Flywheel and Battery Solution Working Together to Lower Drilling Rig Emissions by Taking Generator Sets Offline
Authors: Thomas Borsholm , Richard Verhoef 
Published: March 2023

Abstract
Emission reduction is the prime focus for the drilling industry, and zero or low emission drillling is the ultimate goal. Zero or low emission drilling in this context is considered to be drilling without the use of the drilling installations generators. The rig is powered by an external (shore) power source. True zero emission drilling will be the case where the power is generated by a zero-emission power source like wind and solar power, hydro power or hydrogen. Operating offshore drilling installations without the use of the onboard generator sets is technically possible by using power peak shaving technology (energy storage system) combined with a DC grid system.
Power peak shaving is essential to stabilize the power demand from the rig onto the external power source. Without power peak shaving the difference between the average (normal) power consumption and the maximum (short) power consumption is too big for external power sources to efficiently to cope with. The power peaks during the drilling process are generated by the rig equipment and are determined by the operations ongoing. Some equipment has a relative steady power consumption, like mud pumps, but one of the biggest causes for peak power is the drawworks. Drawworks have a relatively small energy consumption due to their intermittent use, but during that use, the peak power (the difference between acceleration and steady hoisting) they demand is huge. The peak shaving solution best suitable here is the flywheel and battery system, where the power peaks are delivered from the energy stored in the rotating flywheel and the battery combined. The major advantage is that the flywheel can absorb a huge amount of power in short periods, while the batteries will supply the steadier power supply. The bonus here is that the breaking energy (i.e., from lowering a drill string into the well) generated by the drawworks can be used to power up the flywheel battery system.
Offshore drilling installations typically have a bus system, to distribute the power from the generators to the users. Power reliability is critical for the operation of the vessel and a complete power system black out can be disastrous. By having a split between the generators and users, extra care is taken that a single generator failure can lead to complete system black out. This bus system will prevent communication between one bus and a second bus, unless closed bus (bus tie) drilling is done. It also means that not all users are connected to one bus only; the drawworks motors are power by 2-3 separate busses, which in turn mean that the same number of generators will also be running. For shore power situations, this becomes impractical; there is only one power source (‘the shore power’) and yet, this source needs to distribute the power over the available busses on board the rig. The way to safely achieve this is by having a DC/DC grid system, which provides better redundancy compared to closed tie/closed bus drilling. This paper will describe the peak shaving and DC/DC grid solution in more detail.