SAGD has another Desal option

Fresh water is crucial to the production of heavy oil in Alberta,
Canada’s oil sands region. However, the region’s steam-assisted gravity
drainage (SAGD) oil producers are under strict regulatory requirements
to limit the use of fresh makeup water to approximately 10 percent of
their total water requirements. This means that produced water must be
treated to the point that it can be reused as feedwater to generate the
steam used in SAGD oil production.

In the early 2000s, oil companies began using vertical tube falling
film evaporators as the final step in a treatment scheme to produce
steam generator feed water. Evaporator distillate became feedwater for
the steam generator, while the evaporator blowdown was introduced to a
zero liquid discharge (ZLD) crystallizer.

In 2004, Deer Creek Energy eliminated the traditional warm lime
softening and weak acid cation exchange processes ahead of the high pH
evaporator/crystallizer system, which was followed by a drum boiler.

The system has become a common arrangement in Alberta’s SAGD
operations, and there are now more than 20 projects employing more than
35 evaporator systems in which nearly 100 percent of the produced water
is reused.

A new technology, recently piloted on SAGD produced water, aims to
further simplify the treatment and steam production process, while
lowering the water treatment and steam generation system’s overall
capital cost by up to 35 percent. Keith Minnich, a veteran desalter and
co-founder of Alberta-based Hipvap Technologies, told WDR that
the company’s novel indirect fired steam generator (IFSG) eliminates
produced water cooling and de-oiling and replaces the other water
treatment processes with a unit that simultaneously desalts produced
water and generates high pressure steam.

The single-step IFSG process generates steam using a novel
forced-circulation heat exchanger process that recirculates a hot oil
thermal fluid in a closed loop at a temperature well below that which
causes the steel tubes to lose strength, a problem not uncommon with
once-through steam generators (OTSGs). The process includes a waste
treatment step that produces a solid material suitable for non-hazardous
landfills, and a clear, near-neutral pH brine suitable for conventional
ZLD crystallizers or deep well injection.

“The IFSG combines elements of evaporation with two-phase heat
transfer used in OTSGs. A circulation pump, with a suction pressure
equal to the steam generation pressure, pumps produced water into the
IFSG heat exchanger where the thermal fluid heats it and converts a
portion of it to steam. The steam/water mixture enters the steam
separator and a near 100 percent [dry] quality steam is directed to
injection wells. A portion of the produced water not converted to steam
is discharged as concentrate and the rest is blended with produced water
and recirculated.

“The thermal fluid is heated in an economizer-equipped furnace and
because it doesn’t boil, a third-class power engineer may operate the
facility. The IFSG has an online cleaning system to prevent scale
accumulations on the heat transfer surfaces,” said Minnich.

With the completion of its first demonstration test, the company
plans to move to a field pilot, and will begin to look for additional
funding.

Minnich said that “When compared to other produced water treatment
and steam generation schemes, the IFSG eliminates the waste recycle
stream, consumes less natural gas, reduces electrical power requirements
and generates fewer greenhouse gases per barrel of oil.”