On the evaluation of the performance of asphaltene dispersants
Asphaltene 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 with 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 an 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.