Current passive compensation systems require manual stroke and compensation adjustments associated with tide cycles and sea state variations, which depend on geographic locations and time of year. Operators must maintain constant communication with coiled tubing (CT) operators to understand real-time weight introduced to the wellbore, manually dialing in to safely compensate as intervention continues and weight increases and decreases. Stroke readjustment requires feeding nitrogen or hydraulic fluid to the compensator or bleeding nitrogen or hydraulic fluid out of the compensator system.

Manual manipulation of the block in the derrick or of the compensator within modular well intervention towers is necessary to correct stroke preparation errors and enable adequate compensation requirements. New technology, such as the motion compensation mode of operation implemented into the new compensating CT lift frame (CCTLF) from National Oilwell Varco (NOV), offers operators automatic control with manual override capabilities, eliminating the need for manual stroke and compensation adjustments, and therefore preventing human error and increasing safety.

The lift frame features an automatic tide adjustment, bleeding and feeding using pressure variance recognition in compression and tension as well as real-time weight monitoring. All hydraulic functions are wireless, contributing to a safer, more userfriendly system. Real-time monitoring shows the exact stroke and fluid levels, detecting leaks and low fluids. An alarm system notifies users when parameters are outside of scope, affording efficient troubleshooting methodologies when applicable. With even weight distribution across the upper frame assembly, down the two main beam structures and back to center at the lower frame assembly with a hydraulic elevator door, the system allows well-center rigup of CT, wireline and slickline.

NOV implemented the new motion compensation mode of operation into the CCTLF based on past global completion and post-completion intervention projects throughout more than a decade, designing the system to enhance safety, increase weather working window capabilities, overcome crane limitations, improve well integrity and withstand aggressive sea state conditions. The new operation mode also is implemented into all existing inline and modular compensating well intervention towers from NOV.

P&A case study

From early 2006 through January 2008, a customer in the Gulf of Mexico (GoM) required a compensation system to perform CT and wireline services onboard a floating intervention vessel. The system needed to provide a rigless, modular, compensating well intervention tower for CT and wireline operations. Devin, part of NOV’s intervention and stimulation equipment business unit, provided a cost-effective modular compensating well intervention tower system for the accommodation vessel.

The system used the dual Devin Inline Motion Eliminator (DIME) traveling head compensation system. Configuring the inline compensators outboard of the well intervention tower afforded a greater work window within the tower and reduced overall tower height requirements to accommodate well control and lubricator stack-up needs. The installation resulted in successful plugging and abandonment of multiple wells over a three-phase program with minimal downtime. The compensation systems provided a safe, economic solution that resulted in minimal downtime during inclement weather or tidal conditions.

Subsea CT and wireline P&A campaign case study

From 2010 to 2011, an operator in the GoM required a compensation system to perform CT and wireline subsea plug and abandonment (P&A) operations. Using DIME systems, the operator compensated for slickline and e-line riserless subsea operations in nearly 91 m (300 ft) of water. The system accounted for tidal variations, inclement weather, surface winds as well as 3.6-m (12-ft) swells by ensuring downhole precision tool placement.

The DIME system provided primary means of compensation and independent well intervention support for subsea CT operations by ensuring the injector head and well control stack-up maintained relativity to the seafloor. Allowing the crane to work independently for added diver assistance and day-to-day logistical support enabled simultaneous operating capabilities. The combination of products enabled a savings of $300,000 per day of simultaneous operations. In addition, the systems contributed to a 38% cost savings compared to semisubmersible options and up to 78% cost savings compared to drillship options. The operator successfully completed P&A operations on nine subsea wells. The system increased the weather working window each time winds exceeded 30 mph because of crane boom limitations.

Motion CCTLF case study

A company performing offshore operations in Nigeria from May 2013 through January 2014 had a CCTLF stored in original shipping crates. The company needed a rigup option to meet requirements regarding its immediate upcoming operations and requested a location inventory, assembly and system integration test of the CCTLF. With four wells to complete, the operator required specialized offshore motion compensation technicians to successfully rig up and operate the CCTLF throughout the duration of the operations. A team of offshore technicians from NOV rigged up the CCTLF in multiple stages to meet the rig crane capac ity of 86,000 lb and performed a complete system integration test in the derrick of the rig.

They operated the CCTLF during the landing of the completion and compensated over well-center while working in up to 4.2-m (14-ft) heave conditions. As a result, the company saved significant time and money by eliminating the need to source a CCTLF externally or from another rig. They minimized downtime to 30 minutes with more than 1,000 hours of operation compensating over well-center during the four-well campaign.

Floating spar case study

From December 2015 through February 2016, an operator on a floating spar in the GoM had an objective to clean up paraffin and scale in two wells. The operation required compensation and intervention equipment rigged up from well to well that would account for high and low tide cycle variations, enabling safe working operations. The ability to increase, decrease and maintain preset levels of drillstring weight by controlling the direct line compensator (DLC) pressure was needed to safely meet the objective.

Devin installed the DLC equipment package within the rigup window and provided a nitrogen compensation skid, which accounted for all tidal movements and inclement weather by maintaining a constant hook height during vessel movement. The package minimized the weight of added intervention equipment and completion string in the existing completion, providing redundant safety measures in the event of a nitrogen failure and during normal well intervention operations.

The team safely transferred the DLC/CCTLF package and other well intervention equipment while skidding the spar 16.7 m (55 ft) to the next well location in the field. Transferring the CCTLF intervention equipment from well A-6 to well A-7 reduced rigup and rig downtime by 36 hours, saving the operator 1.5 days of rig costs. They safely flowed back well A-7 and helped bring well A-10 online to the production facility. The DLC provided the primary means of compensation support for the entire spar on both well operations. The operator successfully compensated the spar for 40 days latched to the seabottom.

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