Over three decades, Alyeska Pipeline Service Co. has operated the trans-Alaska oil pipeline with the assistance of numerous technologies. None, perhaps, is better known than a clever innovation cooked up in the chemical laboratories of Atlantic Richfield Co. called drag reducing agent, or DRA.
A long-chained hydrocarbon polymer, DRA has the consistency of a gooey, clinging gel resembling rubber cement. Technically, DRA is a poly-alpha-olefin, or non-saturated carbon with very large, long-chain molecules composed of hydrogen and carbon atoms.
It proved to be a particularly important development for the pipeline, which was built to handle 1.5 million barrels per day of crude, according Jim Weeks, a senior ARCO manager in Alaska in the 1980s.
In the late 1980s when oil flow through the pipeline climbed to a rate of more than 2 million bpd, Weeks said injections of DRA made the higher throughput possible without additional construction.
“It gave TAPS a 30 percent increase in capacity without adding pipes or pumps or anything else,” Weeks said in a recent interview.
But the story of Alyeska’s love affair with DRA dates back to 1979, two years after startup.
DRA was first injected into the pipeline on July 1, 1979.
The pipeline was initially designed to move 2 million bpd of oil, using 12 pump stations. Each pump station could accommodate four mainline pumps, with three operating and one spare. Each of the pumps was to be driven by a 14,500-horsepower gas turbine.
The pump stations were designed to be built in phases. Phase 1 included building pump stations 1, 3, 4, 8 and 10, with two pumps each, which allowed for pumping 600,000 bpd of crude.
Phase 2 added pump stations 6, 9 and 12, with three pumps each and installed a 3rd pump at pump stations 1, 3, 4, 8 and 10, as throughput climbed to 1.2 million bpd.
Phase 3 was intended to add a fourth pump at pump stations 1, 3, 4, 6, 8, 9, 10 and 12, and to bring on line pump stations 2, 5, 7 and 11, with four pumps each to accommodate a boost in oil flow to 2 million bpd.
Before Phase 3 could be implemented, testing of DRA proved it to be a viable alternative to mechanical horsepower in the trans-Alaska oil pipeline system. As a result, Phase 3 never happened. Instead, pump stations 2 and 7 were built with just two pumps each, and the company shelved plans for building pump stations 5 and 11.
That fourth (spare) pump was never installed at any of the pump stations, but the stations’ gas turbines were modified to produce more power, up to the equivalent of 18,000 horses.
Even without the extra pumps and pump stations originally envisioned, DRA enabled the pipeline to handle peak oil flow of 2.15 million bpd. Maximum capacity without DRA was slightly more than 1.4 million bpd, according to Mike Malvick, operations engineering supervisor.
“DRA use, when injected at strategic locations, allowed 28 pumps to pump 2.1 million bpd of oil and eliminated the need for eight additional operating pumps and gas turbines,” he said.
“I’d say a rough estimate of the cost savings in facility construction from DRA would be approximately $300 million, in 1977 dollars,” Malvick said. “In today’s dollars, that would be in excess of $1 billion.”
Operators master DRADespite its efficacy, DRA required a significant learning curve at Alyeska. Engineers and technicians conducted an ongoing series of tests through the years to assess the substance’s range of capabilities.
Malvick said the original gel-like consistency, which had an active ingredient that required it to be dissolved in kerosene or diesel, was very difficult to use. Handling it was akin to manipulating an extremely sticky batch of melting mozzarella cheese.
“If you dipped up a handful of DRA, it would come away with a strand still attached to the batch that would get thinner and thinner but would never break,” Malvick said. “If you spilled it, the clean-up tools of choice were a shovel and a long pair of shears.”
This feature made DRA ideal for smoothing away turbulence as crude and natural gas liquids rushed through the pipe.
One problem with DRA was it would lose its desirable properties once it passed through a pump station, Weeks said.
Thus, batches of the agent had to be injected in the pipeline at regular intervals to keep the oil flowing smoothly.
But exactly how does DRA work?Malvick says the turbulent flow of crude in the pipeline chews up energy, and DRA acts like a spring or shock absorber, reducing turbulence and thus, the energy needed to move the oil to Valdez.
One factor in Alyeska’s willingness to continue using DRA was its lack of lasting effects on Alaska North Slope petroleum liquids flowing through the pipeline.
“We’ve not seen quality degradation in the crude oil,” Malvick said. “DRA is also injected into some pipelines for refined products in the Lower 48 with no detrimental impact.”
Another key development was the success DRA manufacturers had in converting the substance into slurry products that can be more easily transported, injected and cleaned up than the original gel.
“The slurries appeared in the late 1990s, and they’ve taken the market by storm. So they don’t make the gel anymore,” Malvick said.
New use for DRAAlyeska used DRA to aid crude throughput in the 1980s and 1990s, but in 1995, the company drafted the substance into a different service.
“We started using it for horsepower management. We took the same concept and went in a different direction,” Malvick said.
As North Slope petroleum production declined, Alyeska found that using DRA was more economical than running existing pump stations. The discovery led to shutdowns of Pump Station 8 in 1995, Pump Station 10 in 1996, Pump Station 6 in 1997 and Pump Station 12 in 2003 or 2004, Malvick said.
Today, Alyeska is still using DRA, though now it figures prominently in the company’s strategic reconfiguration process, which called for electrifying the pipeline’s remaining pump stations. Injection of DRA is allowing Alyeska to shut down or scale back power usage at pump stations 7 and 9.
“Depending on the cost of electricity, we may choose to inject DRA rather than run our pumps so hard and save on electricity consumption,” Malvick said.
The decision, like earlier moves to use DRA, hinges on a simple equation.
“When DRA is cheaper than fuel plus station maintenance plus personnel, then we shut down the pump station and inject DRA,” he said.