May 2019 /// Vol 240 No. 5
Features
Fueling fracturing with natural gas: Redefining wellsite power for oilfield services
The challenges of fueling hydraulic fracturing operations come in many forms, including consistent fuel supply, efficiency, emissions and safety. Natural gas power generation and specialized fracturing fleets offer answers to many concerns posed by traditional diesel-powered technology, and present a new paradigm for wellsite power.
Carrie Murtland, Evolution Well Services
On Aug. 24, 2017, Hurricane Harvey was barreling toward the middle of the Texas Gulf Coast shoreline, packing winds up to 145 mph and reports of anticipated rainfall in excess of 36 in. As the storm loomed closer to making landfall, the team at Evolution Well Services was busy evaluating the best plan of action—Harvey’s projected path was headed directly for one of their newly deployed fleets of electric power generation and fracturing equipment in the Eagle Ford shale.
The personnel decision was an easy one; people on location quickly battened down the hatches and promptly evacuated to safety for an undetermined amount of time, not knowing what the severity, length or aftermath of the storm would be. The newly minted equipment, however, still gleaming with its fresh coat of silver-fleck paint, was not going to be so lucky. The decision was made—the fleet was going to ride out the storm where it stood.
Two days after Harvey had passed, the crew was re-deployed to the wellsite. What they found was incredible; no notable damage to any of the equipment. The team spent the day completing safety checks, ensuring that all systems were “go” for resuming fracturing operations later that night. The natural gas line was opened, feeding the custom turbine generator, and momentarily after that, electricity was flowing out to the pump trailers, blender, and ancillary equipment on location. Pumping operations resumed, and business as usual commenced, Fig 1.
Fig. 1. On location in the Eagle Ford, Evolution’s electric fracturing fleet, powered by local natural gas, provides an alternative to traditional diesel engines.
AN ALTERNATIVE FUEL FOR FRACS
What was not realized at the time, was that the majority of the other frac fleets in the basin were still not operational, and they wouldn’t be for many days or weeks yet to come. The situation confirmed a key value of electric-powered fracturing—the insulation from disruption of a continuous diesel supply to location. Harvey had introduced major disruptions into crude refining and fuel logistics across the Gulf Coast region. On the Wednesday of Harvey’s approach, 110 mi east of Houston, the largest crude oil refinery in the U.S. made the decision to close for an undetermined amount of time. According to CNBC reports, 20% of U.S. refining capacity was taken off-line by the storm.
While other pressure pumpers anxiously awaited the arrival of diesel trucks on wellsites across the Eagle Ford and beyond, Evolution was completing stage after stage on the client’s wells. The service was accomplished with a patented, custom-power generation package, fueled solely by natural gas pulled directly from local in-field gathering lines. In this particular case, the fuel source resided just 10 yards away.
The story is reminiscent of how, and why, Evolution got its start in 2010, in British Columbia, Canada. At that time, the large Kitimat LNG export facility was being planned. The nearby Horn River basin held untapped reserves that would feed the facility, and well completions were required to recover them. Once it was determined that the wells could produce enough gas to fuel a fleet of fracturing equipment, it was clear that there was an opportunity at hand to implement a new technology.
The geography, harsh climate, and remote location of the planned operation increased the risk of interruptions in consistent fuel supply, which in the case of a conventional hydraulic fracturing fleet would typically be a continuous string of diesel tankers (roughly six per day for today’s fracturing designs). And so, Evolution began exploring how the Horn River field gas could be used to fuel the fracturing operations, thereby eliminating the need to continuously deliver diesel fuel to the remote locations.
During this concept phase, the company filed their first patents for a scalable, electrically powered fracturing system that uses natural gas to generate onsite electrical power.
ENERGIZING THE WELLSITE
The initial technology used a turnkey gas turbine generator package from General Electric: the GE TM2500+. The package delivered 32 MW of mobile generation capacity, and successfully powered Evolution’s first commercial fleet from 2016 to 2018.
The current system was developed to cut the move time between wellsites, which was taking four to upwards of seven days. This meant that nearly a quarter of each month consisted of non-operating time. Any time spent mobilizing equipment between wellsites signifies dollars lost. The non-productive time is so crucial in fact, that it is recorded in intervals of minutes, not hours.
Optimizing the power generation package. To maximize efficiencies and increase up-time, the power generation package was redesigned to provide a more rugged, rapidly deployable package for hydraulic fracturing and other oilfield applications.
The redesign resulted in a custom-power generation package and creation of an affiliated entity, Dynamis Power Solutions, Fig 2. Dynamis and Evolution designed, patented, and have manufactured six custom turbine generator packages, using the GE LM2500+ G4 turbine engine. In 2018, the engine had a reliability rating of 99.9%. The generator packages have a high power density, with their road-legal dimensions housing 36 MW (roughly 48,000 hp). The packages have reduced average pad move times by more than 50%, allowing clients to bring producing wells online two to four days faster than before.
Fig. 2. Custom 36-MW turbine generator package improves mobility of power generation equipment.
In a February 2019 application, the process of turbine rig-down, mobilization to a location 8 mi away, rig-up and distribution of power to the fleet was accomplished in just 14 hr.
Rounding out the frac fleet. The electric power generation solution opened new opportunities in designing the remainder of the fracturing fleet. Because the pumping trailers no longer had a traditional drive-train (the diesel engine and accompanying transmission) required to power each pump, significant real estate was available on each trailer to do something truly unique.
The most recent generation of pump trailers contain a single 7,000-hp electric motor with a dual shaft. Each end of the dual shaft directly couples to a 3,500-hhp frac pump. The typical frac fleet houses 56,000 pumping horsepower across eight pump trailers.
Controls and automation. The advanced control logic governing the operation of the pump trailers incorporates a balancing process across the two 3,500-hhp frac pumps; this greatly diminishes hydraulic harmonic vibration across the unit. Variable frequency drives control essentially every electric motor on the fleet. Not only does this control provide infinite adjustability to motor speed (and subsequent pump speed—meaning no more having to choose between gears while pumping), but it also provides more efficient use of power and sets the stage for enhanced automation and diagnostic ability. Various data streams from the variable frequency drives are monitored during operations and oftentimes predict component failures prior to an event. When routine pump maintenance is necessary, it is completed safely from ground level—all process equipment is on lay-down trailers that place pumps at a height that does not require elevated maintenance platforms.
Feeding all of the pumping trailers is a custom blender that houses two independent blending systems, each capable of rates of 120 bpm. The need for an external hydration unit was also eliminated with a 250-bbl hydration tank incorporated onto the dual-blending unit. This provides flexibility in blending operations to perform nearly any job design within the footprint of one trailer frame.
Safety implications. Engineering controls are the first line of defense and, ultimately, the most effective way to avoid injury is to keep folks out of harm’s way. Evolution’s custom IMPACT data van allows operation of the entire fleet from safe positions inside the data van. The van, which extends to three separate operating levels once on location, comfortably accommodates the client’s representatives and the entire frac crew, which is half the size of a conventional fracturing crew.
These units, as well as the other custom components that make up the fleet, are all powered by electricity produced by the Dynamis turbine generator package. The generator produces 13,800 V, which feeds through a custom switchgear unit prior to distribution to all process equipment on location, Fig 3.
Fig. 3. Process flow of locally sourced natural gas through the turbine generator, and subsequent electricity distribution to process equipment and ancillary services.
EVOLUTION OF DESIGN
The latest generation of equipment reduces the number of ground cables from 59 to just 16, bundling all power and communication lines into one cable per unit. The system uses a custom-designed, circuit-protected plug and receptacle to connect each piece of equipment. This reduces trip hazards, and saves on cost and maintenance, as well as reduces the amount of time required for rig-up.
Reducing environmental impact. The fracturing fleets have a footprint that is 50% of a conventional hydraulic fracturing fleet. In certain basins where pad sizes are particularly small, the reduced footprint has enabled pumping operations without enlarging the pad size. The capability suggests wellsites could theoretically be built smaller, lessening the environmental impact and the effect on surrounding communities.
A GREENER ALTERNATIVE
In addition to fuel savings achieved by fueling frac fleets with natural gas instead of diesel (which typically range from $1 million to $2 million per fleet, per month), the emissions profile and other health, safety and environmental factors achieve wide-reaching improvements. Since inception, Evolution has conserved nearly 450,000 lb of carbon monoxide from being emitted into the atmosphere, and has hydrocarbon emissions (including methane) that are 95% lower than the Tier IV Final Non-road Compression Ignition Standards set by the EPA in March 2016, Fig 4.
Fig. 4. Comparison between EWS’s custom turbine and Tier IV diesel emissions standards.
Methane from oilfield operations. The topic of methane emissions has recently been in the industry spotlight, and for good reason. While the EPA established carbon dioxide as the reference point for Greenhouse Warming Potential (GWP) with a value of 1, methane, by comparison, has a GWP ranging from 28 to 36. And this is certainly not a game where the high score wins.
Atmospheric impact. In short, the GWP is a metric combining two different factors: radiative efficiency, which is a measure of how much energy the compound can absorb; and lifetime in the atmosphere. While CO2may linger in the atmosphere for a thousand years or more, methane typically only resides there for about 10 years. However, the radiative efficiency of methane is considerably higher, essentially making it a warmer blanket for the earth. Although the industry has reduced methane emissions substantially since 1990, natural gas systems still rate as the second-highest source category for such emissions in the U.S.
E&P drive to reduce emissions. There are other drivers, as well, for working to capture the methane that is escaping from oil and gas operations across the globe. According to Newsweek,53% of U.S. companies tied executive compensation to performance targets aimed at being more environmentally friendly. Just a decade ago, that number was less than 10%.
Less wasted fuel. Additionally, 2016 marked the first time in U.S. history that natural gas fueled more electricity production than coal; 34% was produced from natural gas feedstocks and 30% by coal. Most would agree with the consensus that emissions standards are not likely to be relaxed in any material way in the future, meaning that natural gas will likely have a growing role in electricity production in the near-to-mid term. Therefore, all methane escaping these operations to the atmosphere could be looked at as spilled fuel; not contributing to production of useable power for the demands of growing populations.
APPLYING LEAN PRINCIPLES TO COMPLETIONS
During a time in the industry, where efficiencies are paramount, the process of delivering diesel still contains four of the eight types of waste included in classic Six Sigma principles; movement, waiting, transportation, and extra processing.
Where does diesel come from? Let’s follow the journey of a hydrocarbon molecule destined for use as diesel fuel in fracturing operations. How many times does the hydrocarbon molecule change location and chain of custody? It starts at the wellhead with the E&P company; next it is delivered to the midstream company; it then transfers to a holding facility; then on to the refinery; then back to a holding facility; then to the distribution rack; then to a retailer hauling it back to a wellsite, and then ultimately selling it back to an E&P company.
Ripple effects. What about the emissions from the diesel tankers, delivering fuel to remote wellsites (not to mention the energy intensity of the diesel refining process itself)? Since commercial operations began in 2016, Evolution has conserved nearly 14 million gal of diesel fuel. This equates to over 3,300 tanker truck journeys, Fig 5. In addition, Evolution frac fleets contain fewer than half the number of trailers as a conventional frac fleet, meaning 50% fewer tractors are pulling equipment over the road with every pad move.
Fig. 5. The group of sand silos on the left had been working with Evolution on their electric fleet, while the silos on the right had been working on a conventional diesel wellsite.
Not only is this beneficial from an environmental perspective, but safety and civil infrastructure are impacted, as well. According to the latest reports from the Bureau of Labor Statistics, truck drivers and delivery workers have the highest rate of workplace fatalities.
Eliminating hot fueling. Once fuel trucks arrive on wellsites to fuel conventional diesel-powered equipment, the danger hasn’t yet passed. The refueling of the fracturing process equipment with diesel, while the pumping operations are occurring, is referred to as “hot-fueling.” The design of the standard conventional frac pump trailer, along with the fact that a large amount of equipment is typically parked very tightly together on a wellsite, poses a health and safety risk to those individuals involved in the hot-fueling process.
Combine these factors with the extremely large volumes of combustible fluid at hand, and the frequency with which this operation is done (daily on hundreds of frac sites nationwide), and risk of a potential disaster is increased. There have been dozens of equipment fires on fracturing sites over the past 15 years, with the vast majority of them pointing to hot-fueling operations as the source. Each fire poses risks to health, safety and the environment, as well as immense capital destruction. In 2018, alone, there was over $100 million in insurance claims filed by North American pressure pumpers, due to fracturing equipment lost in wellsite fires.
QUIET TECHNOLOGY
Many well completion operations in places such as the Barnett shale of North Texas are required to operate on “daylight only” schedules, strictly due to the noise produced by conventional frac fleets and associated services. One operator, currently working in close proximity to Oklahoma City, reached out to Evolution recently, because local residents had issued numerous complaints to local congressmen regarding excessive noise coming from nearby wellsites. Conventional diesel fracturing fleets operate at a noise level of 110 decibels or more. OSHA Standard for Occupational Noise Exposure requires hearing protection be worn anytime that the 8-hr time-weighted noise level exceeds 85 dB. Evolution’s fleet comes in at 85 dB or below.
In efforts to reduce the disruption that fracturing fleets might induce, the company has engineered and manufactured custom exhaust equipment for each power package, substantially dampening the noise during operations to levels that will comply with all currently published North American noise standards.
WHAT EVOLVES NEXT FROM THIS TECHNOLOGY?
Recently, Dynamis and Evolution have worked to improve wellsite operations by feeding produced electricity to other service providers on each location.
Powering ancillary wellsite services. Plans are to expand the ability to act as an on-site power provider for other ancillary services such as wireline, water transfer and chemical mixing, including the design and manufacture of custom electric pump-down units, which are planned for deployment in the second quarter.
Recently, Evolution worked with Solaris Oilfield Infrastructure to extend the natural gas-fueled power for use with the Solaris sand delivery systems, in lieu of utilizing their conventional diesel generators for power. This was accomplished in short order, because Solaris also uses electric motors, components and controls, all on variable-frequency drives, typically powered by their own 480-V three-phase generator.
Heat capture. Another patent application that was recently added to the list outlines designs to capture otherwise wasted exhaust heat from the turbine generator, and repurpose that energy to a heat exchanger that can be utilized to heat water for fracing operations in cold-weather scenarios. The thermodynamic calculations predict that water will be heated by 30°F at a rate of 100 bpm.
Data analytics. All of these operations are remotely monitored and, where sensible, are automated, from a joint Evolution and Dynamis Operational Excellence Center that opened this year in The Woodlands, Texas. This space is mission control for all data analytics, predictive maintenance, and artificial intelligence projects currently in the works. WO
The Authors ///
Carrie Murtland is V.P. of technology and marketing for Evolution Well Services. She is responsible for strategy development and deployment for technology, marketing and sales. Ms. Murtland has a Bachelor’s degree in chemical engineering from Michigan Technological University.
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