In the past decades, considerable effort has been put into developing high resolution geological models for oil and gas reservoirs. Although the growth of computational power is rapid, the static model size still exceeds the model size for routine reservoir simulation. We develop and apply a variety of grid coarsening and refinement algorithms and single and multiphase upscaling approaches, applied to tight gas and conventional reservoir models. The proposed research is organized into three areas. First the upgridding of detailed three dimensional geologic models is studied. We propose an improved layer design algorithm with considerations of accuracy and efficiency. This involves developing measures of reservoir heterogeneity and using these measures to design an optimal grouping of geologic model layers for flow simulation. The optimal design is shown to be a tradeoff between the desire to preserve the reservoir heterogeneity and a desire to minimize the simulation time. The statistical analysis is validated by comparison with flow simulation results. Accurate upgridding/upscaling of single-phase parameters is necessary. However, it does not always satisfy the accuracy requirements, especially for the model which is aggressively coarsened. We introduce a pseudoization method with total mobility and effective fractional flow as the major targets. This pseudoization method helps to push upgridding/coarsening degree to the limit but still be able to reproduce the fine scale field performance. In practice, it is common to not use a different set of pseudos for every coarse cell; only a limited number of pseudo functions should be generated for different “rock types” or geological zones. For similar well patterns and well control conditions, applying pseudo is able to reproduce the fine scale performance for different simulation runs. This is the second proposed research area. Finally, it is necessary to increase flow resolution for precise field history matching and forecasting. This has received increasing attention, especially when studying hydraulically fractured wells in unconventional reservoirs. We propose a multiscale reservoir simulation model combining local grid refinement (LGR) and pillar-based upscaling for tight gas reservoir performance prediction. Pillar-based coarsening away from the wells is designed for tight gas reservoirs. It compensates for the extra computational cost from LGR, which is used to represent hydraulic fractures. Overall reservoir performances, including the accuracy and efficiency, are evaluated.

It is common for an oil well to produce a mixture of hydrocarbons that flash when exposed to atmospheric pressure. The separation of oil and gas mixtures on site may prove expensive and lead to higher infrastructure and maintenance costs as well. A multiphase pump offers a good alternative with a lower capital cost and increased overall production. A Progressive Cavity Pump (PCP) is a positive displacement pump type that can be used to pump a wide range of multiphase mixtures, including high viscosity fluids with entrained gas and solid particles in suspension. Despite its advantages, a PCP has a reduced ability to handle high gas-liquid ratios due to limitations of its elastomeric stator material required to overcome thermo and mechanical effects. Also the efficiency decreases significantly with increases in gas volume fractions and reduced differential pressures. The current study focuses on studying the behavior of this unique pump in a wide range of GVFs and studying the effect of this ratio on overall efficiency, temperature and pressure distribution on the stator. The pump exhibits vibration issues at specific differential pressures and they have been studied in this work. This can be of critical value as severe vibration issues can damage the pump components such as couplings and bearings leading to high maintenance costs. Another important issue addressed by this research is the behavior of this pump in transient conditions. Oil well production is highly unpredictable with unexpected rises and drops in GVFs. These transient conditions have been simulated by varying the GVF over wide ranges and studying the pump's behavior in terms of load, temperature rises and instantaneous pressure profiles on the pump stator. This thesis provides a comprehensive study of this pump, its operating ranges and behavior in off-design conditions to assist oil and gas exploration ventures in making an informed choice in pump selection for their applications based on field conditions.

A detailed understanding of mass transport and water behavior in gas diffusion layers (GDLs) for polymer electrolyte membrane fuel cells (PEMFCs) is vital to improving performance. Liquid water fills the porous GDL and electrode components, hindering mass transfer, limiting attainable power and decreasing efficiency. The behavior of liquid water in GDLs is poorly understood, and the specific nature of mass transfer of multiphase flow in GDLs are not known. There is no clear direct correlation between easily measurable ex-situ GDL material properties and mass transfer characteristics. This thesis addresses this knowledge gap through a combination of test procedure development, experimentation and numerical pore scale modeling. Experimental techniques have been developed to measure permeability and capillary properties of water and air in the GDL matrix. Pore network modeling is used to estimate transport properties as a function of GDL water saturation since these are extremely difficult to determine experimentally. A method and apparatus for measuring the relationship between air-water capillary pressure and water saturation in PEMFC gas diffusion layers is described. The developed procedure of Gas Controlled Porosimetry is more effective for understanding the behaviour of water in GDL material then traditional methods such as the method of standard porosimetry and mercury intrusion porosimetry. Capillary pressure data for water injection and withdrawal from typical GDL materials are obtained, which demonstrated permanent hysteresis between water intrusion and water withdrawal. Capillary pressure, defined as the difference between the water and gas pressures at equilibrium, is positive during water injection and negative during water withdrawal. The results contribute to the understanding of liquid water behavior in GDL materials which is necessary for the development of effective PEMFC water management strategies and the design of future GDL materials. The absolute gas permeability of GDL materials was measured. Measurements were made in three perpendicular directions to investigate anisotropic properties of various materials. Most materials were found to be significantly anisotropic, with higher in-plane permeability than through-plane permeability. In-plane permeability was also measured as the GDL was compressed to different thicknesses. Typically, compression of a sample to half its initial thickness resulted in a decrease in permeability by an order of magnitude. The relationship between measured permeability and compressed porosity was compared to various models available in the literature, one of which allows the estimation of anisotropic tortuosity. The results of this work will be useful for 3D modeling studies where knowledge of permeability and effective diffusivity tensors is required. A pore network model of mass transport in GDL materials is developed and validated. The model idealizes the GDL as a regular cubic network of pore bodies and pore throats following respective size distributions of the pores. With the use of experimental data obtained the geometric parameters of the pore network model were calibrated with respect to porosimetry and gas permeability measurements for two common GDL materials. The model was subsequently used to compute the pore-scale distribution of water and gas under drainage conditions using an invasion percolation algorithm. From this information, transport properties of GDLs that are very difficult to measure were estimated, including the relative permeability of water and gas, and the effective gas diffusivity as functions of water saturation. Comparison of the model predictions with those obtained from constitutive relationships commonly used in current PEMFC models indicates that the latter may significantly overestimate the gas phase transport properties. The pore network model was also used to calculate the limiting current in a PEMFC under operating conditions for which transport through the GDL dominates mass transfer resistance. The results suggest that a dry GDL does not limit the performance of a PEMFC, but water flooding becomes a significant source of concentration polarization as the GDL becomes increasingly saturated with water. This work has significantly contributed to the understanding of mass transfer in gas diffusion layers in PEMFC through experimental investigation and pore scale modeling.

A detailed understanding of mass transport and water behavior in gas diffusion layers (GDLs) for polymer electrolyte membrane fuel cells (PEMFCs) is vital to improving performance. Liquid water fills the porous GDL and electrode components, hindering mass transfer, limiting attainable power and decreasing efficiency. The behavior of liquid water in GDLs is poorly understood, and the specific nature of mass transfer of multiphase flow in GDLs are not known. There is no clear direct correlation between easily measurable ex-situ GDL material properties and mass transfer characteristics. This thesis addresses this knowledge gap through a combination of test procedure development, experimentation and numerical pore scale modeling. Experimental techniques have been developed to measure permeability and capillary properties of water and air in the GDL matrix. Pore network modeling is used to estimate transport properties as a function of GDL water saturation since these are extremely difficult to determine experimentally. A method and apparatus for measuring the relationship between air-water capillary pressure and water saturation in PEMFC gas diffusion layers is described. The developed procedure of Gas Controlled Porosimetry is more effective for understanding the behaviour of water in GDL material then traditional methods such as the method of standard porosimetry and mercury intrusion porosimetry. Capillary pressure data for water injection and withdrawal from typical GDL materials are obtained, which demonstrated permanent hysteresis between water intrusion and water withdrawal. Capillary pressure, defined as the difference between the water and gas pressures at equilibrium, is positive during water injection and negative during water withdrawal. The results contribute to the understanding of liquid water behavior in GDL materials which is necessary for the development of effective PEMFC water management strategies and the design of future GDL materials. The absolute gas permeability of GDL materials was measured. Measurements were made in three perpendicular directions to investigate anisotropic properties of various materials. Most materials were found to be significantly anisotropic, with higher in-plane permeability than through-plane permeability. In-plane permeability was also measured as the GDL was compressed to different thicknesses. Typically, compression of a sample to half its initial thickness resulted in a decrease in permeability by an order of magnitude. The relationship between measured permeability and compressed porosity was compared to various models available in the literature, one of which allows the estimation of anisotropic tortuosity. The results of this work will be useful for 3D modeling studies where knowledge of permeability and effective diffusivity tensors is required. A pore network model of mass transport in GDL materials is developed and validated. The model idealizes the GDL as a regular cubic network of pore bodies and pore throats following respective size distributions of the pores. With the use of experimental data obtained the geometric parameters of the pore network model were calibrated with respect to porosimetry and gas permeability measurements for two common GDL materials. The model was subsequently used to compute the pore-scale distribution of water and gas under drainage conditions using an invasion percolation algorithm. From this information, transport properties of GDLs that are very difficult to measure were estimated, including the relative permeability of water and gas, and the effective gas diffusivity as functions of water saturation. Comparison of the model predictions with those obtained from constitutive relationships commonly used in current PEMFC models indicates that the latter may significantly overestimate the gas phase transport properties. The pore network model was also used to calculate the limiting current in a PEMFC under operating conditions for which transport through the GDL dominates mass transfer resistance. The results suggest that a dry GDL does not limit the performance of a PEMFC, but water flooding becomes a significant source of concentration polarization as the GDL becomes increasingly saturated with water. This work has significantly contributed to the understanding of mass transfer in gas diffusion layers in PEMFC through experimental investigation and pore scale modeling.

A VOF based multiphase Lattice Boltzmann method that explicitly prescribes kinematic boundary conditions at the interface is developed. The advantage of the method is the direct control over the surface tension value. The details of the numerical method are presented. The Saffman instability, Taylor instability, and flow of deformable suspensions in a channel are used as example-problems to demonstrate the accuracy of the method. The method allows for relatively large viscosity and density ratios.

A robust understanding and planning of production enhancement and flow assurance is required as petroleum E&P activities are targeting deepwaters and long distances. Different flow assurance issues and their solutions are put together in this work. The use of multiphase pumps as a flow assurance solution is emphasized. Multiphase pumping aids flow assurance in different ways. However, the problem causing most concern is sand erosion. This work involved a detection-based sand monitoring method. Our objectives are to investigate the reliability of an acoustic sand detector and analyze the feasibility of gel injection as a method to mitigate sand erosion. Use of a sand detector coupled with twin-screw pumps is studied under varying flow conditions. The feasibility of gel injection to reduce slip and transport produced solids through twin-screw pump is investigated. A unique full-scale laboratory with multiphase pumps was utilized to carry out the experimental tests. The test results indicate that acoustic sand detection works in a narrow window around the calibration signature. An empirical correlation for predicting the twin-screw pump performance with viscous fluids was developed. It shows good agreement in the practical operational limits – 50% to 100% speed. The results indicate that viscous gel injection should be an effective erosion mitigation approach as it reduces slip, the principle cause of erosive wear. To correlate the performance of viscous fluid injection to hydroabrasive wear, further experimental investigation is needed.

In this thesis, coupled inductors have been applied to multiphase DC-DC converters. Detailed analysis has been done to investigate the benefits of directly coupled inductors and inversely coupled inductors, compared to conventional uncoupled inductors. In general, coupled inductors for multiphase DC-DC converters have inherent benefits such as excellent current sharing characteristics, immunity to component tolerance and reduction in current control complexity. Specifically, by employing directly coupled inductors for multiphase DC-DC converters, overall current ripple can be effectively reduced, compared to that of uncoupled inductors. For inversely coupled inductors, phase current ripple can be reduced if operating points and coupling coefficients are carefully chosen. As for small-signal characteristics, inversely coupled inductors have the advantages of broadening the bandwidth of multiphase DC-DC converters and being more immune to load variation at low frequencies. On the other hand, directly coupled inductors have the benefit of low sensitivity to input variation at high frequencies. In addition, the proposed new structure for multiphase DC-DC converters has excellent current sharing performance and reduced current ripple. Computer simulations have been done and hardware prototypes have been built to validate the concepts.

In November 2000, the 4th Workshop on Measurement Techniques for Stationary and Transient Multiphase Flows took place in Rossendorf. Three previous workshops of this series were national meetings; this time participants from different countries took part. The programme comprised 14 oral presentations, 9 of which are included in these proceedings in full length. A special highlight of the meeting was the main lecture "Ultrasonic doppler method for bubbly flow measurement" of Professor Masanori Aritomi, Dr. Hiroshige Kikura and Dr. Yumiko Suzuki, which was read by Dr. Hiroshige Kikura. The workshop again dealt with high-resolution phase distribution and phase velocity measurement techniques based on electrical conductivity, ultrasound, laser light and high-speed cinematography. A number of presentations were dedicated to the application of wire-mesh sensors developed by FZR for different applications used by the Technical Universities of Delft and Munich and the Tokyo Institute of Technology. The presentations were in particular: M. Aritomi, H. Kikura, Y. Suzuki (Tokyo Institute of Technology): Ultrasonic doppler method for bubbly flow measurement V. V. Kontelev, V. I. Melnikov (TU Nishny Novgorod): An ultrasonic mesh sensor for two-phase flow visualisation A. V. Duncev (TU Nishny Novgorod): Waveguide ultrasonic liquid level transducers for power generating equipment H.-M. Prasser, E. Krepper, D. Lucas, J. Zschau (FZR), D. Peters, G. Pietzsch, W. Taubert, M. Trepte (Teletronic Ingenieurbüro GmbH), Fast wire-mesh sensors for gas-liquid flows and decomposition of gas fraction profiles according to bubble size classes D. Scholz, C. Zippe (FZR): Validation of bubble size measurements with wire-mesh sensors by high-speed video observation A. Manera, H. Hartmann, W.J.M. de Kruijf, T.H.J.J. van der Hagen, R.F. Mudde, (TU Delft, IRI): Low-pressure dynamics of a natural-circulation two-phase flow loop H. Schmidt, O. Herbst, W. Kastner, W. Köhler (Siemens AG KWU): Measuring methods for the investigation of the flow phenomena during external pressure vessel cooling of the boiling water reactor SWR1000 A. Traichel, W. Kästner, S. Schefter, V. Schneider, S. Fleischer, T. Gocht, R. Hampel (HTWS Zittau/Görlitz - IPM): Verification of simulation results of mixture level transients and evaporation processes in level measurement systems using needle-shaped probes S. Richter, M. Aritomi (Tokyo Institute of Technology): Methods for studies on bubbly flow characteristics applying a new electrode-mesh tomograph

Thesis (doctoral)--Universität Kiel, 2000. / Vita. Includes bibliographical references (p. 138-145).

Thesis (Ph. D.)--West Virginia University, 2002. / Title from document title page. Document formatted into pages; contains xi, 107 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 102-107).