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Pore scale interaction between matrix and fracture during miscible and immiscible CO2 injection was studied experimentally using visual models. Initially, visualization experiments were conducted on 2-D glass bead packed models by injecting n-heptane (solvent) displacing different kinds of processed oil. The focus was on the displacement patterns and solvent breakthrough controlled by matrix-fracture interaction and the pore scale behaviour of solvent-oil interaction for different fracture and injection conditions (rate, vertical vs. horizontal injection) as well as oil viscosity. Besides the visual investigation, effluent was also analyzed to calculate the solvent cut and oil recovery. Next, the process was modeled numerically using a commercial compositional simulator and the saturation distribution in the matrix was matched to the experimental data. The key parameters in the matching process were the effective diffusion coefficients and the longitudinal and transverse dispersivities. The diffusion coefficients were specified for each fluid and dispersivities were assigned into grid blocks separately for the fracture and the matrix. Finally, glass etched microfluidic models were used to investigate pore scale interaction between the matrix and the fracture. The models were prepared by etching homogeneous and heterogeneous micro scale pore patterns on glass sheets bonded together and then saturated with colored n-decane as the oleic phase. CO2 was injected at miscible and immiscible conditions. The focus was on visual pore scale analysis of miscibility, breakthrough of CO2 and oil/CO2 transfer between the matrix and the fracture under different miscibility, injection rate and wettability conditions. / Petroleum Engineering

Experimental and numerical simulation studies were conducted to investigate the improvement of light oil recovery in carbonate cores during CO2 injection. The main steps in the study are as follows. First, the minimum miscibility pressure of 31ºAPI west Texas oil and CO2 was measured using the slimtube (miscibility) apparatus. Second, miscible CO2 coreflood experiments were carried out on different modes of injection such as CGI, WF, WAG, and SWAG. Each injection mode was conducted on unfractured and fractured cores. Fractured cores included two types of fracture systems creating two shape models on the core. Also, runs were made with different salinity levels for the injected water, 0 ppm, 60,000 ppm, and 200,000 ppm. Finally, based on the experimental results, a 2-D numerical simulation model was constructed and validated. The simulation model was then extended to conduct sensitivity studies on different parameters such as permeability variations in the core, WAG ratio and slug size, and SWAG ratio. The results of this study indicate that injecting water with CO2 either simultaneously or in alternating cycles increases the oil recovery by at least 10 percent and reduces the CO2 requirements by 50 percent. The salinity of the injected water has shown a detrimental effect on oil recovery only during WAG and SWAG injections. Lowering injected water salinity, which increases the CO2 solubility in water, increases oil recovery by up to 18 percent. Unfractured cores resulted in higher recovery than all fractured ones. CGI in fractured cores resulted in very poor recovery but WAG and SWAG injections improved the oil recovery by at least 25 percent over CGI. This is because of the better conformance provided by the injected water, which decreased CO2 cycling through the fracture. CO2 injection in layered permeability arrangements showed significant decrease in oil recovery (up to 40 percent) compared to the homogenous case. For all injection modes during the layered permeability arrangements, the best oil recovery was obtained when the flow barrier is in the middle of the core. When the permeability was arranged in sequence, each injection mode showed different preference to the permeability arrangements. The WAG ratio study in the homogenous case showed that a 1:2 ratio had the highest oil recovery, but the optimum ratio was 1:1 based on the amount of injected CO2. In contrast, layered permeability arrangements showed different WAG ratio preference depending on the location of the flow barrier.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第17875号 / 工博第3784号 / 新制||工||1579(附属図書館) / 30695 / 京都大学大学院工学研究科都市社会工学専攻 / (主査)教授 松岡 俊文, 教授 大津 宏康, 准教授 村田 澄彦 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

Carbon dioxide (CO2) sequestration is defined as the removal of gas that would be emitted into the atmosphere and its subsequent storage in a safe, sound place. CO2 sequestration in underground formations is currently being considered to reduce the amount of CO2 emitted into the atmosphere. However, a better understanding of the chemical and physical interactions between CO2, water, and formation rock is necessary before sequestration. These interactions can be evaluated by the change in mineral content in the water before and after injection, or from the change in well injectivity during CO2 injection. It may affect the permeability positively due to rock dissolution, or negatively due to precipitation. Several physical and chemical processes cover the CO2 injection operations; multiphase flow in porous media is represented by the flow of the brine and CO2, solute transportation is represented by CO2 dissolution in the brine forming weak carbonic acid, dissolution-deposition kinetics can be seen in the rock dissolution by the carbonic acid and the deposition of the reaction products, hydrodynamic instabilities due to displacement of less viscous brine with more viscous CO2 (viscous fingering), capillary effects and upward movement of CO2 due to gravity effect. The objective of the proposed work is to correlate the formation damage to the other variables, i.e. pressure, temperature, formation rock type, rock porosity, water composition, sulfates concentration in the water, CO2 volume injected, water volume injected, CO2 to water volumetric ratio, CO2 injection rate, and water injection rate. In order to achieve the proposed objective, lab experiments will be conducted on different rock types (carbonates, limestone and dolomite, and sandstone) under pressure and temperature that simulate the field conditions. CO2 will be used at the supercritical phase and different CO2-water-rock chemical interactions will be addressed. Quantitative analysis of the experimental results using a geochemical simulator (CMG-GEM) will also be performed. The results showed that for carbonate cores, maintaining the CO2/brine volumetric ratio above 1.0 reduced bicarbonate formation in the formation brine and helped in minimizing precipitation of calcium carbonate. Additionally, increasing cycle volume in WAG injection reduced the damage introduced to the core. Sulfate precipitation during CO2 sequestration was primarily controlled by temperature. For formation brine with high total dissolved solids (TDS), calcium sulfate precipitation occurs, even at a low sulfate concentration. For dolomite rock, temperature, injection flow rate, and injection scheme don't have a clear impact on the core permeability, the main factor that affects the change in core permeability is the initial core permeability. Sandstone cores showed significant damage; between 35% and 55% loss in core permeability was observed after CO2 injection. For shorter WAG injection the damage was higher; decreasing the brine volume injected per cycle, decreased the damage. At higher temperatures, 200 and 250 degrees F, more damage was noted than at 70 degrees F.

[pt] A degradação do meio ambiente está no topo da agenda de países e empresas. O foco principal é a redução das emissões de gases causadores do efeito estufa, sendo CO2 o maior contribuinte. O consumo elevado de combustíveis fósseis está criando um efeito irreversível no planeta. De forma a contrabalancear seus impactos ambientais, surge o segmento de projetos de captura e sequestro de carbono. O maior entrave seu para crescimento é econômico, daí o uso de CO2 para recuperação avançada de óleo, alavancando sua implementação. Esta dissertação avalia duas estratégias distintas de desenvolvimento de um campo de petróleo offshore, uma através da injeção de água e outra por recuperação avançada com injeção de CO2 (EOR CO2 – enhanced oil recovery) a partir de fonte antropogência. Os maiores desafios técnicos para aplicação de EOR CO2 em ambiente offshore são examinados, mostrando o arcabouço teórico, melhores práticas e soluções ainda não desenvolvidas, em áreas como: gerenciamento de reservatórios, engenharia de poços e plantas de processo, além de captura e transporte de CO2. Em seguida, a viabilidade econômica de ambos os métodos de recuperação são comparados, com pequena vantagem o caso EOR. Entretanto, devido às incertezas de sucesso do método e sua sensibilidade ao preço de importação de CO2, a gama de resultados pode alterar o processo decisório. Um balanço de carbono também é realizado, mostrando a redução esperada de sua concentração na atmosfera ao se selecionar o método de EOR CO2. Ainda, a aplicabilidade de créditos de carbono é discutida, e seu impacto econômico quantificado. Finalmente, há um longo caminho a se percorrer para ampla utilização de projetos EOR com CO2 antropogênico em ambiente offshore. Ao apontar os maiores desafios e entraves a serem superados, incluindo técnicos, comerciais e regulatórios, ao apresentar modelo econômico, e acima de tudo, ao mostrar sua atratividade, esta dissertação tem por objetivo reduzir esta distância. / [en] Environmental issues are on top of governments and companies’ agendas. The main focus is on global warming and means to reduce greenhouse gases, being carbon dioxide the main contributor. The consumption of fossil fuels is creating an irreversible effect on the planet, and it is expected to continue for years to come. In order to offset its usage are the emerging carbon capture and storage (CCS) projects. Their main obstacle is economical, and that’s where enhanced oil recovery through CO2 can help. This dissertation assesses the development options of an offshore Brazilian discovery, by comparing water injection method with carbon dioxide enhanced oil recovery (EOR CO2) imported from an anthropogenic onshore source. The main EOR CO2 technical challenges for offshore application are examined, detailing field proven and yet to be developed solutions, from reservoir management, wells engineering to the production unit, passing through CO2 acquisition and transportation. Next, economical feasibility of both methods are compared, with a slight advantage for EOR on the base case. Nevertheless, due to high uncertainties in method success prior to development and commitment, and also to carbon dioxide import prices, the range of results can shift the decision making, and such sensitivity analysis is also presented. A carbon inventory is also made, showing the net positive balance of selecting EOR CO2, which reduces the component’s concentration in the atmosphere. Finally, the applicability of carbon credits is discussed and its economical impact quantified. There is still a long way to go for the widespread utilization of anthropogenic EOR CO2 in offshore projects. By pointing out the main challenges to be addressed, including technical, commercial and regulatory, by presenting an economical model comprising environmental aspects, and most of all, showing its attractiveness, this dissertation aims to reduce this gap.

Minimum miscibility pressure (MMP) is a key parameter in the design of gas flooding. There are experimental and computational methods to determine MMP. Computational methods are fast and convenient alternatives to otherwise slow and expensive experimental procedures. This research focuses on the computational aspects of MMP estimation. It investigates the shortcomings of the current computational models and offers ways to improve the robustness of MMP estimation. First, we develop a new mixing cell method of estimating MMP that, unlike previous "mixing cell" methods, uses a variable number of cells and is independent of gas-oil ratio, volume of the cells, excess oil volumes, and the amount of gas injected. The new method relies entirely on robust P-T flash calculations using any cubic equation-of-state (EOS). We show that mixing cell MMPs are comparable with those of other analytical and experimental methods, and that our mixing cell method finds all the key tie lines predicted by MOC; however, the method proved to be more robust and reliable than current analytical methods. Second, we identify a number of problems with analytical methods of MMP estimation, and demonstrate them using real oil characterization examples. We show that the current MOC results, which assume that shocks exist from one key tie line to the next may not be reliable and may lead to large errors in MMP estimation. In such cases, the key tie lines determined using the MOC method do not control miscibility, likely as a result of the onset of L₁-L₂-V behavior. We explain the problem with a simplified pseudo-ternary model and offer a procedure for determining when an error exists and for improving the results. Finally, we present a simple mathematical model for predicting the MMP of contaminated gas. Injection-gas compositions often vary during the life of a gasflood because of reinjection and mixing of fluids in situ. Determining the MMP by slim-tube or other methods for each possible variation in the gas-mixture composition is impractical. Our method gives an easy and accurate way to determine impure CO₂ MMPs for variable field solvent compositions on the basis of just a few MMPs. Alternatively, the approach could be used to estimate the enrichment level required to lower the MMP to a desired pressure. / text

CO2 sequestration is one of the proposed methods for reducing anthropogenic CO2 emissions to the atmosphere and therefore mitigating global climate change. Few studies on storing CO2 in an aquifer have been conducted on a regional scale. This study offers a conceptual approach to increasing the storage efficiency of CO2 injection in saline formations and investigates what an actual CO2 storage project might entail using field data for the Woodbine aquifer in East Texas. The study considers three aquifer management strategies for injecting CO2 emissions from nearby coal-fired power plants into the Woodbine aquifer. The aquifer management strategies studied are bulk CO2 injection, and two CO2-brine displacement strategies. A conceptual model performed with homogeneous and average reservoir properties reveals that bulk injection of CO2 pressurizes the aquifer, has a storage efficiency of 0.46% and can only last for 20 years without risk of fracturing the CO2 injection wells. The CO2-brine displacement strategy can continue injecting CO2 for as many as 240 years until CO2 begins to break through in the production wells. This offers 12 times greater CO2 storage efficiency than the bulk injection strategy. A full field simulation with a geological model based on existing aquifer data validates the storage capacity claims made by the conceptual model. A key feature in the geological model is the Mexia-Talco fault system that serves as a likely boundary between the saline aquifer region suitable for CO2 storage and an updip fresh water region. Simulation results show that CO2 does not leak into the fresh water region of the iv aquifer after 1000 years of monitoring if the faults have zero transmissibility, but a negligible volume of brine eventually gets through the mostly sealing fault system as pressure across the faults slowly equilibrates during the monitoring period. However, for fault transmissibilities of 0.1 and 1, both brine and CO2 leak into the fresh water aquifer in increasing amounts for both bulk injection and CO2-brine displacement strategies. In addition, brine production wells draw some fresh water into the saline aquifer if the Mexia-Talco fault system is not sealing. A CO2 storage project in the Woodbine aquifer would impact as many as 15 counties with high-pressure CO2 pipelines stretching as long as 875 km from the CO2 source to the injection site. The required percentage of power plant energy capacity was 7.43% for bulk injection, 7.9% for the external brine disposal case, and 10.2% for the internal saturated brine injection case. The estimated total cost was $0.00132–$0.00146/kWh for the bulk injection, $0.00191–$0.00211/kWh for the external brine disposal case, and $0.0019–$0.00209/kWh for the internal saturated brine injection case.

This thesis explores the concept of displacement of sorbed methane and enhancement of methane recovery by injection of CO2 into coal, while sequestering CO2. The objective of this study was to investigate the diffusion behavior of San Juan Basin coal under single and competitive gas environments. The movement of gas in a coalbed reservoir starts in the coal matrix with diffusion towards the naturally occurring cleat network surrounding the matrix blocks. The gas production potential from coalbed reservoirs under different gas environments was, therefore, estimated by studying the diffusion behavior of the coal type. The results clearly showed that the rate of diffusion increases with decreasing reservoir pressure, the increase being exponential at low/very low pressure. As a final step, a simulation study was carried out using the experimental results to predict long-term gas production from coalbed reservoirs with and without CO2 injection. This was followed by a preliminary economic analysis in order to estimate the feasibility of enhanced recovery method by CO2 injection by calculating the net present value of a project with and without carbon credits. The results showed that it is possible to obtain significant improvement in methane recovery by CO2 injection. However, it becomes economically feasible only with carbon credits.

[pt] Para contribuir com a mitigação das mudanças climáticas, tecnologias com o intuito de promover a redução de emissões dos Gases de Efeito Estufa, como é o caso do dióxido de carbono, tem obtido grande destaque nas pesquisas ultimamente. Uma das alternativas para impedir que todo esse carbono seja liberado para a atmosfera é reinjetar o CO2 nos próprios reservatórios ou em outras formações geológicas próximas. Neste sentido, esta dissertação apresenta uma tecnologia relacionada à captura e armazenamento geológico de CO2 e avalia o processo de injeção de dióxido de carbono em aquíferos salinos. O principal objetivo é avaliar o processo de injeção de dióxido de carbono em aquíferos salinos de rochas carbonáticas, numa escala de tempo de três mil anos, para avaliar o aprisionamento do CO2 em suas diferentes formas, incluindo o armazenamento mineral. Tal estudo também considera na modelagem, as reações químicas entre os componentes na fase aquosa e a difusão molecular do dióxido de carbono na fase aquosa, assim como as reações químicas de dissolução e precipitação mineral. A partir das informações obtidas em literatura, estabeleceu-se as premissas para a simulação do caso base, e gerou-se casos derivados variando individualmente cada uma das seguintes propriedades: difusividade, salinidade, pH e temperatura, no qual avaliou-se a contribuição de cada uma delas nas diferentes formas de armazenamento do CO2. Por fim, concluiu-se que a mineralização do CO2 iniciou-se após aproximadamente 200 anos de simulação. No entanto, devido às lentas taxas da reação de precipitação mineral, a predominância do armazenamento do CO2 ainda foi na forma dissolvida. As propriedades variadas que contribuíram para o aumento do armazenamento mineral de CO2, que é considerada a forma mais estável, foram: menor fator de difusividade, maior salinidade do aquífero, pH básico (pH igual a 8,0) e maior temperatura. / [en] In order to contribute to climatic changes mitigation, technologies aiming the reduction of pollution gases emissions, such as carbon dioxide, have been highlighted in recent researches. One of the alternatives to prevent all this carbon from being released into the atmosphere is to reinject CO2 into reservoirs or in other nearby geological formations. In this sense, this work presents a technology related to the capture and geological storage of CO2 and evaluates the carbon dioxide injection process into saline aquifers. The main objective is to evaluate the carbon dioxide injection process in saline aquifers of carbonate rocks, in a time scale of three thousand years, to evaluate the storage mechanism of CO2 in its different forms, including mineral storage. Such study also considers in the modeling, the chemical reactions between the components in the aqueous phase and the molecular diffusion of the carbon dioxide in the aqueous phase, as well as the chemical reactions of mineral dissolution and precipitation. From the research made and the information gathered in the literature, the premises for the simulation of the base case were established, and derivative cases were generated by individually varying each of the following properties: diffusivity, salinity, pH and temperature, in which the contribution of each property was evaluated on the different CO2 storage forms. Finally, it was concluded that the injected CO2 mineralization process started after approximately 200 years of simulation. However, due to slow rates of the mineral precipitation, the CO2 storage in the dissolved form was still predominant. The different properties that contributed to increase the CO2 mineral storage, which is considered the more estable one, were: lower diffusivity factor, higher aquifer salinity, basic pH (pH equal to 8.0) and higher temperature.