Oil and gas developers first used fracking techniques to release hydrocarbons in 1947 – and the first frac tanks were there to provide support. The modern-day frac tank continues to evolve, offering contractors a tank that will do more, carry more and provide specialized field duty.

“What they called a frac tank back then was very primitive, but designed specifically for oil and gas,” says Brian Barrett, director of sales at PCI Manufacturing, LLC, a manufacturer of frac tanks with headquarters in Sulphur Springs, Texas. “They were commonly built of 10-gauge steel and called ‘slope-tops’ because of the big slanted surface from front to back that you could see from the road.

“Given the thin metal used, the manufacturers put steel rods inside the tanks to support the walls so they’re also commonly called ‘rodded’ tanks,” Barrett elaborates. “You could put fluid into them and get it back out through a simple manifold. These models were most popular in the 1960s and early 1970s and some manufacturers still produce them today.”

The most popular frac tank model to emerge from that period was the 500-barrel flat-top, a square steel box with corrugated walls, a flat roof and V-bottomed floor. “That model became the bread and butter of the industry and the one that companies locked in on and are still widely interested in owning,” says Barrett.

But the versatile nature of the flat-top caused the definition of the frac tank to become diluted, as other industries began to adopt basic models for their own uses, storing and dispensing such fluids as glycol to deice airplanes.

 

VERSATILITY COUNTS

While the flat-top continued to form the backbone of most fracking operations, a new breed of purpose-built and modified frac tanks began to emerge, to serve specific needs in the oil and gas industry.

“In theory the frac tank can store anything from diesel fuel, to drilling fluids, lubricants, and various other chemicals,” says Barrett. “One of the first adaptations was a flowback tank, which was engineered to store flowback fluids. It wasn’t so much a storage tank as a temporary receptacle, built along virtually the same design, but modified to handle higher pressures.”

However, following incidents over the past decade in which flowback tanks had experienced explosions, a new variant was offered – the gas buster tank. The culprit behind the explosions appeared to be a buildup of static electricity resulting from the friction of the rapidly transmitted water, chemicals and sediment, combined with oxygen resulting from air/foam injection drilling and trace amounts of hydrocarbons. A static charge is believed to have jumped from the charged fluid to the downcomer through which fluid enters the tank.

“The gas buster is used in any situations where a high level of gas venting is important,” says Barrett.

Tank manufacturers approached the problem by re-engineering the tanks to decrease the velocity of the gas and fluids entering the tank, discouraging the generation of static electricity and grounding them both internally and externally. Venting allows gas to escape as fluid levels rise.

“We approached the design by using a slotted pipe inside the tank, which allows the fluid to fall down into the tank and the gas to vent upwards. The pipes are located at the top of the tanks, with either a completely open top or flip-top style doors,” says Barrett.

Drillers are also adapting traditional frac tanks to use as mud tanks, storing and mixing drilling mud using low-horsepower motors, before the mud is pumped downhole.

“These are a different style, with a rounded bottom that makes it much easier to circulate the mud during drilling and much easier to clean,” says Barrett.

 

TANKS FOR ANY CLIMATE

Given the wide geographic range in which frac tanks are now used – from Texas to Pennsylvania and north into Canada – tanks are also adapted for cold weather. However, the large volumes of water contained in the frac tanks are usually stored only for a short time before use in fracking operations.

“If you have 20,000 gallons of water, even in an extremely cold temperature, it’s going to take a lot of cold over a long period of time to freeze that water,” says Barrett. “The odds of a tank itself freezing up are slim, but we’re seeing more customer requests for spray-on insulation to maintain water temperature inside.”

Tanks used in warmer climates typically use external manifolds, while tanks used in colder climates can be designed with internal manifolds to limit exposure to cold.

However, when a large number of tanks are interconnected, external manifolds may require extra heating to keep water flowing to the wellbore.

“In the Pennsylvania shale plays, we’re now seeing multiple wells being drilled on a single platform and horizontal drilling, which requires greater volumes of water,” says Barrett. “A battery of tanks may be as large as 250 units.”

Mitigating the need to keep frac tanks warm is the practice of warming frac water to between 85 and 95 degrees before being mixed with gel and sand, and then pumped downhole. Engineers determine the optimum temperature of the frac water, based on the engineering reports for each well.

“One warming method is to run the water through a superheater, then pipe it back into the frac tank battery, where it’s held until ready for mixing,” says Barrett. “The second more recent method is known as ‘heating on the fly’ where water is quickly heated by a specialized superheater just prior to the mixer where it’s blended with gel and sand and immediately pumped downhole. Either way, the water is too warm to freeze.”

 

EXTENDING TANK LIFE

The lifespan of a standard frac tank ranges from eight to 12 years, depending on environmental conditions and maintenance, says Barrett. “A tank placed in the Gulf Coast region and exposed to saltwater will erode more quickly than a tank in Pennsylvania, for example,” he says. “We’re now also doing a lot more interior coating using two-part epoxy 10 to 20 mils thick that is chemically resistant.”

Contractors should also consider the design of the bottom of the tank, to help ensure that the units don’t sink into soft ground.

“Tanks with broad footprints minimize the risk of sinking in soft soils,” says Barrett. “The less the tank sinks, the less likely it will freeze or get stuck in the mud.”

Tanks that employ a wire harness also limit the likelihood that wires will drop onto the ground and be pulled loose in soft or frozen soil.

“Good quality paint also helps minimize exterior rust,” says Barrett. “A quality coating applied to a minimum 15 mils ensures the interior will be protected, and coating the undercarriage with an epoxy reduces damage to the floor structure.”

Another tank concept that’s more recently become popular is the aboveground frac water pond, an engineered pond assembled on site to replace individual frac tanks.

“It’s one of those old ideas that’s become new again,” says Barrett. “It’s essentially like an industrial version of an aboveground swimming pool.”

The Pinnacle variation offers ponds 125 feet in diameter that hold 24,000 barrels of water, 150 feet to hold 36,000 barrels or 175 feet to hold 48,000 barrels. The ponds are erected on a pad and liner surrounded by 12-foot-high walls made of 3/16-inch steel sections, which are pinned together on site. The ponds can optionally be covered and heated.

“A six-man crew equipped with a crane can set up the sections required to build a frac pond in about 14 hours,” says Barrett. “Companies will often use both ponds and tanks on a frac job. The ponds can be erected a distance away from the actual site while several steel tanks are often kept close to the well site. The economics come into play when you need high volumes of water. Does it make more sense to have 100-plus steel frac tanks or a pond on site?”

 

INDUSTRY TRENDS

Barrett notes that tank service and rental companies are leaning toward procuring standardized models to minimize time required to set up sites for fracking. That means they may favor one manufacturer over another to maintain that standardization for their customers.

“Manufacturers never got together to decide on an exact standard, so different models may have wider or narrower manifolds, with some located slightly higher and others lower,” he says. “When tanks are laid out only inches from each other, manifold to manifold, you want to make sure they’re all at the same location with the same hoses fitting firmly with no leaks. In some cases, a mismatched frac tank can only be tied into another one through manual intervention and a forklift. Time is money, so the faster you can connect the tanks, the better.”

Likewise, on mismatched tanks operators need to climb up and down stairs on each individual tank to check fluid levels. On newer models, the stairways fit together, so the operator can walk across one continuous stairway, all connected.

Beginning in 2009, Barrett says tank demand has skyrocketed.

“Horizontal drilling allowed higher levels of production than the vertical shafts used previously. With all areas open to production, we saw a surge in business once the economy recovered a bit,” Barrett says. “Things are beginning to look very promising in terms of shale production through this year and into 2013. We’re getting calls for as many frac tanks as we can deliver to some locations – 200 to 300 tanks in an order – with the clients asking us, ‘How quickly can you deliver?’”

 

DEMAND TO GROW

While Barrett says that the market for specialized tanks continues, clients are currently sticking with the basics, asking mostly for the standard bread-and-butter 500-barrel flat tank.

“The need for specialized tanks is currently dwarfed by the need for frac tanks of any sort,” he says. “Many producers have stopped actively drilling gas wells because natural gas prices are currently too low, so demand for the tanks slowed slightly over the past few months as gas drilling ceased. But they are gearing up again for shale oil with prices over $100 a barrel. Many characterize this as an ‘industry reset.’ We expect demand for tanks to rise again as companies redirect resources to the newer oil shale plays.”