Direct Assessment of Inhibitor and Solvent Effects on the Deposition Mechanism of Asphaltenes in a Brazilian Crude Oil

Abstract

The study of the asphaltene deposition mechanism is critical to understand and solve important problems in the petroleum industry. The same is valid for the selection of inhibitors to control or prevent asphaltene flocculation and/or deposition. However, most of the current information on these processes is obtained by experiments performed using model solvent systems. In the present study, we used quartz crystal microbalance (QCM) measurements as well as laser scanning confocal microscopy to characterize the asphaltene deposition directly measured in a Brazilian crude oil at different conditions of flocculant concentration and using inhibitors with different chemical features. Measurements under accelerated sedimentation (LUMiSizer) were also employed to evaluate inhibitor capacity in crude oil systems, in this case using a large excess of n-heptane. Overall, QCM results suggest that the diffusion-limited aggregation (DLA) model can be used to describe systems close to or above the concentration of the onset of asphaltene precipitation. The transition to a behavior that follows the reaction-limited aggregation (RLA) model occurs when an inhibitor added or the flocculant concentration is reduced farther from the onset. Moreover, accelerated sedimentation shows that the inhibitors tested act by preventing aggregate growth. Therefore, these results highlight the importance of performing time-dependent experiments directly in crude oils and support the use of these methodologies to optimize inhibitor selection for different crude oils.

Recent Developments on the Elucidation of Colloidal Aspects of Asphaltenes and Their Relevance to Oilfield Problems

“…In this sense, the proposition of molecules searches for structures that present acid-base interactions and/or involve steric stabilization. 20,21 Based on the selection of inhibition considering steric stabilization, as early as 1994 Chang and Fogler 15 indicated that the length and shape of the alkyl chain is very important for the additive efficiency, being similar steric interference for the aggregate growth.…”

“…58 In line with this observation, oil + inhibitor systems showed perturbations exclusively in submicron and micrometer size ranges through experiments conducted using a quartz crystal microbalance (QCM) and an analytical centrifuge (LUMiSizer). 21 As an example, results from the LUMiSizer showed that in case of precipitation, the inhibitor acts at the submicrometric scale, avoiding the stacking of nanoaggregates in even larger structures, thus reducing the size of objects by up to an order of magnitude. 21 This result indicates that probably the best starting point for the development of new inhibitors should be to assess the colloidal stability of nanoaggregates.…”

“…21 As an example, results from the LUMiSizer showed that in case of precipitation, the inhibitor acts at the submicrometric scale, avoiding the stacking of nanoaggregates in even larger structures, thus reducing the size of objects by up to an order of magnitude. 21 This result indicates that probably the best starting point for the development of new inhibitors should be to assess the colloidal stability of nanoaggregates. Therefore, the sole concern with specific chemical interactions may fail.…”

“…Reducing flocculant concentration or inhibitor addition at appropriate concentration leads to deposition behavior for RLA adjustment. 21 The authors of this review were also interested in the direct visualization of these aggregates on the colloidal scale, developing a simple methodology employed in an atomic force microscope that can be accessed in detail in the reference. 61 Figure 6 shows a 3D map of a 1 × 1 μm region, indicating spherical morphology of the particles and their nature as individual units.…”

“…These particles appear to grow under certain circumstances (such as the addition of flocculants) that may represent instability conditions in the field and process plants. One key aspect related to their colloidal behavior is the kinetics of their aggregation, 21,53,54,57 that has been not fully considered with respect to experimental studies, regardless of sound evidences supporting its importance. Finally, there are evidences that the performance of inhibitors for asphaltenes aggregation and deposition involves colloidal interactions and not exclusively specific interactions.…”