عنوان مقاله [English]
Service vessels in offshore oil industry have a noticeable logistics role in protection and continuity of quality and quantity of oil production. Offshore oil production takes place on oil wellhead platforms. In order to maintain oil production in offshore areas, the National Iranian Oil Company, using supportive vessels and mobile wellhead vessels, periodically provides public services and well services to equipment located on oil wellhead platforms. But in the meantime, mobile wellhead servants, themselves need to receive service from supportive vessels in specific periods and also specific time windows. In fact, mobile wellhead servants have a dual role. On the one hand, they have a role to play in providing well services for oil wellhead platforms and, on the other hand, they have the role of receiving public services from supportive vessels. Service vessels are few in number compared to service requirements, but they have a high shipping cost instead. Therefore, using them without an appropriate plan, from one side leads to significant lost opportunity cost of oil production due to service shortages, and from the other side, imposes high shipping cost. In order to determine periodic routing of service vessels, a mixed integer programming model is proposed with the goal of minimizing the cost of shipping and the lack of services. Given that the mathematical model is Np-hard, a heuristic algorithm based on the problem practical conditions has been introduced to solve the problem and its performance is evaluated using real life instances related to different oilfields located in Iranian side in the Persian Gulf. Numerical results indicate the algorithm’s speed in achieving the appropriate solutions at a very low time compared to existing algorithms. In fact, implementing the heuristic algorithm, leads us to create very good solutions in the primary iterations of running the heuristic algorithm and to improve them in the next iterations.