and Plugging Issues in Husky Energy’s Lloydminster Thermal Projects
Article by Franklin Foster, Ph.D., with the assistance of
[note: this article made possible by support and funding from the
Petroleum Society of CIM, Lloydminster Section]
Producing Heavy Oil is a challenge. This website
describes many of the ways and means that this challenge has been met over
the years. One approach is to heat the heavy crude to make it flow more
easily. The general term for applying heat is "thermal recovery". One of
the oldest and most successful thermal projects is one currently operated
by Husky Energy east of Lloydminster and referred to as the Pikes Peak
Pikes Peak has seen an evolution of thermal techniques which in turn have
spun off to broader applications. The site began production in 1981 using
Cyclic Steam Stimulation (CSS). In this approach, high temperature, high
pressure steam is injected into a well for a period of time and then the
well is put into production until produced volumes fall off noticeably.
Then steam is injected again following which production is resumed, and so
on. The length of time for steam injection and production may vary from
well to well depending on a number of variables.
A somewhat later technique, again applied at Pikes Peak, was Steam Drive.
In this approach, steam is injected continuously down a separate well from
the production well, once interwell communication has been established
(normally after 3-4 CSS cycles). The effect of the steam drive, where
injectors and producers are arranged in regular "patterns" (inverted
7-spot, or 1 injector for every 6 producers, in the case of Pikes Peak)
greatly increases "sweep" of the oil and improved recovery over CSS.
The third era of thermal techniques focused on Steam Assisted Gravity
Drainage (SAGD), mainly over thicker bottom-water areas on the edges of
Pikes Peak. In this approach, thanks to directional drilling, pairs of
horizontal well bores are drilled. Steam is injected into the upper well
bore causing oil to precipitate downward into the lower well bore from
where it is produced.
Currently (2007) the Pikes Peak site is home to 239 directional wells, 5
SAGD pairs and 2 horizontal producers. The site produces approximately
8,000 barrels per day (bbls/d) but even more impressive is that this now
mature field has seen recovery factors as high as 85 percent. In fact, in
25 years of production, Pikes Peak has produced an estimated 55 million
barrels of crude oil. This has made it one of the most successful Thermal
Recovery projects in the world. Other Thermal Projects in the Lloydminster
area at Bolney Celtic and Lashburn bring Husky's current Thermal
Production up to 20,000 barrels per day.
The oil produced at Lloydminster comes from the Lower Cretaceous
Mannville Group, approximately 500 meters below the surface. The pay zones
are generally 15 to 25 meters thick and some areas have bottom water (i.e.
the oil is floating on top of pools of salt water). The oil is measured at
12° API in terms of viscosity or 22,000 centipoise at 15° C [i.e. about
20,000 times as viscous as water]. The steam injected is at 230° C and
typically 100% steam quality in the SAGD Areas.
Most horizontal well bores are not completed with pipe casing but rather
with a permeable liner or wire-wrapped screen. It is these that are
subject to plugging, thus restricting the flow of oil and decreasing the
well's production. There are many causes of the plugging ranging from fine
particulate matter such as quartz, feldspar, clays, or
pyrrhotites; typically "glued" or "baked" together by
asphaltenes and waxes in the crude oil; to carbonate and other
chemically based scaling. Each of these plugging mechanisms require a
different response so it is important to try and identify the exact cause
One case study might illustrate both the challenge and the method.
Laboratory analysis of a recovered well liner from a Bolney well indicated
that the plugging resulted mainly from silicate particles which had
effectively been glued to the liner by asphaltenes and wax, whereas
experience with screens recovered at Pikes Peak indicated a Calcium
Carbonate based scale, likely with a heavy oil coating. The response was
to flush the horizontal well bore with various acid treatments such as a
complex staged hydroflouric acid treatment (with a solvent pre-flush),
which evolved over time to simply bull-heading 1% HCl acid down the
annulus (termed "poor-boy" acid jobs) as a much cheaper and operationally
easier alternative of boosting oil production. Eventually, coiled tubing
with a special rotating jetting tool (which sprays the acid at high
pressure) was used to improve placement of the 1% HCl acid solution along
the entire horizontal well bore length.
Plugging mechanisms continue to be variable from well-to-well and poorly
understood. Sample analysis reveals complex combinations of particulates,
waxes, asphaltenes, and carbonate scales. Different remediation techniques
(and stimulation fluids) have yielded mixed results over time but efforts
continue to learn more about plugging and scaling mechanisms and adapt
best practices to the solution. It has been observed that there is a
generally declining response to repeated acid treatments performed on the
Husky Energy's horizontal well optimizations continue to evolve with new,
more cost-effective technologies (such as running calipers inside the
liner and under-reaming or "drilling-out" any buildups inside the liner)
and ongoing experimentation with solvents/surfactants and modifications to
the stimulation fluids. It is indeed vital to continue to meet these
challenges as plugging and scaling in horizontal wells has a major
negative impact on well productivity in Thermal Projects.