Air Water Land:
SAGD operators embrace new water treatment options
Originally published in New Technology Magazine
Mushrooming production, growing strains on Alberta’s water systems, and increasing public concerns about issues such as global warming and water security are putting the squeeze on the oilsands industry. As a result oil companies are focusing on water conservation like never before. So when a new and more water-efficient technology comes along, it’s hardly surprising—once the technology is proven—that companies jump on the bandwagon and adopt it en masse.
And so when a new set of eyes looked at the in situ oilsands production method of choice for most companies—steam assisted gravity drainage (SAGD)—and saw a better and less water-intensive way to deal with produced water, the only task was to prove it worked.
Bill Heins, Bellevue, Washington-based business leader for RCC Thermal Products, GE Infrastructure, a unit of General Electric Company, was that new set of eyes. Back in the late 1990s, he conceived of a vision to revamp the entire process, discarding traditional water treatment methods that seemed to be used because of familiarity over any other reason, and replacing it with technology adapted from other industries. It may have taken the better part of a decade, but his vision has firmly taken hold among most of northern Alberta’s SAGD producers.
Those producers inject high-quality steam into one horizontal well to liquefy bitumen so it can be produced through a second horizontal well running parallel to the first. At surface, the water produced with the bitumen goes through three processes: it is separated from the produced bitumen, treated to remove impurities, and recycled back to steam for re-injection.
In what has amounted to a paradigm shift in produced water treatment techniques, companies are abandoning the use of warm lime softening (used for silica and magnesium removal) and weak acid cation ion exchange (for calcium removal) and embracing instead evaporator technology, specifically what is referred to as falling film, mechanical vapour compression evaporation.
The beauty of that system is that, due to its superior water quality output—almost four orders of magnitude better—evaporators can be coupled with standard drum boilers to produce the steam, replacing the once-through steam generators (OTSG) traditionally used for steam production. Not only are standard drum boilers more reliable, less costly to operate, and less water-intensive, but they can be powered by any number of fuel options, including bitumen, coke, and waste gas. Once-through steam generators are generally designed to run on natural gas, an increasingly valuable commodity.
“Of all the new SAGD facilities being installed in Alberta right now, we are seeing probably 80 to 90 per cent going with this new evaporative technology versus the traditional approach. That’s from zero per cent five years ago, so it’s been a huge shift,” says Heins, a former nuclear engineer in the United States Naval Submarine Program who has specialized in the design of zero-liquid discharge (ZLD) systems, crystallizers and brine concentrators at GE (formerly Ionics RCC) for the past 10 years.
As the main promoter of the switchover, it cost GE millions to bring about—and it left the company, which patented innovations in the technology, as the current dominant player in SAGD water treatment.
“It was something that our company over the last eight years really saw as a market that was going to be developing very rapidly and we invested millions of dollars of R&D and resources into developing it, piloting it, and bringing about its full-scale implementation.
“The reason it took eight years to get from where it was then to where it is today is that this industry is one in which change is taken very seriously and undertaken very slowly. What we had to do was prove the process technically. Usually the industry says unless something is proven, either with a large-scale pilot or on a full-scale basis for six months to a year, industry people won’t even consider it. We had to take it on ourselves to undertake that proof, so that when the data was available, people could say, ‘Okay you have proven it out, we are comfortable going with it.’ Now that we have done that, I think industry is very accepting of the technology.”
Part of the catalyst for the changeover is the fact that SAGD, unlike other thermal processes such as cyclic steam stimulation (CSS), requires 100 per cent quality steam. While CSS can thrive on a mix of 80 per cent steam and 20 per cent water or brine, SAGD operators needed to add an extra step—external separators—to the process to bring the mix to 100 per cent steam. The new construct could do away with that fourth step entirely.
OTSGs—which, unlike drum boilers, can produce high-pressure steam from water high in total dissolved solids—“are a great fit for CSS; that’s why they were used, historically. Out the tail end came 80 per cent steam and 20 per cent water that went straight downhole. But once SAGD came along, you were kind of force-fitting this older method into a new technology, and that’s what we saw as not quite making sense,” says Heins.
Drum boilers can’t handle water high in total dissolved solids. So it was only with the advent of evaporators, with higher-quality output, that drum boilers could be considered.
“That’s one of the major reasons that you want to go with that [evaporator] approach is to produce that high quality of water for the drum boilers.”
As long as the goal for SAGD operators is to produce 100 per cent quality steam for downhole injection, Heins says, “it just didn’t make sense that you had a process where you were only producing 80 per cent quality steam, then having to take that 80 per cent quality steam and running it through a series of vapour-liquid separators to ultimately get the 100 per cent quality steam you need to put down into the ground. That is a very complicated process, and it’s quite expensive. So the vision at the time was to say, ‘Why don’t you substitute it with something much more simplistic and economical,’ and just put in an evaporator and a drum boiler.”
Besides its improved performance and energy efficiency—an important component when 80 to 95 per cent of operating expenses are fuel costs—the new technique has several other advantages, Heins points out. For one thing, it significantly reduces the blowdown, or concentrated brine stream, associated with OTSGs that must be handled and disposed of, typically via deep-well injection.
“Conventional treatment of produced water using an OTSG produces a blowdown, which is about 20 per cent of the boiler feedwater volume and results in a brine stream, which is about fivefold the concentration of the boiler feed. Something like 10 per cent of the water ends up being lost; it’s just blown down into a deep well and that’s gone from the water cycle for good,” says Heins. “With evaporation, basically all of the water you are processing, you are recovering and reusing over and over again.”
Using evaporator technology, blowdown from drum boilers can be fed back through the evaporators, which by comparison produces about two per cent blowdown, resulting in much smaller quantities to deep-well inject or to send to a crystallizer system if ZLD is the goal. ZLD can be an attractive option, Heins says, in cases where deep-well injection of brine is too costly or not feasible due to factors such as geologically tight formations. “All you end up getting out of the [crystallizer] system is a dry solid suitable for disposal. Not only does it eliminate the cost of deep-well disposal, but it’s more environmentally friendly because you are not putting very highly concentrated brine back into the ground.”
And since the recycling factor is better, evaporation systems require 50 to 70 per cent less makeup water to operate. “The amount of freshwater makeup here is minimized to the greatest extent possible,” says Heins. “You can actually eliminate freshwater makeup completely because the evaporator systems allow you to use, in a lot of cases, brackish water makeup. If you have an underground brackish water supply to use as makeup water, you don’t have to depend on any freshwater aquifers or rivers or anything like that. So that’s a huge deal from an environmental standpoint.”
The first step in the evolution to the new approach occurred between 1999 and 2002, when GE installed the world’s first SAGD ZLD systems at Petro-Canada’s MacKay River facility, using a combination evaporator and crystallizer system. All water was recycled with just solids discharged off site, Heins says, providing proof of concept of the evaporation of produced water with high reliability.
That success led to the selection of evaporation to supplant the warm lime softening and weak acid cation combination to treat wastewater at Suncor Energy’s Firebag Stage 2 facility, in this case with OTSG retained as the steam production method. Heins says there was not yet enough data then to prove the evaporation process could produce water of sufficient quality for high-pressure drum boilers. Two more similar systems installed in 2002 and 2003 helped to produce the necessary data.
Then, in 2004, Total E&P Canada (then Deer Creek Energy) took the next step, replacing the OTSG with standard drum boilers at its Joslyn Phase 2 project to become the first SAGD facility to use the full combination of evaporators, drum boilers, and zero-discharge crystallizers.
Others have followed suit. Connacher Oil and Gas Limited, which began sequential injection of steam into 15 SAGD well pairs at its 10,000 barrels per day Great Divide Pod One project in September, will be duplicating the Total approach, says Rob McNeill, project manager for both projects.
“We staked the whole reputation on that one,” McNeill says of the Deer Creek installation, one that proved the entire package. “Once we took the risk at Deer Creek and proved that it’s a viable technology and that the advantages predicted did in fact come true, I think there is a lot more interest in going this route now than there was before,” he says.
Heins estimates there are about 16 produced water evaporators operating or under construction in Alberta and elsewhere, with dozens more in the planning stages and due to be released for construction, some later this year. “We have got installations in Kazakhstan, Kuwait, and it’s being considered in a lot of other countries, too, in Middle Eastern countries as well as other areas of the world.”