Doctoral Theses (Energy, Geoscience, Infrastructure and Society)
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Item Water-alternating-gas enhanced oil recovery optimisation for greater CO2 storage and oil recovery in a mature turbidite reservoir : case study of the Niger Delta(Energy, Geoscience, Infrastructure and Society, 2023-01) Ogbeiwi, Precious; Stephen, Associate Professor KarlThe alternating injection of water and CO2 gas (WAG) is applied to improve hydrocarbon production left behind by primary and secondary recovery techniques, securely stored the injected CO2 in the subsurface, and increase the economic value of the turbidite reservoirs. However, the numerical simulations and optimisation studies of WAG projects in these reservoirs are plagued with inherent geological and other associated uncertainties that result from petrophysical, geological, and geophysical assumptions, as well as measurement errors, limited sampling, insufficient data, etc. Also, the prediction and optimisation of the economic value of the WAG project would require that relevant uncertainties in oil and gas prices and other associated uncertainties are considered. In this thesis, the Markowitz classical optimisation theory was applied for the robust optimisation of WAG injection in a Niger-Delta turbidite reservoirs under geological and economic uncertainties. This was coupled with a Non-Dominated Sorting Algorithm to obtain the engineering control parameters that optimise the Net Present Value (NPV) of the WAG project. To reduce the computational cost associated with the optimisation routine, we applied approximation methods to construct suitable surrogate models of selected reservoir outputs. An assessment of the technical feasibility of CO2EOR processes in the Niger Delta was carried out. Then, relevant geological uncertainties that plague CO2 EOR processes were described and quantified. We also developed and described a new economic model for predicting the economic value and quantifying economic uncertainties during CO2 EOR processes in the Niger Delta. Finally, the robust optimisation of the WAG project under geological and economic uncertainties was carried out using suitable data-driven approximation models. There are four significant contributions relating to WAG simulation and optimisation in reservoirs in the Niger-Delta hydrocarbon basin that are presented in this thesis. Firstly, the technical feasibility of CO2 EOR and storage in reservoirs of the hydrocarbon basin is presented. Secondly, an improved understanding of micro-scale and macro-scale physical instabilities/ heterogeneities such as the interplay of viscous fingering and permeability channelling in fine-scale grids is presented. These effects are also upscaled from the fine-scale grids to more realistic coarse grids. Thirdly, a new economic model for quantifying the economic value of CO2 EOR and storage processes in the Niger-Delta is presented. Finally, the applicability of data-driven proxy models for the robust optimisation of WAG processes under geological and economic uncertainties is presented.Item The role of mutual solvents in scale inhibitor squeeze treatments(Heriot-Watt University, 2023-12) Sanchez Telesforo, Hugo Antonio; Mackay, Professor Eric James; Singleton, MichaelThe role of mutual solvents in scale inhibitor (SI) squeeze treatments is to improve contact surface area between the SI and the rock to increase SI retention and thereby extend squeeze lifetime. For this to occur the mutual solvent is applied as a pre-flush before the main SI injection stage. This is important because squeeze treatments are used to avoid the formation of mineral scale in oil and gas wells, and maximising squeeze lifetime is essential to extending well protection and minimising cost, logistical complexity, and footprint of repeated squeeze treatments. The method used in this study to address the question of how mutual solvents interact with the rock substrate was to perform different coreflood tests, and to use two analytical techniques, UV-Vis and ICP-OES, for tracing the mutual solvents (traced with trans-Stilbene) and brines (traced with I for UV-Vis or Li for ICP-OES). This gave information on time of breakthrough of the various components, and hence on degree of interaction with the in-situ fluids and mineral surfaces. Additionally, pressure differentials across the core were measured to assess the risk of formation damage or the improvement in fluid mobility. Effluent samples were analysed visually for evidence of changes in phase behaviour. An early finding was that Ethanol creates cloudiness when it contacts sulphate free seawater in a Clashach core. Furthermore, this work identified that longer Mild Miscible cleaning needs to be undertaken in these types of Clashach cores for such experimental tests. Furthermore, EGMBE creates striations when applied in similar coreflood experiments. Also, we could not solve the problem of UV-Vis interference using trans-Stilbene for both Ethanol and EGMBE. The experiments demonstrated that EGMBE increases the SI (in this case, DETPMP) retention (adsorption), by removing synthetic mineral oil (Multipar-H) from the Clashach core, allowing for greater, prolonged squeeze lifetime. Then, a higher residual oil saturation was achieved by reducing the pump rate during Multipar-H injection. Moreover, the higher the EGMBE concentration, the better the removal of Multipar H from the Clashach core. In addition, the MS concentration is more important than volume when trying to remove residual oil saturation. According to the results it is proposed that using mutual solvent as a pre-flush enhances scale inhibitor squeeze lifetime, by increasing scale inhibitor adsorption/retention, due to a wettability change towards more water-wet – as evidenced by the reduction in residual oil saturation. Additionally, more pore volumes of aqueous phase main treatment (up to seven) were required to displace the residual phase when lower mutual solvent concentrations were used in the coreflood pre-flush stage. The results of this work indicate that mutual solvent concentration, and the ratio of main treatment volume to pre-flush volume should be carefully considered when designing squeeze treatments, since the contact between the aqueous scale inhibitor solution and the rock will be affected by the ability of the mutual solvent to displace oil, and by the volume of main treatment required to displace the mutual solvent rich pre-flush. Finally, modelling work was undertaken using the isotherms generated from the corefloods to demonstrate the impact on squeeze life of various mutual solvent applications.Item Effect of fluid-fluid interactions on the performance of low salinity water injection in crude oil reservoirs(Heriot-Watt University, 2022-12) Fattahi Mehraban, Mohammad; Farzaneh, Doctor Amir; Sohrabi, Professor MehranOne of the most promising enhanced oil recovery (EOR) methods is low salinity water injection (LSWI) that has faced several critical challenges, of which understanding the underlying mechanism is still of utmost importance. The importance of understanding the underlying mechanism is essential when screening for suitable oil reservoirs for application of this EOR method. A satisfactory screening method requires a solid data set in the literature of waterflooding and a reliable shred of information about the underlying compounds of crude oil for the positive effect of LSWI. In this treatise, the mechanism of LSWI is scrutinised over a wide range length scale, ranging from micro to pore and core scale. At the beginning, the thesis starts to elaborate on the screening of an extensive crude oil databank including 116 different crude oil samples sourced from different parts of the world. Formation of microdispersion is confirmed by Karl Fischer Titration method (KFT) as a dominant interaction at the oil/water interface, which is promoted by asphaltene molecules of crude oil samples. Following the confirmation of a reliable screening tool for LSWI, the mechanisms of this EOR method are elucidated over pore (chapter 3) and core scale (chapter 4 and chapter 5) experiments. It is visually shown that when crude oil encounters Low Salinity Water (LSW), microdispersion forms spontaneously leading to wettability alteration and crude oil swelling within the porous media. Furthermore, fluid displacement experiments with coreflooding reveal an undeniable link between the potencies of crude oils to from microdispersion and additional oil recovery during tertiary LSWI in sandstones and carbonates. In this dissertation, a comprehensive compositional analysis is carried out to determine the underlying compounds of crude oil that cause microdispersion and additional oil recovery. Wettability alteration and crude oil swelling are shown as the outcomes of microdispersion formation at the oil/water interface leading to additional oil recovery during LSWI. These outcomes of microdispersion will be called low salinity effect (LSE) and it connects the mechanism and the results of the mechanism in terms of additional oil recovery. Using the ionisation techniques of Fourier Transform Ion Cyclotron Resonance Mass Spectroscopy (FT-ICR MS), it was discovered that asphaltene molecules and carboxylic acids with carbon number of C16-C26 and double bond equivalent (DBE) of 1- 4 are mainly involved in microdispersion formation and LSE. Moreover, formation of microdispersion by carboxylic acids and/or acidic asphaltenes and partitioning of low molecular weight carboxylic acids from crude oil into water phase were shown as the dominant interactions at the oil/water interface. It is indicated that formation of microdispersion results in a slightly higher interfacial tension, which stem from engagements of surface-active compounds in microdispersion structures leading to a lower effective concentration at the interface. For the first time, a systematic experimental study on the fluid-fluid interactions between crude oil and water with different salinities was conducted that led to a clear understanding about the mechanism of LSWI. Microdispersion is confidently proposed as the main mechanism of LSWI triggered by carboxylic acids and/or acidic asphaltene molecules. Wettability alteration and crude oil swelling owing to microdispersion were visually substantiated through microfluidic experiments. After determining the underlying compounds of crude oil for LSE, coreflooding experiments corroborate that additional oil recovery by LSWI is only achievable when the crude oil is potent enough to form microdispersion. The findings of this thesis contribute to a reliable screening tool through which suitable crude oil reservoirs for LSWI can be identified and the performance of waterflooding can be controlled based on microdispersion criterion.Item Imaging solutions for 4D quantitative interpretation(Heriot-Watt University, 2022-12) Izadian, Saeed; MacBeth, Professor Colin; Amini, Doctor HamedDuring the production of a geomechanically active reservoir, massive pressure depletion happens giving rise to geomechanical changes which can lead to significant time-lapse signals across the reservoir and its surrounding. Therefore, geomechanical characterisation of the reservoir and monitoring are very important for this type of reservoir. In this thesis, I use pre-stack time-lapse time-shifts observed between 4D seismic surveys for the geomechanical characterisation of the Ekofisk field which is a geomechanically active field in the North Sea. This thesis consists of three parts. Before using pre-stack time-shifts, post-stack time shifts can be a valuable guide toward the geomechanical activities of the reservoir. In the first part, I estimate the post-stack time-shifts using various methods. Then, I evaluate the advantages and disadvantages of each method in terms of their performance in revealing the local time-lapse signals such as time-strains. I have found that all the time-shift methods can successfully measure time-shifts. Among them, NLI is the most outstanding method as it gives smooth time-shifts with relatively good accuracy and the time-strains derived from there are more stable and interpretable. In the second part, I use the reflectivity and velocity models of the Ekofisk field and perform a finite-difference simulation to generate synthetic seismic data, followed by imaging the generated data. Migrating baseline and monitor datasets with baseline velocity model caused considerable mispositioning in the overburden resulting in false amplitude-differences in the overburden. The analysis of the images shows that it is not simply a matter of mispositioning that contaminates the seismic images. A more serious problem caused by migration with an erroneous velocity model is the defocusing of amplitudes. This problem cannot be solved by warping and requires a more sophisticated remedy to correct the monitor’s migration velocity model. In the third part, which is the major development of this thesis I measure the pre-stack time-shifts and design a tomographic approach to utilise them for estimating the time lapse changes. First, I show how to measure the pre-stack time-shifts and discuss the practical aspects of the process. Second, I design a ray-based tomography customised for 4D application in order to utilise the pre-stack time-shifts and invert for velocity changes that cause the time-shifts. Finally, I extend the tomography method into an anisotropic inversion where both the time-lapse velocity changes and the ratio of lateral-to-vertical strains are inverted in a two-step inversion process. The two products of the inversion can be used extensively in the geomechanical model calibration of the reservoirs. Overall, my PhD research has successfully measured the time-lapse velocity changes and the ratio of lateral-to-vertical strains. The anisotropic time-lapse tomography is a new paradigm in the pre-stack time-lapse seismic analysis and will be an integrated part of the geomechanical characterisation of the reservoirs.Item Smart construction and industry 4.0 challenges and opportunities : a strategic and operational framework to unlock digital transformation(Heriot-Watt University, 2024-11) El-Hawary, Maged Sayed Amin Naguib; Nielsen, Doctor YaseminThe construction industry is always fragmented, labour-intensive, and has slow technology adoption and low-profit margins. Nevertheless, with the development of different global sectors, improvement becomes mandated, especially given the complexity, tight budgets, and squeezed time frames. Rethinking the delivery of construction projects became vital to planning, operating, delivering, and measuring success as the world witnessed a historically unprecedented industrial disruption. This revolution entails transforming humankind. Unlike any predecessor with a linear pace of expansion, Industry 4.0 is spreading exponentially, renovating all traditional strategies and aiming to transform business models across countries, governments, companies, industries, and societies. Like other industries, the construction industry has struggled to take advantage of technology significantly. A fourth industrial revolution and its subsequent "Industry 4.0 and construction 4.0" terminology are invading advanced industries, calling for fully integrated digitalised value chains across ecosystems. The Internet of Things (IoT), digitalisation and offsite construction became the essence of overcoming industry pitfalls. Construction is moving from a Resource-based industry to a knowledge-based sector, considering the borderless boundaries between different sectors by adapting the cross-industry cooperation concept. The research investigates industry 4.0 opportunities and their potential impact on the construction industry throughout the project life cycles from inception to asset management. It seeks to improve physical site delivery by reviewing related concepts, technologies, and supply chains. Emerging technology priority areas are identified, implementation mandates are explored, and challenges and enablers are distinguished. A framework and Roadmap for incorporating industry 4.0 concepts and technologies are proposed. A triangulation approach was adopted throughout the research to integrate results from a literature review and other field works. Focus group workshops helped to understand industry issues and were a key input towards questionnaire design. Survey questionnaires highlighted industry drawbacks and expected improvement of emerging technology implementation, concentrating on linking potential technology and industry inefficient practices. Interviews with industry experts were crucial in associating the findings with corporate strategic objectives and initiating the roadmap. The fieldwork was conducted to satisfy pre-defined research objectives and Initiate/validate the proposed framework for successful implementation at both operational and strategic levels. The primary outcome of the research is a framework and roadmap for digital transformation initiatives with a concentration on the main contractors operating in the GCC area to empower the utilisation of industry 4.0 technologies; both were developed from the field/desk works and validated with different stakeholders operating in the construction industry as the pandemic situation of COVID-19 enforced the need for more technology utilisation and enhanced industry professional awareness and willingness to adapt and change the conventional methods of entire project delivery.Item Enhancing energy demand forecasting and data imputation using deep learning : an integrated approach(Heriot-Watt University, 2024-11) Lotfipoor, Ashkan; Patidar, Doctor Sandhya; Jenkins, Professor David P.This PhD thesis introduces an integrated approach that leverages deep learning techniques to advance household electricity demand forecasting and data imputation within the UK energy sector. The research focuses on creating a novel system incorporating state-of-the-art machine learning solutions for electricity demand processing and prediction. The study involves data collection from appropriate electricity demand datasets, conducting comprehensive exploratory data analysis to uncover underlying patterns. A framework is established to process these datasets, encompassing data imputation, outlier handling, transformations, and feature scaling. A novel missing value imputation model is developed, employing a Transformer neural network and a K-means clustering algorithm to address missing data effectively. Subsequently, a forecasting framework for short-term residential load prediction is presented. This modelling framework integrates a Bayesian optimisation strategy, feature decomposition techniques, feature engineering, and percentile-based bias correction algorithms with a CNN-LSTM network to enhance prediction accuracy. The research contributes significantly to the field of household electricity demand forecasting and data imputation by offering a scalable and transferable framework. The application of these methodologies yields valuable insights, not only for the UK energy sector but also for broader applications, enabling precise predictions and efficient demand data processing. The findings promote energy efficiency and sustainable energy management practices.Item Applying ANN technology to determine acceptable control parameters for the National Library of Scotland’s collections to inform energy efficiency improvements in the UK heritage sector(Heriot-Watt University, 2024-12) Han, Bo; Wang, Doctor Fan; Taylor, Professor NickThe National Library of Scotland (NLS) uses purpose-built storage enclosures to protect their heritage collections. These enclosures can moderate micro-environmental temperature and humidity fluctuations inside. This study aims to determine an acceptable macro-environment in storage room to inform energy efficiency improvements based on a relaxing macro-environmental control. There are four objectives: 1) to assess the feasibility of using the enclosure’s buffering capacity and to obtain its hygrothermal properties; 2) to determine an acceptable macro-environment; 3) to achieve real-time micro-environment predictions; and 4) to assess potential energy savings from the relaxed control strategy. Correspondingly, the methodology comprises four parts: 1) using laboratory measures to quantify the buffering capacity of an enclosure and associated hygrothermal properties; 2) using a heat, air, and moisture (HAM) transfer model to simulate the hygrothermal interaction between macro- and micro-environments, and using a trial-and-error method with this model simulation to determine the acceptable macro-environment; 3) training a long short-term memory neural network; and 4) using a transform function to create the energy consumption model. The results show that 1) The enclosure’s buffering capacity is feasible to moderate the short-term micro-environmental temperature and RH fluctuations. 2) The acceptable macro-environment was determined to be 33%~65% RH and 15-25 °C control bands with ±16% RH and 5 °C 24 h fluctuations while there is no any detrimental effect on collections. 3) The trained Long Short-term Memory (LSTM) neural network can is robust for real-time prediction of micro-environment. 4) Implementing the relaxed control strategy presents a promising way to achieve the NLS's targeted annual reduction rate of 7.6% over the next decade. In conclusion, this study confirms that relaxed macro-environmental controls, enabled by the enclosure’s buffering capacity, ensure collection safety while achieving significant energy savings. Additionally, this control strategy advances the NLS’s building management toward smarter, energy-efficient control and offers scalable solutions for other heritage institutions.Item The use of offset-dependent time-shifts to characterize dynamic overburden effects in 4D seismic data(Heriot-Watt University, 2023-04) Dvorak, Ilona; MacBeth, Professor ColinTime-lapse seismic surveying is used for the monitoring and management of hydrocarbon fields in order to evaluate production-related subsurface changes that occur in the reservoir system. The time-lapse seismic method conventionally analyses 4D attributes of the reservoir which are generated from stacked versions of the base and monitor datasets which, in turn, are imaged using a common velocity model. A drawback of this approach is that changes that are observed in the time-lapse data that occur in the overburden above the reservoir unit may not be corrected for in the seismic workflow. This lack of update degrades the quality and reliability of the resultant reservoir time-lapse analysis. This research project investigates the effects of dynamic changes in the overburden, i.e., variations in conditions in the medium above the producing reservoir, which occur between the acquisition of the baseline and monitoring survey datasets. The objective of this research is to evaluate the dynamic overburden effects on the monitoring programme of the target time-lapse reservoir, to interpret dynamic overburden effects through the use of 4D time-shift attributes and design methodologies to compensate for dynamic overburden variations. The focus of this research is the Shearwater field, a high-pressure, high-temperature central North Sea field, which exhibits a common dynamic overburden system of extensional stress-arching as a reaction to compaction in the Jurassic reservoir unit. A synthetic modelling study of a variety of dynamic overburden features shows variability in the magnitude of time-shift responses as a function of the source-receiver offset at common midpoint locations beneath the overburden anomalies. These pre-stack, 4D, time-shift variations are found to be sensitive to the geometry and distribution of the 4D overburden anomalies, according to the relative exposure of the seismic ray-paths that transect the 4D effect. Dynamic overburden effects in the Shearwater field are interpreted via the derivation of pre-stack time attributes of time-shift intercept and time-shift gradient, which are generated via least-squares fitting of time shifts as a function of offset derived from the base and monitor datasets. There is agreement between the pre-stack time-shift attributes and the established overburden extension system. A weak negative gradient of time-shift is noted at the Top Fulmar reservoir. These attributes are also found to agree with those from an analogue at the South Arne field, in which a decrease in time-shift is reported from near to far offsets. The interpretation of the pre-stack, time-shift attributes for the Shearwater field indicates the value that can be achieved through analysis of pre-stack 4D data, as its use can enable the characterisation of 4D anisotropy velocity effects and the derivation of geomechanical attributes such as the stress path parameter. Two techniques are developed to derive the perturbation velocity from the pre-stack time-shift. The perturbation velocity is defined as the change in seismic velocity between the base and monitor surveys. Derivation of the perturbation velocity offers the opportunity to compensate for dynamic overburden effects that are traditionally ignored in the seismic workflow, via monitor survey imaging. The first method utilises bi-linear stacking in the offset domain and relocation of the 4D effect to its implied subsurface location, based on a geometrical relationship. The application of this method to the Shearwater dataset enables the derivation of a model that shows alignment to the overburden extensional slow-down and local variations that coincide with fracture closures in the Hod formation. The second method involves linear least-squares tomography of pre-stack time-shifts. Application of this technique to Shearwater leads to the derivation of a model that is aligned with a vertical strain field generated from a Geertsma model produced from post-stack time-shift data. This project demonstrates the value of pre-stack inversion in 4D seismic methods and its potential to improve accuracy in 4D analysis and to deliver information from post-stack analysis that goes beyond conventionally established workflows.Item Exploring the impact of sewer-derived airflows on the air-pressure dynamics within building drainage systems(Heriot-Watt University, 2024-10) Sharif, Khanda S.; Gormley, Professor MichaelThe performance of a building drainage system (BDS) relies on complex internal airflow and pressure dynamics, governed primarily by the unsteady wastewater flows from randomly discharging appliances such as WCs, sinks and baths. Designers attempt to optimise the safety of the system by including pressure equalisation strategies in the form of ventilation pipes and more active devices such as pressure attenuators and air admittance valves. Failures within these systems can compromise water trap seals, allowing hazardous sewer gases to enter buildings. While these measures can equalise the air pressure within the above ground drainage system, air coming from the sewer can have an effect on the performance also. Traditionally, above and below ground drainage systems are designed in isolation and there is no recognition of the influence of one on the other. This thesis documents the development of a novel model to represent the impact of sewer air on the performance characteristics of a BDS, leading to the development of new conceptual diagrams describing the interaction, that illustrate the correlation between newly introduced terms, such as; modified entrained air and modified air pressures, when the system is exposed to both BDS operation and sewer air. Laboratory experiments were conducted using a full-scale drainage test rig representing both low rise (3 storey) and high rise (34 storey) buildings that together provide empirical insights scalable to real-world applications. This approach bridges the gap between laboratory experiments and real-world dynamics, thereby enhancing the reliability and applicability of the research findings. The research confirmed that the airflow and air pressure regime within the vertical BDS stack is modified by and influenced by the connection to the main sewer in a manner consistent with an interaction analogous to a fan and system loss curve, requiring the solution of simultaneous equations describing both. The findings of this study confirm a direct correlation between pressure fluctuations and building height when exposed to sewer air.Item Immiscible fingering in porous media under different wetting conditions and its role in polymer flooding(Heriot-Watt University, 2024-11) Beteta, Alan; Sorbie, Professor Kenneth Stuart; Mackay, Professor Eric JamesImmiscible viscous fingering occurs when a low viscosity fluid immiscibly displaces a high viscosity fluid. In the field of geoenergy, this is typically a major problem whether in gas storage or in oil recovery. When water is injected into the reservoir to aid recovery, it can finger through a viscous oil, leaving large volumes bypassed and giving early water breakthrough – neither of which is ideal from an economic or carbon footprint viewpoint. Three major questions present themselves with regard to viscous fingering in such systems: how can fingering be modelled correctly?; how can fingering be evaluated in the laboratory?; and how can it be remedied? These are the 3 main areas of research that will be addressed in this thesis. A novel simulation methodology is used to directly model viscous fingers using standard, commercial numerical simulators. In this work, this approach is validated against literature experiments at a range of unstable viscosity ratios (μo/μw ~400 to 7,000). It is then applied to model conventional core flood experiments, conducted as part of this thesis, where μo/μw = 100. The simulation method is then used to upscale the core flood results using scaling theory to a series of conceptual and sector models of the Captain reservoir, which is currently undergoing polymer flooding in the North Sea. The same numerical method is used to demonstrate how laboratory scale unstable displacement experiments are sensitive to the suppression of viscous fingering by capillary dispersion. This is then shown to occur even under extremely weak wetting conditions. Using scaling theory, it is then shown how fingering “remerges” as the system size is increased towards the field scale. These observations are then further supported by carrying out laboratory 2D slab flood experiments under different wetting conditions for an unstable immiscible displacement with viscosity ratio μo/μw = 100. The systems studied include a weakly water-wet case which shows an apparently stable front, while the equivalent weakly oil-wet system is highly fingered. By applying scaling theory, it is demonstrated that capillary forces must be made negligible at the laboratory scale in order to maintain the same viscous-capillary force balance which applies at the field scale system. Finally, the well-established enhanced oil recovery technique of polymer flooding is re-evaluated in the context of these findings. It is demonstrated both by simulation and experiment that the principal increased recovery mechanism of the polymer is through viscous crossflow. This mechanism is shown to be responsible for the large and very rapid response in oil recovery on polymer injection – even in highly viscous systems (>2,000 mPa.s) - as bypassed oil crossflows into established water channels (fingers). This mechanism is evident in the laboratory when viscous fingers are allowed to form (viscous-dominated) and supports the conjecture that both polymer flooding and water flooding are best examined without the stabilising effect of capillarity. In addition, the findings of this thesis cast doubt on the conventional methods of “measuring” relative permeability in the laboratory for application in adverse viscosity ratio immiscible displacements in the field.