by William Birch, Kate Mick and Neal Hennegan (Shell E&P Company) and Glen Wirth (Simio LLC)
As presented at the 2015 Winter Simulation Conference
Introduction
Shell Gulf of Mexico (GoM) Logistics moves more than 50,000 tons of materials and equipment to offshore facilities each month using 40+ offshore supply vessels. The shipments are separated into voyages which include loading of the vessel, transiting to offshore locations, transferring of materials offshore, returning to port, unloading, and possibly tank cleaning. The offshore facilities vary from 30 miles to more than 300 miles offshore. In a typical month, Shell will schedule over 200 voyages transporting more than 9,000 tracked items where an item could be a simple pallet of chemicals to 20,000 feet of tubular goods. The offshore supply vessels employed come in variety of sizes and configurations. The vessels range in length of 100 to over 350 feet with cargo capacities ranging from 500 to 6,000 tons. Open back deck areas range from 20’ x 80’ to 65’ x 260’. Below deck storage varies in terms of capacities and types of storage. Many vessels are designed to carry both liquid and dry bulk.
Problem
The challenge is one of size and complexity. The traditional process revolves around shipping requests, which identify materials and equipment that need to be shipped in the next 5-10 days. The requests include the pick-up and delivery points, descriptions, quantities, dimensions, weights, and time constraints. (Offshore facilities have limited storage capacities and carefully plan when material is delivered and picked up offshore.) The shore base can sometimes meet the demand for shipments with regularly scheduled “milk runs” that run to each offshore location at scheduled intervals, but more than not, the demand for cargo is not regular and must be met by scheduling voyages to meet the pick-up and delivery constraints of the offshore location. The manual planning and scheduling of shipments has proven challenging due to frequent shifts in delivery windows, large number of items, variability in transit times and weather, and congestion within the port facilities. A study of “non-productive” vessel time brought to light a significant opportunity to improve the effectiveness of the scheduling process.