Many oil wells in Brazilian onshore fields rely on artificial lift methods. Maintenance services such as cleaning, reinstatement, stimulation and others are essential to these wells. These services are performed by workover rigs, which are avaliable on a limited number with respect to the number of wells demanding service. The decision of which workover rig should be sent to perform some maintenance service is based on factors such as the well production, the current location of the workover rig in relation to the demanding well, and the type of service to be performed. The problem of scheduling workover rigs consists in finding the best schedule for the available workover rigs, so as to minimize the production loss associated with the wells awaiting for service. We propose a VNS heuristic for this problem. Computational results on synthetical and real-life problems are reported and compared with those obtained by other approaches. This project was sponsored by the Brazilian agency FINEP (Financiadora de Estudos e Projetos), in the framework of the CTPETRO Brazilian national plan of science and technology for oil and natural gas.
Research report submitted for publication, 2003.