Asphaltene Studies in On-shore Abu Dhabi Oil Fields, PART II: Investigation and Mitigation of Asphaltene Deposition - A Case Study

Abstract

Abstract Asphaltene is the heavy component of a crude oil that constitutes a potential problem because of its tendency to precipitate and deposit causing blockage in tubulars, pipelines and surface facilities leading to decline in oil production. There are a number of wells affected with asphaltene in an onshore field in Abu Dhabi and this is likely to increase in the future with the implementation of Artificial Lift (AL) and HC/CO2 gas injection for EOR. Mitigation strategies in the field have been concentrating on design of remedial solvent treatments in combination with mechanical methods for removal of deposits. The company’s approach has been shifting in dealing with asphaltenes from reactive to proactive by conducting studies to: understand asphaltene stability in the different fluids, model the behavior across the whole field, look at the effect of HC/CO2 gas injection on asphaltene stability and finally develop optimal preventative techniques to reduce treatment costs. The study in this onshore field in Abu Dhabi was conducted on oils collected from different zones. The first part of the study involved analysis of different stock tank oil properties, e.g. API, Sulfur content, Nickel content, asphaltene content and viscosity to look for correlations that can help in identifying the problematic areas in the field. The second part of the study involved asphaltene stability screening tests, e.g. SARA screen, to determine whether the fluids from the different zones are stable or unstable with respect to asphaltene. Live-oil depressurization experiments were conducted on selected wells to determine the Asphaltene Onset Pressure (AOP) at different production conditions using solids detection system with Near Infra-Red (NIR) and High Pressure Microscopy (HPM) for visual confirmation of asphaltene particles. The data from the live-oil testing was then used to calibrate Shell’s thermodynamic model which was then used to investigate the effect of changes in process conditions on asphaltene stability phase envelopes. Results of thermodynamic modeling can be applied on the full field which will aid in developing appropriate inhibition and remediation strategies to deal with the asphaltene challenges.