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Carbon Capture and Storage (CCS) technology could help reduce anthropogenic CO2 emissions to the atmosphere. So far, CCS has failed to attract government support in the UK due to high costs of implementation. The broad deployment of CO2-EOR could aid the development of CCS by providing additional revenue streams for investors. The success of the CO2- EOR in the United States has raised the question of whether this success could be replicated in the UKCS. This thesis answers these questions by introducing two distinct models, which analyse the similarities and differences between the two oil provinces from the subsurface and economic perspectives. The first model integrates into the economic framework the behaviour of oil and CO2 in a reservoir. The model is applied to an oil field in the North Sea. It analyses whether the screening criteria developed based on the onshore US experience to screen for oil field candidates for the CO2 would be suitable for the oil fields in the UKCS. The second model is a theoretical CO2-EOR with storage model, which analyses how the inclusion of permanent storage changes the economics of CO2-EOR. The CO2-EOR with storage model allows for an endogenous switching point between the CO2-EOR and the permanent CO2 storage phase depending on the various economic factors, such as oil prices, sequestration subsidies and fees, CO2 price, and oil and gas tax rates. The CO2-EOR with storage model shows different behaviour compared to the case without permanent storage. On the policy level, the main difference between the two countries revealed that the UK strongly focuses on cutting CO2 emissions while the U.S. on boosting domestic oil production. Therefore, the third study in this thesis investigates the net carbon footprint of the CO2-EOR activity in the North Sea.

Carbon dioxide enhanced oil recovery (CO2EOR) is a proven and available technology used to produce incremental oil from depleted fields. Although this technology has been used successfully onshore in North America and Europe, projects have maximised oil recovery and not CO2 storage. While the majority of onshore CO2EOR projects to date have used CO2 from natural sources, CO2EOR is now more and more being considered as a storage option for captured anthropogenic CO2. In the North Sea the lack of low cost CO2, in large volumes, has meant that no EOR projects have utilised CO2 as an injection fluid. However CO2EOR has the highest potential of all EOR techniques to maximise recovery from depleted UK oil fields. With the prospect of Carbon Capture and Storage (CCS) capturing large tonnages of CO2 from point source emission sites, the feasibility of CO2EOR deployment in the North Sea is high. This thesis primarily aims to address a number of discrete issues which assess the effectiveness of CO2EOR to both produce oil and store CO2. Given the fundamental shift in approach proposed in North Sea CO2EOR projects, the carbon balance of such projects is examined. Using a life cycle accounting approach on a theoretical North Sea field, we examine whether offshore CO2EOR can store more CO2 than onshore projects traditionally have, and whether CO2 storage can offset additional emissions produced through offshore operations and incremental oil production. Using two design scenarios which optimise oil production and CO2 storage, we find that that net GHG emissions were negative in both ‘oil optimised’ and ‘CO2 storage optimised’. However when emissions from transporting, refining and combusting the produced crude oil are incorporated into the life cycle calculations the ‘oil optimised scenario’ became a net emitter of GHG and highlights the importance of continuing CO2 import and injection after oil production has been maximised at a field. This is something that has not traditionally occurred. After assessing rates of flaring and venting of produced associated gas at UK oil fields it is found that the flaring or venting of reproduced CH4 and CO2 has a large control on emissions. Much like currently operating UK oil fields the rates of flaring and venting has a control on the carbon intensity of oil produced. Here values for the carbon intensity of oil produced through CO2EOR are presented. Carbon intensity values are found to be similar to levels of current UK oil production and significantly lower than other unconventional sources. As well as assessing the climate benefits of CO2EOR, a new assessment of CO2EOR potential in Residual Oil Zones (ROZ) is also made. ROZ resource, which is thought to add significant potential to both the oil reserves and CO2 storage potential in some US basins, is here identified in the North Sea for the first time. Based on the foundation of North Sea hydrodynamics study, this thesis identifies the Pierce field as a candidate ROZ field where hydrodynamic tilting of the oil water contact has naturally occurred leaving a zone of residual oil. To test the feasibility of CO2EOR in such a zone a methodology is presented and applied. Notably the study highlights that in this case study recoverable reserves from the ROZ may approach 20% of total field recoverable reserves and have the capability to store up to 11Mt of CO2. While highlighting the CO2EOR potential in the ROZ the thesis discusses the importance in expanding the analysis to quantify its importance on a basin scale. Discussion is also made on whether new resource identification is necessary in a mature basin like the North Sea. With CO2EOR being considered as a feasible option for storing captured anthropogenic CO2, it is important to assess the security of storage in CO2EOR. Using real geochemical and production data from a pilot CO2EOR development in Western Canada two approaches are used to assess the partitioning of CO2 between reservoir fluids through time. Using a number of correlations it is found that CO2 dissolution in oil is up to 7 times greater than in reservoir brine when saturations between the two fluids are equal. It is found that after two years of CO2 injection solubility trapping accounts for 26% of injected CO2. The finding that significantly more dissolution occurs in oil rather than brine indicates that CO2 storage in EOR is safer than in brine storage. However a number of factors such as the increase in oil/CO2 mobility due to CO2 injection is also discussed. The overall conclusion from the work is that CO2EOR in the North Sea has the potential to be an effective way of producing oil and storing CO2 in the North Sea. A number of design, operational and accounting factors are however essential to operate an exemplar CO2EOR project where low carbon intensity oil can be produced from a mature basin while storing large tonnages of captured anthropogenic CO2.

This thesis focuses on applying microfluidic techniques to analyze two carbon management methods; underground carbon sequestration and enhanced oil recovery. The small scale nature of microfluidic methods enables direct visualization of relevant pore-scale phenomena, enabling elucidation of parameters such as diffusion coefficients and critical compositions. In this work, a microfluidic platform was developed to control a two-phase carbon dioxide (CO2)-water interface for diffusive quantification with fluorescent techniques. It was found that the diffusion coefficient of CO2 in pure water was constant (1.86 [± 0.26] x10-9 m2/s) over a range of pressures. The effects of salinity on diffusivity were also measured in solutions, it was found that the diffusion coefficient varied up to 3 times. A microfluidic technique able to determine the critical composition of a model ternary mixture was also successfully implemented. Results indicate potential application of this approach to minimum miscibility pressure measurements used in enhanced oil recovery.

With the production from mature oil fields declining, the increasing demand of oil urges towards more effective recovery of the available resources. Currently, the CO2 Floods are the second most applied EOR processes in the world behind steam injection. With more than 30 years of experience gained from CO2 flooding, successful projects have showed incremental oil recovery ranging from 7 to 15 % of the oil initially in place. Despite all of the anticipated success of CO2 floods, its viscosity nature is in heterogeneous and naturally fractured reservoirs is challenging; CO2 will flow preferentially through the easiest paths resulting in early breakthrough and extraction ineffectiveness leaving zones of oil intact. This research aims at investigating gel treatments and viscosified water-alternating-gas CO2 mobility control techniques. A set of experiments have been conducted to verify the effectiveness and practicality of the proposed mobility control approaches. Our research employed an imaging technique integrating an X-Ray CT scanner with a CT friendly aluminum coreflood cell. With the integrated systems, we were able to obtain real time images when processed provide qualitative and qualitative evaluations to the coreflood. The research studies included preliminary studies of CO2 and water injection performance in fractured and unfractured cores. These experiments provided a base performance to which the performances of the mobility control attempts were compared. We have applied the same methodology in evaluation of the experimental results to both conformance control gel treatments and viscosified water-alternating-gas CO2 mobility control. The gel conformance control studies showed encouraging results in minimizing the effect of heterogeneities directing the injected CO2 to extract more oil from the low permeability zones; the gel strength was evaluated in terms of breakdown and leakoff utilizing the production data aided with CT imaging analysis. The viscosified water coupled with CO2 investigations showed great promising results proving the superiority over neat CO2 injection. This research serves as a preliminary understanding to the applicability of tested mobility control approaches providing a base to future studies in this category of research.

The focus of this thesis was conducting experiments which would help in understanding mechanisms and in design of surfactant enhanced oil recovery (EOR) processes in various scenarios close to reservoir conditions such as heterogeneity, effects of crude oil, wettability, etc. Foam generated in situ by surfactant alternating gas injection was demonstrated as a substitute for polymer drive in a 1-D FOR process. It was effective in a similar process for a 266 cp crude oil even though the system did not have favorable mobility control. Foam enhanced sweep efficiency in a layered sandpack with a 19:1 permeability ratio. Foam diverted surfactant from the high- to the low-permeability layer. Ahead of the foam front, liquid in the low-permeability layer crossflowed into the high-permeability layer. Foam completely swept the system in 1.3 TPV (total pore volume) fluid injection while waterflood required 8 TPV. When the same 2-D system was oil-wet, the recovery by watertlood was only 49.1% of original oil-in-place (OOIP) due to injected water flowing through high-permeability zone leaving low-permeability zone unswept. To improve recovery, an anionic surfactant blend (NI) was injected that altered the wettability and lowered the interfacial tension (IFT) and consequently enabled gravity and capillary pressure driven vertical counter-current flow to occur and exchange fluids between layers during a 42-day system shut-in. Cumulative recovery after a subsequent foamflood was 94.6% OOIP. The addition of lauryl betaine to NI at a weight ratio of 2:1 made the new NIB a good IFT-reducing and foaming agent with crude oil present. It showed effectiveness in water-wet homogeneous and oil-wet heterogeneous sandpacks. The unique attribute of foam with higher apparent viscosity in high- than in low-permeability regions makes it a better mobility control agent than polymer in heterogeneous systems. One single surfactant formulation such as NIB in this study that can simultaneously reduce IFT and generate foam will improve the microscopic displacement and sweep efficiency from the beginning of a chemical flooding process. Foam generation mechanisms, alkaline/surfactant processes, and foam stability in presence of crude oil were investigated in a glass micro model. Total acid number measurement with spiking method was discussed.

The use of foam-forming surfactants offers promise to improve sweep efficiency and mobility control for enhanced oil recovery (EOR). This thesis provides an in depth understanding of transport of surfactant and foam through porous media using a combination of laboratory experiments and numerical simulations. In particular, there are several issues in foam EOR processes that are examined. These include screening of surfactant adsorption onto representative rock surfaces, modeling of foam flow through porous media, and studying the effects of surface wettability and porous media heterogeneity. Surfactant adsorption onto rock surfaces is a main cause of foam chromatographic retardation as well as increased process cost. Successful foam application requires low surfactant adsorption on reservoir rock. The focus of this thesis is natural carbonate rock surfaces, such as dolomite. Surfactant adsorption was found to be highly dependent on electrostatic interactions between surfactants and rock surface. For example, the nonionic surfactant Tergitol 15-S-30 exhibits low adsorption on dolomite under alkaline conditions. In contrast, high adsorption of cationic surfactants was observed on some natural carbonate surfaces. XPS analysis reveals silicon and aluminum impurities exist in natural carbonates, but not in synthetic calcite. The high adsorption is due to the strong electrostatic interactions between the cationic surfactants and negative binding sites in silica and/or clay. There are a number of commercial foam simulators, but an approach to estimate foam modeling parameters from laboratory experiments is needed to simulate foam transport. A one-dimensional foam simulator is developed to simulate foam flow. Chromatographic retardation of surfactants caused by adsorption and by partition between phases is investigated. The parameters in the foam model are estimated with an approach utilizing both steady-state and transient experiments. By superimposing contour plots of the transition foam quality and the foam apparent viscosity, one can estimate the reference mobility reduction factor (fmmob) and the critical water saturation (fmdry) using the STARS foam model. The parameter epdry, which regulates the abruptness of the foam dry-out effect, can be estimated by a transient foam experiment in which 100% gas displaces surfactant solution at 100% water saturation. Micromodel experiments allow for pore-level visualization of foam transport. We have developed model porous media systems using polydimethylsiloxane. We developed a simple method to tune and pattern the wettability of polydimethylsiloxane (PDMS) to generate porous media models with specific structure and wettability. The effect of wettability on flow patterns is observed in gas-liquid flow. The use of foam to divert flow from high permeable to low permeable regions is demonstrated in a heterogeneous porous micromodel. Compared with 100% gas injection, surfactant-stabilized foam effectively improves the sweep of the aqueous fluid in both high and low permeability regions of the micromodel. The best performance of foam on fluid diversion is observed in the lamella-separated foam regime, where the presence of foam can enhance gas saturation in the low permeable region up to 45.1% at the time of gas breakthrough. In conclusion, this thesis provides new findings in surfactant adsorption onto mineral surfaces, in the methodology of estimating foam parameters for reservoir simulation, and in micromodel observations of foam flow through porous media. These findings will be useful to design foam flooding in EOR processes.

Nuclear magnetic resonance (NMR) has become an indispensable tool in petroleum industry for formation evaluation. This dissertation addresses two problems. • We aim at developing a theory to better understand the phenomena of transverse relaxation in the presence of internal field gradients. • Chracterizing the pore structure of vuggy carbonates. We have developed a two dimensional model to study a system of claylined pore. We have identified three distinct relaxation regimes. The interplay of three time parameters characterize the transverse relaxation in three different regimes. In future work, useful geometric information can be extracted from from SEM images and the pore size distribution analysis of North Burbank sandstone to simulate transverse relaxation using our 2-D clay flake model and study diffusional coupling in the presence of internal field gradients. Carbonates reservoirs exhibit complex pore structure with micropores and macropores/vugs. Vuggy pore space can be divided into separate-vugs and touching-vugs, depending on vug interconnection. Separate vugs are connected only through interparticle pore networks and do not contribute to permeability. Touching vugs are independent of rock fabric and form an interconnected pore system enhancing the permeability. Accurate characterization of pore structure of carbonate reservoirs is essential for design and implementation of enhanced oil recovery processes. However, characterizing pore structure in carbonates is a complex task due to the diverse variety of pore types seen in carbonates and extreme pore level heterogeneity. The carbonate samples which are focus of this study are very heterogeneous in pore structures. Some of the sample rocks are breccia and other samples are fractured. In order to characterize the pore size in vuggy carbonates, we use NMR along with tracer analysis. The distribution of porosity between micro and macro-porosity can be measured by NMR. However, NMR cannot predict if different sized vugs are connected or isolated. Tracer analysis is used to characterize the connectivity of the vug system and matrix. Modified version of differential capacitance model of Coats and Smith (1964) and a solution procedure developed by Baker (1975) is used to study dispersion and capacitance effects in core-samples. The model has three dimensionless groups: 1) flowing fraction (f), 2) dimensionless group for mass transfer (NM) characterizing the mass transfer between flowing and stagnant phase and 3) dimensionless group for dispersion (NK) characterizing the extent of dispersion. In order to obtain unique set of model parameters from experimental data, we have developed an algorithm which uses effluent concentration data at two different flow rates to obtain the fitted parameter for both cases simultaneously. Tracer analysis gives valuable insight on fraction of dead-end pores and dispersion and mass transfer effects at core scale. This can be used to model the flow of surfactant solution through vuggy and fractured carbonates to evaluate the loss of surfactant due to dynamic adsorption.

This laboratory project has been done to evaluate pressure pulsing as an Enhanced Oil Recovery (EOR) technique. To perform the study, a consistent laboratory methodology was developed, including the construction of a Consistent Pulsing Source (CPS). Tests compared pulsed and non-pulsed waterfloods in a paraffin or crude oil saturated medium, which also contained connate water (an irreducible water saturation). Results revealed that pulsed tests had maximum flow rates 2. 5--3 times higher, greater oil recovery rates, and final sweep efficiencies that were more than 10% greater than non-pulsed tests. The CPS design has proven very successful, and has since been copied by a major oil corporation. However, there are two limitations, both caused by fluctuating water reservoir levels. Longer pulsed tests (reservoir-depletion tests) were periodically paused to refill the water reservoir, resulting in reservoir depressurization and lower flow rates. The final effect of this was impossible to quantify without correcting the problem. The second CPS limitation was the change in pulse shape with time. However, it is not expected that this had any major effect on the results. The pulse pressure and period studies were limited by early tests, which did not have the necessary time duration. Both increasing pulse pressure and decreasing pulse period were found to increase the final sweep efficiency. Slightly decreasing porosity (0. 4% lower) was found to lower sweep efficiencies. However, the 34. 9% porosity results were not done until reservoir depletion, so it is difficult to quantitatively compare results. An emulsion appeared after water breakthrough when using the CPS on light oils (mineral oil). This may have been the result of isolated oil ganglia being torn apart by the sharp pulses. Although it is difficult to apply laboratory results to the field, this study indicates that pressure pulsing as an EOR technique would be beneficial. Doubled or tripled oil recovery rates and 10% more oil recovery than waterflooding would be significant numbers in a field operation. A valuable application would be in pulsing excitation wells to both pressurize the reservoir and enhance the conformance of the displacing fluid over a long-term period. It would also be valuable for short-term chemical injections, where mixing with the largest volume possible is desirable.

The process of vapor extraction (VAPEX) is a recovery process which targets the heavy oil and bitumen resources. Owing to high viscosity values for these unconventional types of oil, the recovery processes in such reserves are still challenging. The unconventional oil recovery processes usually include a mechanism for reducing the oil viscosity by means of heat, solvent, or both. The process of VAPEX utilizes the injection of a light hydrocarbon solvent into a reservoir for recovering the viscous oil in place by diffusing into the oil and by providing sufficient mobility to the oil upon dilution. Although this process offers a variety of advantages over the alternative thermal recovery processes such as SAGD or CSS, it suffers from two major drawbacks. First, the oil production rates obtained in the VAPEX process are considerably lower than those obtained in the thermal processes. Second, the solvent cost is considerably high. We tried to tackle these two problems during this research and we searched for potentials for an improved VAPEX process. Three potentially improved occurrences of a VAPEX project were found when: 1) the injected solvent was superheated, 2) the wettability of media was altered to oil-wet, and 3) the vugs were distributed in the porous media. Warm VAPEX process is introduced in which the VAPEX process is thermally augmented through superheating the solvent vapor. An attractive feature of this process is the capability of the solvent in being able to condense at the bitumen-solvent interface, which provides the opportunity for the bitumen to be upgraded in-situ through asphaltene precipitation. The asphaltene precipitation was not observed during the conventional vapor extraction process and was only observed during the warm VAPEX process. Upon a moderate level of superheating, the production rate of bitumen was sufficiently improved while the solvent content of the produced oil was significantly decreased as a result of decreased solubility of solvent in the oil at elevated temperatures. Therefore, more oil was produced at lower costs. The warm VAPEX experiments were conducted at 4 temperature levels in high and low permeability media using Cold Lake bitumen and Lloydminster heavy oil blend, n-pentane was used as solvent. The warm VAPEX process was found to be more effective for Cold Lake bitumen and for less permeable media. The potential of in-situ upgrading decreased when the level of superheating increased. The second potential for an improved VAPEX process obtained when the wettability of porous medium was altered to oil-wet conditions. Although this wettability condition is harmful to steam-based recovery processes, such as SAGD, it becomes beneficial to VAPEX. For the application of VAPEX process in fractionally wet media the wettability of glass beads was altered to oil-wet conditions through silylation process, and the VAPEX experiments were conducted in a random packing of water-wet and oil-wet beads of similar size at 7 different compositions. A substantial increase in the oil production rate was observed in a completely oil-wet medium, compared to the water-wet medium. By increasing the fraction of oil-wet beads in the packing up to a critical composition, the production rate of live oil increased linearly with the increase in the fraction of oil-wet beads in the packing during the vapor extraction process. Beyond this critical composition, however, the production rate of live oil did not change significantly with further increase in the fraction of the oil-wet beads in the randomly packed medium. Vugs were also found to be beneficial to the production performance of the VAPEX process. The presence of vugs was investigated in synthesized vugular media at 4 different levels of vuggy-to-total pore volume ratios. The performance of vugular media was compared to that of the homogeneous sintered media. The vugs facilitated the production of oil during the VAPEX process by providing flow communication between the vugs and the surrounding matrix, and therefore, by providing a local high permeability pathways towards the production well. A peak in the oil production rate was observed whenever a series of vugs were simultaneously invaded by the solvent vapor. The overall production rate of oil was higher in vuggy media compared to a homogeneous media at the same overall porosity and permeability. Furthermore, the magnitude of residual oil saturation left behind was also slightly lower in vuggy medium because the vugs were perfectly drained. Finally, a constant rate air injection (CRAI) porosimetry method was developed for characterization of vugs in a vugular media. This method was successfully tested in different synthetic vugular media, and the results illustrated higher accuracy in CRAI porosimetry method compared to constant rate mercury porosimetry. CRAI porosimetry method was also employed for identification of higher permeability regions embedded in a matrix of lower permeability. The analysis of a typical porosimetry signal was also modified.