Asphaltene Flow Assurance Risks: How Are Pitfalls Brought into the Open?

Abstract

Four case studies involving asphaltene precipitation risks in oilfields are used to demonstrate how pitfalls can be minimized by multidisciplinary approach using all available information. Three cases are presented from a gas injection aspect and the fourth from a geochemical aspect under conditions of uneven asphaltene risk distribution. The evaluations show how to practically interpret laboratory-derived information with regard to actual on-site phenomena. Numerical asphaltene fluid models calibrated using measured asphaltene onset pressure (AOP) were generated to evaluate asphaltene precipitation envelopes (APE) by applying the cubic plus association equation of state. Sensitivity analysis based on the numerical model was performed in each study to investigate the impact of development scenario on APE behavior. The case studies cover a range of technical subjects, including injection gas type, gas mixing ratio, fluid dynamics such as the vaporizing gas drive (VGD) process, and local variation of asphaltene contents. These technical subjects pose potential pitfalls that may be hidden from the viewpoint of a single discipline. The results successfully reveal the following insights: (1) risks offset by dry gas can be considered whereas a general understanding is required of gas injection-related risks; (2) VGD-process enrichment of the injection gas should be considered; (3) asphaltene risks can vary with the fluid dynamics timing, such as higher enriched gas accumulation and lower lean gas accumulation near wellbore; (4) a pseudo APE concept can be useful in the absence of experimental AOP data; and (5) oil migration history can be related to asphaltene risk distribution.

Graphical Abstract