While hybrid power systems are by no means a novel idea within the offshore industry, rig owners have been slow to adopt this technology. Even though various offshore drilling contractors have explored and continue to evaluate hybrid systems, there are still very few rigs within the global fleet utilising this technology.
Today, however, hybrid systems are getting a new look.
“A parallel need is emerging for the offshore drilling segment to become both more efficient and greener,” says Joel Thigpen, Wärtsilä's General Manager for Offshore Drilling. “Wärtsilä has extensive experience in developing sustainable hybrid power systems designed to optimise operational efficiency and minimise environmental impact for a variety of marine and offshore applications.”
Combatting inefficiency
Thigpen explains that the typical rig operating profile is comprised of multiple engines running at low loads with frequent and dramatic load swings.
“Secure, reliable and safe operations are the number one priority in the offshore segment, where operators simply can't risk having a rig go down, even for a moment,” he says, adding that this is the reason most drilling rigs are equipped with more engines than they need, most of which normally run at loads between 20 to 40 percent.
“Even peak load demands rarely reach the maximum available power,” says Thigpen.
This operating profile is far from ideal for standard marine engines, which are normally designed to run at 70-80 percent load.
Despite this glaring inefficiency, employing an excessive number of engines allows operators to rest easy, safe in the knowledge that there will always be power available for the rig. This peace of mind comes at a high cost, however. Running more engines than necessary with a less-than-optimal operating profile increases fuel costs and consumption and results in higher engine maintenance costs as well. This adds to the cumulative field development costs, while increased fuel consumption also produces more emissions, causing a greater environmental impact.
Hybrid technologies are uniquely positioned to alleviate some of these inefficiencies, driving down overall operating and lifecycle costs while significantly improving the efficiency and performance of the installation. Hybrid power systems are available in various configurations for the offshore market, often designed around batteries, fly wheels or super-capacitors. These systems allow the rig to be run on fewer engines, operating at constant and optimal loads instead of the traditional low loads that are inefficient putting excessive hours on engines, potentially increasing the risk of downtime and unscheduled maintenance.
“Fewer engines allow the operator to use less fuel and reduce wear and tear on the engines, thereby cutting both maintenance costs and emission levels,” says Thigpen.
Less fuel = lower costs and lower emissions
Hybrid systems have a demonstrated capacity to reduce the emissions of offshore installations and all vessels with dynamic position (DP) applications. Wärtsilä has already developed and delivered hybrid solutions to the offshore market that have allowed some customers to reduce fuel consumption by up to 30-40 percent. This is key in an era when environmental concerns are taking centre stage.
“Emissions are becoming a real concern both due to current and anticipated environmental legislation and public perception of environmental performance, which affects the social license for companies to operate,” says Thigpen.
These concerns are particularly acute in the oil and gas sector, which has faced pressure from both governments and environmental groups to address its impact on the marine environment.
Wärtsilä's hybrid journey began in the oil and gas sector, and it understands the unique challenges facing the industry.
The company has more than 10 years of extensive experience installing hybrid systems on offshore installations and in-depth knowledge of how hybrid systems will interact with the other power and marine components on a rig. Advanced Energy Management Systems have been developed to ensure optimal, safe and easy operation of the hybrid solutions.
In 2018, a Wärtsilä HY upgrade solution was installed on the North Sea Giant, an advanced subsea construction vessel. The vessel's owner was seeking a greener solution in line with its customers' demands and also saw an opportunity to reduce fuel consumption. After the rebuild, the North Sea Giant was managing 80 percent of its dynamic positioning operations with only one engine running – a process that had previously involved a minimum of three of its six engines online at low loads. By handling peak loads with the battery and optimal loading of the engine, the vessel increased fuel efficiency up to 40 percent in this operating mode, indicating the potential for long-term fuel savings. The North Sea Giant was the first DP3 vessel that received DNV-GL approval to run a DP3 operation on only one engine.
Joel Thigpen explains that all DP applications – including offshore drilling rigs – could potentially reap the same kind of benefits from hybrid systems. Like offshore construction vessels, offshore drilling rigs require secure, stable power supply.
“Despite their differences, these two operating profiles actually share many of the same drivers and needs,” Thigpen says, adding that the current business priorities for both types of operation include the need to reduce costs, reduce emissions, minimise maintenance, optimise engine loads and maximise efficiency, while ensuring maximum safety and reliability at all times.
Wärtsilä has installed hybrid systems on both new builds and retrofits – proving the potential and benefits that this technology can provide to a variety of offshore vessels and applications across the entire offshore industry, from drilling rigs, production vessels, support and supply vessels, as well as construction, pipe-lay and seismic vessels.
In addition to the fuel cost savings that hybrid solutions offer, the reduced fuel requirement also delivers indirect savings from logistics operations, since fewer supply boats are needed, thereby reducing the need for fuel for these boats, as well as the emissions they produce. Meanwhile downtime is also minimised, as less time is spent on bunkering operations. Another advantage is the reduction in maintenance costs and extended overhaul intervals that result from the engines running at a constant, optimal load, instead of a low load, which has been proven to cause excessive wear and tear to the engine.
More affordable, smaller and safer
Despite the evidence in favour of hybrid technology, Thigpen acknowledges that many drilling contractors have thus far been reluctant to install these systems on their rigs. The first, and probably most apparent, deterrent has been cost. When battery hybrid systems were first introduced, the cost of batteries was exorbitant, and a sound financial case could not be made, especially when the drilling contractor was not paying the fuel bill for their rigs. Over the last decade, however, the cost of batteries has come down by more than 50 percent, and prices continue to improve as the technology evolves. As contractual obligations change, and in cases where the rig owner is responsible for the cost of the fuel or incentivised for reducing fuel consumption, hybrid battery systems may begin to make more financial sense. In some parts of the world, government subsidies or other financial incentives may be available to companies that install equipment to reduce environmental impact.
Apart from the expense of installing these systems, offshore drilling operators have also been concerned about the space required by the batteries on a rig. Rig designs of the past did not leave room for these hybrid battery banks, so most retrofit or upgrade options would have required a space-consuming containerised solution to be placed near the drill floor. However, since 2007, the storage capacity of batteries has improved, reducing the size by half and resulting in a smaller physical footprint, either on the deck or in the hull of the rig.
Another concern has been the safety factor, the threat of thermal runaway from batteries. Thermal runaway is a short circuit within a battery cell that causes a rapid increase in temperature and pressure which are then transferred to neighbouring cells and this could lead to a fire, or even an explosion in parts of the battery. In recent years, the design of these batteries has changed to include safety measures to prevent thermal runaway within the battery, along with additional safeguards that together ensure multiple layers of safety and redundancy.
“A hybrid power system for offshore drilling rigs is not a new concept, but it's a technology that has up to now been overlooked, or discarded, for various reasons. However, given its potential and the huge evolution of this technology in recent years, we at Wärtsilä believe it is an efficient way for eliminating waste, reducing emissions and improving safety in the offshore environment going forward,” concludes Joel Thigpen.
Source: Wärtsilä