Understanding Asphaltene Precipitation Dynamics in Flow Assurance Risk Management of an Offshore Field in Abu Dhabi

Abstract

Asphaltenes are polyaromatic fractions of crude oil that can precipitate due to temperature, pressure, or composition changes inherent in oil recovery processes. In Field A, the precipitation and deposition of asphaltenes at various points along the production path poses challenges: deposition in tubing blocks well access, while deposition in multi-phase flowmeters leads to inaccurate readings. Furthermore, precipitation can lead to facilities process upset. Understanding and managing asphaltene behavior is crucial for efficient and profitable operations. The insights of a flow assurance evaluation including asphaltene evaluation were integrated with additional analysis for de-risking purposes. The study involved a comprehensive approach from bottom hole sampling to asphaltene phase diagram (P-T) by measuring saturation and Asphaltene Onset Pressures (AOP) at different temperatures. High-pressure microscopy (HPM) was used to understand asphaltene deposition particles' morphological characteristics. The amount of asphaltenes precipitated was determined through a high-pressure filtration system. The effects of hydrocarbon gas injection on reservoir fluids were also investigated in the laboratory, using the same technique to establish the AOP with Pressure-Gas Concentration diagram (P-X). The initial validation analysis showed that the collected bottom hole samples were representative of PVT behavior and reservoir fluid composition. However, high variability in asphaltene precipitation behavior was observed due to different sampling techniques. Asphaltene was detected in the reservoir fluid at lower temperatures during the isothermal depressurization experiment and in hydrocarbon gas injections at different temperatures. Asphaltene particle size distributions were quantified through statistical image analysis. Bottom hole sampling technique with a nitrogen chamber for pressure compensation was the most suitable for asphaltene samples, as the likelihood of asphaltene precipitation increases with higher hydrocarbon gas concentrations and lower temperatures. Analyzing asphaltene behavior, using single-phase samples providing critical insights for accurate AOP data, helps operators to take preventive measures to avoid costly downtime. In Field A, suitable well intervention procedures were developed for wells where asphaltene precipitation is predicted, while pro-active solvent flushing schedules were implemented in multi-phase flowmeters to ensure accurate readings. Similarly, facility design was adapted, and operational procedures implemented to smoothly handle precipitated asphaltenes. Accurate assessment of asphaltene onset pressure is crucial for managing flow assurance risk in offshore oil fields. It helps operators devise strategies to maintain uninterrupted oil production and mitigate risks associated with deposition and blockages along the entire oil production path. Accurate assessment of asphaltene onset pressure is essential for maximizing operational efficiency and minimizing downtime.