Flow Assurance Testing with Re-Livened Oil: A Cost-Effective Analogue for Live Oil

Abstract

It is widely accepted that live crude oil samples provide the most field representative fluids when investigating asphaltenes and paraffin wax problems in laboratory testing. However, this approach is limited by availability of live samples and the potential that samples collected during drilling will be insufficiently representative due to contamination. This paper demonstrates that re-livened oil comprising dead oil and just 1 or 2 solvents can be an acceptable replacement where live oil of sufficient quality is not available. We outline a best-of-both approach: using readily available dead oil but replacing the volatile ends with components that reproduce much of the solvating and phase behaviour of live oil, and where they differ from it, they do so in a predictable manner, which can be readily modelled using an equation of state (EoS) simulator. This avoids the expense and time required to restore the oil to a precise replica of live fluid while still generating laboratory data to increase confidence in predictions for the actual live oil composition generated by the EoS software. Illustrative examples are given to demonstrate different ways in which re-livened oil can be designed to mimic key features of live oil behaviour, and any differences can be modelled. Wax appearance measurements were made for re-livened oil and used to calibrate an EoS model. When used to simulate data for a live oil, the calibrated model gave excellent agreement with field data. Subsequently, deposition tests were carried out with re-livened oil and used to qualify a wax inhibitor for subsea application. Measurement of the Asphaltenes Onset Pressure (AOP) for re-livened oil was used to tune the EoS model for the analogous live oil, yielding predictions of the asphaltenes precipitation envelope (APE) that were consistent with those obtained using the live oil. This illustrates that live oil may not always be necessary to obtain a reliable APE, especially when the only live oil samples are of questionable quality. Solubility theory was applied to the selection of conditions for asphaltenes flow-loop deposition, wherein a precipitant is added to dead oil to induce deposition. This approach can determine both the identity and correct proportion of a suitable precipitant to simulate conditions close to the bubble point where deposition commonly occurs. Our work shows how experimental results (both laboratory and field) were used to validate the methodology presented here. The findings of our work will lead to significant cost-savings in performing both flow assurance risk assessments and inhibitor qualification. Rather than going to the significant expense and operational difficulty and risk of collecting and transporting live samples, such screenings can be performed on re-livened fluids that are both field representative and cost-effective.