Integrated physicochemical characterization of a Vaca Muerta paraffinic crude and wax deposits: linking composition, rheology, and thermal behavior

Paraffin deposition is one of the main flow assurance challenges in unconventional reservoirs. Detailed physicochemical characterization of crude oil and their wax fractions is therefore essential to understand deposition behavior and support effective mitigation strategies. This work presents a comprehensive characterization of a Vaca Muerta Formation crude oil (Neuquén Basin) and associated paraffin fractions using complementary rheological, chromatographic, thermal, and spectroscopic techniques. Crude oil was collected at an Early Production Facility (sample Nq-Oil). Paraffin fractions were obtained from (i) an isolated wax fraction of Nq-Oil (P-S), (ii) a production well deposit (P-W), and (iii) a clogged pipeline deposit (P-C). Nq-Oil was analyzed by rotational and
oscillatory rheology, high-temperature gas chromatography with flame ionization detection (HT-GC-FID), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC) to relate flow properties to hydrocarbon distribution and wax crystallization. The HT-GC-FID results of Nq-Oil sample show a chromatographic profile consistent with a highly paraffinic crude, with a substantial series of well-resolved n-paraffins up to C49, and a moderate content of unresolved complex mixture (UCM), suggesting low biodegradation.
Oscillatory rheology evidence that crude oil exhibits a strong temperature dependence, with a crossover of viscoelastic moduli (G’/G’’) at ~22 °C, consistent with wax crystallization. This agrees with a wax appearance temperature (WAT)
of 21°C measured by DSC. Paraffin fractions were further characterized by elemental analysis, Fourier Transform Infrared spectroscopy (FTIR-ATR), Differential Scanning Calorimetry (DSC), Nuclear Magnetic Resonance (¹H and ¹³C NMR), and GC-FID. All waxes exhibit predominantly aliphatic composition with very low aromatic content. Waxes obtained by cold stress test (P-S) display shorter average alkyl chain lengths relative to deposit waxes (P-W and P-C). DSC melting profiles reveal significant differences among paraffin samples, reflecting variations in molecular weight distribution and crystalline order. Overall, these results establish a direct relationship between the paraffinic composition of Nq-Oil, its rheological response, and the thermal behavior of associated waxes, providing key inputs for the development and evaluation of paraffin deposition control strategies in unconventional production systems.