Managing Stealth Asphaltene Flow Assurance Potential Risk in Gas Injection Field Based on Data Science Using Over 20 years Accumulated Dataset

Abstract

Gas injection into oil field is generally recognized to bring not only oil recovery improvement but also asphaltene destabilizing risks. Fortunately, a subject field has not caused any asphaltene-induced production deterioration in two main producing reservoirs during long term lean hydrocarbon gas injection. However, the recent first discovery of asphaltene deposits from the historical no-issued area in the field motivated us to do an immediate investigation for evaluating how critical risks might lurk and considering appropriate mitigation. The field has been applying pressure maintenance of peripheral powered sea water injection with the crestal lean hydrocarbon gas injection for two decades creating secondary gas cap surrounded by high GOR area. The first asphaltene deposits were observed from a producer near high but stable GOR area in the upper reservoir. Through the analysis of single phase bottomhole fluid from a similar positional relationship well near GOC in the lower reservoir, asphaltene precipitation behavior was investigated. The sample contained 0.1 wt% asphaltene with high colloidal instability index. Asphaltene onset was detected from lean hydrocarbon gas mixed-fluid using laser light scattering technique; however, the visual measurement using high pressure microscopy (minimum detection=1 μm) could not detect any asphaltene particles. This result implied that the gas injection causes asphaltene precipitation obviously but no aggregation leading deterioration of oil production. Namely, the precipitated but invisible asphaltenes can be still flowable. This stealth asphaltene behavior could well explain a possible mechanism of the first asphaltene observation in the upper reservoir. In the high GOR area, the stealth asphaltenes are precipitated and then flowed towards the asphaltene-observed well. After a certain amount of stealth asphaltene accumulation, the detectable deposits were finally observed. Since this mechanism might have possibility to expand, several mitigations were discussed for a future possible conservative scenario even keeping asphaltene problem-free production at this moment.