by geochemical allocation and by production logging. The individuals performing the geochemical allocation were kept blind from the results of the production logging until the studies were completed. Close agreement between the geochemistry-based allocation values and the production-logging-based allocation values resulted in AOGCC approval of continued use of the geochemical method for oil production monitoring of these two wells. Two additional case studies presented here illustrate how geochemical allocation can be used to monitor the effects on production of (1) changes in water injection into nearby wells, and (2) closing or opening perforations within a well.
A novel technique to evaluate the geometrical accuracy of CT-MR image fusion in Gamma Knife radiosurgery procedures
Authors: Thomas Sajeev , Sampath S. , IndiraDevi B. , Bhanumathy G. , Supe Sanjay , Musthafa M. 
Published: May 2011

A novel technique to evaluate the geometrical accuracy of CT-MR image fusion in Gamma Knife radiosurgery procedures
In order to optimize the accuracy of imaging in Gamma Knife radiosurgery using the image fusion options available in the Leksell gamma plan. Phantom images from 1.5 Tesla MRI Scan (Magnetom vision - Siemens) and Computed Tomography images from Philips Brilliance 16 CT scanner were used for image fusion in Gammaplan treatment planning system. The images were fused using co-registration technique using multiview and imagemerge modules. Stereotactic coordinates were then calculated for known targets. Vector distances from the centre of the Leksell coordinate system to five known targets were measured in CT, MR and CT-MR fused images and compared with geometrical measurements. The mean values of maximum absolute errors were 0.34 mm, 0.41 mm.0.38 mm (along x-axis), 0.43 mm, 1.53 mm, 0.62 mm (along y-axis) and 0.75 mm 2.02 mm, 0.93 mm (along z-axis) for CT, MR and CT-MR fused image data respectively. The mean error in calculating the vector distances from the center of the Leksell coordinate system (100, 100, 100) to the known target volumes are 0.22 mm, 0.8 mm and 0.43 mm for CT, MR and CT-MR fused images, respectively. Image fusion functions available in gamma plan are useful for combining the features of CT and MR imaging modalities. These methods are highly useful in clinical situations where the error associated with Magnetic Resonance Imaging is beyond acceptable levels.
Estimating mental fatigue based on electroencephalogram and heart rate variability
Authors: Zhang Chong , Yu Xiaolin 
Published: May 2011

Estimating mental fatigue based on electroencephalogram and heart rate variability
The effects of long term mental arithmetic task on psychology are investigated by subjective self-reporting measures and action performance test. Based on electroencephalogram (EEG) and heart rate variability (HRV), the impacts of prolonged cognitive activity on central nervous system and autonomic nervous system are observed and analyzed. Wavelet packet parameters of EEG and power spectral indices of HRV are combined to estimate the change of mental fatigue. Then wavelet packet parameters of EEG which change significantly are extracted as the features of brain activity in different mental fatigue state, support vector machine (SVM) algorithm is applied to differentiate two mental fatigue states. The experimental results show that long term mental arithmetic task induces the mental fatigue. The wavelet packet parameters of EEG and power spectral indices of HRV are strongly correlated with mental fatigue. The predominant activity of autonomic nervous system of subjects turns to the sympathetic activity from parasympathetic activity after the task. Moreover, the slow waves of EEG increase, the fast waves of EEG and the degree of disorder of brain decrease compared with the pre-task. The SVM algorithm can effectively differentiate two mental fatigue states, which achieves the maximum classification accuracy (91%). The SVM algorithm could be a promising tool for the evaluation of mental fatigue.
Fatigue, especially mental fatigue, is a common phenomenon in modern life, is a persistent occupational hazard for professional. Mental fatigue is usually accompanied with a sense of weariness, reduced alertness, and reduced mental performance, which would lead the accidents in life, decrease productivity in workplace and harm the health. Therefore, the evaluation of mental fatigue is important for the occupational risk protection, productivity, and occupational health.
Application of a PExSim for modeling a POLVAD artificial heart and the human circulatory system with left ventricle assistance
Authors: Siewnicka Alicja , Fajdek Bartlomiej , Janiszowski Krzysztof 
Published: May 2011

Application of a PExSim for modeling a POLVAD artificial heart and the human circulatory system with left ventricle assistance
This paper presents a model of the human circulatory system with the possible addition of a parallel assist device, which was developed for the purpose of artificial heart monitoring. Information about an identification experiment of an extracorporeal ventricle assist device POLVAD is included. The modelling methods applied and the corresponding functional blocks in a PExSim package are presented. The results of the simulation for physiological conditions, left ventricle failure and pathological conditions with parallel assistance are included.
Quand la puissance publique fait surgir et équipe une mobilisation protestataire
Authors: Huyard Caroline 
Published: May 2011

Résumé Alors que nombre de travaux s’interrogent sur la capacité des mobilisations dites de malades à influencer les politiques de santé, l’invention des maladies rares oblige à saisir l’élaboration conjointe d’une cause et d’une action publique. Une décision de la puissance publique américaine crée un « public », dont les personnes atteintes d’affections peu fréquentes sont une composante, qui s’organise. En réponse à leur activisme, l’administration américaine invente la catégorie des maladies rares, instrument de l’action publique et identité nouvelle pour les protestataires. En Europe, l’administration française fait de cet instrument le problème à résoudre, et initie pour le porter une mobilisation des malades.