Browsing by Subject "Flocculation"
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Item Development of a non-isothermal compositional reservoir simulator to model asphaltene precipitation, flocculation, and deposition and remediation(2014-05) Darabi, Hamed; Sepehrnoori, Kamy, 1951-Asphaltene precipitation, flocculation, and deposition in the reservoir and producing wells cause serious damages to the production equipment and possible failure to develop the reservoirs. From the field production prospective, predicting asphaltene precipitation, flocculation, and deposition in the reservoir and wellbore may avoid high expenditures associated with the reservoir remediation, well intervention techniques, and field production interruption. Since asphaltene precipitation, flocculation, and deposition strongly depend on the pressure, temperature, and composition variations (e.g. phase instability due to CO2 injection), it is important to have a model that can track the asphaltene behavior during the entire production system from the injection well to the production well, which is absent in the literature. Due to economic concerns for asphaltene related problems, companies spend a lot of money to design their own asphaltene inhibition and remediation procedures. However, due to the complexity and the lack of knowledge on the asphaltene problems, these asphaltene inhibition and remediation programs are not always successful. Near-wellbore asphaltene inhibition and remediation techniques can be divided into two categories: changing operating conditions, and chemical treatment of the reservoir. Although, the field applications of these procedures are discussed in the literature, a dynamic model that can handle asphaltene inhibition and remediation in the reservoir is missing. In this dissertation, a comprehensive non-isothermal compositional reservoir simulator with the capability of modeling near-wellbore asphaltene inhibition and remediation is developed to address the effect of asphaltene deposition on the reservoir performance. This simulator has many additional features compared to the available asphaltene reservoir simulators. We are able to model asphaltene behavior during primary, secondary, and EOR stages. A new approach is presented to model asphaltene precipitation and flocculation. Adsorption, entrainment, and pore-throat plugging are considered as the main mechanisms of the asphaltene deposition. Moreover, we consider porosity, absolute permeability, and oil viscosity reductions due to asphaltene. It is well known that the asphaltene deposition on the rock surface changes the wettability of the rock towards oil-wet condition. Although many experiments in the literature have been conducted to understand the physics underlying wettability alteration due to asphaltene deposition, a comprehensive mathematical model describing this phenomenon is absent. Based on the available experimental data, a wettability alteration model due to asphaltene deposition is proposed and implemented into the simulator. Furthermore, the reservoir simulator is coupled to a wellbore simulator to model asphaltene deposition in the entire production system, from the injection well to the production well. The coupled reservoir/wellbore model can be used to track asphaltene deposition, to diagnose the potential of asphaltene problems in the wellbore and reservoir, and to find the optimum operating conditions of the well that minimizes asphaltene problems. In addition, the simulator is capable of modeling near-wellbore asphaltene remediation using chemical treatment. Based on the mechanisms of the asphaltene-dispersant interactions, a dynamic modeling approach for the near-wellbore asphaltene chemical treatments is proposed and implemented in the simulator. Using the dynamic asphaltene remediation model, we can optimize the asphaltene treatment plan to reduce asphaltene related problems in a field. The results of our simulations show that asphaltene precipitation, flocculation, and deposition in the reservoir and wellbore are dynamic processes. Many parameters, such as oil velocity, wettability alteration, pressure, temperature, and composition variations influence the trend of these processes. In the simulation test cases, we observe that asphaltene precipitation, flocculation, and deposition can occur in primary production, secondary production, or EOR stages. In addition, our results show that the wettability alteration has the major effect on the performance of the reservoir, comparing to the permeability reduction. During CO2 flooding, asphaltene precipitation occurs mostly at the front, and asphaltene deposition is at its maximum close to the reservoir boundaries where the front velocity is at its minimum. In addition, the results of the coupled reservoir/wellbore simulator show that the behavior of asphaltene in the wellbore and reservoir are fully coupled with each other. Therefore, a standalone reservoir or wellbore simulator is not able to predict the asphaltene behavior properly in the entire system. Finally, we show that the efficiency of an asphaltene chemical treatment plan depends on the type of dispersant, amount of dispersant, soaking time, number of treatment jobs, and the time period between two treatment jobs.Item Highly supersaturated aqueous solutions by design of amorphous pharmaceutical nanoparticles(2007-12) Matteucci, Michal Elizabeth, 1977-; Johnston, Keith P., 1955-; Williams, Robert O., 1956-For 40% of currently discovered drugs which are poorly water soluble, engineering amorphous nanoparticles with rapid dissolution and enhanced solubility can improve their absorption. Antisolvent precipitation by mixing organic drug solutions with aqueous solutions produced sub-300 nm amorphous nanoparticle dispersions. Polymeric stabilizers increased the nucleation rate by lowering the interfacial tension and adsorbed to particle surfaces to inhibit growth by condensation and coagulation. An increase in the stabilizer concentration decreased the average particle size until reaching a threshold where the particles were < 300 nm for the poorly water soluble drug, itraconazole. The amorphous itraconazole nanoparticle dispersions dissolved at pH 1.2 to produce high supersaturation levels up to 90-times the equilibrium solubility. The supersaturation increased with particle curvature, as described qualitatively by the Kelvin equation. A thermodynamic analysis indicated the stabilizer maintained amorphous ITZ in the solid phase with a fugacity 90-times the crystalline value, while it did not influence the activity coefficient of ITZ in the aqueous phase. Recovery of the amorphous nanoparticles from water was achieved by adding salt to desolvate the polymeric stabilizers and flocculate the particles, which could then be rapidly filtered. The flocculation under constant particle volume fraction produced open flocs which were redispersible in water to their original ~300 nm size, after filtration and drying. Amorphous particles were preserved, as flocs were formed below the drug's glass transition temperature. After flocculation/filtration, medium surface area (2-5 m²/g) particles dissolved rapidly in pH 6.8 buffer with 0.17% surfactant to an unusually large supersaturation up to 17, comparable to that for high surface area (13-36 m²/g) particles. However, the decay in supersaturation was much slower for the medium surface area particles, as the smaller excess surface area of undissolved particles produced slower nucleation and growth from solution. In contrast, the maximum supersaturation was far lower for more conventional low surface area solid dispersions of drug in polymers, because of crystallization of undissolved solid during slow dissolution. The ability to design the particle morphology to manipulate the level in supersaturation in pH 6.8 media, offers new opportunities in raising bioavailability in gastrointestinal delivery.Item pH-induced flocculation/deflocculation process for harvesting microalgae from water(2014-08) Choi, Jin-Yong, Ph. D.; Kinney, Kerry A.; Katz, Lynn Ellen; Kinney, Kerry A.; Katz, Lynn E.Historically, the presence of microalgae (algae hereafter) in natural waters has been viewed as a nuisance due to its adverse impact on water quality. More recently, however, algae are being investigated as potential sources of biofuel and a range of natural products. These applications require the development of large-scale cultivation systems for mass production that include growth, harvesting, concentration, and product recovery components. While challenges still remain with respect to many of the processes involved in mass production, one of the most technically and economically challenging steps is harvesting the algae from dilute growth cultures, especially in systems where chemical additives are of concern either within the algae concentrate or the effluent water. For this reason, a pH-induced flocculation/deflocculation method using the hydroxides of alkali or alkaline earth metals (e.g., lime, caustic soda) is of particular interest for algae harvesting as Na, Ca and Mg are typically present in natural waters. The goal of this research was to determine the underlying mechanisms responsible for algae coagulation by magnesium and calcium and to evaluate the potential of these mechanisms for harvesting algae for a range of synthetic and field source water chemistries. In the first two phases of this research, the mechanisms for coagulation with magnesium and calcium were studied independently. A series of bench-scale experiments were designed to isolate the potential mechanisms of algae destabilization associated with each of these cations as a function of water chemistry, and microscopic analyses were performed to characterize the flocculated algae/precipitate mixtures. In the third phase of this research, removal of algae in field source waters was evaluated with respect to the underlying science elucidated in the previous phases. The results indicate that the dominant algae destabilization mechanism associated with magnesium shifts from Mg adsorption/charge neutralization to Mg(OH)₂[subscript (S)] precipitation-enhanced coagulation with increasing pH. Moreover, dissolved Mg²⁺ adsorption to the algae surface led to effective algae coagulation, while minimizing the mass of precipitated Mg(OH)₂[subscript (S)] . For Ca, this research identified the importance of the nucleation process (heterogeneous vs. homogeneous nucleation) on algae removal efficiency. Heterogeneous nucleation is a key factor for optimizing algae removal; thus, the degree of oversaturation with respect to CaCO₃[subscript (S)] is a crucial operating parameter. This research demonstrated that the algae harvesting process using pH-induced flocculation/deflocculation method can be optimized for a wide range of source waters if the water chemistry (e.g. pH, ion concentration, alkalinity, ionic strength) is properly incorporated into the system design.Item Quantitative understanding of nanoparticle flocculation in water treatment(2017-05-03) Youn, Sungmin; Lawler, Desmond F.; Katz, Lynn E; Liljestrand, Howard M; Saleh, Navid; Sepehrnoori, KamyFlocculation is critical in drinking water treatment; in flocculation, the particle size distribution changes from a large number of small particles to a small number of larger particles. Larger particles are effectively removed by settling and filtration processes that follow flocculation. In recent years, manufacturing of engineered nanoparticles has skyrocketed, and these nanoparticles can enter our water supplies, but knowledge of their fate in water treatment is limited. The objective of this research was to update knowledge of flocculation by extending previous work at the microscale to the nanoscale. Flocculation involves transport of particles to the vicinity of one another and subsequent attachment if interactions at close distances are favorable. Transport and possible collisions are brought about by Brownian motion, differential sedimentation, and fluid shear; these processes, even at the nanoscale, are well understood. Whether collisions and attachment actually occur, however, depend on a balance of hydrodynamic interactions, van der Waals attraction, and electrostatic repulsion; this research quantitatively assessed, for the first time, this balance for collisions of nanoparticles by all three collision mechanisms using a well-established trajectory analysis approach. The collision efficiency (α) is the ratio of the number of successful collisions (attachment) to the number of collisions predicted by the transport equations. The analysis was performed with and without electrostatic repulsion, which occurs if particles are charged. In all cases, Brownian motion was the dominant flocculation mechanism. However, without electrostatic repulsion, differential sedimentation and fluid shear were found to be far more important than heretofore expected because the α value can be substantially higher than one, contrary to all previous understanding. With electrostatic repulsion, collisions by these two mechanisms were found to occur only if the particles are substantially different in size. Experiments in which the changes in particle size distributions of nanoparticles were carefully monitored were also performed, and the results compared to the mathematical predictions. Although not perfect, excellent agreement between the measured and predicted particle size distributions was found. The conclusion is optimistic: if nanoparticles are properly destabilized to reduce or eliminate surface charge, they will be well removed in conventional water treatment plants.Item Reducing turbidity of construction site runoff via coagulation with polyacrylamide and chitosan(2012-05) Rounce, David Robert; Lawler, Desmond F.; Barrett, Michael E.The U.S. Environmental Protection Agency is in the process of developing a nationwide standard for turbidity in construction site runoff. It is widely expected that this standard cannot be met with conventional erosion and sediment control measures; consequently, innovative practices for managing sediment on construction sites must be developed. The objective of this research was to develop an understanding of how soil characteristics and polymer properties affect the amount of turbidity reduction that can be achieved through flocculation. The polymers used were PAMs, a proprietary product, and chitosan. The charge density of the PAMs ranged from 0% to 50% and the molecular weights ranged from 0.2 to 14 Mg/mol. A protocol for creating modified synthetic stormwater runoff for soil samples was developed and used on soils from seven construction sites. Particle size distributions were used to compare the modified synthetic stormwater runoff with grab samples of stormwater from one site and showed the synthetic runoff was representative of the actual runoff. Flocculation tests were performed on the synthetic runoffs with PAM and chitosan doses from 0.03 to 10 mg/L. The non-ionic PAM, proprietary product, and chitosan were found to be the most effective at reducing the turbidity of all the synthetic runoff below 200 NTU. The high molecular weight anionic PAMs were effective on only two of the seven synthetic runoff samples. Hardness tests were performed indicating interparticle bridging to be the bonding mechanism of the PAM. Electrophoretic mobility tests were performed on two of the soil suspensions and indicated the bonding mechanism of PAM to be interparticle bridging, and the bonding mechanism of chitosan to be a combination of charge neutralization and interparticle bridging. Tests showed as the charge density of the PAM increased, their effectiveness decreased.Item Simulation of asphaltene deposition during CO₂ flooding(2011-08) Al Qasim, Abdulaziz Salem; Sepehrnoori, Kamy, 1951-; Kalaei, Hosein M.; Sepehrnoori, Kamy, 1951-This Thesis presents the results of phase behavior calculations and simulation of asphaltene precipitation, flocculation, and deposition in five Middle-Eastern wells from different fields, based on a reliable experimental data provided for this purpose. The asphaltene precipitation, flocculation, and deposition have been simulated throughout the primary (pressure depletion), secondary (Waterflooding) and tertiary recovery (CO₂ injection) stages. Asphaltene precipitation becomes a serious problem especially when it causes plugging of the formation, wellbore, or production facilities, which will significantly affect the productivity and final recovery of the area. To help preventing asphaltene precipitation a bottomhole pressure higher than the asphaltene onset pressure (AOP) has been applied. Also, water and CO₂ injection has provided enough support for pressure maintenance, which helps in preventing asphaltene. Several scenarios were tested to investigate and identify the cases with lowest asphaltene precipitation and higher recovery. It has been considered obligatory to have a representative numerical simulation model that can predict the phase behavior of asphaltene precipitation, flocculation, and deposition accurately. The first part of this thesis includes a comprehensive literature review of asphaltene precipitation flocculation, and deposition that include asphaltene structure, models and prevention techniques. The second part of the thesis includes a detailed study of modeling asphaltene precipitation phase behavior utilizing experimental and real field data obtained from five Middle-Eastern wells from different fields. Experimental data include measurements of asphaltene onset pressure (AOP), saturation pressure, and PVT data. Asphaltene precipitation was modeled by using WinProp (a phase behavior utility from CMG) which uses Nghiem solid model. Saturation pressures, PVT, and AOP data were used to match Peng-Robinson EOS and the precipitation model was matched by the experimental data of AOP. The third part of the thesis includes a one-dimensional simulation comparison study of asphaltene precipitation between three different compositional simulators; UTCOMP, ECLIPSE and CMG/GEM. The last part of the thesis includes a full field scale study based on a heterogeneous three-dimensional cartesian single-well model. The objective of this study was to assess the effect of asphaltene precipitation, flocculation, and deposition in the well productivity and the economic impacts related to it. Different production practices were applied to define the most appropriate and efficient production strategy. This study includes a discussion and comparison of production rates with and without asphaltene precipitation, flocculation, and deposition and a comparison of asphaltene precipitation, flocculation, and deposition at different times using different bottomhole and production rate constraints. Several cases (i.e., WAG cycles, completion, target layers of injection, etc.) will be tested to come up with the optimum completion and operating strategy in the presences asphaltene. Despite the work devoted to understanding this subject, asphaltene still represents a challenging and unresolved problem. This thesis will help bridge the gap of this limited understanding in the field of asphaltene.