With the downturn taking many drillships off the market, ABS’ Dave Forsyth and Landon Fields discuss how to bring those ships back up to speed when the market recovers.
Safe and rapid reactivation following lay-up is a top priority for owners of high specification drillships. © am70/Shutterstock.com
Sustained low oil prices have forced drilling contractors to lay-up assets, including deepwater drillships. According to Rigzone, 44 drillships have been stacked since the inception of the current downturn. These are sobering numbers, but the fact is that oil and gas is a cyclical industry, and a downturn inevitably is followed by an upswing in prices that will lead in time to demand for out-of-service assets. In anticipation of a market rebound, asset owners want to be prepared to reactivate units as rapidly as possible when they are needed.
The process of reactivating an asset is equally critical to the process of laying it up. After sitting idle, rigs need to be inspected to make sure they are fit for service before they can be reactivated, which poses a particular challenge for owners of high-specification drillships. Most of these complex assets are operated by programmable logic controllers with sophisticated onboard computer systems and advanced dynamic positioning systems. Owners want reactivation plans that are specially designed for each drillship so they can be sure the unit can be brought back into service as quickly and safely as possible.
Plan in place
Part of a responsible plan for laying up a drillship is identifying the strategic steps required to bring the asset back into service. To help asset owners develop those plans, ABS has developed the Guide for Lay-Up and Reactivation of Mobile Offshore Drilling Units, which outlines how a survey would take place when the time comes to reactivate an idle asset. The basis of the plan factors in the amount of time the drillship has been in lay-up, major weather events such as severe storms, hurricanes or typhoons, corrosion that has occurred and any equipment that is found to be inoperable at the time of re-commissioning.
An extensive review of machinery and equipment is critical before a drillship is redeployed. © am70/Shutterstock.com
Machinery and equipment
The inspection that precedes reactivation includes an extensive review of machinery and equipment. Drilling systems including the blowout preventer stack control system, derrick skidding system, braking system, heave compensation and riser tensioning hydraulic systems are checked for contamination or chemical degradation. Any system that is unserviceable is drained and sterilized if bacterial deterioration is present before being refilled with new oil or fluid. Prior to reinstallation, the drilling and well control equipment are thoroughly examined to verify that all equipment is in proper working condition.
Within the scope of machinery, the ballast system and bilge pumping arrangements are tested along with all watertight and weathertight doors, fire dampers, ventilators, hatches and closing devices. The survey inspection also involves cleaning and flushing potable water tanks. Diesel engines and accessory gears are selectively opened and examined for corrosion, excess wear, damage, proper tensioning and torque. The drillship’s low-speed engine crankshaft deflections are recorded, and protective trips and alarms are verified. As with the drilling equipment fluids, engine lubricating oil, stern bearing and steering system hydraulic fluids are analyzed for contamination.
Drillships that have experienced extreme events while laid up require a nondestructive trial of the underwater connections and an underwater examination of the hull and thruster system to determine if it is necessary to remove any marine growth. On the surface, cleaning underneath the drillship might appear to be an insignificant step in the reactivation process, but it is critical that no foreign objects compromise operations. A mooring system that is blocked or clogged will not function properly.
When a drillship that has a mooring system is being reactivated, it is critical to test the system to determine its ability to hold the drillship in place in real operating conditions; so evaluations of holding capacity have to be carried out using relevant wind, waves and current data. The dynamic positioning system also undergoes a full failure mode effects analysis (FMEA) trial to confirm that all of the systems are fully operational. If there have been any changes in the software that enables communication between systems, the FMEA trial will bring it to light, and any failures will be corrected prior to drilling. Testing provides a complete performance evaluation of the dynamic positioning system that includes all operation modes with simulations of different failure conditions.
Mooring chains, fairleads and anchors also are operationally tested before the vessel is reactivated. For a drillship that has spent more than five years in lay-up, it is prudent to check any mooring chains that are used for permanent mooring and to test fairleads using nondestructive examination.
Hardware and electrical systems
Today’s drillships are equipped with the latest and most advanced computers, which means a pre-activation survey has to make sure the onboard computer system hardware is functioning properly.
During the time the drillship has been in lay-up, computer systems may have been subjected to software updates that haven’t been tested to determine if the changes to the software will have an unexpected impact on operations.
A computer is responsible for activating thrusters in the dynamic positioning system to keep the drillship in place and to monitor winds and waves to adjust the thrusters accordingly. Hardware has to be tested for compatibility with the software to confirm all of the functions are operating correctly. It is critical to ensure there are no computer glitches before a drillship is redeployed.
Because equipment that has not been in operation for a period of time can be affected by moisture and corrosion, it is important to evaluate functionality. For onboard electrical systems, this means inspection should be carried out on insulation resistance for all power and lighting circuits as well as generators, motors and switchgears to isolate deficiencies. Testing includes lighting, fixtures and instrumentation in hazardous areas and all fire and gas detection systems to confirm that everything is in working order.
The value of a plan
Depending on its status and condition, a drillship can take one to two months to reactivate safely. Having a systematic plan in place expedites the process and allows owners to get these valuable assets back into service safely.
For drillships with an average cost of US$600 million, getting them back on contract in good working condition is a top priority for owners.
Dave Forsyth is chief surveyor/offshore for ABS in the Corporate Classification department. He has been with ABS for more than 36 years. During his career, Forsyth has held the positions of surveyor, senior surveyor, principal surveyor, and assistant chief surveyor/offshore. He holds a BS in marine engineering technology from Mississippi State University.
Landon Fields is divisional lead surveyor offshore of North America for ABS. In his current role, Fields provides guidance and oversees classification and statutory survey work. He verifies that surveys are in compliance with ABS rules, guidelines and statutory requirements. Fields has more than 20 years of experience in the offshore industry.