Societal Aspects of Weather
Undoubtedly, the biggest impact on production operations comes from tropical cyclones. Shut-downs impact operating companies more severely than royalty owners, since the operating companies incur the costs associated with deferral of production, transportation of crews to safety and back, downtime for damage assessment, and the costs of facility repairs prior to resuming safe operations. While fixed structures usually come back on-line within 48 to 72 hours of evacuation. Floating production systems, like those now operating in deep waters, may take up to one week to resume production. Most companies include 5 to 7 days of weather related production losses each year in their business plans. Improved storm track and landfall forecasts could potentially save 3 days of production shut-down for companies operating offshore. If one assumes producers have an after tax, net income margin of $5 per barrel, the cost of deferred production alone for a Gulf-wide production shut-down might be $15 million per day. The oil production is not lost, only deferred to the future with a reduced net present value.
Today most operating companies transport crews offshore in helicopters, rotating crews on a 14 day schedule. Unscheduled, weather-related evacuations add approximately $10,000 per production facility and $50,000 per drilling rig, over and above normal transportation costs. Dense fog is commonplace along the Gulf Coast, often preventing flight operations for days at a time during the winter months. Operating companies working the eastern and central Gulf have shore bases in the Mississippi delta that provide normal resupply via marine vessels known as crew boats or work boats. Once flights are grounded, boats make more trips through the already crowded Mississippi river navigation system. For facilities 50 miles offshore, travel time from the shore bases in good weather is 3 hours on a crew boat, 6 hours on a work boat. Foggy conditions in southern Louisiana can cause additional delays up to 24 hours.
Offshore platforms function primarily as the processing facility of hydrocarbon fluids which then enter product pipelines. Pipeline operators set specific conditions which produced fluids must meet prior to entering the product pipelines, typically temperature, pressure, and water content. Producers whose products fail to meet pipeline specifications must take measures to reach compliance, or risk curtailment. Pipeline input temperature is a common specification for produced gas. In the high ambient surface temperatures of the summer months, many operators must route produced gases through heat exchangers to reduce temperatures to pipeline specifications. Although subsurface teams and facility designers attempt to characterize reservoir fluid properties before fabrication and installation of processing equipment, modifications are frequently required. A modification to add gas cooling on a facility can cost $300,000, allowing the operator to optimize both oil and gas production.
Presently, offshore drilling methods depend on highly specialized lengths of pipe, known as drilling risers, to connect the well head and blow-out preventer equipment at the sea floor to the drilling and fluid handling equipment located on the surface vessel. Tension loads on these drilling risers are carefully monitored via position indicators, and remotely operated vehicle (ROV) dives which monitor riser flex and measure current profiles. Loop currents and the eddies associated with them are common phenomena the warm waters of the Gulf, especially in the prospective deep water areas. These strong ocean currents can have velocities exceeding 3 knots in the upper 1000 meters of water, producing unsafe loads on risers due to rig offset. Another potential hazard is riser failure due to stress from vortex induced vibration. For the period from 1989 to 1995, excessive currents forced 126 days of delays in drilling operations, at an estimated cost to BP exceeding $6.5 million dollars. (Wheatley, 1995) Seismic acquisition projects are also impacted. Using ocean current data and forecasts obtained from public and private sources, the industry monitors loop currents and associated eddies, attempting to minimize their effects by avoiding operating in effected areas during the late summer and fall when these eddies tend to reach maximum extent and speeds.
Conventional structures are used in water depths up to about 400 meters. Drilling operations from fixed platforms also experience delays associated with wind velocity and wave heights exceeding safe operating conditions for supply vessels. Wave heights greater than 3 meters, and wind speeds over 25 knots create unsafe conditions for loading and unloading heavy equipment and fluids from shallow drafted supply vessels. Operators attempt to prevent delays associated with wind and waves by monitoring forecasts and transporting critical items in advance of adverse conditions. In December 1996, a single BP drilling operation incurred 10 days of delays from wind and waves, with a direct cost of $300,000. Additional costs for standby time for contract personnel and services accumulated while drilling operations waited for the essential items such as rig engine fuel, potable water, and drilling fluids.
Rooney, T., (1993): "Offshore Platforms and Research Opportunities: An Industry Perspective," Marine Technology Society Journal, Vol. 27, No. 2, p. 81.
Dokken, Q. (1993): "Flower Gardens Ocean Research Project: Using Offshore Platforms As Research Stations," Marine Technology Society Journal, Vol. 27, No. 2, pp. 45-50.
Societal Aspects of Weather