Thesis (Ph.D.)--University of Iowa, 2006. / Supervisors: Larry J. Weber, George Constantinescu. Includes vita. Includes bibliographical references (leaves 220-222).

The global offshore oil and gas industry is constantly challenged with complex operational activities, increasing uncertainties, strict regulations and delicate health, safety and environmental issues. That has made offshore deepwater drilling operation the most time sensitive activity in the upstream oil and gas industry with high probabilities of cost and time overrun. Unfortunately, the current cost estimation models are not robust enough to deal with the multi-variables associated with cost overrun in the offshore deepwater drilling industry in the Sub-Sahara Africa. This study therefore developed a mathematical model that can give accurate estimations with limited data, precisely capture risk elements and factor probability results of all the possible cost variables in the offshore deep-water drilling operations. The study combined Bayesian approach with Activity-based costing (ABC) model to address the limitations of most existing models using primary data collected and secondary data extrapolated from past literatures, published official drilling data and companies’ financial and operational reports. The integrated model showed promising results when tested against three offshore fields’ data across three different countries (Erha-Nigeria, Jubilee-Ghana and Luanda-Angola). Findings from the analysis of the three fields showed cost estimates to be 10% more accurate than the estimates from existing cost estimation models in Sub-Sahara Africa. Further analysis also demonstrated the ability of the model to reduce the regional cost overrun from about 40% to 20%, thereby underlining the efficacy of the model in estimating offshore drilling cost. The strengths, weaknesses as well as the implications of using the model were also discussed. Additionally, the study developed an improved elicitation framework and guidelines to help facilitate cost estimation in the offshore deep-water drilling operations based on the Bayesian approach. The developed elicitation process was used to collect the primary data for this work and generated probabilistic response on the known unknowns and unknown unknowns’ variables in the oil and gas industry Finally, the research analysed and produced findings on cost reduction techniques for the offshore drilling industry.

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Recent developments of electro-hydraulic disc valves at Surrey University have shown that with a careful balance between the hydraulic and magnetic forces, this type of valve can be used as a digital or proportional device. As the valve is simpler in construction and involves very few critical dimension compared with a servo-valve, the sensitivity to contamination is considerably reduced. The dynamic response of the valve is fast due to utilising high electro-magnetic and fluid forces for actuation. The research described in this thesis is an extension of earlier work by Yuksel and Usman to improve electro-hydraulic disc valves by applying closed-loop position or pressure control to the disc. From an investigation of an unbalanced single disc valve, it was found that using position feedback can help to stabilise the disc under varying load conditions. A special differential capacitive transducer to measure the disc position was designed and constructed and was found to perform satisfactorily. As the pressure-flow characteristic of the valve can be varied by controlling the disc position, the function of the valve is similar to an electrically controlled variable orifice. Various modular configurations are proposed to perform more complicated control functions. In the final part of the research, a double disc valve is described for used in an application study to control the damping characteristic of a modified vehicle shock absorber. Initially, the valve was designed for closed-loop position control due to the non-linear hydraulic and magnetic forces. Results show that the valve can be controlled to generate the required range of damping force and has adequate dynamic performance with a response time in the range of 10 to 30 msec. However, tests using direct pressure control were also carried out. Preliminary results indicate that pressure feedback is preferable to position feedback and that by using lead compensation together with a proportional plus integral controller, stable operation is possible.

The UK sector of the North Sea is a mature oil and gas basin subjected to some of the harshest offshore environments with a majority of the oil and gas installations approaching or having exceeded their original design life, often specified as 25 years. It is likely that the operation of these installations will continue for a substantial period in the foreseeable future. However, the ageing nature of these installations present significant challenges to the delivery of high standards of health and safety required by the UK Health and Safety Executive. The issue of ageing installations has been shown to be an important factor in offshore incidents and accidents, leading to an increased risk of accidental loss of hydrocarbon and failures due to equipment deterioration. Two major hazards resulting from ignition of accidental hydrocarbon release are fires and explosions. Failure to minimise the effects of fires and explosions can bring about significant damage to the structural integrity of offshore installations and pose a risk to personnel safety as evidenced by the 1988 Piper Alpha Disaster and the 2010 Deepwater Horizon Explosion and Oil Spill. This thesis presents a practical tool that can be used to predict the costs, risks and service reliability of any given asset management policy for an offshore oil and gas installation. The tool is implemented using a standard Petri Net technique with already adopted and newly proposed high level extensions, and fluid flow modelling technique. The tool is further divided into two sub models that work in conjunction with one another: (1) the Petri Net based Offshore Safety System Degradation and Maintenance Model and (2) the Offshore Fire and Explosion Model based on fluid flow modelling techniques. The aim of the Offshore Safety System Degradation and Maintenance Model is to concurrently simulate the degradation, failure, inspection and maintenance of four safety systems which includes the fire and gas detection system, process isolation, process blowdown, and the deluge system. Simulation of the model generates a variety of statistics such as the estimated operational costs and unavailability associated with implementing any given asset management policy. The Offshore Fire and Explosion Model is then used to model the occurrence of a hydrocarbon leak from a process vessel located within three enclosed modules; wellhead, separation and compression, of an offshore installation. The aim of this model is to predict the frequencies of fires and explosions in the event that the safety systems previously modelled in the Offshore Safety System Degradation and Maintenance Model fail to function on demand in the presence of an ignition source. The model utilises fluid flow modelling to calculate parameters such as the hydrocarbon discharge rate, gas cloud build-up and dispersion, oil-pool build-up and reduction. These parameters can then be used to predict the magnitude of the fires and explosions in terms of the flame length produced in the event of a fire and the overpressures generated in the event of an explosion. The results and statistics generated are highly beneficial to offshore asset operations managers as they can be used to predict the number of maintenance interventions necessary to ensure safety systems are in an acceptable condition. From this, associated costs can be determined enabling offshore managers to allocate resources and budget accordingly. Finally, an optimisation study is carried out using Genetic Algorithm to identify the optimum inspection, maintenance and repair strategy for the offshore safety systems with an acceptable risk level. The methodology presented in this research considers the offshore safety systems and the processes described above in more detail compared to previous literature associated with asset management offshore oil and gas installation. Additionally, the research demonstrates the suitability of Petri Nets for integrating fire and explosion modelling within the asset management framework which is first of its kind. The model can be successfully used to predict costs, risks and service reliability, and to support asset management decisions when the model is implemented in an optimisation framework.

With the increase in human activity associated with the recent rise in Kuwait’s oil production, there is greater need for an optimised solution to protect the Kuwaiti coastline and islands from wave attacks and erosion. This thesis describes a programme of research conducted to support the development of a cost-effective method of protecting the Kuwaiti coastline with a breakwater system that also provides an opportunity to generate energy by locally increasing the energy density of waves to make wave energy conversion (WEC) more efficient, cost-effective and commercially competitive. A comprehensive review of the historical development and current state-of-the-art regarding breakwater and WEC technologies is presented. On the basis of these evaluations, a floating breakwater combined with point absorber device is identified as appropriate for use in the Kuwaiti near shore marine environment. The need for increasing the local energy density at the point absorber is highlighted and the concept of using a parabolic concentrator in combination with point absorber is suggested and developed. An analytical study extends the understanding of the role of damping in the response of an idealised point absorber device. A steady-state harmonic model is developed to simulate the motion of a single buoy with one degree of freedom (heave) along the vertical axis to optimise its geometrical and control parameters and maximise its power absorption from incident waves. Evaluating different buoy shapes namely: bullet, spike, and bi-cone (60o/120o) indicates that for each buoy shape, there is an optimum operating range for the power take-off (PTO) that drives the generator where wave energy capture and thus electrical power would be greatest. In the model, comprising a spring-damper system, the PTO is represented as a damper with a constant damping coefficient (〖 c〗_1) and the radiation force is represented by a linear radiation damping term (〖 c〗_2). The model reveals that the best performance is obtained at the optimum value for c_1 which is c_1= c_2=k/ω. This condition is met when the buoy with optimum mass is at resonance with the peak frequency of the sea state at ω^2=k/m. Evaluating the power absorption as a function of 〖 c〗_2 in the model also reveals that at resonance, a buoy of any shape will have two types of behaviour: one driven by low radiation damping and the other by high radiation damping range of values. Operation in the low 〖 c〗_2 region is difficult to achieve in practice, and hence, it is recommended that devices should be designed to operate in the high 〖 c〗_2 region to maximise power capture. Data is presented from wave tank testing conducted using a flume at the Kuwaiti Institute for Scientific Research (KISR). This is used to evaluate the capability of the proposed parabolic concentrator elements to increase potential wave energy harvesting. A wealth of data, both visualisation and numerical, was obtained and this compares well with the computational analyses. The results indicate that a parabola-buoy system would be capable of absorbing almost 260 kW of power at prototype scale (1:16). A computational modelling approach using the commercial CFD code ANSYS-Fluent is developed, applying the volume of fluid approach combined with a wave boundary condition. The KISR wave tank was modelled with parabolic element installed and data is compared to that obtained experimentally. Good agreement between CFD and experimental data is obtained validating the modelling choices made. Additional modelling results for the behaviour of waves near an anchored buoy in combination with a parabolic concentrator are presented. The work presented in this thesis shows that there is the potential for substantial benefit for power absorption through using a combined parabolic concentrator-point absorber device. Future modelling work with fluid-structure interaction and moving buoy will permit further optimisation and development paving the way for full-scale developments in the future.

This thesis proposes the initial stages of the development of a NUI – Asset Integrity Case (Normally Unattended Installation). An NUI – Asset Integrity Case will enable the user to determine the impact of deficiencies in asset integrity and demonstrate that integrity is being managed. A key driver for improved asset integrity monitoring is centred on the level of accurate reporting of incidents. This stems from incidents to key offshore systems and areas. For example, gas turbine driven generators where 22% of fuel gas leaks were undetected with 60% of these 22% having been found to have ignited. Accordingly, there is a need for dynamic risk assessment and improved asset integrity monitoring. The immediate objective of this research is to investigate how a dynamic risk model can be developed for an offshore system. Subsequently, two dynamic risk assessment models were developed for an offshore gas turbine driven electrical power generation system. Bayesian Networks provided the base theory and algorithms to develop the models. The first model focuses on the consequences of one component failure. While the second model focuses on the consequences of a fuel gas release with escalated fire and explosion, based upon several initiating failures. This research also provides a Multiple Attribute Decision Analysis (MADA) to determine the most suitable Wireless Sensor Network (WSN) configuration for asset integrity monitoring. The WSN is applied to the same gas turbine system as in the dynamic risk assessment models. In the future, this work can be expanded to other systems and industries by applying the developed Asset Integrity Case framework and methodology. The framework outlines the steps to develop a dynamic risk assessment model along with MADA for the most suitable remote sensing and detection methods.

Orientador: Chang Hung Kiang / Banca: Everton de Oliveira / Banca: Gerson Cardoso da Silva Junior / Resumo: A Região Metropolitana de São Paulo apresenta áreas de embasamento cristalino alterado, densamente ocupadas, que sofreram os mais diversos impactos ambientais, comprometendo os aqüíferos presentes. Este trabalho teve por objetivo a caracterização da condutividade hidráulica da porção saturada de dois domínios hidrogeológicos do embasamento cristalino alterado, um relacionado às rochas metassedimentares e outro às rochas gnáissicas. A condutividade hidráulica de ambos os domínios foi determinada através da realização de testes de slug em 63 poços de monitoramento. Os testes foram realizados utilizando-se transdutor de pressão de alta precisão. Os dados obtidos foram armazenados e analisados, utilizando-se os métodos de Hvorslev (1951) e Bower & Rice (1976). Os valores de condutividade hidráulica de cada domínio hidrogeológico, obtidos por ambos métodos, foram comparados através de análises estatísticas. Procurou-se estabelecer a relação entre os valores de condutividade hidráulica e a profundidade do meio saturado, bem como a influência das heterogeneidades presentes nos dois domínios hidrogeológicos. Os resultados dos testes revelaram que a condutividade hidráulica média das rochas gnáissicas alteradas é de 7,51x10-4 cm/s, segundo o método de Hvorslev (1951), e 2,34 x10-3 cm/s para o método de Bouwer & Rice (1976). Para as rochas metassedimentares alteradas foram obtidos valores médios de 5,01x10-5 cm/s e 7,99x10-5 cm/s, respectivamente. / Abstract: The São Paulo Metropolitan Region (RMSP) is located on crystalline rock areas. The region is highly populated and has suffered different environmental impacts, affecting the aquifers. The objective of this work is to characterize the of the satured portion of two different hydrogeological domains, consisting of weathered basement, one related to the metassedimentary rocks and another to gneissic rocks. The hydraulic conductivities of both domains were determined by a series of slug tests in 63 monitoring wells. The tests were executed using a high precision pressure transducer. The data from the tests were collected, stored and analyzed using new analytical tools based on Hvorslev (1951) and Bower and Rice (1976) methods. The conductivity values obtained from both methods were evaluated using statistical analysis, looking for relationships among hydraulic conductivity, depth of satured zone, as well as heterogeneity present on both hydrogeologic domains. Hydraulic conductivity values for weathered gneiss were 7,51x10-4 cm/s and 2,34 x10-3 cm/s obtained using Hvorslev (1951) and Bower and Rice (1976), respectively. For metassedimentary rocks hydraulic conductivity values were 5,01x10-5 cm/s and 7,99x10-5 cm/s, respectively. / Mestre

The recovery of placer gold from 20 mesh to 150 mesh in common sluicebox configurations was investigated. Two types of riffles, 1-10H expanded metal (1.5"x.75"x.25") and 1.25" angle iron riffles (dredge riffles), were used in conjunction with 3/8" thick "Nomad" matting for 25 tests. The effects of variations in upper feed size, water flow rate, sluice gradient, and solids feed rate on the recovery of placer gold particles are documented. The gold and test gravel were obtained from the Teck Corporation sluicing operation on Sulphur Creek, Yukon Territory during July, 1985. Approximately nine troy ounces of placer gold and fifteen tons of gravel were transported to Vancouver.B.C. A test sluice facility was constructed in Coquitlam,B.C. to simulate operating conditions in a typical Yukon placer operation. The sluicebox was 12" wide and 8' long with clear plexiglass sidewalls. Screened gravel of either 3/4" or 1/4" upper feed size was fed to this sluice from a hopper at rates of up to 1260 lb/min. The water pumping capacity was a maximum of 400 USGPM. Between 75 and 90 grams of each of three sizes of placer gold (-20+28#, -35+48#, -65+100# ) were premixed with the gravel for most tests. The final test used 25 grams of -100+150 mesh gold. Sluicing, when properly controlled, was found to be a highly effective means of concentrating placer gold as small as 150 mesh. Expanded metal riffles were far superior to dredge riffles in concentrating gold of this size range. Recovery of the -65+100# size fraction frequently exceeded 90% when using expanded metal riffles. Visual observation of eddies formed downstream of the riffles showed that scour depth between riffles was the one characteristic of the slurry flow that gave the best indication of the resulting gold recovery. For expanded metal, scour depths between 1/2 and 3/4 of the riffle depth were found the most effective. / Applied Science, Faculty of / Mining Engineering, Keevil Institute of / Graduate