Emerging Numerical-Modeling Technique To Evaluate Asphaltene-Inhibitor Efficiency During Entire Field Life

Abstract

Summary This work sought to establish a robust asphaltene flow-assurance engineering with asphaltene inhibitor to mitigate the risk of asphaltene precipitation in tubing. For this purpose, the best candidate was selected through the asphaltene dispersant test (ADT). Furthermore, its inhibiting efficiency was evaluated by generating a numerical model. The purpose of this evaluation was to predict how its efficiency varied during entire field life in which production conditions changed in early and late life. Through the two-stage ADT, the best inhibitor IB-23 was selected from a total of nineteen samples. The IB-23 revealed a high inhibiting efficiency of more than 80% at 200 ppm concentration, and maintained its efficiency more than 70% even at 10 ppm. Currently, any commercial software is not available for the modeling of asphaltene inhibitor caused by confidentiality for inhibitor physical data. This study achieved modeling of inhibiting efficiency by treating an inhibitor as a pseudoresin and/or pseudocomponent. It could be defined with limited physical data that were available in a publicly accessible material-safety data sheet (MSDS). The numerical model was generated with a cubic-plus-association (CPA) equation of state (EOS) together with the conventional fluid characterization to characterize the asphaltene crudes. This paper demonstrates that the numerical model expressed the inhibiting efficiency as a size-reduction of asphaltene-precipitation envelope (APE) and a decrease in the amount of asphaltene precipitated. The model validity was checked by comparing with experimentally measured weight data of asphaltene deposits during the ADT. Assuming natural depletion, the APEs were compared with a variation of vertical lifting curves (VLCs) in tubing. Two VLCs were assumed to represent early and late field conditions (i.e., high wellhead/reservoir pressures and depleted ones). The no-inhibitor case revealed that precipitating risk existed over most of the tubing section. In contrast, the inhibitor-dosed case could significantly reduce the risks in the early stage in particular. Even in the late stage, the risks could be minimized because the interception of VLC on the APE became shorter than that of the no-inhibitor case. Asphaltene inhibitor is a typical countermeasure; however, most of the applications offer only temporary relief. Through an entire field life, the production conditions vary such as pressure decline, gas/oil ratio (GOR) increase, and others. Accordingly, the efficiency of the inhibitor, initially selected as the best, fades away. Then, another screening would be required to select an alternative one that can adapt effectiveness to the new operating condition. This paper contributes to estimating its inhibiting efficiency during a whole field life.