Enhanced oil recovery as a result of earthquake events has been repeatedly observed and reported. The main advantage of a seismic wave-based EOR is that it is not costly and is easy to deploy. However, the method has not yet been fully investigated; the production enhancement mechanisms need to be identified and confirmed. This thesis shows a possible production mechanism and preliminary estimate of incremental oil recovery due to seismic wave stimulation. The production mechanism is improved sweep efficiency through viscous cross-flow between different permeability layers of a reservoir as a result of fluid pressure oscillations. In this thesis, we studied a possible viscous cross-flow generation between a fracture and a rock matrix of a fractured reservoir model as a result of fluid pressure oscillations. We considered time-harmonic water flooding as a way of sending seismic waves to the reservoir model. To calculate a cross-flow pressure gradient, we investigated oscillatory pressure propagation equations within the rock matrix and the fracture of the reservoir model. According to our results, the volume of the mobilized oil because of the time-harmonic water flooding during one day of stimulation from the fractured reservoir model is in the order of several barrels. / text

The first goal of this research was to develop and experimentally test new and improved chemical formulations for enhanced oil recovery using a new class of branched large-hydrophobe alkoxy carboxylate surfactants mixed with novel co-surfactants and co-solvents to both lower IFT and alter wettability at high temperatures and high salinities. These novel alkoxy carboxylate surfactants with large branched hydrophobes were tested and found to show excellent performance in corefloods over a wide range of reservoir conditions up to at least 120°C. The number of PO and EO groups in these new surfactants were optimized for a wide variety of oils over a broad range of salinity, hardness and temperature and mixed with various co-surfactants and co-solvents to develop high-performance formulations based on the microemulsion phase behavior. Both ultra-low IFT and clear aqueous solutions at optimum salinity were obtained for both active and inactive oils and both light and medium gravity oils over a wide range of temperatures. Both sandstone and carbonate corefloods using these carboxylate surfactants showed excellent performance at high temperature, high hardness and high salinity as indicated by high oil recovery, low pressure gradients and low surfactant retention. The advent of such a new class of cost-effective surfactants significantly broadens the potential application of chemical enhanced oil recovery processes using surfactants under harsh reservoir conditions. The second goal of this research was to evaluate the effect of buoyancy on oil recovery from cores using ultra-low IFT surfactant formulations under conditions where the use of polymer for mobility control is either difficult or unnecessary, determine the conditions that are favorable for a gravity-stable surfactant flood, and further improve the performance of gravity-stable surfactant floods by optimizing the microemulsion properties, especially its viscosity. The microemulsion viscosity can be varied by adjusting the structure of the surfactants and co-solvents and their concentrations. Predictions made using classical stability theory applied to surfactant flooding experiments were determined to be inaccurate because such theory does not take into account the microemulsion phase that forms in-situ when surfactant mixes with the oil. The modification of the classical theory to account for the effect of the microemulsion on the critical velocity for a stable displacement is one of the major contributions of this research. New experiments were done to test the modified theory and it was found to be in good agreement with these experiments. Furthermore, a new method to increase the stable velocity by optimizing the microemulsion viscosity was proposed and validated by a series of coreflood experiments designed and conducted for that specific purpose. / text

The injection of nanoparticles is a promising and novel approach to enhancing oil recovery in depleted fields. Nanoparticles have one dimension that is smaller than 100 nm and have many unique properties that are useful when it comes to oil recovery. Their small size and the ability to manipulate particle properties are a couple of the advantageous properties. The small size of nanoparticle allows them to easily pass through porous media. Manipulating nanoparticle properties allows for wettability modifications or controlled release of chemicals at a precise location in the formation. Injection of nanoparticle dispersions for secondary or tertiary recovery in corefloods has yielded positive results. Field tests using nanoparticles have also yielded positive results with increased oil recovery. While there has been a sizable amount of work related to corefloods, limited investigation has been reported using micromodels. Micromodels are valuable because they allow for pore scale viewing of the oil recovery, which is not possible with corefloods. In this research both polydimethylsiloxane (PDMS) and glass microfluidic devices were fabricated to test the EOR potential of different types of nanoparticles. Much of the work described in this thesis involved the use of a dead-end pore geometry to trap oil. First the pore space was filled with oil and then waterflooded. This left some oil trapped in the dead-end pores. PDMS micromodels proved difficult to trap oil in the dead-end pores; because of this glass micromodels were tested. After trapping oil, a nanoparticle dispersion was injected into the pore space to test the potential of the dispersion to reduce the residual oil saturation in the dead-end pores. The nanoparticle dispersion was injected at different flow rates (1 [mu]l/hr to 50 [mu]l/hr) to test the effect of flow rate on residual oil recovery. / text

Teapot Dome field is located 35 miles north of Casper, Wyoming in Natrona County. This field has been selected by the U.S. Department of Energy to implement a field-size CO2 storage project. With a projected storage of 2.6 million tons of carbon dioxide a year under fully operational conditions in 2006, the multiple-partner Teapot Dome project could be one of the world's largest CO2 storage sites. CO2 injection has been used for decades to improve oil recovery from depleted hydrocarbon reservoirs. In the CO2 sequestration technique, the aim is to "co-optimize" CO2 storage and oil recovery. In order to achieve the goal of CO2 sequestration, this study uses reservoir simulation to predict the amount of CO2 that can be stored in the Tensleep Formation and the amount of oil that can be produced as a side benefit of CO2 injection. This research discusses the effects of using different reservoir fluid models from EOS regression and fracture permeability in dual porosity models on enhanced oil recovery and CO2 storage in the Tensleep Formation. Oil and gas production behavior obtained from the fluid models were completely different. Fully compositional and pseudo-miscible black oil fluid models were tested in a quarter of a five spot pattern. Compositional fluid model is more convenient for enhanced oil recovery evaluation. Detailed reservoir characterization was performed to represent the complex characteristics of the reservoir. A 3D black oil reservoir simulation model was used to evaluate the effects of fractures in reservoir fluids production. Single porosity simulation model results were compared with those from the dual porosity model. Based on the results obtained from each simulation model, it has been concluded that the pseudo-miscible model can not be used to represent the CO2 injection process in Teapot Dome. Dual porosity models with variable fracture permeability provided a better reproduction of oil and water rates in the highly fractured Tensleep Formation.

Heavy oil resources are huge and are currently produced largely with steam-driven technology. The purpose of this research was to evaluate an alternative to steam flooding in heavy oils: chemical EOR. Acidic components abundant in heavy crude oils can be converted to soaps at high pH with alkali, reducing the interfacial tension (IFT) between oil and water to ultra-low levels. In an attempt to harness this property, engineers developed alkaline and alkaline-polymer (AP) flooding EOR processes, which met limited success. The primary problem with AP flooding was the soap is usually too hydrophobic, its optimum salinity is low and the ultra-low IFT salinity range narrow (Nelson 1983). Adding a hydrophilic co-surfactant to the process solved the problem, and is known as ASP flooding. AP floods also form persistent, unpredictable and often highly viscous emulsions, which result in high pressure drops and low injection rates. Addition of co-solvents such as a light alcohol (typically 1 wt %) improves the performance of AP floods; researchers at the University of Texas at Austin have coined the term ACP (Alkaline Co-solvent Polymer) for this new process. ACP has significant advantages relative to other chemical flooding modes to recover heavy oils. It is less costly than using surfactant, and has none of the design challenges associated with surfactant. It shows the benefit of nearly 100% displacement sweep efficiency in core floods when properly implemented, as heavy oils tend to produce significant IFT reducing soaps. The use of polymer for mobility control ensures good sweep efficiency is also achieved. Since heavy oils can be extremely viscous at reservoir temperature, moderate reservoir heating to reduce oil viscosity is beneficial. In a series of core flood experiments, moderately elevated temperatures (25-75°C) were used in evaluating ACP flooding in heavy oils. The experiments used only small amounts of inexpensive co-solvents while recovering >90% of remaining heavy oil in a core, without need for any surfactant. The most successful experiments showed that a small increase in temperature (25°) can have very positive impacts on core flood performance. These results are very encouraging for heavy oil recovery with chemical EOR. / text

Surfactant-Polymer (SP) and Alkaline-Surfactant-Polymer (ASP) floods are tertiary oil recovery processes that mobilize residual oil to waterflood. These Chemical EOR processes are most valuable when the residual oil saturation of a target reservoir to waterflood is high. The first steps of designing a SP or ASP flood are performed in a laboratory by developing a surfactant formulation and by performing core flood experiments to assess the performance of the flood to recovery residual oil to waterflood. The two criteria for a technically successful laboratory SP or ASP core flood are recovering greater than 90% of residual oil to waterflood leaving behind less than 5% of residual oil and accomplishing this at a field scalable pressure gradient across the porous medium of approximately 1 psi per foot. This thesis documents the laboratory development of SP and ASP core floods for a continental Unites States oil reservoir reported to contain the minerals anhydrite and gypsum. The significance of these minerals is that they provide an infinite acting source of calcium within the reservoir that makes using the traditional alkali sodium carbonate unfeasible using conventional Chemical EOR methods. This is because sodium carbonate will precipitate as calcite in the presence of free calcium ions. Secondly, this thesis investigates two novel alkalis that are compatible with free calcium ions, sodium acetate and tetrasodium EDTA, for their viability for use in ASP floods for reservoirs containing anhydrite or gypsum. / text

Steam Assisted Gravity Drainage (SAGD) is used widely as a thermal recovery technique in Canada to produce a very viscous bitumen formation. The main research objectives of this simulation and experimental study are to investigate oil recovery mechanisms under SAGD process with different injection fluids, including steam, solvent or steam with solvent. 2D simulation studies based on typical Athabasca reservoir properties have been performed. Results show that a successful solvent co-injection design can utilize the advantages of solvent and steam. There is an optimal solvent type and concentration ratio range for a particular reservoir and operating condition. Long, continuous shale barriers located vertically above or near the wellbore delay production performance significantly. Co-injecting a multi-component solvent can flush out the oil in different areas with different drainage mechanisms from vaporized and liquid components. Placing an additional injector at the top of the reservoir results only in marginal improvement. The pure high-temperature diluent injection appears feasible, although further technical and economic evaluation of the process is required. A 2D scaled physical model was fabricated that represented in cross-section a half symmetry element of a typical SAGD drainage volume in Athabasca. The experimental results show co-injecting a solvent mixture of C7 and xylene with steam gives better production performance than the injection of pure steam or steam with C7 at the study condition. Compared to pure steam injection runs ( Run 0 and 1), coinjecting C7 (Run 2) with steam increases the ultimate recovery factor of oil inside the cell from 25 percent to 29 percent and decreases the ultimate CSOR from 2.2 to 1.9 and the ultimate CEOR from 4892 J/cm 3 to 4326 J/cm 3 ; coinjecting C7 and Xylene (Run 3) increases the ultimate recovery factor of oil from 25 percent to 34 percent, and decreases the ultimate CSOR 2.2 to 1.6 and the ultimate CEOR from 4892 J/cm 3 to 3629 J/cm 3 . Analyses of the experimental results indicate that partial pressure and the near wellbore flow play important roles in production performance. In conclusion, a successful solvent injection design can effectively improve the production performance of SAGD. Further research on evaluating the performance of various hydrocarbon types as steam additives is desirable and recommended.

This study presents the results of nano-particle and surfactant-stabilized solvent-based emulsion core flooding studies under laboratory conditions that investigate the recovery mechanisms of chemical flooding in a heavy oil reservoir. In the study, bench tests, including the phase behavior test, rheology studies and interfacial tension measurement are performed and reported for the optimum selecting method for the nano-emulsion. Specifically, nano-emulsion systems with high viscosity have been injected into sandstone cores containing Alaska North Slope West Sak heavy oil with 16 API, which was dewatered in the laboratory condition. The experiment results suggest that the potential application of this kind of emulsion flooding is a promising EOR (enhanced oil recovery) process for some heavy oil reservoirs in Alaska, Canada and Venezuela after primary production. Heavy oil lacks mobility under reservoir conditions and is not suitable for the application of the thermal recovery method because of environmental issues or technical problems. Core flooding experiments were performed on cores with varied permeabilities. Comparisons between direct injection of nano-emulsion systems and nano-emulsion injections after water flooding were conducted. Oil recovery information is obtained by material balance calculation. In this study, we try to combine the advantages of solvent, surfactant, and nano-particles together. As we know, pure miscible solvent used as an injection fluid in developing the heavy oil reservoir does have the desirable recovery feature, however it is not economical. The idea of nano-particle application in an EOR area has been recently raised by researchers who are interested in its feature-reaction catalysis-which could reduce in situ oil viscosity and generate emulsion without surfactant. Also, the nano-particle stabilized emulsions can long-distance drive oil in the reservoir, since the nano-particle size is 2-4 times smaller than the pore throat. In conclusion, the nano-emulsion flooding can be an effective enhancement for an oil recovery method for a heavy oil reservoir which is technically sensitive to the thermal recovery method.

This thesis presents a comprehensive simulation study on the impact of natural fractures on the performance of surfactant polymer flood in a field scale surfactantpolymer flood. The simulation model utilized for the study is a dual porosity dual permeability model representing 1/8 of a 20-acre 5-spot pattern. The model parameters studied include wettability alteration, IFT changes and mobility reduction effect. The results of this study clearly indicate the importance of reservoir description and fracture modeling for a successful surfactant-polymer flood. Naturally fractured carbonate reservoirs are usually characterized by mixed wettablility and low matrix permeability which leads to low oil recovery and high remaining oil saturation. Enhanced oil recovery methods such as surfactant-polymer flood (SPF) enhance the recovery by increasing the spontaneous imbibitions either by lowering the interfacial tension or altering the wettability. However, one of the main reasons for failed surfactant-polymer floods is under-estimating the importance of the reservoir especially the description of natural fractures and their effect on recovery. Sensitivity runs were made to compare oil recovery capillary force, buoyancy force and viscous force. The simulation study indicates that critical water saturation should be reached before the start of surfactant-polymer flood to maximize oil recovery and utilize the capillary force. Also, when a surfactant alters the rock wettability, an optimum IFT should be identified for faster and higher imbibitions. The study shows that a contrast in permeability between that of the fracture and that of the matrix will result in a slightly lower oil recovery. Having the fracture perpendicular to the injector producer will result in a higher areal sweep and lower residual oil. A sensitivity study on the effect of the size of surfactant polymer slug was not conclusive. Maximum adsorption capacity was reached which was one of the causes of low imbibitions rate. Following the surfactant-polymer with water flood was able to reverse the adsorption and restore some of the movable oil. The results show that if the enhanced fluid that alter the wettability, imbibed in the matrix, injecting high IFT brine will increase the rate of imbibition. The study calls for further investigation of this phenomenon through research using a scaled laboratory model to verify the simulation results.

The objective of this research was to determine whether the use of polymer compounds with elastic properties can reduce residual oil saturation in porous media below that of brine or inelastic polymerized solutions. One hypothesis is that long-chain polymer molecules experience stress and a resulting strain when they flow through pore throat constrictions. If the fluid residence time in larger pore spaces is insufficient to allow full relaxation, then strain can accumulate. Sufficient strain results in normal forces which can impinge on oil interfaces and potentially mobilize them. A second hypothesis suggests that polymerized solutions can temporarily protect flowing oil filaments from snap off, allowing them to flow longer and de-saturate further than they would otherwise. The approach taken in this thesis was to conduct a series of core floods in several different sandstones using displacement fluids with elasticity ranging from none to those with extremely high relaxation times. Accelerated flow rate was also employed to reduce residence time and maximize the accumulation of elastic strain and normal force potential. Experiments were designed to provide direct comparisons between both non-elastic and elastic floods but also multiple floods with increasing elasticity. The results were inconclusive with some experiments showing additional oil recovery that could be attributed to elastic mechanisms. Most experiments, however, showed no significant difference between elastic and non-elastic floods when experimental parameters were controlled within narrow limits. This research did refine the experimental context in which elastic effects are most likely to be observed. As such, it can serve as a precursor to additional core flooding in oil-wet systems, experiments conducted at reservoir temperature, and those where the pressure gradient of the flood is held constant and the flow rate allowed to vary. Computer aided tomography could also be employed to visualize the mobilization of oil with different displacement fluids, identify where bypassed oil occurs with unstable floods, and determine how oil is subsequently mobilized with better conformance and or elasticity. / text