Engineering

Publication Search Results

Now showing 1 - 10 of 47
  • (2021) Siddiqui, Mohammed Abdul Qadeer
    Thesis
    Hydraulic fracturing (HF) is the most common technology in the development of shale reservoirs. It consumes large amounts of chemically treated water of which 60- 95% is often not recovered in flowback operations. This massive water loss can lead to significant environmental concerns and cause many economic and technical issues for operators. Despite past research, a comprehensive theoretical model coupling micro-scale mechanisms involved in the problem of water loss in shale is still lacking. In this dissertation, a constitutive theory is developed using non-equilibrium thermodynamics and continuum mechanics which couples fluid flow with the mechanics of chemically active materials in the shale matrix. First, a micro-scale experimental investigation of damage behaviour in shale is performed under the coupled effect of stresses and fluid interactions. The observations are used to develop a novel two-phase flow, damage chemo-poroelastic constitutive model. Further experimental investigations are conducted to assess the extent to which these mechanisms contribute to the water loss phenomenon in the shale matrix and provide inputs to the model. To accomplish this objective, several techniques such as spontaneous imbibition, contact angle measurement, X-ray micro-computed tomography (micro-CT), neutron-CT, and pore pressure transmission tests are utilised. Next, the COMSOL Multiphysics platform is used to numerically solve the coupled set of partial differential equations using the finite element method. Numerical results provide novel insights into the poromechanical behaviour of water and gas saturated shales. They indicate that, where chemical swelling stresses are negligible, shale’s poroelastic and chemo-poroelastic responses are similar unless the micro-structural deterioration of the matrix with time is considered. This implies that, even when the swelling stress is low, the chemical effects – acting to lower the rock strength – induce significant changes in the stress distribution in the matrix and modify the fluid flow paths. The micro-structural deterioration occurs only in the water-saturated region increasing its storage capacity thus significantly contributing to the water loss. The main contributions of this research are the theoretical development and modelling of two-phase flow, damage chemo-poroelastic behaviour of shale as well as the novel experimental investigation of involved physical and chemical processes. The research findings provide valuable insights into the chemo-poromechanics coupling in shale matrix and its important role in causing water loss.

  • (2021) Vu, Phung Nhu Hao
    Thesis
    With the current increase in demand for cleaner energy sources and natural gas in particular, the requirement for better understandings of fluid transportation in porous media is also on the rise. This thesis is focusing on the sorption and diffusion process of hydrocarbon in different formations, a process not well understood in the oil and gas industry. In the first major section, this thesis addresses the main disadvantages of the current models for the sorption/diffusion process, which is the independence of diffusion rate with respect to time and the saturation of gas in the adsorbent. Furthermore, these models assume all the pore sizes within the coal are of constant size, which is not representative of the real rock. We propose a new model based on the reaction-diffusion theory to improve upon the popular unipore model. The model separates the adsorption process from the effective diffusivity by coupling in a reaction term. Moreover, this model also describes the dependence of the gas transportation rate on temperature, activation energy, and gas concentration rate. Together with the new model, a hypothetical experimental and analysis procedure is presented to validate this modification. The new findings of the latter part of the thesis call, however, for an extension of this approach. In the second part of the thesis, Transmission Electron Microscopy (TEM) and Guinier Analysis on Small-Angle Neutron Scattering (SANS) data were performed, revealing the complex nanopore structure of the silica aerogel at 3 different sizes: 3 nm, 9 nm and 0.18 nm. Contrast-match (CM) SANS was employed to investigate the sorption behaviour of methane in these pore regions, using CD4 with fluid pressure up to 1 kbar. The CM-SANS experiment discovered the following sorption behaviour of CD4 in the pore region of 3 nm and 9 nm: (1) all the pores are accessible to CD4, (2) CD4 pressure within the pore is equal to the bulk CD4 pressure, and (3) no adsorption layer on the pore-matrix interface was found. Analysis of SANS data for the 0.18 nm pores indicates capillary condensation is the major factor controlling the CD4 sorption behaviour. After the pressure cycling process to up to 1000 bar, when returning to vacuum, the silica structure at this scale is permanently damaged due to the invading gas

  • (2021) Chen, Xiao
    Thesis
    Carbonate rocks have a diversity of uses, including engineering construction (e.g., road/railway base, building stone), environmental applications (carbon dioxide sequestration, nuclear waste disposal) and energy extraction and storage (hydrocarbon and geothermal operations). Before planning and operating energy and civil engineering applications, it is crucial to obtain an understanding of the mechanical properties, the criterion and evolution of failure and the resultant permeability evolution of carbonate rocks under various geological and engineering loads. This doctoral thesis presents a comprehensive experimental investigation into the dynamic evolution of deformation bands, their nucleation and propagation in highly porous carbonates and their impact on permeability evolution. Mt Gambier limestone - a fossil-rich, highly porous carbonate rock - is the main subject of this study. Two different sizes of the specimens were tested under various loading conditions representing in situ geological scenarios. A newly built in-situ X-ray transparent cell has been used to provide a microscopic perspective of the dynamic evolution through time-lapse triaxial compression experiments. These analyses were supplemented by macroscopic observations using standard triaxial compression experiments on larger samples. The transition of failure modes was examined by testing the sample response under various confining pressures to determine the critical parameters for nucleation of compaction bands. Using advanced imaging techniques (e.g., X-ray tomography, 2D digital image correlation and 3D digital volume correlation), the nucleation of the compaction bands was shown to be highly affected by local heterogeneity. The growth of the thickness of compaction bands shows a simple linear relationship with axial strain. A special emphasis for reservoir application is an understanding of the permeability evolution during the formation of compaction bands. This was analysed using qualitative and quantitative methods, X-ray CT based, micro-structurally enriched continuum models and fractal analysis. Experiments performed under dry conditions at room temperature, as well as inert gas (Helium) and fluid (purified Kerosene) saturated samples at temperatures ranging from 25 °C to 80 °C were performed to investigate the effect of coupled thermal-hydro-mechanical-chemical (THMC) processes on formation of compaction bands. The analysis found that a moderate temperature rise can result in a drastic transition of deformation mode from dominantly ductile diffuse band growth at a lower temperature to prevailing brittle growth at a higher temperature. This unusual material behaviour has been proposed to be due to a transition in nucleation mechanism from rate-sensitive creep process-controlled at low temperature to ideal plastic pore collapse at high temperature. In order to evaluate the critical factors controlling the nucleation and dynamic evolution of compaction bands, a series of artificial materials were tested using a digital imaging assisted experimental setup. It was found that not all porous materials formed discrete compaction bands, and the nucleation of bands was restricted to granular and porous solid materials that show a competition between local processes. Compaction bands were found to nucleate only when the competing processes of collapsing macro-pores and the microporous skeleton deformation triggered incompatibilities with the large-scale force equilibrium condition.

  • (2021) Muin, Syeda
    Thesis
    Soft matter systems, such as foams and emulsions, play a central role in numerous applications for consumer goods, mineral beneficiation, and enhanced oil recovery. Detailed microstructural information of the soft matter system enables accurate modeling of its aging mechanisms and bulk mechanical properties. Foams and emulsions are traditionally characterized in 2D using microscopy or evaluating bulk properties, which lack the full 3D vision of the internal structure of the system. Herein, X-ray computed microtomography (µ-CT) coupled with advanced image processing tools is used for extracting detailed microstructural information of foams and emulsions. The derived morphological information is used for evaluating the aging mechanisms of liquid foams, and the arrested coalescence of oil-in-water emulsions. Firstly, a workflow for 3D µ-CT imaging and pore network modeling (PNM) is developed to characterize drainage, coalescence, and diffusive-coarsening in liquid foams. PNM is useful for decomposition of the Plateau borders and nodes within the liquid structure of the foams, while µ-CT provides time-lapsed spatial information. Foam permeability (ĸ) simulations conducted on the extracted PNM are shown to aid foam drainage modeling by the extraction of ĸ versus liquid fraction relationships. Secondly, challenges in using laboratory µ-CT systems are dealt with by the implementation of deep learning. It is demonstrated that deep learning can reduce scan times to only 5 minutes, thus, allowing high temporal resolution for the study of fast-aging liquid foams. These developments are achieved using a laboratory µ-CT system that is traditionally used for imaging static systems over hour-long scan time. Thirdly, novel measurements for droplet networks of oil-in-water emulsions formed via arrested coalescence are presented. Combination of topological and geometrical measurements is demonstrated as effective means for evaluating the stabilizing forces present in the arrested system. Particularly, linear strain measurements of the 3D droplet network elucidate the distribution of strain and stresses within the network, which is not possible to observe in 2D studies. Overall, the dissertation is a step forward in advancing 3D µ-CT imaging for characterizing and modeling soft matter systems.

  • (2021) Alohali, Ruaa Tawfiq A
    Thesis
    The Arabian basin was subject to several tectonic events, including Lower Cambrian Najd rifting, the Carboniferous Hercynian Orogeny, Triassic Zagros rifting, and the Early/Cretaceous and Late/Tertiary Alpine orogenic events. These events reactivated Precambrian basement structures and affected the structural configuration of the overlying Paleozoic cover succession. In addition to a 2D seismic array and several drill well logs, a newly acquired, processed 3D seismic image of the subsurface in part of the basin covering an area of approximately 1051 km2 has been provided to improve the understanding of the regional tectonic evolution associated with these deformation events. In this study, a manual interpretation is presented of six main horizons from the Late Ordovician to the Middle Triassic. Faults and folds were also mapped to further constrain the stratigraphic and structural framework. Collectively, this data is used to build a geological model of the region and develop a timeline of geological events. Results show that a lower Paleozoic sedimentary succession between the Late Silurian to the Early Permian was subject to localised tilting, uplift, and erosion during the Carboniferous Hercynian Orogeny, forming a regional unconformity. Subsequent deposition occurred from the Paleozoic to the Mesozoic, producing a relatively thick, conformable, upper succession. The juxtaposition of the Silurian rocks and Permian formations allows a direct fluid flow between the two intervals. Seismic analysis also indicated two major fault generations. A younger NNW-striking fault set with a component of reverse, east-side-up displacement affected the Lower Triassic succession and is most likely related to the Cretaceous and Tertiary Alpine Events that reactivated the Najd fault system. These fault structures allow vertical migration that could act as conduits to form structural traps. Manual mapping of fault structures in the study area required significant time and effort. To simplify and accelerate the manual faults interpretation in the study area, a fault segmentation method was developed using a Convolutional Neural Network. This method was implemented using the 3D seismic data acquired from the Arabian Basin. The network was trained, validated, and tested with samples that included a seismic cube and fault images that were labelled manually corresponding to the seismic cube. The model successfully identified faults with an accuracy of 96% and an error rate of 0.12 on the training dataset. To achieve a more robust model, the prediction results were further enhanced using postprocessing by linking discontinued segments of the same fault and thus, reducing the number of detected faults. This method improved the accuracy of the prediction results of the proposed model using the test dataset by 77.5%. Additionally, an efficient framework was introduced to correlate the predictions and the ground truth by measuring their average distance value. This technique was also applied to the F3 Netherlands survey, which showed promising results in another region with complex fault geometries. As a result of the automated technique developed here, fault detection and diagnosis were achieved efficiently with structures similar to the trained dataset and has a huge potential in improving exploration targets that are structurally controlled by faults.

  • (2021) Wang, Changbin
    Thesis
    With the increasing mining depth in recent decades, the high in-situ stress and challenging environments in deep underground mines result in multiple mining hazards. Coal bursts and rockbursts are one of the most formidable mining hazards in underground mines, causing the dynamic failure of coal and/or rock mass and violent ejections of material into mine openings. After more than half a century of research, the mechanisms of coal bursts and rockbursts are not yet fully understood because of the large variability and uncertainty in the causal factors. Seismic monitoring is the most popular technique to help forecast, prevent and control burst hazards. It uses seismic waves generated from coal and rock mass to locate internal damage, which provides a powerful means to detect dynamic rock failure and understand the burst damage mechanism. The dynamic impact from seismic waves is an essential cause of rock failure. However, as dynamic impacts in underground coal mines have been rarely studied, the triggering mechanism of seismic waves for coal bursts is poorly understood. Apart from that, due to the complex underground environment, the recorded seismic data may have high location errors and low data integrity, which significantly limits the accuracy of the seismic methods. Therefore, this thesis investigated dynamic impacts of mining induced seismicity in underground mines and enhanced the seismic data quality in assessing the associated risks. Based on seismic data in a burst-prone coal mine in China, the research investigated the ground motion characteristics in the target longwall blocks. It is found that coal bursts are usually triggered by the dynamic impacts when the coal and rock mass are already under critical stress levels. The roadway zones that have experienced more intensive ground motions are more susceptible to coal bursts. The characteristics of location error in the studied longwall were investigated, and a modified seismic clustering method was proposed to assess burst risks. The result revealed that location errors are highly anisotropic and vary along with the geophone movement. The proposed seismic clustering method that considers the influence of location errors had a strong correlation with coal burst damage. The characteristics of seismic data integrity in the studied longwall were investigated by assessing the detection probabilities of the seismic monitoring system. Geophones had various capabilities to detect seismic events at different locations and energy magnitudes. Based on the detection probability results, a method was proposed to correct the integrity of seismic data, which shows more event counts and seismic energy release in front of the longwall face. The concept of “reinforced seismic data” was proposed to correct location errors in the raw seismic data and improve data integrity. The relationship between the spatial variation of seismicity and burst risks was also investigated by using reinforced seismic data. It is found that seismic energy has a strong correlation with coal burst damage, which can be used as an essential precursor of impending burst hazards. The outcome of this thesis can provide insights on the burst damage mechanism and evaluation of seismic data quality in underground coal mines. The proposed seismic methods identify burst risks in terms of ground motions, seismic clusters and variations of seismicity, which can be used individually or together to improve burst hazard forecasting.

  • (2022) Altulyan, May
    Thesis
    With the rapid growth in the number of things that can be connected to the internet, Recommendation Systems for the IoT (RSIoT) have become more significant in helping a variety of applications to meet user preferences, and such applications can be smart home, smart tourism, smart parking, m-health and so on. In this thesis, we propose a unified recommendation framework for data-driven, people-centric smart home applications. The framework involves three main stages: complex activity detection, constructing recommendations in timely manner, and insuring the data integrity. First, we review the latest state-of-the-art recommendations methods and development of applications for recommender system in the IoT so, as to form an overview of the current research progress. Challenges of using IoT for recommendation systems are introduced and explained. A reference framework to compare the existing studies and guide future research and practices is provided. In order to meet the requirements of complex activity detection that helps our system to understand what activity or activities our user is undertaking in relatively high level. We provide adequate resources to be fit for the recommender system. Furthermore, we consider two inherent challenges of RSIoT, that is, capturing dynamicity patterns of human activities and system update without a focus on user feedback. Based on these, we design a Reminder Care System (RCS) which harnesses the advantages of deep reinforcement learning (DQN) to further address these challenges. Then we utilize a contextual bandit approach for improving the quality of recommendations by considering the context as an input. We aim to address not only the two previous challenges of RSIoT but also to learn the best action in different scenarios and treat each state independently. Last but not least, we utilize a blockchain technology to ensure the safety of data storage in addition to decentralized feature. In the last part, we discuss a few open issues and provide some insights for future directions.

  • (2022) Shapoval, Artur
    Thesis
    This thesis presents a pore-scale investigation into the mechanisms governing the interactions between water, oil and carbonate rocks using a series of core-flood experiments coupled with micro-CT imaging. Firstly, rock-fluid interactions leading to wettability alteration by seawater (injected in the secondary mode) and modified seawater (by addition or depletion of Ca2+ ion, injected in tertiary mode) are assessed using in-situ contact angle measurements. While the results have confirmed wettability alteration due to injection of the modified seawater (in tertiary mode), this change in wettability was found to be insufficient to fully explain the observed improvement of oil recovery. Secondly, a fluid-fluid interactions analysis methodology was developed and applied to the data generated as part of this thesis (Ca2+ ­enriched brine, Ca2+ depleted brine, SO42- enriched brine). The results show that emulsification is another mechanism responsible for enhancing oil recovery which is caused by reduction in interfacial tension. Data from multiple experiments (micro-CT imaging, stability analysis, surface tension measurements) also suggests that the amount of emulsion generated, and its stability depend on the type of ion added to seawater to modify the water chemistry. Specifically, Ca2+ depleted brine has shown to generate large amount of emulsion. As part of this thesis, a pore-scale direct flow simulation using the Volume-of-Fluid method was developed to model the mechanisms observed in the experimental studies, such as wettability alteration, viscous fingering and interfacial tension reduction. These mechanisms were grouped into two types, capillary-force affecting (contact angle and interfacial tension), and viscous-force affecting (viscous fingering reduction). When comparing the data between the two approaches (laboratory- and numerical experiments) the results show that capillary-force driven mechanisms were insufficient to predict the oil recovery due to development of flow stagnation zones in the sample. However, when the viscous forces were taken in account in estimation of sweep efficiency the displacement is significantly improved and the experimental data match well with that of numerical experiment. As a result, this thesis provides a first comprehensive pore-scale investigation of the physicochemical interactions between oil, water and carbonate rock related to the tertiary injections of modified seawater.

  • (2022) Saavedra Moreno, Yesenia
    Thesis
    Frothers are widely used in flotation to primarily generate air bubbles, aid gas dispersion, and form a stable froth that provides a selective separation of particles. The current frother classification approaches are based on only three characteristics of the frothers. A number of studies have reported the use of characteristics of frothers including critical coalescence concentration and the ability to create an effective foam under dynamic conditions, as well as foam stability to group frothers. Moreover, the majority of studies are based on a two-phase system, ignoring to some extent the effect of particles, which is relevant to flotation. This thesis explores the effect of frother type on foam stability under dynamic and static conditions and provides a framework to classify frothers based on their foam generation ability. Three foam stability variables, dynamic foam stability index, static foam stability index, and decay rate index are quantified for eighteen different frothers. Four more frothers characteristics reported in the literature, MW, HLB, CCC, DL were defined. The hierarchical cluster analysis was conducted to group frothers based on similarity and provide a category system. Based on the similarities, frothers were grouped into four categories as opposed to the binary frother classification reported in the literature. The selectivity of frothers increases from Group 1 to Group 4, whereas frothers decrease their powerfulness from Group 1 to Group 4. To complement the proposed frother classification and assess the relevance to flotation, the effect of particles on the foam generation under dynamic conditions was explored for four frothers from different families. In terms of froth stability, the three-phase system showed a similar frother ranking to the two-phase system, except that TPG behaved as a more powerful frother in the presence of hydrophobic particles than MIBC. It was also found that the proposed frother classification system in a two-phase system translates well to the three-phase system as frothers were clustered in the same groups. Further insight into the changes of foam stability was gained by simulating the coalescence of two air bubbles at various frother concentrations using the volume of fluid method (VOF). It was observed that an increase in frother concentration damped the oscillation of coalesced bubbles by the surface elasticity, suggesting that the bubble surface area moves at a lower velocity, which may reduce the motion of particles attached to the interface and consequently, their detachment during the merging of two bubbles.

  • (2022) Makuluni, Patrick
    Thesis
    The Australian North West Shelf (NWS) has a complex geological history that has been affected by several phases of extension and rifting, creating features like the failed rift system in the Northern Carnarvon Basin (NCB). The NWS has been impacted by several regional tectonic events, most notably Gondwana’s dispersal and Australia’s collision with Southeast Asia. Such events created the various sub-basins of the Shelf and impacted the vertical and lateral – or kinematic – motions of these basins. To date, no studies have fully quantified the spatial and temporal distribution of these motions and their impacts on the region’s resource systems. This thesis proposes that accurate basin kinematic evolution models can reveal the time-dependent evolution of basins and how such evolution affects the development of resource systems in those basins. The NWS has a rich coverage of geological and geophysical datasets, hence an excellent location for building such models. I have built detailed kinematic evolution models of the Shelf basins using backstripping, decompaction and thermochronology techniques. The models extend vertical motion analysis from the traditional single-well analysis to accurate regional analysis by combining datasets from multiple wells and seismic sections. They also extend lateral motion analysis from traditional inter-plate analyses into intraplate settings to precisely reconstruct the pre-rift deformation of intracontinental rifts using novel methods. The thesis has modelled the spatial and temporal distribution of subsidence, rift-related lateral motions and exhumation in the NWS basins. The results reveal a northeast propagating rift in the NCB with rapid subsidence and sedimentation rates (up to 80 m/Ma) from the Jurassic to the Cretaceous. Based on this data, I developed a reconstruction model of this NCB rift system, which reveals multiphase anomalous rifting rates (8 mm/yr), correlating Gondwana dispersal events. The exhumation models reveal a complex multiphase Mesozoic-present exhumation of up to ~2.5 km across the NWS, likely caused by magmatic underplating, compression and depth-dependent extension. The exhumation impeded the development of various Jurassic-Cretaceous petroleum systems in the central Bonaparte Basin and the Exmouth Plateau, NCB. This thesis improves the understanding of the NWS basins’ evolution, considers the implications for CO2 and H2 storage locations, and has significant applications in resource exploration.