by Jeff Thomas
For decades, the water produced by the Wellington oil field was used by local farmers.
The water was run into a large holding tank, and the remaining oil and other petrochemical byproducts were gravity segregated and occasionally flamed off when levels got too high. Then the water was allowed to discharge directly into local irrigation ditches and surface waters, said Brad Pomeroy, owner and operator of the oil field. “The farmers loved it, and the ranchers loved it.”
That “drill and spill” scenario is still employed in areas, but things have changed for most oil field operators in recent decades. Pomeroy has fully embraced those changes, going so far as to build a Wellington Water Works treatment plant for the Wellington oil field water.
While Pomeroy and partner Richard Seaworth, a local rancher, are keeping the final cost of the 10-year-old plant fairly close to the vest, they admit it was extremely expensive.
“We know now that there is a lot of new technology they are using in Canada that we might have used,” Seaworth said. Being the first out of the gate in Colorado, however, came with a pretty hefty price tag, Pomeroy said.
First, they had to spend two years proving to the state engineer’s office that the water coming from a mile under the earth wasn’t affecting any surface waters. Then they spent another two years in front of the water court getting a right established.
“Our discharge standards are strict—for instance, they allow us to discharge only five parts per trillion of benzene, instead of 10,” Pomeroy said. “And they held us to strict construction standards as well.”
All in all, putting together a team of water lawyers and other experts good enough to get the state’s first produced water right was quite a chore. However, Pomeroy and Seaworth said they were lucky that environmental engineer Dave Stewart, who has served as an adjunct professor for both Colorado State University and Colorado School of Mines, happened to be located nearby.
The partners said that the water itself, which comes from the Big Muddy oil-bearing formation, is fairly clean, compared to other locations. Once the oil is separated from the water, the treatment plant Stewart designed is brought into play.
Stewart said the water coming into the system is a lot easier to work with than other produced water.
“The total dissolved solids (or salt content) of the water is about 1,500 to 2,000 parts per million,” he said. “In parts of the D-J (Denver-Julesburg oil) basin it could be closer to 20,000 to 30,000 mg/l (or parts per million).”
The first part of the treatment process for the oil field water is an aeration tank, allowing some of the volatile organic chemicals, such as toluene and benzene, to dissipate into the atmosphere. This requires an air-discharge permit, Stewart said.
From there, the water is run through a filter consisting primarily of finely crushed walnut shells.
“Walnut shells have an affinity for oil,” Stewart said.
The final filter was supposed to be a ceramic microfilter designed to take out the remaining scaling compound, but it was determined this was not necessary at Wellington Water Works and was removed. Instead, the final filter process now is activated carbon, which removes any remaining volatile organics such as the benzene.
“If we had been in parts of the D-J, we would have had to gone to reverse osmosis for the final treatment step” where the water is forced through the filter, Stewart said. The gravity-fed operation that the Wellington Water Works plant runs has significant savings in power over reverse osmosis.
Before the plant went into operation, most of the produced water was deep-well injected back into the Big Muddy — a fairly expensive proposition that Pomeroy once estimated at costing $1 per barrel. He said the cost of operating the plant is fairly similar, though it does produce about 16,000 acre feet of usable water each year.
“When we started, it was more of an experiment,” Pomeroy said. “But now that we’ve got it done, we haven’t been able to monetize the water to justify the expense.”