Hybrid rig power system enables fuel savings, emissions reduction

System uses batteries and engine automation, working in parallel with a rig’s diesel gensets, to reduce fuel consumption

By Jessica Whiteside, Contributor

A drilling rig in the Marcellus Shale slashed fuel costs and emissions after installing a new hybrid energy management system (hEMS) that was able to satisfy power demand while minimizing the number of generator sets operating at once, according to a presentation at the 2020 IADC/SPE International Drilling Conference.

CleanDesign Power Systems, which developed the hEMS, collaborated with Patterson-UTI Drilling Company and natural gas producer EQT Corp to field-test the system on a rig, following initial testing at a rig construction facility. The field work, launched in July 2018, has yielded decreases in fuel consumption, power-related downtime, generator set run time – down an average 30% per month – as well as emissions, including declines in carbon monoxide and particulate matter.

“As we know, this is an increasingly relevant point given ESG (environment, social and governance) initiatives,” Memet Bilgin, a Principal and CTO for CleanDesign, said about the emissions performance.

Marcel Snijder, Product Development Manager, Drilling Automation, for Patterson-UTI, also noted during the presentation: “We’re really excited to say that we have the world’s first successful, fully hybrid drilling rig.”

The hEMS consists of a heavy steel skid housing three major components: a battery rack that stores energy in lithium-ion batteries and connects to a battery management system; a bidirectional inverter designed for reliable power flow; and a system controller that runs machine learning, computes optimization strategies, logs data, enforces operating parameters and executes commands to equipment.

Battery power

The project team installed the hEMS into the rig’s power house alongside three existing diesel gensets. By linking the hEMS to an existing AC connection designed for a fourth genset, the team minimized the need to alter original rig equipment.

Once integrated with the rig’s control systems, the hEMS works in parallel with the three gensets. It stores energy in its batteries to use when there is a need for continual power – such as when a genset is warming up or undergoing maintenance – or to provide instant extra power when there is a spike in demand because of activities such as tripping. For example, an operation traditionally requiring three gensets could get the job done with only two once the hEMS batteries kick in to meet demand beyond the capacity of two gensets.

Unlike a diesel genset, which may take up to 10 seconds to warm up to full power, the hEMS can leap to full power in about 30 milliseconds, in part because it is kept continually online, ready to fulfill potential power needs. The system’s batteries recharge rapidly during periods of low power demand, such as connections.

Mr Bilgin described a situation when hEMS support would help to conserve fuel by curbing excess use of a genset.

“Traditionally on a rig, power generation consists of three to four gens running on some form of load-sharing microgrid. If the tools consume more than the gens are capable of delivering, we will get what’s called power limit, and this will ramp down the tools and is essentially a nuisance to operations,” he said. “To avoid these nuisance interruptions, the rig crew will oftentimes proactively launch gens so that they are never caught without enough power.”

This “just in case” tactic can lead to a genset operating – and consuming fuel – even if it ends up being surplus to actual power demand. With hEMS, the system automatically turns gensets on and off depending on the rig load and the charge status of its batteries, addressing fluctuations in power demand seamlessly without the crew even noticing.

Load size matters

One of the parameters the hEMS uses to manage how many gensets should be online at once is load size. The project aimed for engine loads of 60% or more, since diesel gensets operate more efficiently with higher loads, Mr Bilgin said.

Each online genset will share the rig’s total power demand evenly with any other online genset. This means that, in response to the same level of power demand, two gensets would carry higher loads than three. To achieve the high loads required for efficient fuel consumption, the right number of gensets must be online to fulfill the power demand at any one time. With a traditional power plant, the crew decides whether to bring a genset online or shut it down – a challenge given the unpredictable fluctuations in a rig’s power demand. The hEMS shoulders that burden for the crew.

Optimizing load level with an eye to higher, more efficient loads could reduce maintenance requirements. That’s because operating a diesel genset at less than 30% for long periods risks damage and degraded performance. In the Marcellus project, the hEMS made a substantial impact on keeping genset loads above this critical threshold. In December 2018, it achieved a 66% reduction in the accumulated time gensets spent running with sub-30% loads.

Detecting irregularities

The hEMS relies heavily on machine learning methods to improve engine start and automation, as well as to construct performance optimization strategies. These methods include both offline learning based on historic activity and real-time, online learning that spots trends in rig power demand and monitors the real-time performance of each genset. If the system finds anomalies in relation to operating parameters, it automatically acts to resolve the situation, including notifying the crew, if needed.

This approach improves reliability, Mr Snijder said, making it less likely that any issue in the power system will result in a bigger problem. In the case of a genset going offline unexpectedly, the rig won’t be blacked out because the batteries will step in with their stored energy.

“Data monitoring was implemented to allow us to recognize issues quickly, diagnose them, resolve them and then follow up to ensure that they’re not coming back,” Mr Snijder said.

Commercial viability

With a rig consuming $1 million to $3 million in fuel annually, improving efficiency to reduce expenditure on fuel was a primary goal for the hEMS project. The hybrid approach achieved an average monthly fuel savings of $17,861, compared with baseline assumptions for the rig used in the project. Mr Snijder added that the team selected the most efficient rig for the project’s baseline case, even though it would be the most difficult to optimize.

“It was a challenge we wanted to take on,” he said, adding that the baseline for different rigs in a fleet could vary significantly.

While the savings discussed so far were achieved on wells that already had pre-drilled vertical sections, the companies involved say they believe fuel savings would be even higher when drilling from the surface as it would provide more opportunity for optimization.

Mr Bilgin also added that payback on the investments made can be expected in two to three years. “The entire project has been focussed from day one on profitability,” he said. “A lot of our effort has gone into sizing the battery appropriately for the financial return.” DC