Decision-making of spare subsea trees with multi-restrictive factors in deepwater development

In order to quantify the influential factors of subsea trees’ maintenance proactively, multiple restrictive factors first are elaborated, such as locale meteorological conditions (i.e. weather), transport resources, heavy intervention vessels, maintenance technicians, spare trees and so on. Then, the focus is on three vital factors: weather, intervention vessel and spare trees. These restrictions dramatically impact the cost and accessibility of maintenance. For the inaccessible duration of significant wave height in weather model for computing non-feasibility days, we utilized the statistic data from the ERA Interim dataset. An analytical model is established to simplify the calculation of maintenance costs. As the predictive maintenances are seldom performed in subsea field, the built maintenance model only considers the corrective maintenance. Results show that hostile weather as well as the shortage of adequate spare subsea trees can induce severe downtime cost. The comparison of two contractual alternatives indicates that the better way to reduce the maintenance cost is to make the intervention vessel available enough. It is significant to provide quantitative views of subsea maintenance and to supply a method for the decision-making of spare subsea trees with multiple restrictive factors from the proposed model.