Inhibitor-Wax Interactions and Wax Crystallization: New Experimental Approaches and Techniques

Abstract

Issues related to wax crystallization are one of the major challenges faced during crude oil production. Wax inhibitors and pour point depressants (PPD) are in common use for wax prevention, as they can delay gelling and ensure low enough crude oil viscosity even after wax precipitation. Understanding underlying phenomena is therefore paramount for successful wax control.

This thesis has consequently been dedicated to (i) new procedures and techniques for investigating wax crystallization and inhibition, and (ii) application of these for a better understanding of inhibitor‑wax interactions. Extensive experimental work was performed to introduce or improve methodologies that enable:

(1) More accurate assessment of WAT from experimental data.

(2) Expanding research on inhibitor‑wax interactions via the use of isothermal titration calorimetry (ITC), nuclear magnetic resonance (NMR) spectroscopy, and gas chromatography (GC).

(3) Fractionation of asphaltenes or wax inhibitors into groups with more distinct properties.

Results indicate that ITC technique is suitable for qualitative studies only, but procedures developed for NMR and GC could reflect inhibitor efficiency to some extent. The effect of asphaltene or inhibitor characteristics on wax crystallization was studied via fractionation procedures, but corresponding procedures could also be used for other applications. The results in this thesis match the common perception that inhibitors act by affecting wax nucleation, wax crystal morphology, and wax solubility. In addition, wax inhibitors were shown to differ in interaction strength and to influence wax precipitation, compositional changes, and liquid wax mobility.