Frequency‑dependent microwave absorption of crude oil correlated with FTIR‑derived structural indices and asphaltene fraction

This study presents a correlation-based analytical approach to understand crude oil microwave absorption, focusing on the asphaltene fraction. Loss tangent and FTIR analyses were performed on seven crude oils and their asphaltene fraction at 1, 2.45, and 5 GHz. Microwave absorption is strongly frequency‑dependent, with crude oil sample B showing an exceptionally high loss tangent at 2.45 GHz ( \\(\\:\\text{t}\\text{a}\\text{n}{\\updelta\\:}\\:=\\:0.2099\\) ). However, the correlation between crude oil and asphaltene loss tangent was weak at all frequencies ( \\(\\:\\text{r}\\:\\le\\:\\:0.1667\\) ), indicating that asphaltene dielectric behavior does not directly govern the bulk oil response. FTIR indices show associations with dielectric behavior, with LCI highest in crude oil (0.5551) and SAC in asphaltene (0.2617). Due to small sample size ( \\(\\:\\text{n}\\:=\\:7\\) ), most correlations were not significant ( \\(\\:\\text{p}\\:>\\:0.05\\) ). Linear regression between asphaltene content and loss tangent revealed weak correlations ( \\(\\:\\text{r}\\:\\le\\:\\:0.1320\\) , \\(\\:R^{2} \\: \\le \\:\\:0.0174\\) , \\(\\:\\text{p}\\:>\\:0.05\\) ) at all frequencies, suggesting asphaltene alone is not a reliable predictor. No significant relationship was found at 1 and 2.45 GHz, except at 5 GHz a strong correlation exists. Thus, asphaltene does not appear to dominate across all frequencies; other components (saturates, aromatics, resins, polar hydrocarbons) may contribute.