Asphaltene inhibitor performance as a function of the asphaltene molecular/aggregate characteristics: Evaluation by interfacial rheology measurement and bulk methods

Abstract

Asphaltene precipitation/deposition in well tubing and porous media is categorized as asphaltene damage. Addressing this issue, this study offers an asphaltene inhibitor (namely BZSS-012) and highlights the mutual dependence of the inhibitor-asphaltene molecular structure/functional groups for a successful inhibition performance. Asphaltenes were extracted from two dead oil samples, designated as A- and F- oil, characterized well and dissolved in n-hexane/toluene mixture to prepare A- and F-model oil. Interfacial rheology measurements, in addition to conventional asphaltene dispersant test (ADT), was introduced as a new test approach to evaluate the inhibitor performance. The dynamic interfacial tension (IFT) and dilational elasticity of the model oils-water interface were measured. In addition, the standard deviation from the Young-Laplace drop shape (YL-STD) during a high-amplitude compression-expansion of the interface was calculated. Compared to the F-asphaltene, the A-asphaltene molecules have a larger aromatic sheet size, shorter peripheral chains, higher heteroatom content, and higher density of hydroxyl groups, leading to a higher self-association tendency. However, the aggregates size of the F-asphaltene is larger than that of the A-asphaltene in the model oil. Despite its larger aggregates, the F-asphaltene has an enough extent and strength of interactions with the inhibitor, leading to the efficiency of 99.2% in the ADT test, much higher than 66.7% efficiency for the A-model oil. In addition, compared to the A-model oil, the F-model oil exhibits lower IFT values with a slower dynamic in-line with the F-asphaltene larger aggregates and revealing their outward functional groups. The addition of the inhibitor accelerates the dynamic of the IFT and results in lower IFT values. No sharp peak in the YL-STD of the F-model oil dosed with 50 ppmv of the inhibitor is observed. This reflects the inhibitor efficiency for controlling the association and networking of the asphaltene aggregates to inhibit interfacial asphaltenic film evolution. Monitoring the YL-STD seems to be an appropriate method to screen asphaltene inhibitors.