Doctoral Theses (Energy, Geoscience, Infrastructure and Society)
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Item A conceptual procedural framework for effective scheduling to enhance efficient use of construction resources on the jobsite(Built Environment, 2009-04) Efole, Friday E.; Kaka, Professor AmmarSelection of construction methods, scheduling, site layout and component procurement arrangement affect efficiency of operations on the jobsite. Efficiency has been previously measured by such parameters as; budget, on time completion and meeting specification standards. Little attention has been given to the interim processes which create these. Efficiency in man- and machine-hour management may translate to cost and time gains and enhanced quality. The study reported recognises that there are numerous aspects to the question of efficiency of operations. To focus the study and narrow the scope to a manageable size, the issues of efficiency that can be addressed in the scheduling process are those considered. Extensive and thorough literature search identified guidelines for effective construction scheduling. Empirical data were collected following these guidelines to develop a scheduling procedure aimed at making the process more effective and which may enhance efficient use of construction resources on the jobsite. The developed framework show that activity criticality based on time analysis alone is a necessary condition but not usually sufficient to declare an activity critical. Other tasks not on the critical path which have very high delay potential should be considered. Therefore though the study does not out rightly refute the idea of criticality based on time analysis alone, it adds to it that if criticality means those things that should be done so as to progress the works to a scheduled finish, criticality should be re-assessed to include several other tasks not hitherto identified on the critical path.Item Hydrates in sediments : their role in wellbore/casing integrity and CO2 sequestration(Heriot-Watt University, 2009-12) Salehabadi, ManoochehrGas hydrates have attracted much interest among researchers recently because of their wide range of applications. The impact of natural gas hydrates in subsea sediments on the development of conventional hydrocarbon reservoirs in deep offshore and the potential role of CO2 hydrates as a secondary safety factor in subsurface storage of CO2 are the key areas in this thesis. Several experiments were conducted on synthetic samples containing methane hydrate with different hydrate saturations to measure their geophysical properties, mechanical properties and understand their mechanical behaviour at realistic conditions. A numerical model was also developed with ABAQUS (a finite element package) to investigate the casing stability of the wellbore drilled in gas hydrate bearing sediments in deep offshore environments using the measured properties of gas hydrate bearing sediments under different scenarios. The role of hydrates in subsurface storage of CO2 was studied using a unique experimental set-up by simulating geothermal temperature gradient. The objective was to investigate whether CO2 leaked from subsurface storage sites can be converted into hydrates, providing a secondary seal against further CO2 leakage to ocean/atmosphere.Item Inversion for reservoir pressure change using overburden strain measurements determined from 4D seismic(Heriot-Watt University, 2009-11) Hodgson, NeilWhen significant pore pressure changes occur because of production from a hydrocarbon reservoir the rocks both inside and outside of the reservoir deform. This deformation results in traveltime changes between reflection events on timelapse seismic data, because the distance between reflection events is altered and the seismic velocity changes with the strain. These traveltime differences are referred to as time-lapse time shifts. In this thesis, time-lapse time shifts observed in the overburden are used as an input to a linear inversion for reservoir pressure. Measurements from the overburden are used because, in general, time shift estimates are more stable, the strain deformations can be considered linear, and fluid effects are negligible, compared to the reservoirlevel signal. A critical examination of methods currently available to measure time-lapse time shifts is offered. It is found that available methods are most accurate when the time shifts are slowly varying with pressure and changes in the seismic reflectivity are negligible. While both of these conditions are generally met in the overburden they are rarely met at reservoir level. Next, a geomechanical model that linearly relates the overburden time-lapse time shifts to reservoir pressure is considered. This model takes a semi-analytical approach by numerical integration of a nucleus of strain in a homogeneous poroelastic halfspace. Although this model has the potentially limiting assumption of a homogenous medium, it allows for reservoirs of arbitrary geometries, and, in contrast to the complex numerical approaches, it is simple to parameterise and compututationally efficient. This model is used to create a linear inversion scheme which is first tested on synthetic data output from complex finite-element model. Despite the simplifications of the i inversion operator the pressure change is recovered to within ±10% normalised error of the true pressure distribution. Next, the inversion scheme is applied to two real data cases in different geological settings. First to a sector of the Valhall Field, a compacting chalk reservoir in the Norwegian Sea, and then the Genesis Field, a stacked turbidite in the Gulf of Mexico. In both cases the results give good qualitative matches to existing reservoir simulator estimates of compaction or pressure depletion. It is possible that updating of the simulation model may be assisted by these results. Further avenues of investigation are proposed to test the robustness of the simplified geomechanical approach in the presence of more complex geomechanical features such as faults and strong material contrasts.Item Pressure estimation using time-lapse seismic in compacting reservoirs(Heriot-Watt University, 2009-10) Corzo Mojica, Margarita Maria; MacBeth, ColinThis thesis focuses on developing a new approach to estimate pressure changes from 4D amplitude attributes in compacting reservoirs. The time-lapse seismic signal in these types of reservoirs results from the combination of pressure depletion, rock compaction and stress redistribution within the reservoir and throughout the surrounding rocks. Simulations using iterative coupling are performed to understand the link between geomechanics, fuid fow and the seismic response. The analysis of synthetic data defines a power law equation (eq.1) which relates pressure changes (¢P) to 4D amplitude attributes (¢A). The coefficients (C1 and C2) are a function of initial porosity. The pressure predictions show an agreement with the output from the reservoir modelling. However the results indicate that the rock compaction has considerable effect on the normal average stress, and the 4D seismic response shows a stronger correlation with effective stress than with pore pressure. ¢A = C1 ¤ (¢PC2) (1) The technique is applied to the south east flank of the Valhall Field, Norwegian North Sea. The areas where the initial porosities are above 38 % show a good correlation between the pressure changes predicted from 4D amplitude and the pressure changes from the reservoir model. However, major differences between both outputs occur in areas where no 4D signal is observed; these areas are correlated with low porosity zones where the porosity reduction has not been significant enough to enhance the 4D signal. Furthermore, the pressure predictions from the 4D seismic identify areas where the reservoir has not been properly drained. The impact of geological structure and gas saturation on the technique is assessed. Strong thickness variations within the reservoir interval increase the errors on the pressure prediction. This is mitigated if relative values instead of absolute values are used to estimate pressure changes, i.e. equation 1 becomes equation 2. Furthermore, the presence of gas on the reservoir requires a modification of the i equation 1 in order to accurately predict the pressure changes and account for the presence of free gas on the reservoir (eq. 3). ¢A A1 = C1 ¤ ( ¢P P1 )C2 (2) ¢A = (C3 ¤ ¢P) + C4 (3) Finally, sensitivity analysis suggests that uncertainties in the elastic properties of the overburden (rarely measured with accuracy) have little impact on the reservoir 4D amplitude response. Synthetic models show that variations between 10 % to 15 % in the Poisson's ratio and Young's modulus of the layer immediately above the reservoir causes negligible changes (less than 4 %) in the 4D amplitude response.Item Phase equilibria modelling of petroleum reservoir fluids containing water, hydrate inhibitors and electrolyte solutions(Heriot-Watt University, 2009-10) Haghighi, Hooman; Tohidi, Professor Bahman; Chapoy, Doctor AntoninFormation of gas hydrates can lead to serious operational, economic and safety problems in the petroleum industry due to potential blockage of oil and gas equipment. Thermodynamic inhibitors are widely used to reduce the risks associated with gas hydrate formation. Thus, accurate knowledge of hydrate phase equilibrium in the presence of inhibitors is crucial to avoid gas hydrate formation problems and to design/optimize production, transportation and processing facilities. The work presented in this thesis is the result of a study on the phase equilibria of petroleum reservoir fluids containing aqueous salt(s) and/or hydrate inhibitor(s) solutions. The incipient equilibrium methane and natural gas hydrate conditions in presence of salt(s) and/or thermodynamic inhibitor(s) have been experimentally obtained, in addition to experimental freezing point depression data for aqueous solution of methanol, ethanol, monoethylene glycol and single or mixed salt(s) aqueous solutions, are conducted. A statistical thermodynamic approach, with the Cubic-Plus-Association equation of state, has been employed to model the phase equilibria. The hydrate-forming conditions are modelled by the solid solution theory of van der Waals and Platteeuw. Predictions of the developed model have been validated against independent experimental data from the open literature and the data generated in this work. The predictions were found to agree well with the experimental data.Item Changes in the nature and governance of public spaces in the historic city centre : the case of Damascus(Heriot-Watt University, 2009-09) Haddad, Rema Goerge; Smith, Harry; Forsyth, LesliePublic space is a component of our physical environment which has an important role in city life. This thesis is primarily about investigating public space and public realm in the historic city centre of Damascus in order to understand the potential for its improvement, and secondarily about recommending specific actions towards this. The research takes a qualitative approach focusing on public space as a ‘product’ which is the result of a process. In terms of the product, the nature, morphological and functional aspects of public spaces in Damascus are examined. The governance process is analysed at local level to define main actors, the rules they interact with and the rationalities they use to intervene in public space. This analysis includes locality-specific literature review and interviews with key informants. Such case study analysis is undertaken against the background of a survey of public space regeneration in selected cities around the Mediterranean. Public spaces in Damascus historically developed under strong endogenous social and cultural rules creating a hierarchy of ‘traditional’ spaces which supported public, parochial and private realms. In the contemporary period, these spaces have gone through modernisation in their governance process through introducing new actors and more formal rules, which have led to more ‘publicness’ and tension between tradition and modernisation. This has affected their nature as well as morphological and functional aspects. Analysis showed that strong centralised political and public sector control is found over the governance process through a top-down representative approach. Capacities, interests and perception of public spaces among actors, in addition to poor management, strict legislation and lack of qualified cadres, have all contributed to the continuing deteriorating situation of public spaces. Moreover, interventions for improvement occurred on a short-term basis and mainly to restore historical monuments and improve traffic. An integrated approach to upgrading open spaces is still needed on a long term basis, subject to the available financial resources, with wider governance arrangements and further collaboration and integration between different governmental bodies.Item Stress intensity factors for ship details(Heriot-Watt University, 2009-04) Roy, Michael RobertItem Policy and practice of urban neighbourhood renewal and regeneration : what can China learn from British experiences?(Heriot-Watt University, 2009-07) Qian, Yun; Wang, Professor Ya Ping; McIntosh, SarahUrban neighbourhood renewal and regeneration have a long history in Western industrialised societies like Britain. The renewal or regeneration strategies, visions, approaches and implementations often reflect the particular political, economic, social and cultural contexts of each development period. There are abundant research literatures on the theoretical and practical elements of neighbourhood renewal/regeneration in the UK, which provide valuable references and lessons to the industrialising countries. In rapidly urbanising countries like China, traditional urban neighbourhoods are redeveloped at an unprecedented scale. Urban renewal and redevelopment projects have affected the life of a large number of urban residents. The renewal process, the mechanism and its social and economic effects were, however, understudied. This research aims to evaluate the evolution, achievements and problems of neighbourhood renewal process in Chinese cities, by following a cross-national approach. It reviews the evolution of urban renewal and regeneration theories and practice in Britain: the earliest industralised country in the world. Based on the findings, an analytical framework is established which is then used to examine and evaluate the recent urban redevelopment practice in Chinese cities. The research is based on both quantitative and qualitative data and information collected in the two countries through literature and policy reviews, fieldworks, key player interviews and a household survey in the two case study neighbourhoods: Shichahai and Jinyuchi in the inner city area of Beijing. The research found that the developments of British and Chinese neighbourhood renewal share a similar “zigzag” trajectory in which the renewal strategies focus either on economic or social objectives alternatively. Especially in recent years, urban renewal and regeneration challenges in Britain and China became more similar. Disadvantaged neighbourhoods in both countries face problems of multi-dimensional deprivation across the areas of housing, employment, education, healthcare, safety and others. This means that the British regeneration strategies and approaches could be more valuable to Chinese policy-makers and practitioners. In China, neighbourhood renewal projects always bear the influence from the West, but for the different national contexts, renewal iii projects in every period only targeted at one or several particular aspects of the “urban problems” at the time. The positive effects of renewal projects were often very limited while the negative impacts led to the emergence of unexpected new problems. Since 2000 some experimental renewal projects have a much wider remits than before, but they still focus on the “visible” problems only. The improvement of local housing condition and physical environment was very obvious and dramatic. The achievements were however cutback by the process of gentrification and population replacement. Although the new renewal mechanisms emphasised multi-sectoral cooperation, the operational and administrative structures were still far from the ideal partnership, particularly in relation to the rights of original residents. Based on the findings, a series of recommendations have been developed to improve the neighbourhood renewal practice in Chinese cities.Item Fire safety models for high-rise residential buildings in Malaysia(Heriot-Watt University, 2009-02) Yatim, Yahya Mohamad; Harris, Doctor Douglas J.This research investigated the effects of escape route design and specification, and time taken on evacuation process in high-rise residential buildings in Malaysia. The aim is to produce a fire safety model on how fire safety standards in high-rise residential buildings can be achieved by investigating the relationship between human behaviour and structural design, particularly escape route design and specification. In Malaysia, research on fire safety is very new, particularly research on provision of fire safety in high-rise residential buildings. The number of fire cases involved residential buildings is significantly high compared to other building types. Thus, escape routes in high-rise residential buildings should be designed and constructed to enable the occupants to evacuate the building as soon as fire has been detected. Mixed methodologies i.e. quantitative and qualitative methods were adopted in this research. There are three research methods adopted i.e. observation, simulation and questionnaire. Observations were carried out to identify any problems encountered and to develop the study models for further analysis. Investigations of the effects of escape route design and specification on evacuation process were carried out using specialist software, i.e. Simulex, which simulates the evacuation of people from the building. The aim is to study escape route specifications i.e. staircase, fire door and corridor. Questionnaire surveys were than carried out to investigate the occupant’s characteristics, behaviours, perceptions and motivation factors to evacuate the building. From this research, fire safety models proposed for high-rise residential buildings as follows, (1) Fire safety model to achieve fire safety standard in high-rise residential buildings, (2) Escape route designs and specifications, and, (3) Human behaviour model. There are five fire safety components that need to be enhanced i.e. (1) Fire Safety Awareness, (2) Fire Safety Design, (3) Fire Safety Equipments and Evacuation Skill, (4) Fire Safety Audit, and (5) Fire Safety Enforcement. Besides, there are four factors which highly influence the evacuation process, fire and casualty risk i.e.: (1) People behaviour – knowledge and experience, (2) building element and escape routes design, (3) active fire protection system, and (4) legislation and enforcement.Item Processing and analysis of transient data from permanent down-hole gauges (PDG)(Heriot-Watt University, 2009-07) Li, Xiaogang; Zheng, Doctor ShiyiThe Permanent Downhole Gauge (PDG) can monitor the reservoir in real time over a long period of time. This produces a huge amount of real time data which can potentially provide more information about wells and reservoirs. However, processing large numbers of data and extracting useful information from these data brings new challenges for industry and engineers. A new workflow for processing the PDG data is proposed in this study. The new approach processes PDG data from the view of gauge, well and reservoir. The gauge information is first filtered with data preprocessing and outlier removal. Then, the well event is identified using an improved wavelet approach. The further processing step of data denoise and data reduction is carried out before analyzing the reservoir information. The accurate production history is very essential for data analysis. However, the accurate production rate is hard to be acquired. Therefore, a new approach is created to recover flow rate history from the accumulated production and PDG pressure data. This new approach is based on the theory that the relation between production rate and the amplitude of detail coefficient are in direct proportion after wavelet transform. With accurate pressure and rate data, traditional well testing is applied to analyze the PDG pressure data to get dynamic reservoir parameters. The numerical well testing approach is also carried out to analyze more complex reservoir model with a new toolbox. However, these two approaches all suffer from the nonlinear problem of PDG pressure. So, a dynamic forward modelling approach is proposed to analyze PDG pressure data. The new approach uses the deconvolution method to diagnose the linear region in the nonlinear system. The nonlinear system can be divided into different linear systems which can be analyzed with the numerical well testing approach. Finally, a toolbox which includes a PDG data processing module and PDG data analysis module is designed with Matlab.