Abstract
Recent studies revealed that field deposits collected from production tubing of offshore wells often exhibit compositional varieties pointing to a more complex fouling process under field operations than original predictions purely based on asphaltene instability. Asphaltenes are estimated to constitute only 50 - 60% of total field deposit. The objective of this work was to understand the strong affinity between paraffin wax and asphaltenes resulting in co-precipitation of "waxphaltenes" and their impact on overall Asphaltene Inhibitor (AI) performance efficiency. This approach allows more objective and reliable product development and recommendation strategy to be adopted for offshore production with flow assurance management challenges caused by waxphaltenes deposition.
Routine screenings and initial chemical treatments were found unsuccessful and not reliable for samples received from offshore deep-water fields. In this study, the oil sample was fully characterized though Fourier Transform InfraRed (FTIR) spectroscopy and High Temperature Gas Chromatography (HTGC). A series of dispersion and deposition tests were then conducted in order to identify potential chemistries for treatment. Dispersion testing was mainly carried out using Asphaltene Differential Aggregation Probe Test (ADAPT) technique, whereas deposition tests were conducted on a customized Asphaltene Dynamic Deposition Loop (ADDL) test. Crude oil characterization indicated presence of unstable asphaltene fraction within the analyzed crude oil sample. Dispersion efficiency with different asphaltene inhibitors revealed possible co-precipitation issue of other crude oil solubility fractions. Futher characterization analyses highlighted heavier paraffinic components to have very high affinity towards the asphaltene clusters and creating waxphaltene precipitation issue. Efficiency of traditional asphaltene inhibitor chemistries were observed to not perform well for waxphaltene deposition. Imporvement in the chemical treatment program and product development based on the knowledge obtained through this work resulted in better inhibitor formulation. The deposition test results using the improved inhibitor chemistry was tested on ADDL and showed better performance than the traditional asphaltene inhibitor.
The new approach presents a unique opportunity to revisit the way product development is performed allowing chemical treatment strategy to be adopted and aligned based on actual deposit characteristics. Findings from this work shed light for more innovation in methods and products to tackle unforeseen waxphaltene deposition in offshore production systems.
