An Investigation of the Destabilization, Aggregation, and Deposition of Asphaltenes

Asphaltene;Deposition;Chemical Engineering;Engineering;Chemical Engineering

Vilas Boas Favero, ClaudioLarson, Ronald G ;

University of Michigan

关键词: Asphaltene;    Deposition;    Chemical Engineering;    Engineering;    Chemical Engineering;   

Others  :  https://deepblue.lib.umich.edu/bitstream/handle/2027.42/145912/cfavero_1.pdf?sequence=1&isAllowed=y

瑞士|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Asphaltenes are a class of molecules in crude oil that are soluble in aromatic solvents, such as toluene, and insoluble in n-alkanes, such as heptane. The amount of asphaltenes that is destabilized and the rate of aggregation of the destabilized asphaltenes increases as the volume fraction of n-alkane in oil increases. In the oil field, as pressure of oil decreases there is an increase in the volume fraction of n-alkane, such as methane, causing asphaltenes to destabilize and deposit in the pore space of reservoir and on the walls of pipelines and production equipment. In this dissertation, a mechanistic study of asphaltene deposition as well as investigation on asphaltene destabilization and aggregation are presented. For the first time, experimental results of asphaltene deposition from crude oil of different origins and different chemical compositions were obtained and used to validate the diffusion-limited deposition model. The effect amphiphilic molecules on asphaltene destabilization and deposition was also investigated. The dissolution of solid asphaltenes in solvents were measured and results are briefly discussed.In the study of asphaltene deposition, a new apparatus was designed and built to measure rates of asphaltene deposition. This apparatus consists of a glass column packed with stainless steel beads over which oil-heptane mixture is flown. It was found that only the unstable asphaltenes can form a multi-layer deposit on the surface of the beads. As asphaltene precipitate and grow in size from nano to micro-meter, the micro-meter sized particles tend to flow through the packed bed without depositing. For the case of unstable asphaltenes in the nano-meter size in oil-heptane mixture under Stokes flow, a single deposition mechanism, a diffusion-limited process, is able to explain the deposition of asphaltenes from crude oils of different origins. The validity of deposition mechanism was not verified for other geometries, such as a pipe geometry. Additionally, the diffusion-limited deposition mechanism cannot explain the deposition process observed for inertial flow regime (Re > 1), when the deposition rate decreases as fluid flow velocity increases. Addition of amphiphilic compounds, namely dodecylbenzene sulfonic acid and dodecylphenol, to oil can result in either an increase or decrease of amount of asphaltenes depositing, depending on the crude oil and on the functional group of the amphiphile.The stability of asphaltenes extracted from different crude oils to form model oils was investigated using measurements of asphaltene detection times. The experimental results show that when asphaltenes from different crude oils are fractionated under same conditions, i.e., same heptane concentration and oil-heptane contact time, the model oil of these fractions will have identical detection times curves. These fractions of same detection time curves were found to have different chemical composition in terms of hydrogen, carbon, and nitrogen content. Further characterization of these fractions could help relate asphaltene stability to asphaltene molecular properties and perhaps reveal the mechanism of asphaltene destabilization by n-alkanes. This study of asphaltene destabilization, aggregation and deposition reinforces the concept that there is no such thing as an ;;onset concentration” of asphaltene precipitation.