This paper describes the evaluation of paraffin and scale risk management based on real production samples, and how this differed to the assumptions made during the basis of design. The production facility has two unmanned tiebacks with a field total of just under 20 wells. For first oil the paraffin and scale management strategy, like most of the flow assurance strategy, was based on pre-production samples. Two years after first oil, almost all the wells were sampled – the first such exercise of it’s kind – gathering large and representative chemical free crude oil and produced water. Produced water samples were analyzed enabling a system-wide scale review for production wells, departing pipelines and major processing vessels and equipment. Some scale had already been observed in the process, in the hydrocyclones and heat exchangers, and this evaluation helped to highlight the other key risk areas and develop appropriate mitigation strategies – not based on pre-production data and samples. This aided the operator in instigating a more robust scale inhibitor injection strategy, in particular for the subsea in-field flow lines. The areas identified as having a paraffin deposition risk in the field were the fluids arriving from the subsea tiebacks where the arrival temperatures were lower than the cloud points. Cold finger testing identified that greater than 60% inhibition efficacy was realized when 10 to 50 ppm of the incumbent wax inhibitor was used. Details are given on some of the shortcomings in the chemical injection system, capturing the lessons learned in control of wax and scale inhibitor distribution through the subsea injection system. Information is given on how this was countered using the most efficient and cost effective chemical mitigation strategy. Practical advice is then offered on how to better interpret pre-production samples to better predict and design flow assurance strategies prior to first oil.
展开▼
