a b s t r a c tAsphaltene precipitation and subsequent deposition is a potential flow assurance problem for the oil industry nowadays. Moreover, because oil production is moving to more difficult production environments -e.g. deeper waters -or is focusing on extracting residual oil using enhanced oil recovery techniques, the significant changes of pressure, temperature and/or composition can aggravate the asphaltene deposition problems. One of the most common strategies to prevent or at least reduce asphaltene deposition is the utilization of chemical additives. However, there are still several unresolved challenges associated to the utilization of these chemicals: First, the experimental conditions and results obtained in the lab are not always consistent with the field observations. Also, in some cases these chemical additives seem to worsen the deposition problem in the field. Therefore, there is a clear need to revisit the commercial techniques that are used to test the performance of asphaltene inhibitors and to provide a better interpretation of the results obtained. In this work, a technique based on NIR spectroscopy is presented to evaluate the performance of three commercial asphaltene dispersants. The method presented in this work is faster and more reproducible compared to the available methods such as the Asphaltene Dispersion Test (ADT) and the Solid Detection System (SDS). Also, unlike the ADT test, our proposed method can evaluate the performance of the dispersants in a wide range of temperatures and compositions. The experimental evidence shows that the asphaltene dispersants neither shift the actual onset of asphaltene precipitation nor reduce the amount of asphaltene precipitated. We believe that some results that have been reported that suggest that asphaltene dispersants can actually shift the onset of asphaltene precipitation are an unfortunate combination of insufficient sensitivity of the commercial instruments used and the slowing down of the asphaltene aggregation process by the effect of the added dispersants. The chemical additive dosage, aging time and temperature effect on the asphaltene aggregation process are also discussed in this manuscript.With this work we aim to contribute to a better understanding of the variables that affect the performance of asphaltene dispersants, and the effect that these chemicals have on the complex multi-step mechanism of asphaltene precipitation and aggregation.

Asphaltene precipitation and subsequent deposition is a potential problem in oil production because the significant costs for wellbore cleaning and the associated production loss. To better understand the mechanisms by which asphaltenes precipitate and deposit, in this work we present experimental evidence that supports the idea that precipitation and aggregation of asphaltenes is a multi-step process, where the former is driven primarily by thermodynamics whereas the latter is driven by kinetics. Under this multi-step mechanism, asphaltene precipitation is a fully reversible process. On the other hand, from the precipitated phase, subsequent aggregation and aging leads to the formation of more solid-like structures. Furthermore, we also present experimental results that suggest that the currently available commercial technologies to detect asphaltene precipitation (i.e. NIR spectroscopy and High Pressure Microscopy) might not be appropriate to detect the exact point of asphaltene precipitation, but instead they give a combined reading of precipitation plus aggregation. For this reason, the results obtained using these methods are very sensitive to the depressurization rates. The better understanding of the asphaltene behavior has enabled the development of an enhanced modeling approach based on the Perturbed Chain version of the Statistical Associating Fluid Theory equation of state (PC-SAFT EOS), which is used to predict the precipitation of asphaltenes at reservoir conditions and requires fewer simulation parameters than previous methods. A case study is presented in which our modeling technique was proven useful for the detection and correction of inconsistencies in experiments done using a bottom-hole sample at reservoir conditions.

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Microscopy in a vertical capillary provided the ability to continuously observe the dynamic particle phenomena on microscopic objects levitated by an imposed flow. Such a technique was developed and used to monitor flow-levitated droplets, by manually regulating the imposed flow so as to keep the droplets suspended in the area of view. Local sudden increases and decreases in temperature were achieved with an external heating filament, which produced rapid changes in the fluids' properties (viscosity and density). Even in such cases it was possible to control the levitated drop's position in the microscope's field of vision by adjusting the levitating fluid's vertical flow. The shrinkage and alteration of levitated acid drops that react with the basic nanoparticles of levitating oil, verified that, when compared to static conditions, fluid flow significantly accelerated the neutralization of the acid drop by the oil's basic nanoparticles. Allowing droplets to levitate and rotate due to the flow of another fluid in high-temperature regions, this technique may be used as an improved way to mix contents in suspended microscopic droplets.

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