Asphaltene-asphaltene cohesion on roughened surfaces

Abstract

Challenges of asphaltene deposition continue to profoundly compromise oil production. Partial tool-based cleaning of well columns may leave behind a roughened asphaltene-deposited layer, which, in turn, affects the subsequent asphaltene deposit layers due to enhanced asphaltene spreading. This study determines the cohesive energies between asphaltene particles and asphaltene layers to examine the effect of surface roughness on asphaltene deposition. For doing so, three asphaltene-coated surfaces were prepared: two from asphaltene particles extracted from crude oils of Z-55 and R-95 wells while the third one was from a deposit sample taken from well Z-55. The first two were characterized at smooth and roughened states using a surface energy approach. Key findings reveal that the cohesion of asphaltene on the Z-55-coated surface increased approximately 33-fold with increased surface roughness. On the contrary, the cohesion of asphaltene on the R-95-coated surface decreased by about 192 % with increased surface roughness. Such contradictions can be attributed to differences in the molecular properties of the extracted asphaltenes. The R-95 asphaltene exhibited higher aromaticity (53.9 % vs. 37.5 %) and aromatic hydrogen content (13 % vs. 9 %) compared to Z-55, despite having a lower asphaltene content (3.24 wt% vs. 5.6 wt%). The profoundly greater molecular weight of R-95 (1205.76 g/mol) compared to Z-55 (505.73 g/mol) suggests that R-95 molecules were larger and more complex. This likely leads to less efficient packing on rough surfaces, which explains the observed reduction in deposition propensity. Consequently, the impact of roughness and crude oil properties on asphaltene deposition can be considered as highly interconnected.