Theses (Engineering)
http://hdl.handle.net/10059/91
2017-06-08T04:28:18ZProperties of a high-current discharge in alkali-metal-seeded rare gases.
http://hdl.handle.net/10059/2313
Properties of a high-current discharge in alkali-metal-seeded rare gases.
Ellington, Henry I.
This thesis is an account of a detailed investigation of the properties of a recently-discovered gas discharge - a discharge that operates at a few volts or tens of volts, and which carries a current of the order of amps through a mixture consisting of a hot, atmospheric-pressure rare gas (the "diluent") to which a small amount of alkali metal vapour has been added as an easily-ionised "seed". It is shown that the establishment of the discharge under study is brought about by the breakdown of the gas, which occurs at a breakdown voltage that depends mainly on the electrode spacing, seed pressure, and choice of diluent gas. The discharge itself is shown to consist of two main regions, namely, a constricted, cylindrical positive column that extends from the anode to within a short distance of the cathode, and a thin, glowing sheath that covers the entire cathode surface; the two regions are separated by a dark space. The positive column is shown to expand as current increases, while the value of its electric field is shown to depend mainly on the discharge current, seed pressure, and choice of diluent gas, and hardly at all on the gas temperature or choice of seed metal. The cathode fall is shown to depend mainly on the discharge current, seed pressure, and choice of seed metal. The breakdown of the gas, the positive column of the discharge, and the cathode regions of the discharge are discussed in successive chapters.
1969-04-01T00:00:00ZGas-condensate flow modelling for shale gas reservoirs.
http://hdl.handle.net/10059/2144
Gas-condensate flow modelling for shale gas reservoirs.
Labed, Ismail
In the last decade, shale reservoirs emerged as one of the fast growing hydrocarbon
resources in the world unlocking vast reserves and reshaping the landscape of the oil and
gas global market. Gas-condensate reservoirs represent an important part of these
resources. The key feature of these reservoirs is the condensate banking which reduces
significantly the well deliverability when the condensate forms in the reservoir below the
dew point pressure. Although the condensate banking is a well-known problem in
conventional reservoirs, the very low permeability of shale matrix and unavailability of
proven pressure maintenance techniques make it more challenging in shale reservoirs.
The nanoscale range of the pore size in the shale matrix affects the gas flow which deviates
from laminar Darcy flow to Knudsen flow resulting in enhanced gas permeability.
Furthermore, the phase behaviour of gas-condensate fluids is affected by the high capillary
pressure in the matrix causing higher condensate saturation than in bulk conditions. A good
understanding and an accurate evaluation of how the condensate builds up in the reservoir
and how it affects the gas flow is very important to manage successfully the development of
these high-cost hydrocarbon resources.
This work investigates the gas Knudsen flow under condensate saturation effect and phase
behaviour deviation under capillary pressure of gas-condensate fluids in shale matrix with
pore size distribution; and evaluates their effect on well productivity.
Supplementary MATLAB codes are provided elsewhere on OpenAIR: http://hdl.handle.net/10059/2145
2016-10-01T00:00:00ZAn investigation of energy-based planned maintenance of offshore drilling mud pumps.
http://hdl.handle.net/10059/2136
An investigation of energy-based planned maintenance of offshore drilling mud pumps.
Mok, Soon H.
Mud pumps used on offshore installations for drilling operations have been known to experience unpredictable breakdowns, including during critical stages of drilling. The fluid end has been identified as requiring more maintenance work due to component failure, compared to the power end. The most common maintenance strategies in use include breakdown maintenance, time-based maintenance and condition monitoring. Time-based maintenance, based on running hours, is the most commonly preferred method by most, if not all, mud pump operators. However, the nature of drilling operations require pump performance with variable loads (pressures), variable speed characteristics and time-based maintenance would not be able to account for the different operating conditions within any identical time frames. To address this shortcoming, this research looked at the postulation that material wear loss is related to the energy expended and developed a dedicated reciprocating wear test system to identify and investigate the effect of operating variables on the wear loss of piston rubbers, which was considered to be the most problematic of the fluid end components.
1994-07-01T00:00:00ZComputational fluid dynamics (CFD) modelling of critical velocity for sand transport flow regimes in multiphase pipe bends.
http://hdl.handle.net/10059/2118
Computational fluid dynamics (CFD) modelling of critical velocity for sand transport flow regimes in multiphase pipe bends.
Tebowei, Roland
The production and transportation of hydrocarbon fluids in multiphase pipelines could be severely hindered by particulate solids deposit such as produced sand particles which accompany hydrocarbon production. Knowledge of the flow characteristics of solid particles in fluids transported in pipelines is important in order to accurately predict solid particles deposition in pipelines. This research thesis presents the development of a three-dimensional (3D) Computational Fluids Dynamics (CFD) modelling technique for the prediction of liquid-solids multiphase flow in pipes, with special emphasis on the flow in V-inclined pipe bends. The Euler-Euler (two-fluid) multiphase modelling methodology has been adopted and the multiphase model equations and closure models describing the liquid-solids flow have been implemented and calculated using the finite volume method in a CFD code software. The liquid phase turbulence has been modelled using a two-equation k−ε turbulence model which contains additional terms to account for the effects of the solid-particles phase on the multiphase turbulence structure.
The developed CFD numerical framework has been verified for the relevant forces and all the possible interaction mechanisms of the liquid-solids multiphase flow by investigating four different numerical frameworks, in order to determine the optimum numerical framework that captures the underlying physics and covers the interaction mechanisms that lead to sand deposition and the range of sand transport flow regimes in pipes. The flow of liquid-sand in pipe has been studied extensively and the numerical results of sand concentration distribution across pipe and other flow properties are in good agreement with published experimental data on validation. The numerical framework has been employed to investigate the multiphase flow in V-inclined pipe bends of ±4o−6o, seemingly small inclined bend angles. The predicted results which include the sand segregation, deposition velocity and flow turbulence modulation in the pipe bend show that the seemingly small pipe bends have significant effect on the flow differently from that of horizontal pipes. The pipe bend causes abrupt local change in the multiphase flow characteristic and formation of stationary sand deposit in the pipe at a relatively high flow velocity. The threshold velocity to keep sand entrained in liquid in pipe bends is significantly higher than that required for flow horizontal pipes. A critical implication of this is that the correlations for predicting sand deposition in pipelines must account for the effect of pipe bend on flow characteristics in order to provide accurate predictions of the critical sand transport velocity (MTV) in subsea petroleum flowlines, which V-inclined pipe bends are inevitable due to seabed topology.
2016-09-01T00:00:00Z